ESE's works engine tuner

[andreas]

Also, the 70/75% recommendation is not universal. I think it would be less on such a big bore. Or relieve the port.

[wobbly]

Two things I can see need attention.
The Ex port STA is too big - fill in the bottom corner radi and narrow the width to reduce the area below TPO. This will help big time with short circuiting from the A ports,
and increase the blowdown velocity.
Secondly why are you running all the transfers at the same height , that scavenging regime was abandond by everyone over 30 years ago.
Running normal stagger ie boost port lowest favours a broader power range , ideal for something without a PV , if its top end and overev you are looking for then the A port lowest is the go
as per Aprilia - but that was just as much needed to be able to increase the Aux Ex ports area as well , not relevant here.

[wax]

From looking at your port drawing, without dimensions, it is hard to tell whether the engine will live. But anyway, an exhaust port with a shape that is safe for the piston ring and with a width of 75% of the bore, will give less, not more, blowdown time.area than a 70%-wide safe port.
A 75%-wide port requires bigger corner radii to keep the piston ring alive, which reduces the uppermost parts of the blowdown area (the yellow areas in the left-hand drawing) that are the most important because they are open for the longest time.
The right-hand drawing can help you establish the safe shape for any exhaust port, assuming good quality steel piston rings.
347584 347583
Thank you Frits I can put that into the software and change it about

[wax]

Two things I can see need attention.
The Ex port STA is too big - fill in the bottom corner radi and narrow the width to reduce the area below TPO. This will help big time with short circuiting from the A ports,
and increase the blowdown velocity.
Secondly why are you running all the transfers at the same height , that scavenging regime was abandond by everyone over 30 years ago.
Running normal stagger ie boost port lowest favours a broader power range , ideal for something without a PV , if its top end and overev you are looking for then the A port lowest is the go
as per Aprilia - but that was just as much needed to be able to increase the Aux Ex ports area as well , not relevant here.
Thanks Wobbly
I can stagger the ports easy enough as I have to rasie the transfers anyway. They are down at 116 at the moment. Is a stagger normmaly about 2 degrees of duration
IN regard to the exhaust port I will see what I can do in regards to that as its pretty much set in this cylinder and I am trying to avoid pulling the sleeves out to weld up the cylidner. Yes its a case iron sleeve cylinder. old school. Can you actually get epoxy that wil live in a exhaust port ??

[wobbly]

For normal stagger the durations are around 132 129 126.
A port axial at 25* , B port at 12* , Boost at 55*.
Check the Ex duct exit area also , general rule is 90% of the port effective ie Chordal area X Cosine of the roof down angle - but thats shown in EngMod anyway.

[wax]

For normal stagger the durations are around 132 129 126.
A port axial at 25* , B port at 12* , Boost at 55*.
Check the Ex duct exit area also , general rule is 90% of the port effective ie Chordal area X Cosine of the roof down angle - but thats shown in EngMod anyway.
Thanks I will work all that out and post the sta up here when its done. Thanks guys

[Condyn]

Are the crank shields commonly observed on case reeds absolutely necessary? As previously mentioned, I removed reed blocks from an existing engine and am welding them to another. I have angled them axially towards the transfer ducts.

[wobbly]

The case shields , and the question about the reed box duct exit area are sort of the same question but with slightly differing reasons for the answer.
In the kart engines , the crank rotation is radially opposing the incoming flow , so the shields do two things.

Lifting the floor , and thus reducing the exit area , and also reducing the effect of the crank spin.
The pic of the Vortex DJT is a good example , where the reed block is very short and has a steep angle , so they have lifted the floor to form the shields and dropped the roof to reduce what would have
been a huge area increase past the petal ends.

In a normal engine with a case reed and the crank is spinning with the incoming flow - the floor ramps over the crank help to reduce the area change , but also push the flow upward toward the transfer duct entries.
This can be enhanced as well by a big difference in petal stiffnes , the top reeds ( and backups ) being much softer to bias flow exiting the block upward as well.

[Condyn]

Thanks as always Wobbly. I wish I would have been sucked into the two stroke pit 10 years ago as I am sure I force everyone to repeat themselves.
The varying petal thickness flow control is interesting and I will take note to experiment with that.

[husaberg]

You're right Philou. Below you'll find the Aprilia RSA pipe, codename Tubo102, once more.
The pipe in your above drawing is probably an early Rotax pipe, maybe model VSK150 or thereabouts, from before 1990, or a derivative thereof.
The partly visible logo on the right of your drawing belongs to Gazzaniga, an Italian producer of underwear who ran a 125cc GP racing team around 1990 with my friend Dolph van der Woude as designer/constructor. Dolph can probably tell us more about your drawing if he happens to drop in.
347579347578


Some of the pipes done at Rotax in the early days of the 256 and 128 had some quite different designs, alot of which I had never seen before.
Yes I think that is VSK 150 - I always wondered what VSK represented, or who actually did the new designs at Rotax back then.
This pipe if I remember correctly we used as a basis at JL, when trying to get the same power out of fully blown manufacture, except the first thing I changed was to a single rear cone.
We were sick of making the 180* U-turn for the front pipe on the Tandem twin for Superkarts.
Making that part front U part blown worked, but we could never get equal power by doing the rest . Hand made cones were always better.

I found these in stuff I posted before, the first one I assumed was the pipe in the first quote .
but it's not....
the second in the second attachment I thought was from a 256? that Frits had in the Frits files.
the others are all named. The last is the Honda KTM pipe for comparison.plus the FGrits rules of thumbs for plugging dykes
From memory there were two versions Frits posted in the Frits files of the Tubo 102 which I assumed were a front and rear pipe?

347593

347592347591

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/FOnBaxcxyIY" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[wax]

OK Here is it changed around
I was a little confused on the perfect exhaust port shape. It locks me in at about 95 hp but that will have to do.
Im going to try the piston opening the very bottom of the exhaust port as you suggested Wob
Thanks Guys for all the input, This is the engine by the way

[Muhr]

Hello
It is impressive how many dimensions a gear can have ...
Is there anyone who can answer regarding whether RSA's bevel gear on the balance shaft only has a press fit?

[Wos]

OK Here is it changed around
I was a little confused on the perfect exhaust port shape. It locks me in at about 95 hp but that will have to do.
Im going to try the piston opening the very bottom of the exhaust port as you suggested Wob
Thanks Guys for all the input, This is the engine by the way

Think your sketch Shows not max possible blowdown area :(

Have a second look at frits advice...in blowdown area the right and left sidewalls of the duct are vertical ;)

[Wos]

OK Here is it changed around
I was a little confused on the perfect exhaust port shape. It locks me in at about 95 hp but that will have to do.
Im going to try the piston opening the very bottom of the exhaust port as you suggested Wob
Thanks Guys for all the input, This is the engine by the way

Think your sketch Shows not max possible blowdown area :(

Have a second look at frits advice...in blowdown area the right and left sidewalls of the duct are vertical ;)

[Frits Overmars]

Hello
It is impressive how many dimensions a gear can have ...
Is there anyone who can answer regarding whether RSA's bevel gear on the balance shaft only has a press fit?
347610
What you need is RSA125 manuale_ingranaggi_conici_2010_rev3.PDF , but I see no options of uploading PDF files here, so I copied the relevant pages for you, Muhr.
The conical gear is a sliding fit on the balance shaft. It is keyed into position with a 2,5 x 3,3 mm needle, # 9 in the center drawing, and the assembly is locked by the nut that also clamps the left-hand balance disc.
By the way, did you notice that the direction of the inlet disc rotation in your drawing is opposite to that of the RSA?

[Muhr]

What you need is RSA125 manuale_ingranaggi_conici_2010_rev3.PDF , but I see no options of uploading PDF files here, so I copied the relevant pages for you, Muhr.
The conical gear is a sliding fit on the balance shaft. It is keyed into position with a 2,5 x 3,3 mm needle, # 9 in the center drawing, and the assembly is locked by the nut that also clamps the left-hand balance disc.
By the way, did you notice that the direction of the inlet disc rotation in your drawing is opposite to that of the RSA?

Thanks Frits! super stuff.
Yes it was an active choice but the consequence thought was non-existent.
I just tried to get the weights as close to the centum as I could
I guess it will be richer in the opening phase and liner in closing (RSA), but what it would mean in practice I do not know … Probably bad as you mention it.:brick:
Harder to start when it opens above as well?

(I got around 17NM with a press fit, that's when I started to anticipate trouble)

[husaberg]

What you need is RSA125 manuale_ingranaggi_conici_2010_rev3.PDF , but I see no options of uploading PDF files here, so I copied the relevant pages for you, Muhr.
The conical gear is a sliding fit on the balance shaft. It is keyed into position with a 2,5 x 3,3 mm needle, # 9 in the center drawing, and the assembly is locked by the nut that also clamps the left-hand balance disc.
By the way, did you notice that the direction of the inlet disc rotation in your drawing is opposite to that of the RSA?

.....................................


Here.
Let's hear it for Mental Trousers: he created a way for me to upload BIG files.
I will be offline for a couple of days, but this might keep you busy:

http://www.kiwibiker.co.nz/manual/Aprilia-1.zip
http://www.kiwibiker.co.nz/manual/Aprilia-2.zip
http://www.kiwibiker.co.nz/manual/Aprilia-3.zip
http://www.kiwibiker.co.nz/manual/Aprilia-4.zip
http://www.kiwibiker.co.nz/manual/Aprilia-5.zip

One request:
Don't spread the contents all over the world wide web.
Then I might upload some collected data of other racing brands as well.

Enjoy.
https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner/page378?p=1130210694#post1130210694

[wax]

Think your sketch Shows not max possible blowdown area :(

Have a second look at frits advice...in blowdown area the right and left sidewalls of the duct are vertical ;)
Yes ok thanks for pointing that out.
I will change again

[SwePatrick]

Made some small adjustments to the timingcurve, gained about 1hp, lost very little torque, but gained a lot of power above earlier peak.
The same peak ignition point, but a bit less advance where max torque was before and about 1500rpm earlier also.
This carried more heat in the pipes when running though the rpm band.

347612

[jfn2]

These are beautiful, Thank you Frits. And Husaberg.
Mine downloaded perfectly.

[Maxdelta]

Frits - Perhaps I'm not understanding correctly, but on the FOS port shape image it lists the center top radius should be 75% of bore. In the attached Aprilia image the top radius appears to be 95mm on a 53mm bore (179% of bore). Much larger then the 75% listed.

[Muhr]

By the way, did you notice that the direction of the inlet disc rotation in your drawing is opposite to that of the RSA?

I made some small changes and changed direction of rotation, Now I could run in both directions.

[wobbly]

The section drawing shows an easy way to add some power - continue the case water passage around up behind the RV , and have the majority of cold water enter the cylinder each side
of the boost port.
Then just a pair of small 3.5mm drillings up under each side of the Ex duct to ensure flow occurs right around this and isnt into a dead end near the Ex flange.
Having all the cold water heated first by the Ex duct is looses exactly 1 Hp in 50.
Also the water cavity should extend right up to the back face of the Ex spigot to cool this - no gasket.
I am about to test adding a water jacket system , as proof of concept , around the transfer ducts , right from the case split line upward.
So the whole transfer duct is cooled , not just the last part of the bend into the port.

[Muhr]

The section drawing shows an easy way to add some power - continue the case water passage around up behind the RV , and have the majority of cold water enter the cylinder each side
of the boost port.
Then just a pair of small 3.5mm drillings up under each side of the Ex duct to ensure flow occurs right around this and isnt into a dead end near the Ex flange.
Having all the cold water heated first by the Ex duct is looses exactly 1 Hp in 50.
Also the water cavity should extend right up to the back face of the Ex spigot to cool this - no gasket.
I am about to test adding a water jacket system , as proof of concept , around the transfer ducts , right from the case split line upward.
So the whole transfer duct is cooled , not just the last part of the bend into the port.

Thanks for the suggestions Wobb
extend the water right up to the back face of the Ex spigot should be possible without any major problems
I have done what I understood RSA had in the end in terms of cooling?

[wobbly]

Several homologations ago now the TM Kart engines had all the water enter the cylinder under the Exhaust duct - like the Aprilia and most every other engine at the time.
This was simple and seemed effective , but a test was done by blanking the water feed holes out of the case , and a hose was fitted around the outside to have all the cold water flow across the top
of the Exhaust duct ( where its the hottest ). This made more power than the original method.

I then tried a test where I extended the side hose around to the front of the cylinder and bored/threaded a hole directly above the boost port.
This system cooled the transfer tops first , then the Exhaust duct , then up into the head.
That made 1 Hp for about 5 minutes work - wish they were all that easy.

The real way to do this properly would be to have the cold water entry at the bottom of the case , with a cavity up between the gearbox wall to the small bleed holes under the Exhaust duct.
But the main flow should also then travel forward , over the main bearings , cooling the transfer duct entry area in the case from behind , then go around to enter the cylinder each side of the boost port.
Not easy with the big reed cavity in a TM , but real easy with only the RV inlet duct under the boost port.

Jan found power by having a water duct cooling the area between the bore and the inner transfer walls .
So I believe the same thing would occur by cooling properly all the outside of the transfer ducts , not just the small area where they curve inward toward the port - the way every cylinder is made now.
That test is about to happen , as Ken from WA has made me some 3D printed water covers to try cooling the sides of the cylinder with water.

[ken seeber]

Here's the kit. 2 * 3D printed sidecovers connected to some irrigation fittings (Bunnings is your friend for those below the equator). These, as a system, essentially take the place of the current external hose (from crankcase outlet to inlet at top of cylinder) that Wobbly was referring to.

I just can't wait. I just suppose that Wobbly's dyno is waterproof...

347621347622347623347624

[Schumae2]

[QUOTE=ken seeber;1131175336]Here's the kit. 2 * 3D printed sidecovers connected to some irrigation fittings (Bunnings is your friend for those below the equator). These, as a system, essentially take the place of the current external hose (from crankcase outlet to inlet at top of cylinder) that Wobbly was referring to.

I just can't wait. I just suppose that Wobbly's dyno is waterproof...

From WobblyÂ’s post I understand the performance merit in cooling the cylinder in the way youÂ’ve prototyped, though I was wondering if doing so, or the method Wobbly described modifying an older TM-KZ have any appreciable effect on bore distortion?

The reason IÂ’m inquiring about durability based drawbacks to changing the where the bulk of the coolest water is sent to the cylinder is; I race a shifter kart in the US and during colder weather events most competitors have either 3-D printed cylinder cover or fabric based blankets that reduce air based cooling to ONLY the front of the cylinder. There justification is it reduces non-uniform cooling.....hopefully helping to prevent seizure. Hearing this stopped me in the past from entertaining similar cooling modifications to what Wobbly tested on the TM-KZ.

Simply-put; will the modifications described by Wobbly and/or the prototyped cooling arrangement you fabricated necessitate additional bore clearance to account for distortion, or additional relief of port bridges (EX: more relief than normal in a T-exhaust-port type engine)?

BTW; awesome work!!! ;)

[Vannik]

Jan found power by having a water duct cooling the area between the bore and the inner transfer walls .
So I believe the same thing would occur by cooling properly all the outside of the transfer ducts , not just the small area where they curve inward toward the port - the way every cylinder is made now.
That test is about to happen , as Ken from WA has made me some 3D printed water covers to try cooling the sides of the cylinder with water.

I have been waiting for someone to test this for many years now, since I added transfer passage temperature as an independent variable in my software and always predicted more power with less temperature. With Jan adding the cooling passage between the transfer duct and the bore and getting more power this confirmed the prediction in a small way but now... I am super exited!

[SwePatrick]

Is that really a good idea?

Water is about 50c degree hot or more.
Surrounding air is about 20-30c hot when aiming air at them.

Make some flat surfaces instead and mount copperfins, aim air at them with some ducts and hoses from high pressure area in front of vehicle.
The inner radius is ofcourse better to run water inside because it´s hard to point surrounding air into them, but with some engineering it would be possible to lead air into some channels, but with quite low effiancy.

[Larry Wiechman]

Maybe the next step would be two separate liquid cooling systems. One configured to cool the incoming charge. The other to deal with the heat from combustion.

[Vannik]

Is that really a good idea?

Water is about 50c degree hot or more.
Surrounding air is about 20-30c hot when aiming air at them.

Make some flat surfaces instead and mount copperfins, aim air at them with some ducts and hoses from high pressure area in front of vehicle.
The inner radius is ofcourse better to run water inside because it´s hard to point surrounding air into them, but with some engineering it would be possible to lead air into some channels, but with quite low effiancy.

https://physics.stackexchange.com/questions/244989/water-vs-air-heat-absorption-capacity

[Frits Overmars]

Frits - Perhaps I'm not understanding correctly, but on the FOS port shape image it lists the center top radius should be 75% of bore. In the attached Aprilia image the top radius appears to be 95mm on a 53mm bore (179% of bore). Much larger then the 75% listed.Max, the bore dimension on that drawing is "Ø 53,1 (Prelavorato)" which, as Google Translator will tell you, means raw, unfinished. The same goes for other dimensions in that drawing, like the exhaust port height and its center and corner radii. Besides, that drawing is quite an oldie; it doesn't show the RSA cylinder.


Is that really a good idea?
Water is about 50c degree hot or more. Surrounding air is about 20-30c hot when aiming air at them.
Make some flat surfaces instead and mount copperfins, aim air at them with some ducts and hoses from high pressure area in front of vehicle. The inner radius is ofcourse better to run water inside because it´s hard to point surrounding air into them, but with some engineering it would be possible to lead air into some channels, but with quite low effiancy.Patrick, the water temp in an Aprilia RSA125 is about 40°C (in the RSA250 it was about 50°C because otherwise the radiator size would have to be huge) but I'll admit that the cooling water is hotter than the surrounding air.
Following your reasoning, I should switch from watercooling to aircooling. Something tells me there has to be a catch. For example that a liquid will absorb heat a thousand times better than a gas, more than compensating for the smaller temperature difference between coolant and the object being cooled.

[SwePatrick]

Max, the bore dimension on that drawing is "Ø 53,1 (Prelavorato)" which, as Google Translator will tell you, means raw, unfinished. The same goes for other dimensions in that drawing, like the exhaust port height and its center and corner radii. Besides, that drawing is quite an oldie; it doesn't show the RSA cylinder.

Patrick, the water temp in an Aprilia RSA125 is about 40°C (in the RSA250 it was about 50°C because otherwise the radiator size would have to be huge) but I'll admit that the cooling water is hotter than the surrounding air.
Following your reasoning, I should switch from watercooling to aircooling. Something tells me there has to be a catch. For example that a liquid will absorb heat a thousand times better than a gas, more than compensating for the smaller temperature difference between coolant and the object being cooled.

Yes i know water transports heat a lot better, but i would almost guess it actually heats up the transfers instead of cooling them, inside the cylinder and more upwards there´s a whole other problem, due to combustionheat very close to the piston,liner etc etc.(i was also guesstimating the coolingtemp)
The outside of the transfers are quite far away from the heat, especially when having water upwards in cooling jacket as a 'barrier'.
But if having a separate system with about 25-30degree water it would cool them, a lot!
It would in my world be far better if isolating the heat transfer from the gearbox(as some already do) and coolingfins under the crankhousing(as some already have, and aim air to them from the fairings high pressure zone)

The small amount of powerincrease one might gain from cooling the transfers outside would probably be eaten up by needing bigger waterpump, etc etc.

One can also coat the whole crankcase together with the transfers with some heat barrier, this to get 'free' energy that doesn't cost energy at some other place.

And if having possibilities, run methanol fuel and get 'too cold' problems instead ;)

[andreas]

Regarding cooling:
1. Separate ex duct cooling system
2. no PV to shade the upper duct face, use a retarded atac or other means
3. Those aux ex ducts i.e the bridges must be particulary bad for heating the return charge- and they dont do much to aid the wave intesity in the first place? Maybe they can be omitted from the main exhaust circuit and just waste into the atmosohere?

[Frits Overmars]

The outside of the transfers are quite far away from the heat, especially when having water upwards in cooling jacket as a 'barrier'. But if having a separate system with about 25-30degree water it would cool them, a lot!With ambient temperatures of 25° to 30° you would need an infinitely large radiator with infinitely low efficiency and infinitely high air resistance.
If there is room for a larger radiator, it is much more efficient to use it to cool the really hot water.


It would in my world be far better if isolating the heat transfer from the gearbox (as some already do) and coolingfins under the crankhousing.... One can also coat the whole crankcase together with the transfers with some heat barrier...Isolating the gearbox heat is effective; cooling fins under the crankcase can work as well, but they may be counterproductive if the exhaust pipe is right below them.
That is why the Aprilia RSA125 had a carbon fiber heat shield between the cases and the pipe.
347625

My favorite is barrier-coating all surfaces that are hotter than the gas passing over them (that excludes the exhaust duct because of the even hotter exhaust gases).

[ken seeber]

The thought behind doing this was driven loosely on KZs, but it is equally applicable to any engine (virtually all) with the exposed transfer passages.

With a piston crown around 250 deg, the intake charge has no chance to do anything but heat up on its journey into the transfer passages. Say a KZ was running at 39 kW and it obeyed the rule of thumb that 30% of fuel energy went to power, 30% to coolant and 30% to exhaust, then we could make a guess that the piston received 40% of the coolant energy = (39/3)*0.4 = 5.2 kW.

Air flow rate into a KZ, making some assumptions = 0.125 * a delivery ratio of 2.5 = 0.312 lit/rev @ 12500 rpm = 3750 lit/min = 62.5 lit/sec = 0.0625 met^3/sec @ 1.2 kg/met^3 = 0.075 kg/sec.

Using Q (kilowatt) = M (kg/sec) * Cp (kJ/kg) * ∆t (deg)

5.200 = 0.075 * 1.005 * ∆t

Therefore ∆t = 66 deg

So, if air-in temp was 25 deg, then after heating via the crankcase, it would then rise to 91 deg. So I could be wrong in my assumptions, the units or the maths but, if not, one can see that the air is already hot without any blowback from the exhaust when not at max power revs being added to the picture.

With a coolant temp of say 40 deg from the radiator, then this can only be of help in reducing the charge temp, hence increasing density and power and reducing the tendency for detonation.

Unfortunately this would not be an allowable addition or modification to a rule abiding KZ engine, but only something that could be introduced by the manufacturer for a subsequent 3 year homologation period.

Apologies if any of the above calcs are wrong.

[SwePatrick]

Ken, to think about:
Heat transfer from cylinder into airstream isn´t 100% effective.
The fresh gasses are traveling very fast and only the boundary layer is touching the transferwalls.
Thereby there´s a very little transfer of heat into the main bulk flow, it is some yes, but it´s very very hard to calculate.


Not quoting Ken:
I would say a barrier between gearbox and crankcase would be best if having a channel that is flowed with air from the fairing and away from engine somewhere suitable just to flush away the heated air in the channel.
I´m assuming this as i did a quite similar modifications in AMG mercedes, i put a flexible hose to pressurized duct in front of car(only 40mm diam), then lead it to flow cold air underneeth the intake manifold(v8 engine) this made a really noticable performancegain, if driving slow it did almost nothing, as expected, but if runing at 100km/h the inlet air temp sank about 13 degrees.
And if braking fast and rapidly take off again, i gained almost 0.2s 0-100km/h, this is almost free power to be had =)

[Vannik]

Ken,

Your calculations is spot on but conservative. A typical crankcase gas temperature for a watercooled but not crankcase cooled racing 2T 125cc making around 45hp is measured around 110degC to 120degC. Anyone that had to emergency strip one of these engines after a race will tell you the crank webs are above boiling point.

The flow through the transfers is highly turbulent and highly unsteady so no boundary layer worth anything has time to form. I find it strange that engine builders like to quote fully developed steady flow boundary layers derived for steady tube flow as being similar to what happens in an engine's ports. They are totally non similar.

[Muhr]

https://farnam-custom.com/resources/calculators

[jbiplane]

A bit offtopic question dont related to cooling. But my question can be very simple for local Gurus.
Does anyone have an idea where to source good quality easy to get helical gears to use in light engenes one stage reducers?
Yes it is possible to produce, but using of shelf components says of moto could cut the cost.
For this power range helical gears with module 1.5mm (1.75 or 2 if 1.5mm problematic) will work fine.
Big gear can have 56...60 teeth and small 17...20

[Condyn]

Does laminar flow even occur in two strokes?

I have a question for whoever has experience testing, in regards to cooling air cooled engines. ( I think TZ covered this some 2000 pages ago )
The copper “ gaskets “ that extend out from between the clamping surfaces and transform into cooling fins. I know copper conducts heat better than aluminum. I have been tossing the idea around of making a 4mm cylinder spacer out of copper that extends outwards to dissipate heat. Good idea? Bad idea? What other tricks have proven worthy of assisting in cooling an air cooled?

[wobbly]

The whole idea of cooling the transfer duct outer faces , was started by Jans sucess ( as is usual ) in cooling the opposite face , near the bore.
The kart engines have the carb and airbox directly in front of the crankcase - finning in this area does nothing , as there is no airflow.

I fitted a clamped on under plug temp sensor to the TM , with a tapped hole on the transfer duct face about 1/2 way up between the gasket split line and the water jascket.
The water exiting the head , on track , was at 42* , the cylinder outer wall temp I data logged at almost twice that - even with 142Km/Hr air passing over it at 22*

And the case behind the ignition ie the transfer entry area , maybe even hotter - im still unsure as to the temp of the oil in the clutch side cover on the other side.
But my idea to cool the transfer duct entry area in the case , with water flowing over the main bearings , would cool the trapped air behind the ignition , as well as the side cover oil.

In my opinion the idea of having a cylinder air shield facing the oncoming high speed air would have no discerable effect.
The whole upper cylinder liner is surrounded by water , any cooling of the cylinder outer water jacket would have virtually nill effect on the shape of the bore due to any temp delta across the alloy.

[SwePatrick]

Does laminar flow even occur in two strokes?



I would say never in any engine, just more or less turbulent.

As far as i know, there is a boundary layer even if the airmass is turbulent, just different 'size/thickness'.

And i´m with Einstein, there isn´t any free power if 'mechanicly' power the system that allows for a power increase.
Perpeteum mobile you know..

So if wasting energy in the pit/garage with a heatbarrier you gain the energy back on the track= win!
Wasting energy on the track to get energy on the track = fail!

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/fcsxupBBNs8" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[F5 Dave]

So, gearbox oil cooler? Whether the drag would be worth it.

Dyno, 20l container, battery oil pump replenishing the gearbox. In filler - out sump plug. Could monitor external temp . Would give you several runs at correct water temp but lower than normal bottom end temp to tell if worth pursuing an on track solution.


Geez Kens concern about leaks would knotch up a few levels.:lol:

[jamathi]

Maybe the next step would be two separate liquid cooling systems. One configured to cool the incoming charge. The other to deal with the heat from combustion.

A friend of mine, named Herman Meijer, did this 50 years ago! On his own self designed engine, made from solid aluminium.
It was not particularly successful...
2 radiators, 2 water pumps, very complicated.
The water passage on the inside of the transfer walls gave 0,5 HP more on the Aprilia RSA
I am convinced that we would have had still more power with the transfers cooled on the outside as well!!!
And by cooling the C-port side as well....
We once measured the temperature of the cylinder bottom flange.
I don't remember the exact temperature, but it was frightening, about 100°C
It was measured at the back side.

[husaberg]

So, gearbox oil cooler? Whether the drag would be worth it.
.:lol:
i think according to to Cameron On the KR250s they ran at Daytona one year they lowered the gearbox oil level as the oil was heating the rear crankcase enough to cause an alarming amount of power fade.
I think they even added a baffle to keep the very hot oil away from the crankcase.

[philou]

Cylinder head for tm kz

347635

Nostalgic bultaco engine

347636

[SwePatrick]

In our surroundings around us, what are the best media to isolate heat?

[jonny quest]

Didn't old Rotax square cylinders basically have water around the whole outside of cylinder?

I know this is ineffective because of. Let's say stale water movement?

[AndreasL]

Hi all,

Going through my "2 stroke files" I realized that I couldn't find my FOS-zip...that i'm (almost) sure I downloaded. All of them. :brick:

KiwiBiker to the rescue I thought and tried the original link Ken posted at page 2169...
https://drive.google.com/drive/folders/18l2ShH-MzrnTO0uEk9rNTk89_KgwgWof?usp=sharing
But no luck as it was over 1 year ago this was first posted. So that's understandable.

Anyone having access to the 2.2 GB of information to share?
Thanks in advance!

Please help me. :weep:

[Wos]

I am no physician:not:

But what about the idea of water aerosole cooling outside the transfers? ... using it only to overtake your competitor would reduce the volume and weight of water carry with... :scratch:

Finns and air outside duct:scratch:

Know some irrigation jets for plants that spay drops of a few 1/1000 mm ...4 liters a/ hour...at pressure 4 bar ...in german called nebeldüse...fogg jet:scratch:

I use this jets to cool down the inlet temprerature of my house Ventilation system...very effektiv :niceone:


:scratch:

Grüße Wolfgang

[Flettner]

Or, what about atomizing fuel on the inside of the transfer ports, TPI.
E85 would be a good fuel / refrigerant for this.

[wobbly]

The Rotax cylinders had about 1/2 the transfer duct length "under water ".
If the plastic printed water covers are a sucess , I plan to then extend the test to reroute all the water into the cylinder on each side of the boost port, as there is a cavity already there.
Having all the water enter directly above the boost , then flow forward over the transfer tops was worth exactly 1 Hp , so the combined test should be quite revealing.

[ken seeber]

I am no physician:not:

But what about the idea of water aerosole cooling outside the transfers? ... using it only to overtake your competitor would reduce the volume and weight of water carry with... :scratch:

Finns and air outside duct:scratch:

Know some irrigation jets for plants that spay drops of a few 1/1000 mm ...4 liters a/ hour...at pressure 4 bar ...in german called nebeldüse...fogg jet:scratch:

I use this jets to cool down the inlet temprerature of my house Ventilation system...very effektiv :niceone:


:scratch:

Grüße Wolfgang

Wolfgang, here is my very first post on ESE in Jan 2014:

"I worked for quite some time at a company called Orbital Engine Company in Perth WA. In the early days of the development of a 3 cyl 1200 cc DI two stroke engine, we decided that the engine, which for simplicity reasons had to incorporate exh valves operating on a single axis parallel to the crank, therefore necessarily the cylinder scavenge axis had to be normal to engine longitudunal axis. This is unlike the skewed scavenge axis which is quite common on multicylinder outboard engines. The skewing allowed the transfer passages to "nest" in to each other allowing the cylinder spacing to be minimised.

In our case, we developed a compact transfer port layout that had 100 mm bore centres with an 84 bore. To compare its performance with other 400 cc engines (of the day 100 years ago) we set up a Suzuki PE400 engine in one of our test cells. We made some trial cylinders with our scavenging system (the X porting system we called it), these being able to fit on to the PE400 lower half and this allowed us to directly compare the watercooled X system with the air cooled PE400 cylinder and head.

Getting back to the story, it became clear, as expected, that the air cooled engine very quickly lost its performance as it warmed up. This fact is also well known, particularly in go kart engine circles where air cooling it still used for certain classes (eg Yamaha KT100J and KT100S). Compared to a bike with a gearbox and a half decent exhaust, these have a low specific output, say 18 hp for 100 cc.

So, how to combat this? Firstly we blasted it with strong air flows and this helped, but the best was was to put some micro irrigation jets in front of the barrel and head. The latent heat of vaporization of the water did the rest, quickly bringing the performance up to that of a cold engine.

Getting back to the issue of Kel's cooked 125 air cooled engine, I can offer the following uptions:
1. Carry a small tank of water on the bike with this spraying or dribbling over the motor
2. If you perspire enough, have a catch arrangement inside your race suit and run this via a hose to the engine
3. For karting, I have often wondered if a small "leak" incorporated into the pressure side of the Walbro pumper carb (which is usually in front of the engine on piston ported inlet engines) might be beneficial to allow fuel to flow/trickle over the engine and evaporate. Some tech dudes might see some safety issues with this one however.
4. Back to the racesuit. You could also drink lots of water before your race and, in conjunction with a good controllable diuretic and a hose connected to your good self, perhaps cool the engine that way. Might smell a tad though.


Thanks Ken Strike Products"

[Muhr]

I made some engine mounts where I thought it could work. Then I thought it might be fun if it fit on some frame in this world. Does anyone have any suggestions on a suitable bike for an engine like this? And in that case if anyone has the measurements.

[Flettner]

wouldnt this be easier?

[wobbly]

Re the aircooled. There are readily available thermodynamic analysis calculations to determine the efficiency of finning with air flowing over them.
Basically it comes down to the thickness of the fin , the spacing and the surface area.
A 4mm spacer " heatsink " isnt going to do jack shit , unless it has a heap of added area for air to flow over it.
A thick lump like that will simply absorb heat slowly , not radiate it.
Two 1mm plates with a 2mm spacer between them would be technically superior.

I assume that your regulations specifically say you cant water cool the engine , that being the cylinder and head.
One possible work around would be to use an oil cooler for the gearbox , but have oil pumped up thru the cylinder stud holes and around the case.
This sort of extra "cooling " as per Suzukis original patent of doing all the cooling of a 4T using oil only , I am running this in a XR 200cc based engine ( loosely ) to be used in a 1/4 sized speedway
dirt car for kids racing.
Being enclosed inside the bodywork , the aircooling is not very effective , even with proper ducting and copper extended gaskets , but pumping cool oil thru the cylinder studs works wonders.

[Condyn]

That is a creative solution. The rules state that no liquid cylinders are allowed. You just gave me a few other ideas.... It is for a world championship class oval racing snowmobile ran on ice. 440cc. The heads have not been manufactured yet, they are the only external engine part that can be fully custom. The crankcase must maintain dimensions with the exception of adding reeds to it. And the cylinders must have factory casting numbers in place. I will take a look at the thermodynamics before designing the fins. As I have removed fins from the cylinder and welded in auxiliary exhaust ducts I am sure that will come in handy knowing what should work best. Just trying to do whatever I can to shed heat.
I was greatly inspired by Jeff Henise work with your guidance several months back on his land speed bike. I asked myself “why has nobody done this for this class?“
Thanks wobbly.

[wobbly]

Helping is a pleasure Condyn . Interesting about your engine and class rules.
I had a short discussion some years back on another forum with a few people doing 440 champ engines , where I suggested that their Exhaust port ducts were way too big and the pipes
designed in, of all things Dynomation , were not even close to optimum.
This was greeted with howls of derision that I knew nothing about champ engine technology - and that i should stick to the toy 125s.

I did end up doing a paid in full EngMod sim project for one guy over there , and by doing exactly what i was told would not work , the sim showed something like 10% more peak Hp and a way greater gain 1000 rpm past that.
The conclusion was that the sim code was faulty , so being the complete arsehole i am I told them to fuk off and kept the new pipe design and the cash to myself - their loss not mine.
Funny to me that they were more pissed about me publishing their super secret , not so shit hot , pipe design than anything else.

The 350TZ LSR record holding engine that did 172mph stuck at 12,000 redline in 5th gear we were planning to go 200 this year , but way too hard making that happen with viruses running around even faster.

[andreas]

"Howls of derision" will of course result in a set of exquisite pipes- have we seen them here?

[yatasaki]

Regarding crankcase insulation, did an insulation with polyurethane foam on tomos centrifugal in-gearbox two speed engine. As the clutch is adjusted to slip between 7-8000 rpm (not only for starting but for pulling from corners)it produces certain heat apart from rest of the gearbox.Foam is applied in gearcase around crankcase and it works. Several checks were made for polyurethane being dissolved or detached but it is glued on place. No case temperature measurements were made before or after applying but one is certain, bike is faster than before for 200-300 revs on end of the straight.
Now a five speed gearbox case is being prepared for same foam application and case walls being made rough to keep oil longer attached for cooling..at least keeps my mind satisfied.

[Condyn]

RE 440 champ
The champ engine technology! The principles just will not apply here haha. With design limitations of being restricted to 1985 model cylinders which are air cooled, a champ engine is similar to what I am working on. Some builders now utilize engmod over here but many are stuck on the "end all be all" tom turner stuff. I have only one engine modeled as of now and am patiently waiting to get it on the dyno so I can further develop pipes in engmod. (This is not the engine I am constantly referencing.) As previously discussed I will need to find max power egt and possibly tweak the wall temps so the curves align with real life.
From what I have seen most of the Champ engines use a 198 degree exhaust duration with aux ports out to 100 percent creating a necessity for pin plugs. With the cvt we do not use much, if any, low rpm range. I still have trouble understanding the "why?" behind the large exhaust durations and blowdown sta when we do not exceed 11,000 rpm. It seems as if the pipes would have a hard time being utilized, yet it is seemingly (top secret) standard to see those numbers in champs.

[Peter1962]

Regarding crankcase insulation, did an insulation with polyurethane foam on tomos centrifugal in-gearbox two speed engine. As the clutch is adjusted to slip between 7-8000 rpm (not only for starting but for pulling from corners)it produces certain heat apart from rest of the gearbox.Foam is applied in gearcase around crankcase and it works. Several checks were made for polyurethane being dissolved or detached but it is glued on place. No case temperature measurements were made before or after applying but one is certain, bike is faster than before for 200-300 revs on end of the straight.
Now a five speed gearbox case is being prepared for same foam application and case walls being made rough to keep oil longer attached for cooling..at least keeps my mind satisfied.

This special insulation paint could be of interest for your project.
http://www.pit-lane.biz/t3173p760-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-2-locked

[wobbly]

Apart from the pipe ( that had a 2.1* included header angle ) hahahahahah , the numbers I was given meant the Transfer STA was at 76.5 Hp and the Blowdown was at 60.5.
But when I suggested that the Aux needed to go right around to bore center , and fit pin plugs , again I wasnt preaching to the converted as TSR and Dynomation said all was well.
A bit sad really - but hey they were " fast man , really fast " .

[andreas]

Stray sheep will find their way, not to worry.

[F5 Dave]

Stray sheep are delicious.

[andreas]

https://www.youtube.com/watch?v=_FA85RO89HA

[Pursang]

Cylinder head for tm kz

347635

Nostalgic bultaco engine

347636

Bultaco had all sorts of chamber configurations available... and a dyno.

The bathtub ones probable sacrificed some combustion purity for better control of the scavenging charge and possibly heat distribution.
Some were then fitted with twin spark plugs to even up the combustion rate.

Cheers, Daryl

[SwePatrick]

Does someone have a typical 3d ignition map for twostroke and willing to share?
I need to see the 'shape', it tells me basics of what to think of when adjusting.

[lodgernz]

A recent faecesbook rant by disciple Cotswold, addressed to a non-believer:

"There is only one true faith, and you have your feet firmly on the path to damnation. Did not Jan Thiel say "behold here is a 2t and it is fast, strong and light", all that gazed upon it felt that power and put their knees on the floor and dragged them in delirium and once partaken of, the pull was unrelenting , did not Jan stand back and say "It is good" and it was. The fallen sat upon their misshapen rides with too many strokes, the failing of rods, the snapping of camchains and spilling of oil and they gnashed their teeth in anguish as yet another valve head detached itself to inflict more pain on the mistaken. There is only one true way, the way of the 2T. Braaap"

[breezy]

Max, the bore dimension on that drawing is "Ø 53,1 (Prelavorato)" which, as Google Translator will tell you, means raw, unfinished. The same goes for other dimensions in that drawing, like the exhaust port height and its center and corner radii. Besides, that drawing is quite an oldie; it doesn't show the RSA cylinder.

Patrick, the water temp in an Aprilia RSA125 is about 40°C (in the RSA250 it was about 50°C because otherwise the radiator size would have to be huge) but I'll admit that the cooling water is hotter than the surrounding air.
Following your reasoning, I should switch from watercooling to aircooling. Something tells me there has to be a catch. For example that a liquid will absorb heat a thousand times better than a gas, more than compensating for the smaller temperature difference between coolant and the object being cooled.

Frits,
would you think that modifying an air cooled barrel to be cooled with oil would be better than air? if your engine rules spec that " no WATER cooling allowed," and not "no LIQUID cooling allowed"... could this be a viable option?
regards, Nigel.

[wobbly]

Suzuki had the mainly oil cooled GSXR from 85 to 92.
The cylinders had tiny fins , as they ran two pumps. One high pressure for the usual bearing lube duty , the other circulated low pressure , high volume oil thru cooling galleries.
That system was dead reliable , and made for a very light weight engine assembly.

[husaberg]

Suzuki had the mainly oil cooled GSXR from 85 to 92.
The cylinders had tiny fins , as they ran two pumps. One high pressure for the usual bearing lube duty , the other circulated low pressure, high volume oil thru cooling galleries.
That system was dead reliable, and made for a very light weight engine assembly.

According to the net the dude that developed the system Suzuki later used on the GSXR750 (first made for the XN85 Turbo)
Estuo Yokouchi just copied off what they had done during WW2 for the high performance aero engines.
If what I found was correct some had the pump its self with low pressure and high-pressure outputs.
of course the advantage for Suzuki with the and the aero 4t was they had to have oil anyway.
what I remember most about all Suzuki's from that era was the smell of the cooked stators.
i am not sure which of the turbo bikes first had the under piston oiler jets as the ww2 planes did.
But the CX650T had the oilers as well.
Tom Sifton ran them in his Tuned Harley side valvers in the late40'searly 50's.
i have posted toms work here before not sure if it even mentioned I know the rotating lifters were
https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130226221#post1130226221


https://www.youtube.com/watch?v=PBYaF1BYrCA

[Frits Overmars]

Frits, would you think that modifying an air cooled barrel to be cooled with oil would be better than air? if your engine rules spec "no WATER cooling allowed," and not "no LIQUID cooling allowed"?Yes. But unlike the four-stroke Suzukis that carried a lot of oil anyway, you could choose something more cooling-effective than oil. Glycol, for example.
However, chances are that the rules do not allow other cooling fluids than water, on the basis that spilling some of the stuff on the track could render the track unusable for quite some time (which is also the main reason for not allowing diesel).

[Ns1Montesa]

Didn't old Rotax square cylinders basically have water around the whole outside of cylinder?

I know this is ineffective because of. Let's say stale water movement?


Regarding completely covered transfers. Sachs used pretty big water jackets in the 80s for their 50 and 80cc engines.

But as jonny already sad. Low water movement. Dont know what kind of goal they followed with this huge amonunt of water around the bore.

cheers

347673347674

[Muhr]

What you need is RSA125 manuale_ingranaggi_conici_2010_rev3.PDF , but I see no options of uploading PDF files here, so I copied the relevant pages for you, Muhr.
The conical gear is a sliding fit on the balance shaft. It is keyed into position with a 2,5 x 3,3 mm needle, # 9 in the center drawing, and the assembly is locked by the nut that also clamps the left-hand balance disc.
By the way, did you notice that the direction of the inlet disc rotation in your drawing is opposite to that of the RSA?

I'm preparing to send off for the manufacture of axles and gears, which feels pretty ok. What I don't feel really comfortable with is the lubrication for the bearing closest to the disc valve.
In the pictures you sent Frits, it looks like the distance pipe has a swirl that will take the oil up ?? (nr6)
The options here might be to run full ceramic or a closed bearing.

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/Pq9NEkIEbcc" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[breezy]

is it me or other than not having holes for the wrist pin in these pistons the ring could be pinned in a standard piston through the crown and caps fitted in the wrist pin holes..... or am I missing something...

[husaberg]

ior am I missing something...

Summer, cold Beer, decent governance and your former empire;)

[SwePatrick]

is it me or other than not having holes for the wrist pin in these pistons the ring could be pinned in a standard piston through the crown and caps fitted in the wrist pin holes..... or am I missing something...

Not having wristpin holes in piston is making it possible to run extreme exhaustports without shortcircuiting to the crankcase through the wristpin into the transfers.

[breezy]

Not having wristpin holes in piston is making it possible to run extreme exhaustports without shortcircuiting to the crankcase through the wristpin into the transfers.

yes i understand that issue.....but sealing caps in the wrist pin holes would surley do the same job.... i think now that the continuos piston ring has been abandond this is an expensive way of doing it...now im fully awake, probably a maintanace issue with just removing the piston ring would be difficult...

[breezy]

Summer, cold Beer, decent governance and your former empire;)

Yes husa, pubs are closed.:(.. out of work.:(..nothing wrong with Boris:sweatdrop... who could possibly vote for Corbyn....yes the old empire cinema has finally gone....have we missed anything:lol:

[Pursang]

Regarding completely covered transfers. Sachs used pretty big water jackets in the 80s for their 50 and 80cc engines.

But as jonny already sad. Low water movement. Dont know what kind of goal they followed with this huge amonunt of water around the bore.

cheers

347673347674

I suspect the main reason for those jackets was to create a even temperature to maintain dimensional stability of the cylinder, rather than heat dissipation.

The issue with low flow or thermo-syphon cooling is the occurrence of nucleate boiling at the hot spots.

Boiling water/coolant creates vapour bubbles (steam) on the contact surface. Vapour does not have the thermal conductivity of the liquid coolant.
That point gets hotter and hotter...........

One of the advantages of a high flow system is that the movement of the coolant brushes off the bubbles as they form.

I would like to experiment with a cooling system using some of the highly thermal conductive products used in electronics, for example.

The ideal would be a gel that increases its conductivity with temperature rise. Even temp all round the entire cylinder.

Cheers, Daryl

[trevor amos]

Steady on Nigel, things could get a lot worse especially if the `orange one` cons the supreme court and ends up with four more years , god help the world!

Does anyone see any heat transfer problems with the screwed together piston, lots of different sections in there that will expand and contract at different rates? In the event of a bad seizure how is the piston removed, just thinking.

Trevor

[husaberg]

..have we missed anything:lol:

Its not all bad though, you top the field for Horse burgers and cheese that smells like foot odour.....
Seriously though how is it going there

[ken seeber]

Does anyone see any heat transfer problems with the screwed together piston, lots of different sections in there that will expand and contract at different rates? In the event of a bad seizure how is the piston removed, just thinking.

Trevor

In terms of heat transfer, I think they’ll be ok. Why? There is a lot of sectional contact between the crown/inner piece and the outer skirt, by both the thread and shoulder. With the crown piece having the male thread, this will expand and lock into the skirt female thread, hopefully providing the good necessary contact and also preventing any flogging out and even unscrewing. It was not this way 12 months ago.

The pistons are inevitably & relatively heavy due to their 2 piece construction. Possibly a concern at the 19k rpm.

Seizures, what a negative consideration:nono:. Yep, might be hard to access the pin for removal. I guess that’s why the man invented cordless 5 inch angle grinders.

Either way, it is interesting and good on him/them having a go.

[breezy]

Its not all bad though, you top the field for Horse burgers and cheese that smells like foot odour.....
Seriously though how is it going there

well Husa, i suspect that every body is having the same kind of issues... not knowing whats next up the road is worrying......3 recessions and now a pandemic, what ever next?: war!..:facepalm:

[mantonakakis]

In terms of heat transfer, I think they’ll be ok. Why? There is a lot of sectional contact between the crown/inner piece and the outer skirt, by both the thread and shoulder. With the crown piece having the male thread, this will expand and lock into the skirt female thread, hopefully providing the good necessary contact and also preventing any flogging out and even unscrewing. It was not this way 12 months ago.

In one of the recent videos, it appears that until the threads are fully tightened, there is significant play between them - the two pieces of the piston can "rock" relative to each other (and presumably have some noticeable radial clearance - I'm sure Alex will drop in to clarify). Seems like a relatively simple countermeasure - maybe use selectable shims to set the ring to ring land axial clearance, and either add a more sizeable cylindrical interface with a close radial fit, or tighten the fit if such a feature already exists. My imagination tells me that radial clearance between the two pieces might be the biggest concern, i.e. if the O.D. of the crown is not concentric to the O.D. of the skirt once the pieces are tightened together, some bad things will happen...

Alex, if you do drop in here, if you share a cross-section view of the two pieces of the piston, I'm sure we can provide some feedback/sanity checking re: heat transfer and clearances/tolerances! (Not doubting your/Mark's design decisions, just offering more eyes to double-check or maybe come up with some design improvements).


The pistons are inevitably & relatively heavy due to their 2 piece construction. Possibly a concern at the 19k rpm.
I think I saw Alex mention somewhere recently that they weigh about the same as conventional pistons...

[Flettner]

wouldn't you just use a tapered thread?
For example, good old BSPT comes to mind.

[wobbly]

The original patented L ring piston design was lighter than a stock piston , and Makrs ones were as well , but not sure about the new combined design.
In testing the original design the ring was retained by the clearance given to the vertical L land , but this seems not to have worked for Alex.
Maybe excessive clearance allowing too much expansion into the port must have been the issue there.
The original piston was tested for reliability and siezure " proness " , if anything they seemed to be superior.

[Flettner]

Or this one. The lump on the top is only there to hold on to for finish machining. This is lighter than the comparable standard generic piston.
https://youtu.be/MxyTBXiaFQw

[obelsik]

Alex is a inspiration to garage mechanics with limited tools. I got my YZ250 head cut to 1.5mm squish by a friend on his lathe and then wanted to increase the chamber volume back to achieve 22 cc CCV. So I lay my old janky drill press on its side and chucked up the head using an old spark plug. Then then slowly wood lathed the dome into shape using a file with the end ground to a rounded shape. This way I could do it at home and slowly creep up on the cc I wanted. Surface is finish is not great but ti works.

[andreas]

At second glance, those snowmobiles look quite interesting. So if one were to couple for example a polaris 600 to a conventional gearbox (gears/belt/chain) what would be the best way?

[Flettner]

At second glance, those snowmobiles look quite interesting. So if one were to couple for example a polaris 600 to a conventional gearbox (gears/belt/chain) what would be the best way?

Cast new cases.

[andreas]

Cast new cases.

Thanks, I seem to have used the wrong word, it should say easy.

[wobbly]

Thats exactly what the Tularis project did.Without a balance shaft the big twin vibrated so badly it was all but impossible to ride for any length of time.

[andreas]

Yes I remember, was a 800 I think, The heavy crank gt 500 works fine. 4-600 maybe is accepable, not sure.

[Flettner]

Thanks, I seem to have used the wrong word, it should say easy.

In the long run it will be easier, when you consider all the problems with trying to join everything up with belts etc.
Cast new will make a tidy package and you can design in a balance shaft. A necessity with this type of engine. Been there, done that.

The pattern just needs to be wood, glue, bondifill and some paint. Can do it in the most basic of workshops, been there, done that.

Just saying.

[Condyn]

Here is a photo of Shannon Bacons rotax powered Suzuki with cvt still in place. A bit bulky but I think he is just intending on tooling around with it. 347691

[andreas]

In the long run it will be easier, when you consider all the problems with trying to join everything up with belts etc.
Cast new will make a tidy package and you can design in a balance shaft. A necessity with this type of engine. Been there, done that.

The pattern just needs to be wood, glue, bondifill and some paint. Can do it in the most basic of workshops, been there, done that.

Just saying.

I must investigate this option.
Condyn, Yea on the bulky side, probably fun nonetheless.

[wobbly]

The 'easyness " of this type of project depends upon one skill - CAD .
If you are sufficiently up to speed and can model a case on the screen , it is then way easyer to CNC this from billet than it is to make the cores , cast it , then have to machine most of it anyway.
Cylinders are a little different , in that again they are relatively " easy " to solid model , but to then have them 3D laser printed is not a cheap exercise.
This technology is however becoming more mature and cheaper by the day.
The first example of this approach was , I believe , the BSL500,where everything was CAD modelled.
Then the all CNC case was machined from billet , and the cylinders were 3D laser printed , directly off the models that had material added for all the machined surfaces.
A 5 axis CNC machining center could completely finish a case and the cassette cover in 14 Hrs .
And near on 20 years ago the laser printing of 4 cylinders at a time ( the maximum the platten could hold ) cost $5000 usd.

[Flettner]

I dont know about that. This engines patterns were built with no CNC or CAD models, in fact no drawing at all. Including the cylinder.
Just used some wood working equipment, kiln dried pine, cheap as chips. Each case half was in the order $100 to cast.
CAD / CNC is wonderful, but its not your only option.
I own both, but find it way quicker cheaper to just go out to the pattern shop and just make the pattern.
Not entirely true sometimes its easier to machine the pattern on the CNC. I don't machine big things like cases from solid because the cost of material is just soo high.

[mantonakakis]

I think Alex's 50cc cylinder would have cost ~1300GBP to have printed by Protolabs, for what that's worth.

On a different topic, I'm working on getting a RD125B engine created in EngMod2T. I don't have a dyno, so working on correlating to an old power curve published in a magazine in 1981 (14.8hp to the wheel at 9000-9500rpm). Assuming ~10% drivetrain loss, let's say about 16.5hp at the crank. There are a few challenges/aspects I'm not super confident about while modeling up the stock setup, namely the boost port and the stock pipe. The induction is cylinder reed with essentially a 360deg piston port, but also connected up to a single boost port as shown here (http://erlenbachracing.co/RD125_RD200_TA125.htm):
347697

I treated the boost port as a separate, short port. I used the Yam12 scavenging model, as it is exactly like the A ports. B ports are similar but with a very steep roof angle (~60deg from horizontal). Here's a side-on view of the inlet port/boost port - cylinder side is to the right, a small portion of the reed cavity without the reed block included to show the transition:
347698

The exhaust pipes are modeled as T-pipes; in reality they almost perfectly match the "standard pipe" shown in section 7 of the "Types of exhaust systems" help file. I ran into modeling limitations on the silencers for a multi-cylinder engine, so I just modeled the T-pipe atmospheric end with a very steep baffle cone to the appropriate restrictor diameter, with a 100mm stinger pipe. It at least gives the same peak power RPM and overall curve shape as the dyno data from the old magazine. So, close enough I guess.

My power curve is too optimistic below the power peak, it seems. After the power peak, it's almost identical. Not sure how to get it any more accurate, or if I should just say "good enough" and move on with modeling modifications? The only thing that's gotten it to be a lot more similar is reducing the CCR in the model (1.2 vs 1.34 as measured).

347695

347696

[wobbly]

Playing with the CCR is a software cheat , but it can have all sorts of bad effects when you are trying to improve on the baseline.
It means the baseline is wrong from day one.
If the sim is optimistic down low , I would be looking at what does change , in reality , during a dyno pull.
The egt , and thus the pipe wall temp will vary considerably.
In nearly all the race engines I have worked on , using 325* below the pipe and 425* at peak power gives great realistic results.
For a "stock " engine the numbers can easily be adjusted to change how the sim reacts at very low rpm by simply changing the wall temp.
The software interpolates beween the two temps , so you can add as many jump points as is needed to reflect reality.

[mantonakakis]

The egt , and thus the pipe wall temp will vary considerably.
In nearly all the race engines I have worked on , using 325* below the pipe and 425* at peak power gives great realistic results.
For a "stock " engine the numbers can easily be adjusted to change how the sim reacts at very low rpm by simply changing the wall temp.

Makes sense, thank you, I'll give that a try!

[mantonakakis]

In nearly all the race engines I have worked on , using 325* below the pipe and 425* at peak power gives great realistic results.
For a "stock " engine the numbers can easily be adjusted to change how the sim reacts at very low rpm by simply changing the wall temp.

Alright, after many tries (including double-checking and slightly updating compression ratio and squish clearance, at least as best as I can with a disassembled crank at the moment...), I'm not able to shift the entire curve down in any significant manner by just changing the wall temps. My final run was just a 2-point curve for wall temp, from 4k to 9k, 370deg to 425deg.
The only other really significant factor I could think of that would shift the overall curve down was altering the combustion efficiency - I decreased it from 82% to 70%, and with the above wall temps, got the following result, much closer.
70% seems pretty low, but what else could make such a big constant offset for my model? Maybe that's fine for an old air-cooled engine?
347701

[husaberg]

The 'easyness " of this type of project depends upon one skill - CAD .
If you are sufficiently up to speed and can model a case on the screen , it is then way easyer to CNC this from billet than it is to make the cores , cast it , then have to machine most of it anyway.
Cylinders are a little different , in that again they are relatively " easy " to solid model , but to then have them 3D laser printed is not a cheap exercise.
This technology is however becoming more mature and cheaper by the day.
The first example of this approach was , I believe , the BSL500,where everything was CAD modelled.
Then the all CNC case was machined from billet , and the cylinders were 3D laser printed , directly off the models that had material added for all the machined surfaces.
A 5 axis CNC machining center could completely finish a case and the cassette cover in 14 Hrs .
And near on 20 years ago the laser printing of 4 cylinders at a time ( the maximum the platten could hold ) cost $5000 usd.

Hi Wob that cover boss on the right looks like it has had welds added on?
347704
the other pic I have appears similar in this detail on the gusset/fillet
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=303975&d=1413102457

I don't think I have seen that pic before do you have any others than are not in this album
https://www.kiwibiker.co.nz/forums/album.php?albumid=4865

[41juergen]

Alright, after many tries (including double-checking and slightly updating compression ratio and squish clearance, at least as best as I can with a disassembled crank at the moment...), I'm not able to shift the entire curve down in any significant manner by just changing the wall temps. My final run was just a 2-point curve for wall temp, from 4k to 9k, 370deg to 425deg.
The only other really significant factor I could think of that would shift the overall curve down was altering the combustion efficiency - I decreased it from 82% to 70%, and with the above wall temps, got the following result, much closer.
70% seems pretty low, but what else could make such a big constant offset for my model? Maybe that's fine for an old air-cooled engine?
347701

I have the same issue like you when moddeling my stock 3XV engine. What I found is that first don't trust any workshop manuals or other sources about the ports timings etc. Make sure that you measure them correctly best as you can. Second the stock Yam pipes (at least from my 3XV) have a "heat isolation" mat inside the belly, that changes the ex gas temp setup in the sim from a "typical" tuned pipe. But even doing all this a best as I can, sometimes I get strange power curves..

[philou]

At second glance, those snowmobiles look quite interesting. So if one were to couple for example a polaris 600 to a conventional gearbox (gears/belt/chain) what would be the best way?

Frits I have post it

347706347707

[andreas]

Alright, after many tries (including double-checking and slightly updating compression ratio and squish clearance, at least as best as I can with a disassembled crank at the moment...), I'm not able to shift the entire curve down in any significant manner by just changing the wall temps. My final run was just a 2-point curve for wall temp, from 4k to 9k, 370deg to 425deg.
The only other really significant factor I could think of that would shift the overall curve down was altering the combustion efficiency - I decreased it from 82% to 70%, and with the above wall temps, got the following result, much closer.
70% seems pretty low, but what else could make such a big constant offset for my model? Maybe that's fine for an old air-cooled engine?
347701

First of all it's a great bike, superior to it's successor th Lc. Not sure what you mean by a t-shaped pipe, but it's got individual classic pipes with a diverging part that ultimatly ends in an insert muffler- so it will never be "on the pipe"- needless to say it will greatly benfit from a pair of functional pipes. Also, it has bell-shaped combustion chambers, so no real squish.

[Frits Overmars]

Frits I have post it

347706347707Thanks Philou, I was just going to start looking for those pictures again. in 2016 I asked BRP-Rotax for the specifics of this engine. It turned out that it was nonexistent; Rotax just wanted to gauge potential interest. So instead of some answers I received an extensive questionnaire.
As far as I know this engine still does not exist. Too bad; I wouldn't have minded a 850cc E-Tec version.

[mantonakakis]

I have the same issue like you when moddeling my stock 3XV engine. What I found is that first don't trust any workshop manuals or other sources about the ports timings etc. Make sure that you measure them correctly best as you can. Second the stock Yam pipes (at least from my 3XV) have a "heat isolation" mat inside the belly, that changes the ex gas temp setup in the sim from a "typical" tuned pipe. But even doing all this a best as I can, sometimes I get strange power curves..
Yes, I found some issues with the manual. The exhaust port seemed to have the dimension flipped (i.e. the manual gave the port height, but actually it should have been shown as height from the deck to top of port, roughly 3mm error). The compression ratio is strangely not listed in the repair manual, but the "combustion chamber volume" is in there, listed as 6.7cc - I measured it as 4cc at zero squish clearance, and at least with my engine disassembled, it appears to be 6.2cc with an estimated 1.5mm squish. I'll have to check both of those again once I receive my new conrods and can put the crank back together...

[mantonakakis]

First of all it's a great bike, superior to it's successor th Lc.
Great to hear the positive opinion, I have yet to feel it run with full stock power, as my crank seals were bad and the cylinders are a bit worn out of spec - I started a teardown to freshen up the bottom end, and managed to bend a rod... oops! But even at its less-than-factory performance level, I've fallen in love! I'm really looking forward to seeing what I can do with it once I get the crank back together, and also with a fresh bore/hone. I thankfully have two, possibly three sets of cylinders I can play with, although one set might not be salvageable and the other is in need of a rebore.

Not sure what you mean by a t-shaped pipe, but it's got individual classic pipes with a diverging part that ultimatly ends in an insert muffler- so it will never be "on the pipe"- needless to say it will greatly benefit from a pair of functional pipes.
By T-shaped, I meant as referenced in the Dat2T help file - there is a small perforated pipe that extends into the diffuser by about 65mm, which matches the header diameter. The help file suggested modeling this as a T-pipe to account for the header intruding into the diffuser:
347709
At least on 6.0.0, I can't add a silencer to a T-pipe on a 2-cylinder (single only), and I wanted to model the common airbox, so I needed to stick with the twin engine model. I figured the most important aspect of modeling accuracy for the pipe would be the restrictor diameter, so I approximated as a very steep rear cone.

Also, it has bell-shaped combustion chambers, so no real squish.
There does seem to be a squish band that's roughly parallel to the outer 50% area of the piston crown. Although definitely not a toroidal combustion chamber (~30mm O.D. bell-shaped chamber, ~4cc), and a radiused transition between the two:
347708
I know not to expect really great power with the Yam12-style transfers (iron liner is the inner transfer wall, not much room to carve into more of a teacup shape), but maybe 30hp would be achievable? It'd be nice to give a stock RD350 a run for its money, since the bike weighs roughly 100kg stock! And the sound at really high revs would be great!

[andreas]

Aha I see, there were different versions of the head. Yes, it will withstand 14k on regular basis.

[wobbly]

Have you run a Turbulent Combustion sim and pasted the results into a new file - if you dont know how , let us know and I will do a quick description.
This makes a big difference , especially to very low and very high power sims as "real " Vibe A and Vibe M inputs take into account even small details like squish velocity.

Husa , those " weld " looking marks are due to that being the prototype case. At the time the CNC guys were just learning how to program the tool paths using NZs first seat of Gibbs - as I had introduced
them to having to reproduce real CNC 5 axis shapes off the SolidWorks platform.They had only ever used 2D CAD drawings previously.

Early on we discovered that the software does not " like " having corner radi in the model that matches the radi of the ball nose being used.
It hunts in the corners , trying to copy exactly the shape with hundreds of extra lines of code..
If I removed the model fillets , the final cut ball nose would simply run into the corner , and leave the fillet naturally - and the code file size was about 20% of the original.

Yes I have a bunch of BSL pics on a disc somewhere.

[mantonakakis]

Have you run a Turbulent Combustion sim and pasted the results into a new file - if you dont know how , let us know and I will do a quick description.
This makes a big difference , especially to very low and very high power sims as "real " Vibe A and Vibe M inputs take into account even small details like squish velocity.
Actually yes, just an hour ago! Quite a big difference in duration compared to my previous prescribed values, smaller differences in the other values. Duration was 31-37deg from 4k to 9k, jumped to 50deg at 10k (just after power peak). Delay increased steadily from 7 to 9deg up to 9k, then jumped to 11deg at 10k. VibeA was a bit higher than the default value of 6, from 7.4-8.6, and VibeM was consistently less than the default of 1.25, at 0.75-0.9. Didn't make a huge difference in the power curve, however. "1" is the default values, "2" uses the turbulent sim, and "3" updates the prescribed values to match the turbulent sim:
347710

After some small adjustments to my approximation of the stock pipe, and some wall temperature tweaks (getting remarkably close to your 325/425 recommendation, still iterating), I've gotten pretty close. The biggest single factor that brought the curve down to reality, though, was decreasing combustion efficiency to 70%. Oh, and I updated to the latest software this morning.
347711

One other factor which might be off is AFR - I'm guessing with a relatively simple carb like the stock 18mm Teikei, AFR is not a flat 12:1 as I have it modeled currently. I assume that the 1981 dyno run I found was running relatively richer at the lower RPM range, maybe rich enough to lose some power? The article (http://www.champsclock.com/download/1981-yamaha-rd125-april81-motorcycle-mechanics.pdf) did mention poor fuel economy...

[wobbly]

Yep , now you have a good baseline.
I would say that the rear wheel to crank losses are 12.5 to 15% - so this would increase the dyno adjusted to crank result , and thus increase the combustion efficiency needed.

[mantonakakis]

Yep , now you have a good baseline.
I would say that the rear wheel to crank losses are 12.5 to 15% - so this would increase the dyno adjusted to crank result , and thus increase the combustion efficiency needed.
Thanks for all the help! I'll probably be coming back soon to check some of my plans for making more power - especially for any minor port reshaping or timing changes, and maybe for some advice on exhaust port stuffing (way too big at the exit, 28mm diameter vs. 20x25mm port window).

I need to double-check once I get the engine back together, but stock timing is about 183/127 with a 58% of bore exhaust port width, with all 5 transfer ports opening simultaneously. Annoyingly the B-port floors are 2-3mm below the crown at BDC, but they also have a very steep 50deg roof, so maybe there are a few options... E.g. cutting piston crown on the B ports, cutting in a flatter roof, etc. Anyway, I'll come with port mold photos before asking anything specific.

[Condyn]

Why is it that most twins come from the factory as oversquare engines? Is it an effect from packaging constraints since the engine is already wide, they don’t want to go taller? Or is it a piston speed thing? The reason I ask is the engine I am working on designing is oversquare by 2mm. I would be within the allotted cc limits if I were to stroke it square. Will it pay off enough to go through the hassle of squaring it up?

[wobbly]

Oversquare is an old fashioned precept that simply doesnt work.
Its all to do with the way you have to go about generating port area , and on the other side of that coin is the percieved idea that you can rev a short stroker harder due to lower piston speed.
But all physics aside , look at what history tells us.
In GP racing Yamaha steadfastly stuck to 56x 50.6 and were never even close to winning 125 or 250 titles untill they finally ditched corporate pride and went square in 2000.
That year they blitzed 250GP with Jaques and Nakano.
Due to the port timing limitations , the short stroke 4DP series TZ could never rev harder than the 54 square Honda or Aprilia - as the theory says it should.

There is a completely differing set of reasons for 250MX singles to be very undersquare at 72 stroke - where outright power isnt the issue, its a flat torque curve from low rpm.
But then look at the power results gained by Honda with its RS500V that was 68 x 68.8 square.

The worst example of oversquare idiocy would have to be" the great leaders " V twin GP500 Aprilia.
Its only claim to fame being McWilliams pole at Philip Island , and that was the rider on that day , not the engines power as was predicted ( never actually seen in reality ).

[husaberg]

Oversquare is an old fashioned precept that simply doesnt work.
Its all to do with the way you have to go about generating port area , and on the other side of that coin is the percieved idea that you can rev a short stroker harder due to lower piston speed.
But all physics aside , look at what history tells us.
In GP racing Yamaha steadfastly stuck to 56x 50.6 and were never even close to winning 125 or 250 titles untill they finally ditched corporate pride and went square in 2000.
That year they blitzed 250GP with Jaques and Nakano.
Due to the port timing limitations , the short stroke 4DP series TZ could never rev harder than the 54 square Honda or Aprilia - as the theory says it should.

There is a completely differing set of reasons for 250MX singles to be very undersquare at 72 stroke - where outright power isnt the issue, its a flat torque curve from low rpm.
But then look at the power results gained by Honda with its RS500V that was 68 x 68.8 square.

The worst example of oversquare idiocy would have to be" the great leaders " V twin GP500 Aprilia.
Its only claim to fame being McWilliams pole at Philip Island , and that was the rider on that day , not the engines power as was predicted ( never actually seen in reality ).

My theory was that Yamaha was tied into the oversquare design as it was an offshoot of the 500 team and the 500 program never had the room as the bore centers were to close to have decent transfers so they ran 6 transfer ported oversquare cylinders, did the move to 54x54 also includes move to 4 main transfers or did they do that prior?

[Schumae2]

Oversquare is an old fashioned precept that simply doesnt work.
Its all to do with the way you have to go about generating port area , and on the other side of that coin is the percieved idea that you can rev a short stroker harder due to lower piston speed.
But all physics aside , look at what history tells us.
In GP racing Yamaha steadfastly stuck to 56x 50.6 and were never even close to winning 125 or 250 titles untill they finally ditched corporate pride and went square in 2000.
That year they blitzed 250GP with Jaques and Nakano.
Due to the port timing limitations , the short stroke 4DP series TZ could never rev harder than the 54 square Honda or Aprilia - as the theory says it should.

There is a completely differing set of reasons for 250MX singles to be very undersquare at 72 stroke - where outright power isnt the issue, its a flat torque curve from low rpm.
But then look at the power results gained by Honda with its RS500V that was 68 x 68.8 square.

The worst example of oversquare idiocy would have to be" the great leaders " V twin GP500 Aprilia.
Its only claim to fame being McWilliams pole at Philip Island , and that was the rider on that day , not the engines power as was predicted ( never actually seen in reality ).

Wobbly; with respect to 125GP engines and 125cc KZ/ICC kart engines I was wondering your opinion on connecting rod length. With karts it seems many KZÂ’s have settled on either 110mm-115mm yet some engines such as the Modena MKZ is 106mm and the Honda RS125 is 104mm. I understand how rod length affect piston acceleration and dwell time at TDC / BDC, but in your opinion is there a specific reason why most higher performance 125cc engines utilize a 110mm connecting rod, while less use 115mm and even less around 105mm?

I have read quite a few articles on this in TKart magazine, and the consensus is 110mm is a good trade off based on track length but, thereÂ’s been conflicting evidence in other articles in regards to balance factor and engines that donÂ’t have a power jet, that the shorter rod keeps the pipe hotter due to the less complete of burn around TDC and wasted heat energy being transferred to the pipe.....IÂ’m not sure about this but, VORTEX newest KZÂ’s (RSZ and RTZ are basically the same engine with 2-cylinders and a jug spacer, so crank assemblies and top ends can be switched track to track for both utilizing 110-mm & 115-mm lengths.....VORTEX claims the 115-mm is best for longer tracks).

I would greatly appreciate any insight you would be willing to provide (thank you!!!)

[wobbly]

Husa , na , the 56 bore compromised the transfers even more.
All to do with corporate pride and who was in charge of R&D at the time.
The dual boost port , big bore was a cockup in every direction , but untill managment changed in 99 and they bought a Czech CNC anemometric flow visualizing rig , suddenly they
went square and changed to 5 port designed on the new machines results.
Susan , as was his nickname at the time , the new head of the race dept told me they could accurately predict a Hp curve shape purely off the flow results , and didnt need to dyno dozens of
cylinders anymore - and his new 5 port design was easily way better than anything else they tested.

Schumae , if you really want to look at a positive direction re rod length then as I said before look at historical results.
The RS125/250 Honda had a short rod forever , untill Honda finally got serious as they wanted desperately to win the final season of GP racing.
Suddenly the new bike appeared with 109 rods and beat the Aprilia due to being just fast enough with Aoyama on board , and the Italian boys all stealing points off each other..
Jans RSA went to 120 , as part of getting a really big case volume , that RVs work well with.

The short rod KZ Modena has won nothing - the TM has always had a 109.8 ( an old mistake in CNC programming they never rectified ) very close to 2:1 and has easily the best record over time.
I wanted to go to 113 with the new homologation R1 but Franco flattly refused , and told me to shutup and stick to pipe design.
The 115 rod Vortex does make more top end power ( probably due in main to reduced bore friction ) but the issue with a reed engine is that you have a catch22 regarding case volume and the reed thickness needed.
Big cases under 1.3 ratio ( due to a longer rod ) do work better with aggresive pipes , but the bigger case has a Helmholtz trend that needs thinner and thinner stiffness petals - these quicly loose control due to
the first harmonic frequency - and thus power drops.

In my opinion people raving on about short rods , powerjets and incomplete burn , are trying it on with techno babble rubbish.
The heat transferred into a pipe is completly dependant upon the combustion variables of compression and ignition advance being optimised to suit the Ex ports interaction with the pipe length being used.
Yes , short rods dwell at TDC differntly than long ones , but both can be optimised to give the best result for that set in stone design variable.
And yes a Powerjet can make it easy to reduce the natural tendency of a venturi carb to go progressively rich over the top of the powerband.
But we have a whole bag of tricks to achieve the same effect in a KZ without one - easily able to hit 680*C in the header at 14800 , if the fuel will allow it.

[Schumae2]

Husa , na , the 56 bore compromised the transfers even more.
All to do with corporate pride and who was in charge of R&D at the time.
The dual boost port , big bore was a cockup in every direction , but untill managment changed in 99 and they bought a Czech CNC anemometric flow visualizing rig , suddenly they
went square and changed to 5 port designed on the new machines results.
Susan , as was his nickname at the time , the new head of the race dept told me they could accurately predict a Hp curve shape purely off the flow results , and didnt need to dyno dozens of
cylinders anymore - and his new 5 port design was easily way better than anything else they tested.

Schumae , if you really want to look at a positive direction re rod length then as I said before look at historical results.
The RS125/250 Honda had a short rod forever , untill Honda finally got serious as they wanted desperately to win the final season of GP racing.
Suddenly the new bike appeared with 109 rods and beat the Aprilia due to being just fast enough with Aoyama on board , and the Italian boys all stealing points off each other..
Jans RSA went to 120 , as part of getting a really big case volume , that RVs work well with.

The short rod KZ Modena has won nothing - the TM has always had a 109.8 ( an old mistake in CNC programming they never rectified ) very close to 2:1 and has easily the best record over time.
I wanted to go to 113 with the new homologation R1 but Franco flattly refused , and told me to shutup and stick to pipe design.
The 115 rod Vortex does make more top end power ( probably due in main to reduced bore friction ) but the issue with a reed engine is that you have a catch22 regarding case volume and the reed thickness needed.
Big cases under 1.3 ratio ( due to a longer rod ) do work better with aggresive pipes , but the bigger case has a Helmholtz trend that needs thinner and thinner stiffness petals - these quicly loose control due to
the first harmonic frequency - and thus power drops.

In my opinion people raving on about short rods , powerjets and incomplete burn , are trying it on with techno babble rubbish.
The heat transferred into a pipe is completly dependant upon the combustion variables of compression and ignition advance being optimised to suit the Ex ports interaction with the pipe length being used.
Yes , short rods dwell at TDC differntly than long ones , but both can be optimised to give the best result for that set in stone design variable.
And yes a Powerjet can make it easy to reduce the natural tendency of a venturi carb to go progressively rich over the top of the powerband.
But we have a whole bag of tricks to achieve the same effect in a KZ without one - easily able to hit 680*C in the header at 14800 , if the fuel will allow it.

Wobbly; thank you for the detailed reply, much appreciated!

IÂ’m working on a Honda CR125 based kart engine (the class is called mod-Honda) and the rules are very open in terms of what can be changed...basically the cases must be 97-99 cr125 (modification allowed) and the cylinder can be any CR125 from 99-02.....the ignition, pipe, carburetor, and rotating assembly are all open to modification / replacement.....my current setup is an 02-cylinder that has been extensively ported / welded / filled to be as similar to an RS125 NX4 as possible, and the combustion chamber has had brass inlay added with anti-detonation ring to RS125 dimensions, associated VHM RS125 piston, 38mm non-power jet kehin PWM carb....many pipes / ignitions have been tested and it feels theres more development needed there as well as the reed pack (your input was very helpful, I will put my focus on the pipe, reeds, and ignition opposed to considering a rod length change and all associated changes that would come with it, at this time).

[Condyn]

Excellent information Wobbly. The next issue I am running into is the potential of too much case volume. Stock, this engine came with a 125mm rod and is 66x64. If I increase the rod to a 132 for 2:1 and square the engine I will be adding quite a bit of volume, and it is a reed engine. I will have to find a piston with a high pin and need a spacer. Once i finish welding on the case reed blocks, I will collect the ccr as stock form and see what I am working with as a baseline. But that is all besides the point for right now. 66x66 is where it will end up one way or another.
Ps Schumae, this site does not use apostrophes. I had to adapt myself.

[andreas]

Going from 56x 50.6 to 54x54 gives 2.9% area increase. Sounding a little negative there I realize- just to mention there might be less money&labour intense alternatives.

[wobbly]

The TM is 54 x 54.43 stroke FYI.
Mod Honda , didnt know that class still existed - having won SKUSA Stock Honda 3 times I can tell you that all of the approved class pipes were rubbish.
I tested all of them and looked into making a new approved pipe with alot better power and spread , but the die sets were around 20K I didnt have at the time - so Pro Circuit got that job.
The best power increases came from making a header manifold like the 250GP , with no steps at either end , and I found nearly 2 Hp in the reeds.
First thing to change tho would be the inlet manifold , there is 1.5 Hp in a dead straight late model RS125 rubber.
If you can run a programmable then using the short powerjet carb would be a huge advantage.

[Schumae2]

The TM is 54 x 54.43 stroke FYI.
Mod Honda , didnt know that class still existed - having won SKUSA Stock Honda 3 times I can tell you that all of the approved class pipes were rubbish.
I tested all of them and looked into making a new approved pipe with alot better power and spread , but the die sets were around 20K I didnt have at the time - so Pro Circuit got that job.
The best power increases came from making a header manifold like the 250GP , with no steps at either end , and I found nearly 2 Hp in the reeds.
First thing to change tho would be the inlet manifold , there is 1.5 Hp in a dead straight late model RS125 rubber.
If you can run a programmable then using the short powerjet carb would be a huge advantage.

Yep, its not a popular class anymore (nether is stock Honda as of last years SKUZA rule changes) most everyone that has a shifter kart is running a KZ or the 175-SSE by IAME or a VORTEX-ROK shifter.....many tracks mix all the engines together in the same class to keep the Kart count high, but run them at different weights to try to attempt to keep some performance parity. I have a ROK, but the mod-Honda is mainly a project to me, to see how far it can be developed, and see what I can learn during the process (hopefully with it ending up being competitive).

I have done some of the things you mentioned...Im running V-force-4 reeds (designed for the RS125) with 2-stage petals, and a straight billet inlet manifold that is even a bit shorter than the original RS manifold (the carburetor outlet is about 5-mm from the reed stuffer.......the header manifold is a kart piece from a stock Honda (I will need to look into a making one without steps as there is one at the cylinder but it flows smoothly into the pipe). I have programmable ignition though its a reprogram of the stock CDI from Swedetech for Mod-Honda (looking into changing that soon)......the pipe that has worked best so far is the RLV-R5 pipe, that is meant for road racing (Ive shortened the primary header length by 19mm to get the tuned length to make peak power closer to 13,000 RPM and the stinger diameter has interchangeable pills to reduce the inner diameter [currently at 23.5mm])......I wish I could use a carburetor with a power-jet but, the rules say that all fuel must enter the carburetor through the main jet, so that has limited my options (the only carburetor modification is I have a spare that was oval bored from 38-mm to 40mm in the vertical orientation [i didnt see much of a difference swapping back to a standard unit]).......Ive also played with the combustion chamber CCs bit, but that was more an effort to make the 2-set ignition curves work well with my setup.

Thank you again for the helpful insight! Ive lurked on this thread for a year or so, and have read many of your, Jans, Fritz, and Husas posts over that time, which has been a great supplement to the books I’ve been reading, and now beginning to play with modeling software.

[Schumae2]

Excellent information Wobbly. The next issue I am running into is the potential of too much case volume. Stock, this engine came with a 125mm rod and is 66x64. If I increase the rod to a 132 for 2:1 and square the engine I will be adding quite a bit of volume, and it is a reed engine. I will have to find a piston with a high pin and need a spacer. Once i finish welding on the case reed blocks, I will collect the ccr as stock form and see what I am working with as a baseline. But that is all besides the point for right now. 66x66 is where it will end up one way or another.
Ps Schumae, this site does not use apostrophes. I had to adapt myself.

Thank you Condyn, for the tip on the apostrophes! Im new to posting on this site, and wondered what I was doing wrong.:facepalm:

[andreas]

Hi Schumae, do you know how much hp it's making?

[Schumae2]

Hi Schumae, do you know how much hp it's making?

Hello Andreas;
Im not sure in its current configuration? Based on its relative lap times compared to the VORTEX-ROK, I would suspect that its of somewhat similar power to that engine, though its parity to that engine depends somewhat on track size / gearing differences. VORTEX advertises the ROK shifter to make 43-44hp, but Im unsure what dyno or correction factors are being used to generate that number.

[andreas]

Ok, cool.

[jamathi]

Oversquare is an old fashioned precept that simply doesnt work.
Its all to do with the way you have to go about generating port area , and on the other side of that coin is the percieved idea that you can rev a short stroker harder due to lower piston speed.
But all physics aside , look at what history tells us.
In GP racing Yamaha steadfastly stuck to 56x 50.6 and were never even close to winning 125 or 250 titles untill they finally ditched corporate pride and went square in 2000.
That year they blitzed 250GP with Jaques and Nakano.
Due to the port timing limitations , the short stroke 4DP series TZ could never rev harder than the 54 square Honda or Aprilia - as the theory says it should.

There is a completely differing set of reasons for 250MX singles to be very undersquare at 72 stroke - where outright power isnt the issue, its a flat torque curve from low rpm.
But then look at the power results gained by Honda with its RS500V that was 68 x 68.8 square.

The worst example of oversquare idiocy would have to be" the great leaders " V twin GP500 Aprilia.
Its only claim to fame being McWilliams pole at Philip Island , and that was the rider on that day , not the engines power as was predicted ( never actually seen in reality ).

In 2000 the Yamaha France crew-chief Guy Coulon copied the Honda cylinders, I don't know if this was done with permission of Yamaha or not
Later Yamaha-Japan did the same with the 500cc fours.
They even published a SAE paper about it, incredible!!!!!!!
In 2003 a longer stroke was tried at Aprilia: 53mm bore
The result was less power and more detonation----
Then 52 bore was tried, even less power, and after some tests the piston oin was found, inside the carburetor.
That was the end of Aprilia's long stroke experiments....

[husaberg]

Husa , na , the 56 bore compromised the transfers even more.
All to do with corporate pride and who was in charge of R&D at the time.
The dual boost port , big bore was a cockup in every direction , but untill managment changed in 99 and they bought a Czech CNC anemometric flow visualizing rig , suddenly they
went square and changed to 5 port designed on the new machines results.
Susan , as was his nickname at the time , the new head of the race dept told me they could accurately predict a Hp curve shape purely off the flow results , and didnt need to dyno dozens of
cylinders anymore - and his new 5 port design was easily way better than anything else they tested.

Schumae , if you really want to look at a positive direction re rod length then as I said before look at historical results.
The RS125/250 Honda had a short rod forever , untill Honda finally got serious as they wanted desperately to win the final season of GP racing.
Suddenly the new bike appeared with 109 rods and beat the Aprilia due to being just fast enough with Aoyama on board , and the Italian boys all stealing points off each other..
Jans RSA went to 120 , as part of getting a really big case volume , that RVs work well with.

The short rod KZ Modena has won nothing - the TM has always had a 109.8 ( an old mistake in CNC programming they never rectified ) very close to 2:1 and has easily the best record over time.
I wanted to go to 113 with the new homologation R1 but Franco flattly refused , and told me to shutup and stick to pipe design.
The 115 rod Vortex does make more top end power ( probably due in main to reduced bore friction ) but the issue with a reed engine is that you have a catch22 regarding case volume and the reed thickness needed.
Big cases under 1.3 ratio ( due to a longer rod ) do work better with aggresive pipes , but the bigger case has a Helmholtz trend that needs thinner and thinner stiffness petals - these quicly loose control due to
the first harmonic frequency - and thus power drops.

In my opinion people raving on about short rods , powerjets and incomplete burn , are trying it on with techno babble rubbish.
The heat transferred into a pipe is completly dependant upon the combustion variables of compression and ignition advance being optimised to suit the Ex ports interaction with the pipe length being used.
Yes , short rods dwell at TDC differntly than long ones , but both can be optimised to give the best result for that set in stone design variable.
And yes a Powerjet can make it easy to reduce the natural tendency of a venturi carb to go progressively rich over the top of the powerband.
But we have a whole bag of tricks to achieve the same effect in a KZ without one - easily able to hit 680*C in the header at 14800 , if the fuel will allow it.


In 2000 the Yamaha France crew-chief Guy Coulon copied the Honda cylinders, I don't know if this was done with permission of Yamaha or not
Later Yamaha-Japan did the same with the 500cc fours.
They even published a SAE paper about it, incredible!!!!!!!
In 2003 a longer stroke was tried at Aprilia: 53mm bore
The result was less power and more detonation----
Then 52 bore was tried, even less power, and after some tests the piston oin was found, inside the carburetor.
That was the end of Aprilia's long stroke experiments....

Oddly the most successful model of Cagiva 500 GP campaign te V594 ended the season at least as 54x54.
looking at some pics I have they also had models in this period with Honda like bridged Ex ports and flapper ex valves.
347736

What's odd is the Cagiva was known to so very close to the Yamaha YZR500 that parts could be substituted.
but yes maybe just like the 5 valve head and honda with reeds, maybe pride keep them from changing.


I am still not sure that Yamaha had the room for decent transfers and suspect that this might be why they stuck with 6 main transfers
the spacings compared to Hondas single crank were so close they couldn't even fit in the reeds properly.
347737347738

it seems later yamaha were wider bore centers.

Edit okay Yamaha went bridged in 1997 I did not know this.
347735

[wobbly]

All the Stock Honda spigots as well as a few aftermarket ones I saw had a step at the exit - I knew from my testing on KZ that you get a good top end increase by eliminating that step
such that the spigot end is a sharp edge. I spent most of one night in the tent at Vegas with a drill and a round file modifying one for morning warm up.
The data showed near on 300 rpm extra down the shute - the result was the first Stock Honda win for us.
By the next year I had my own CNC made ones with no steps at all.

Haha Jan - I wonder who the clever dick was at Aprilia who thought long stroke was the way to go.

[jamathi]

All the Stock Honda spigots as well as a few aftermarket ones I saw had a step at the exit - I knew from my testing on KZ that you get a good top end increase by eliminating that step
such that the spigot end is a sharp edge. I spent most of one night in the tent at Vegas with a drill and a round file modifying one for morning warm up.
The data showed near on 300 rpm extra down the shute - the result was the first Stock Honda win for us.
By the next year I had my own CNC made ones with no steps at all.

Haha Jan - I wonder who the clever dick was at Aprilia who thought long stroke was the way to go.

It certainly wasn't me!!!!

[Schumae2]

All the Stock Honda spigots as well as a few aftermarket ones I saw had a step at the exit - I knew from my testing on KZ that you get a good top end increase by eliminating that step
such that the spigot end is a sharp edge. I spent most of one night in the tent at Vegas with a drill and a round file modifying one for morning warm up.
The data showed near on 300 rpm extra down the shute - the result was the first Stock Honda win for us.
By the next year I had my own CNC made ones with no steps at all.

Haha Jan - I wonder who the clever dick was at Aprilia who thought long stroke was the way to go.

Wobbly; thank you for the clarification on the spigot step (I will look into its match up to the pipe).

[wobbly]

I knew that Jan , would love to name and shame the specific idiot , not that it matters to anyone except afficionado 2 stroker historians.

[Frits Overmars]

I wish I could use a carburetor with a power-jet but, the rules say that all fuel must enter the carburetor through the main jet, so that has limited my options..You've got quite a useful option left: instead of reducing the total fuel cross flow area, increase the air flow to the emulsion tube. Take a look at a Suzuki RGV250 engine (also used by Aprila in their street-250) where solenoids control this air flow in order to keep the exhaust gases cleaner at part-throttle. On more than one occasion it has been an engine killer when these solenoids stuck open, so I advised to disconnect them, but in your case they may come in quite handy.
Mind you, the rules may object to any form of kart engine electrification; it's already a miracle that they don't force you to use flint ignition.


Haha Jan - I wonder who the clever dick was at Aprilia who thought long stroke was the way to go.That would have been the same dick that reluctantly approved experiments with smaller bores, provided that the original piston forgings could still be used in order to save money. So the possible steps were very limited and the piston skirts became paper thin.

[katinas]

Then 52 bore was tried, even less power, and after some tests the piston oin was found, inside the carburetor.
That was the end of Aprilia's long stroke experiments....

Jan, very interesting to hear this.
Perhaps Aprilia follows Honda s young group engineers experiments with longer stroke, on the first two crank version of NSR 250 ( 52 mm x 58 mm) in 1998. Looks like, idea was to minimize detonation, with unleaded fuel, but max power decreased although acceleration was better.
Interesting, how smaller bore and longer stroke scheme influence mass flow through engine.

[Schumae2]

Thank you Frits! I had not thought of this method of controlling the carburetor, and was unaware of its use in production. Yes; there are rules limiting electrification......Plainly read it seems as long as air fuel ratio and/or ignition timing changes cannot be made by the driver during operation its permissible to have such components / systems that can make those adjustments, but its murky about making those changes on the fly. I have seen KZ engines have a fuel flow valve, that restricts return flow from the diaphragm pump, thats mounted to the steering wheel (driver adjustable / on the fly) at the super-nationals, which would breach the previously described rule.....I will look into methods of controlling a solenoid like described, and scrutinize the rules a bit.

[husaberg]

I posted a pic of the 97 cylinder map above her I the model changes the year before
OWJ1 (1996)
- Adoption of a 54mm bore piston
The major new feature of the OWJ1 spec YZR500 introduced in 1996 was the new engine with a 54mm bore. By squaring off the bore x stroke at 54mm x 54mm, compared to the previous 56mm x 50.6mm, this engine succeeded in boosting top speed through a better balance of power and torque character based on total intake/exhaust efficiency rather than simply raising rpm. This model was also characterized by its forged "powder metal" piston with excellent heat resistance qualities and a new frame design that eliminated the seat rail. Riding this machine, Norick Abe shaved an amazing two seconds off the fastest lap time at the Japan GP preliminaries and went on to win the race for his first GP victory. Loris Capirossi also won a round this year on the OWJ1 at the Australian GP.

https://global.yamaha-motor.com/race/wgp-50th/race_archive/machines/yzr500_0wj1/img/pic_gallery_yzr500_0wj1_01.jpg
https://global.yamaha-motor.com/race/wgp-50th/race_archive/machines/yzr500_0wj1/

The year before clearly the triple port.
347744

[TZ350]

Older video but a great shot of Alex Degnes's bike.


<iframe width="560" height="315" src="https://www.youtube.com/embed/OGD6h-3gdys" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

[breezy]

so,
Adegnes has got his engine running (you tube):woohoo: what are the benefits of having a larger exhaust port? just more blow down? being able to raise the exhaust port causing less short circuiting? more area for losses due to size? upsetting scavenging? or is this unknown , as its not been done before.

[TZ350]

Alex Degnes's new motor. First startup.

<iframe width="560" height="315" src="https://www.youtube.com/embed/K46ZVL172e4" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

[wobbly]

I am finishing of the sim results for a 20,000 rpm 35cc RC boat engine and was asked if it was possible to turn the cylinder 90* such that the small end pin faces the Ex on one side and the boost port
on the other . This would give a dead straight pipe out the back of the hull , making a very tidy package .
The new engine design has a reed box added on one side pointing upward under the cylinder like a KZ.
I know there are various pro's and con's with turning the cylinder , but I am most concerned about the ring bulging into the Ex port - sideways, not on a thrust face , but the ring pin
could still be positioned opposite the Ex port.
Plus then the inlet flow will be asymetric , a bit like a RV on one side.
But there will be no small end port linking.
What have I missed as being a good or bad technical reason if doing this .

[TZ350]

347765 347766

Team ESE NSR/GP100 110cc engine well into the "Two Hour" endurance race and leading suddenly could not find a gear.

Darn, .... Blair and Nathaniel could have won that race. Congratulations to Team GPR who took the win.

[TZ350]

347767 347768 347769

Sick Dyno. The Team ESE Dyno has become sick. Apparently there is a keeper battery inside the WinPEP electrical stack that keeps everything alive.

According to DynoJet the battery needs replacing and the firmware re flashing. But they no longer support this legacy model.

Replacing the battery looks straight forward.

But ... Help Needed. Has anyone faced this firmware problem before and can help with advice about getting the stack going again.
.

[andreas]

I am finishing of the sim results for a 20,000 rpm 35cc RC boat engine and was asked if it was possible to turn the cylinder 90* such that the small end pin faces the Ex on one side and the boost port
on the other . This would give a dead straight pipe out the back of the hull , making a very tidy package .
The new engine design has a reed box added on one side pointing upward under the cylinder like a KZ.
I know there are various pro's and con's with turning the cylinder , but I am most concerned about the ring bulging into the Ex port - sideways, not on a thrust face , but the ring pin
could still be positioned opposite the Ex port.
Plus then the inlet flow will be asymetric , a bit like a RV on one side.
But there will be no small end port linking.
What have I missed as being a good or bad technical reason if doing this .

I assume it doesn't, but in the event of piston transfer cut-outs there may be two problems.

[Vannik]

I am finishing of the sim results for a 20,000 rpm 35cc RC boat engine and was asked if it was possible to turn the cylinder 90* such that the small end pin faces the Ex on one side and the boost port
on the other . This would give a dead straight pipe out the back of the hull , making a very tidy package .
The new engine design has a reed box added on one side pointing upward under the cylinder like a KZ.
I know there are various pro's and con's with turning the cylinder , but I am most concerned about the ring bulging into the Ex port - sideways, not on a thrust face , but the ring pin
could still be positioned opposite the Ex port.
Plus then the inlet flow will be asymetric , a bit like a RV on one side.
But there will be no small end port linking.
What have I missed as being a good or bad technical reason if doing this .

Biggest issue would be, I think, the piston cam being in the wrong direction, but I am not sure how big this is on small engines.

[Muhr]

What have I missed as being a good or bad technical reason if doing this .

maybe you'll have problems with piston rocking in BDC if you have some unfavorable geometry between piston and cylinder when you turn the cylinder?

[breezy]

Can I just remind everyone that the name of our 2-Stroke Stuffing hero is Alex Degnes, not Agnes. His KB id is adegnes.

there you go, got my glasses on now:rolleyes:

[wobbly]

Neels , something I had not thought of ! , but arent both cam and taper to correct for the temp delta down the skirt , along with the naturally greater expansion of the mass around the pin bosses.
The pistons are being custom made ,so skirt cutouts and cam can be reorientated to suit as is needed , if I take the plunge and spin the cylinder.

[TZ350]

but arent both cam and taper to correct for the temp delta down the skirt , along with the naturally greater expansion of the mass around the pin bosses.


Yes, the taper compensates for the greater expansion at the piston crown and the cam for the greater expansion of the mass around the pin bosses. I expect the orientation of these should be the same regardless of the position of the exhaust port. A four stroke piston will have the area of the ring lands turned down smaller than the skirt. My 2cents worth.

[lohring]

I am finishing of the sim results for a 20,000 rpm 35cc RC boat engine and was asked if it was possible to turn the cylinder 90* such that the small end pin faces the Ex on one side and the boost port
on the other . This would give a dead straight pipe out the back of the hull , making a very tidy package .
The new engine design has a reed box added on one side pointing upward under the cylinder like a KZ.
I know there are various pro's and con's with turning the cylinder , but I am most concerned about the ring bulging into the Ex port - sideways, not on a thrust face , but the ring pin
could still be positioned opposite the Ex port.
Plus then the inlet flow will be asymetric , a bit like a RV on one side.
But there will be no small end port linking.
What have I missed as being a good or bad technical reason if doing this .

For some reason, our testing showed slightly lower power on rear exhaust engines over conventional side exhaust engines. We couldn't come up with a good reason and set records with both side and rear exhaust Quickdraw engines. If the engine has open transfers like the early RCMK engines, you will get very rapid piston wear. Most of us have figured out how to package engines in hulls by tilting the engine when necessary, ie scale boats.

Boaters worry about air resistance, but it is insignificant compared to water resistance. The water drag on an object is 800 times its drag in air. Exposing the cylinder and pipe won't slow down a model boat a measurable amount at the sub 100 mph speeds we run. I won a free lunch from my partner on this issue. We did gain 6 mph at 100 mph with a rudder redesign to a thinner and smaller rudder.

Lohring Miller

[lohring]

My measurements on my 32 to 36 mm bore pistons show very straight and round sides. We often turn down the ring area .001 to .002" to prevent seizing. The water cooled cylinders are slower to expand than the pistons at our considerably higher than stock power. Stock engines, even with tuned pipes, don't need this.

Lohring Miller

[TZ350]

347767 347768 347769

Sick Dyno. The Team ESE Dyno has become sick. Apparently there is a keeper battery inside the WinPEP electrical stack that keeps everything alive.

According to DynoJet the battery needs replacing and the firmware re flashing. But they no longer support this legacy model.

Replacing the battery looks straight forward.

But ... Help Needed. Has anyone faced this firmware problem before and can help with advice about getting the stack going again.
.

347772347773


I measured the old battery’s voltage and it still had 1.7Volts so fingers crossed and following Chambers suggestion I piggy backed another battery onto it.

The Computer now communicates with the Stack.

When I roll the drum by hand the computer registers a change in speed on the screen. So looking hopeful.

I will know more later when we try a dyno run. Hopefully the Stacks brain has not suffered any brain damage from being starved of electrons.

[TZ350]

347774

Flettner riding his 350cc Fuel Injected Kawasaki F5 BigHorn.

[wobbly]

Lohring - the engine is an all new design and will have a CNC case and printed cylinder , with scaled Aprilia inspired teacup transfer ducts so piston wear wont be an issue.
My main + for turning the Ex to the back was getting rid of a 100* bend in the header , but hey , if you have tried this and made less power , thats good enough for me.

[jamathi]

Lohring - the engine is an all new design and will have a CNC case and printed cylinder , with scaled Aprilia inspired teacup transfer ducts so piston wear wont be an issue.
My main + for turning the Ex to the back was getting rid of a 100* bend in the header , but hey , if you have tried this and made less power , thats good enough for me.

Those who tried this had BIG failures, on 50cc engines.
Better have a bend in the exhaust pipe I think.
An engine like this was made for Garelli by an Italian engineer.
In one year it failed to finish one single lap at Monza.
A big failure, it ended in a tribunal.....
One friend of mine in Holland tried the same, also on a 50cc.
It went hopelessly wrong!

[andreas]

https://www.youtube.com/watch?v=khotZMCSzKk
Soon it will look all new

[lohring]

Lohring - the engine is an all new design and will have a CNC case and printed cylinder , with scaled Aprilia inspired teacup transfer ducts so piston wear wont be an issue.
My main + for turning the Ex to the back was getting rid of a 100* bend in the header , but hey , if you have tried this and made less power , thats good enough for me.

We run nitro engines with a 180 degree header bend because they were originally designed for airplanes, not boats. All the side exhaust engines run a variety of pipes with various bends. It doesn't seem to matter from a power standpoint. By the way, how are you going to machine teacup transfers?

Lohring Miller

[mantonakakis]

https://www.youtube.com/watch?v=khotZMCSzKk
Soon it will look all new
Did your RD lose a cylinder??
My RD125 is running again as of yesterday, with freshly-rebuilt crank (new rods, big-end bearings and pins) and bottom end. I chose double the fun for my first attempt at a crankshaft rebuild... Time for a little tuning today, then starting work on porting and pipe plan. One of the main restrictions will be the stock reeds, do you have the main dimensions of your RD250 reed block, or happen to know of bigger reeds to fit the 125?
347777

[mantonakakis]

By the way, how are you going to machine teacup transfers?
Sounds like he will have the cylinder 3D printed?

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/eHLkJNNKwhs" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[andreas]

Mantonakakis

Yes I can see how rebuilding that crank is way fun ,ha. About that lost cylinder, look at some earlier posts. Reeds are bound to be small and the room for enlargement probably ain't great either, don't know really maybe yz80/60 is a good place to start looking. Hope the tuning goes well, and don't be concerned with the B-ports floors not aligning at bdc, is no big deal.

[TZ350]

One of the main restrictions will be the stock reeds, do you have the main dimensions of your RD250 reed block, or happen to know of bigger reeds to fit the 125?
347777

The bolt pattern dimensions on the RD125 reed cage is essentially the same as the RD250 - 350 - 400 and RZ cages which are all much the same except the later RD and RZ cages have fiber reeds.

347779 347778 347780 347781

RD125 reed cage compared to a RD250/350/400 reed cage.

[wobbly]

Thanks everyone on the input . Seems to be too risky to have a big exhaust port sideways on , the ring will bulge outward in that direction, and even with the ring pin opposite I can see
problems.
All just to get rid of a header bend.
The other thing that interests me about this project is that when I review the other engines in opposition ie up to 35cc on unleaded petrol , they all seem to be way ,way off the pace in both technology
and Hp.
its very easy , technically , for this engine to make 15 Hp @ 17,000 rpm - whereas it seems that many are super happy with around 8Hp.
That is only 11.3Bar , 164 psi - bmep , very conservative in relation to many designs I have done.
And at 17,000 + rpm as that is only 17 M/s Mean Piston Speed - again super conservative , with safe compression and completely normal ignition/combustion parameters.

But as is the case in mini aero racing , the boaters seem all consummed with rpm , spinning them to 22,000 rpm even though the Hp peak is way back at 17,000.
Is this something to do with prop efficiency - or some effect I am completely missing here.

[mantonakakis]

Yeah, main issue I will face with bigger reeds is width limitation. I think the opening in the 125 cylinders is about 34mm, approximately 3mm wall thickness? Not too much room to add bigger reeds. Stock reeds are good for ~20hp according to EngMod (21mm effective diameter should be good for much more than 20hp, though? Or maybe Dat2T is converting the two reed blocks into a single effective diameter? In which case, 21mm = 20hp sounds about right).

Just did a short highway test - If I trust the speedo, about 55mph top speed with a very strong crosswind and a big loose jacket, somewhat disappointing. Seems to run out of steam by 9k, power drops off sharply after ~8500. Runs slightly faster in 4th gear than 5th. No EGT sensor, but cylinder head temp seems in the ballpark ~320F after a minute of idling following a long climb (more than 1mile at 8-12% gradient with 50% throttle or more in 3rd gear), jetting seems in the ballpark too. My cylinders are a little out of the roundness spec, but even so I was hoping for a little better with new rings and a fresh bottom end with the stock setup. I am at 6000ft above sea level, I'll run the sim at that altitude and see if it changes the torque peak. Biggest thing I notice is that the bike does not seem to rev out as high as the stock dyno would suggest... Power band start to hit, then it drops out too soon.

EDIT: Sim results at 6000ft vs stock dyno:
347784

[andreas]

Yes, it is tricky, considering the unfortunate long cylinder studs are also an obstacle. But welding, using putty or just grind it a little will fit something larger. One of those reeds was able to send a moped to 70 mph, whatever power that is. Flat on the tank, I remember the rd doing ~77mph stock and ~87 mph with just pipes.

[husaberg]

Did your RD lose a cylinder??
My RD125 is running again as of yesterday, with freshly-rebuilt crank (new rods, big-end bearings and pins) and bottom end. I chose double the fun for my first attempt at a crankshaft rebuild... Time for a little tuning today, then starting work on porting and pipe plan. One of the main restrictions will be the stock reeds, do you have the main dimensions of your RD250 reed block, or happen to know of bigger reeds to fit the 125?
347777

The Rd125 an the Rd200 twins have smaller reeds but the same bolt pattern. as the RD250/350/400 and many others
Not sure if the reed cavity area is big enough for Rd250 reeds without some welding, but MX100 DT100 AG100or similar might be about, in between size. Plus are the same bolt pattern.
if I wanted to tune a small twin maybe start with a 200. As it s bigger.

[lohring]

Thanks everyone on the input . Seems to be too risky to have a big exhaust port sideways on , the ring will bulge outward in that direction, and even with the ring pin opposite I can see
problems.
All just to get rid of a header bend.
The other thing that interests me about this project is that when I review the other engines in opposition ie up to 35cc on unleaded petrol , they all seem to be way ,way off the pace in both technology
and Hp.
its very easy , technically , for this engine to make 15 Hp @ 17,000 rpm - whereas it seems that many are super happy with around 8Hp.
That is only 11.3Bar , 164 psi - bmep , very conservative in relation to many designs I have done.
And at 17,000 + rpm as that is only 17 M/s Mean Piston Speed - again super conservative , with safe compression and completely normal ignition/combustion parameters.

But as is the case in mini aero racing , the boaters seem all consummed with rpm , spinning them to 22,000 rpm even though the Hp peak is way back at 17,000.
Is this something to do with prop efficiency - or some effect I am completely missing here.

We needed rpm because the available props had limited pitch. We got around this by cutting and re pitching the blades, but that is still limited. We were thinking about a two speed, gear up transmission, but Covid postponed the project.

I have a lot of data on the 35 cc engine we modified for straight line records a few years ago. The picture shows the stock engine with the stock pipe. Just shortening the pipe and header was good for a big power gain. We threw this away with a shorter pipe for more rpm. Water injection got back a lot of the low end which helped accelerate up to the speed trap. Below is the full article.

Lohring Miller

347795
347796347797

[mantonakakis]

The Rd125 an the Rd200 twins have smaller reeds but the same bolt pattern. as the RD250/350/400 and many others
Not sure if the reed cavity area is big enough for Rd250 reeds without some welding, but MX100 DT100 AG100or similar might be about, in between size. Plus are the same bolt pattern.
if I wanted to tune a small twin maybe start with a 200. As it s bigger.
Taking measurements off of my computer screen on eBay ads, it looks like older DT100/RX50/etc reeds should work without modification to the cylinder and provide a good upgrade - they should fill the reed cavity nicely without having to cut, and it seems like they have about 30% more flow area. I suppose I could cut out the bridge on each side to gain some extra flow area as well, and cut new carbon reeds.

Sim results on a slightly modified engine (wider exhaust port top width to 70% of bore, 190deg duration, 2-stage auto-generated "modern" pipe with 1.8 horn, 0.7 tailpipe, 3.5 center - just a first pass) aren't showing much improvement from bigger reeds alone. The bigger reeds with stiffer petals, however (0.15mm steel vs 0.25mm carbon, to get 1st resonance up to the middle of Dat2T's recommendation), gave 5-10% more power across the whole range, cool.

[F5 Dave]

Yeah, main issue I will face with bigger reeds is width limitation. I think the opening in the 125 cylinders is about 34mm, approximately 3mm wall thickness? Not too much room to add bigger reeds. Stock reeds are good for ~20hp according to EngMod (21mm effective diameter should be good for much more than 20hp, though? Or maybe Dat2T is converting the two reed blocks into a single effective diameter? In which case, 21mm = 20hp sounds about right).

Just did a short highway test - If I trust the speedo, about 55mph top speed with a very strong crosswind and a big loose jacket, somewhat disappointing. Seems to run out of steam by 9k, power drops off sharply after ~8500. Runs slightly faster in 4th gear than 5th. No EGT sensor, but cylinder head temp seems in the ballpark ~320F after a minute of idling following a long climb (more than 1mile at 8-12% gradient with 50% throttle or more in 3rd gear), jetting seems in the ballpark too. My cylinders are a little out of the roundness spec, but even so I was hoping for a little better with new rings and a fresh bottom end with the stock setup. I am at 6000ft above sea level, I'll run the sim at that altitude and see if it changes the torque peak. Biggest thing I notice is that the bike does not seem to rev out as high as the stock dyno would suggest... Power band start to hit, then it drops out too soon.

EDIT: Sim results at 6000ft vs stock dyno:
347784

Perhaps some duct tape would help?

Either that or a smaller jacket. :innocent:

[teriks]

Thanks everyone on the input . Seems to be too risky to have a big exhaust port sideways on , the ring will bulge outward in that direction, and even with the ring pin opposite I can see
problems.
All just to get rid of a header bend.
The other thing that interests me about this project is that when I review the other engines in opposition ie up to 35cc on unleaded petrol , they all seem to be way ,way off the pace in both technology
and Hp.
its very easy , technically , for this engine to make 15 Hp @ 17,000 rpm - whereas it seems that many are super happy with around 8Hp.
That is only 11.3Bar , 164 psi - bmep , very conservative in relation to many designs I have done.
And at 17,000 + rpm as that is only 17 M/s Mean Piston Speed - again super conservative , with safe compression and completely normal ignition/combustion parameters.

But as is the case in mini aero racing , the boaters seem all consummed with rpm , spinning them to 22,000 rpm even though the Hp peak is way back at 17,000.
Is this something to do with prop efficiency - or some effect I am completely missing here.
Nah, quite the opposite on the aero side, we want large diameter props for efficiency, but have to keep the tips away from M1.
Id say the lack of ignition system is why we have to shoot for rpm instead of crazy bmep, glow plug ignition is a mess.
We do run rear exhausts though, with ports up to 180deg width. Then again, we don't have to worry about a piston ring.


For some reason, our testing showed slightly lower power on rear exhaust engines over conventional side exhaust engines. We couldn't come up with a good reason and set records with both side and rear exhaust Quickdraw engines. If the engine has open transfers like the early RCMK engines, you will get very rapid piston wear.
Did all of the rear exhaust engines have those open transfers? If yes, wouldn't that excessive piston wear be a prime suspect for the missing power.
That issue wont be there on the new design, that just leaves any potential issues with the ring... depending on lohrings answer that is.
EDIT: Now that would be too obvious, surely lohring would have seen that connection if my interpretation were true...

[mantonakakis]

Perhaps some duct tape would help?

Either that or a smaller jacket. :innocent:

I need a full streamliner!

[husaberg]

Taking measurements off of my computer screen on eBay ads, it looks like older DT100/RX50/etc reeds should work without modification to the cylinder and provide a good upgrade - they should fill the reed cavity nicely without having to cut, and it seems like they have about 30% more flow area. I suppose I could cut out the bridge on each side to gain some extra flow area as well, and cut new carbon reeds.

Sim results on a slightly modified engine (wider exhaust port top width to 70% of bore, 190deg duration, 2-stage auto-generated "modern" pipe with 1.8 horn, 0.7 tailpipe, 3.5 center - just a first pass) aren't showing much improvement from bigger reeds alone. The bigger reeds with stiffer petals, however (0.15mm steel vs 0.25mm carbon, to get 1st resonance up to the middle of Dat2T's recommendation), gave 5-10% more power across the whole range, cool.

we had a Ag100 which was the in between size I assumed the MX100/DT100 was the same looking at this it might not have been.
maybe earlier was smaller same as the AG100? while later one are bigger.
looking at the parts fiche the AG100 is likely the same size. as what you have.

edit looked the RD125 looks smaller
what I have found is one of the earlier CT2 which had the similar bolt on manifold which would give a straightish inlet
https://i.ebayimg.com/images/g/Ts4AAOSwHIlZwo2l/s-l500.jpg which looks te same size as the AG100 its made for a 22mm carb and I bet the stub is available cheap.
https://www.allensperformance.co.uk/carb-kit/carburettor-mounting-rubber-manifold-dimension-information-page/
okay found this also
https://yamaha-rd125.blogspot.com/2016/12/new-mikuni-vm20-carbs-yamaha-rd125-a.html

https://www.cmsnl.com/yamaha-ag100h-1996-3ha9-oceania-263ha-700e1_model38175/reed-valve-assy_53v1361000/#.X76jzGgzaUk


https://www.ebay.com/itm/Yamaha-RX125-DT100-DT175-RT180-RD250-RD350-TY250-MX100-Reed-Valve-345-13613-70.
Yamaha RX125 DT100 DT175 RT180 RD250 RD350 TY250 MX100 Reed Valve 345-13613-70
the reed dimension or the RD250/400 are well known and the late YZ85 is a single petal design from the factory and V force are available.
https://macshot.de/rd/Reed-Ventile.png

http://erlenbachracing.co/reedcages%20mods.htm

[lohring]

The side and rear exhaust engines we tested had either liners or standard closed transfers. Quickdraw once made crankcases for both types that differed only in the bolt pattern and cutout areas for the transfers. I have one of each type that are going into the proposed opposed piston engine. The ringless piston engines used in smaller models don't seem to have the same issues, but I'm not aware of anyone who has done careful test comparisons. Boaters use a variety if bent headers to run all types of exhausts. Below is the most extreme, a 180 degree header. I've run one of these engines and it was definitely more powerful than the older rear exhaust version. However, the one piece design of the new version was stiffer along with a bigger intake and other factors.

Lohring Miller

347803 347804

[wobbly]

Again I am amazed at the technology ( or lack of it ) in these small RC engines.
Its been shown by tests done years ago that a downward angle of 25* of the Exhaust duct roof gives the best compromise of blowdown flow and duct velocity.
But in the previous post we have a duct pointing upward , surely that alone invalidates any comparison with any other layout considerations.

[teriks]

The side and rear exhaust engines we tested had either liners or standard closed transfers. Quickdraw once made crankcases for both types that differed only in the bolt pattern and cutout areas for the transfers. I have one of each type that are going into the proposed opposed piston engine. The ringless piston engines used in smaller models don't seem to have the same issues, but I'm not aware of anyone who has done careful test comparisons. Boaters use a variety if bent headers to run all types of exhausts. Below is the most extreme, a 180 degree header. I've run one of these engines and it was definitely more powerful than the older rear exhaust version. However, the one piece design of the new version was stiffer along with a bigger intake and other factors.

Lohring Miller

347803 347804
That recons, re. your tests of different cylinder directions.
Those pictures are of ringless engines, right? If not, the 180degree one should be pretty darn similar to the rear exhaust with regards to potential ring/exhaust port issues.


Again I am amazed at the technology ( or lack of it ) in these small RC engines.
Its been shown by tests done years ago that a downward angle of 25* of the Exhaust duct roof gives the best compromise of blowdown flow and duct velocity.
But in the previous post we have a duct pointing upward , surely that alone invalidates any comparison with any other layout considerations.
That duct for sure looks odd. Id guess its to avoid the huge flywheel, in that sense, for sure a side or front exhaust would be better.

There are some quite clever RC engines though, the MB Profi for one.
https://fiorimet.home.xs4all.nl/

[Frits Overmars]

There are some quite clever RC engines though, the MB Profi for one. https://fiorimet.home.xs4all.nl/MB is the brand that brought me into contact with model engines. In the mid 1990s physicist Rob Metmemeijer approached me with the problem that the power curve of his 6,5cc two-stroke engines couldn't handle the power absorption curve of his propellers. Either the engine would not rev past the torque dip at 2/3 of max. torque rpm, or the propeller had to be so light that the engine revved way beyond its maximum power rpm. Rob had heard some whispers about exhaust power valves and I happened to have the drawings of the Cagiva 500-4 cylinder (a carbon-copy of the Yamaha YZR500 cylinder) at my fingertips.
Surprise: a few weeks later Rob showed me a running 6,5cc power valve engine. Now here was a guy that I would like to work with! However, I felt there had to be a more KISS-like solution for the torque dip problem, so after visiting a couple of F3D model pylon races to see what was needed, I came up with an exhaust pipe that is now universal in F3D.
The pipe was followed by a hardchromed sleeveless cylinder (for an engine without piston rings, hardchrome is just as good as nikasil) with teacup-shaped transfer ducts and my idea of port timings and scavenging angles. The engine also got ceramic crankshaft bearings. The result is the current MB40 Profi engine. The '40' stands for the 0.40 cubic inch cylinder capacity and Profi is the Ukrainian firm that takes care of the serial production (everybody wants an MB40) while Rob Metkemeijer still builds the prototpyes.
347805 347808 347807 347806

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/9g54172O_AY" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[lohring]

A long time ago a model speed engine builder told me that piston to liner fit followed by head button design were the most important factors for high performance. The first is due to the big effect of friction in these small engines. The second is because compression along with the glow plug wire diameter sets the ignition timing. All the things we worry about in larger engines are nice refinements. Our 26 cc gasoline engines definitely benefit from better transfers and ports. Frits' design definitely helped the 6.5 cc engine, but the cruder designs of the Nelson 40, now sold by Aero Racing Engines (https://www.aeroracingengines.com/), and Jett engines (http://www.dubjett.com/engines2015.html) are still competitive.

Lohring Miller

[lohring]

MB is the brand that brought me into contact with model engines. In the mid 1990s physicist Rob Metmemeijer approached me with the problem that the power curve of his 6,5cc two-stroke engines couldn't handle the power absorption curve of his propellers. Either the engine would not rev past the torque dip at 2/3 of max. torque rpm, or the propeller had to be so light that the engine revved way beyond its maximum power rpm. Rob had heard some whispers about exhaust power valves and I happened to have the drawings of the Cagiva 500-4 cylinder (a carbon-copy of the Yamaha YZR500 cylinder) at my fingertips.
Surprise: a few weeks later Rob showed me a running 6,5cc power valve engine. Now here was a guy that I would like to work with! However, I felt there had to be a more KISS-like solution for the torque dip problem, so after visiting a couple of F3D model pylon races to see what was needed, I came up with an exhaust pipe that is now universal in F3D.
The pipe was followed by a hardchromed sleeveless cylinder (for an engine without piston rings, hardchrome is just as good as nikasil) with teacup-shaped transfer ducts and my idea of port timings and scavenging angles. The engine also got ceramic crankshaft bearings. The result is the current MB40 Profi engine. The '40' stands for the 0.40 cubic inch cylinder capacity and Profi is the Ukrainian firm that takes care of the serial production (everybody wants an MB40) while Rob Metkemeijer still builds the prototpyes.
347805 347808 347807 347806

Are you sure I didn't braze that pipe? I'm about that neat with my brazed joints. I like the pipe below for real power.

LOL

Lohring Miller

347810

[teriks]

MB is the brand that brought me into contact with model engines. In the mid 1990s physicist Rob Metmemeijer approached me with the problem that the power curve of his 6,5cc two-stroke engines couldn't handle the power absorption curve of his propellers. Either the engine would not rev past the torque dip at 2/3 of max. torque rpm, or the propeller had to be so light that the engine revved way beyond its maximum power rpm. Rob had heard some whispers about exhaust power valves and I happened to have the drawings of the Cagiva 500-4 cylinder (a carbon-copy of the Yamaha YZR500 cylinder) at my fingertips.
Surprise: a few weeks later Rob showed me a running 6,5cc power valve engine. Now here was a guy that I would like to work with! However, I felt there had to be a more KISS-like solution for the torque dip problem, so after visiting a couple of F3D model pylon races to see what was needed, I came up with an exhaust pipe that is now universal in F3D.
The pipe was followed by a hardchromed sleeveless cylinder (for an engine without piston rings, hardchrome is just as good as nikasil) with teacup-shaped transfer ducts and my idea of port timings and scavenging angles. The engine also got ceramic crankshaft bearings. The result is the current MB40 Profi engine. The '40' stands for the 0.40 cubic inch cylinder capacity and Profi is the Ukrainian firm that takes care of the serial production (everybody wants an MB40) while Rob Metkemeijer still builds the prototpyes.
Rob is quite amazing, not only theoretically clever, but extremely efficient in the workshop!
That pipe of yours in not very easy to improve upon, that's for sure.


A long time ago a model speed engine builder told me that piston to liner fit followed by head button design were the most important factors for high performance. The first is due to the big effect of friction in these small engines. The second is because compression along with the glow plug wire diameter sets the ignition timing. All the things we worry about in larger engines are nice refinements. Our 26 cc gasoline engines definitely benefit from better transfers and ports. Frits' design definitely helped the 6.5 cc engine, but the cruder designs of the Nelson 40, now sold by Aero Racing Engines (https://www.aeroracingengines.com/), and Jett engines (http://www.dubjett.com/engines2015.html) are still competitive.
Lohring Miller
Actually neither Jett nor Nelson is competitive in F3d racing, since quite some time.
While there are some other interesting F3d engines, the MB is the only one really commercially available.

[Frits Overmars]

I like the pipe below for real power.
347810Shortly after the first appearance of my F3D pipe, competitors started to rumble about "the Fat Dutch Pipe", so we decided to give them something to rumble about: a picture of an F3D model plane with one of my 125cc dyno test pipes. Left yours truly, right Robbert van den Bosch, many times European F3D champion and some time after this photo was taken, also world champion.
When we first met, I asked him what he did for a living. He answered: "Bus driver". It turned out he was a Boeing 737-captain. His reaction: "Same job, but it pays better".


Rob is quite amazing, not only theoretically clever, but extremely efficient in the workshop!
That pipe of yours in not very easy to improve upon, that's for sure.
Actually neither Jett nor Nelson is competitive in F3d racing, since quite some time. While there are some other interesting F3d engines, the MB is the only one really commercially available.Rob (below) is an amazing person indeed. His daytime playing field is acoustics, for example giving the Royal Albert Hall a once-over, that kind of level. He got into building model engines because he and his late brother Bert took part (and became world champion) in teamracing, another branch of model flying.
Teriks' remark, that the MB40 engine is the only commercially available F3D engine, requires some clarification. From Robs standpoint there is nothing commercial about it: he builds his engines purely to keep the sport going and there is no profit in it for him. Everybody can buy his engines, but active F3D competitors are given priority on the waiting list to keep their chances even.
347825

[mikebmeehan]

Great work Thomas! You are an intelligent person!:

[JanBros]

bought a KDX200 but sadly there are 2 cracks between the exhaust ports on the left. I'm in doubt as to whether have them welded and replated or have it sleeved. if welded, will they weld it through and through and not leave parts of the crack that can grow again? and if they weld it through, I'm in doubt as to if it will not harm the flow if the weld protrudes, hardly being able to correct that.
I know the downsides off sleaving, but it 's just for having some off-road fun, not to ride it at max like a pro.

also first time I've seen a raised exhaust port on a standard cylinder from the early '90ies

[F5 Dave]

Yeah they had a strange rotating power valve to open that and the rack and pinion arrangement used to seize and strip the gears.

Change of needle was best improvement on mine.

[wobbly]

The plater here would vee the crack out , weld it up , bore and grind it back , and replate .
Easy job.

[JanBros]

The plater here would vee the crack out , weld it up , bore and grind it back , and replate .
Easy job.

no problem's welding through and through to avoid re-cracking ?

[wobbly]

A few cylinders are simply a bad design ( 4DP Yamaha TZ ) that crack no matter what , but the weld material is stronger than the cast alloy , so usually the weld is more reliable.

[husaberg]

no problem's welding through and through to avoid re-cracking ?

Closer to your home
https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130610635#post1130610635

[RAW]

A few cylinders are simply a bad design ( 4DP Yamaha TZ ) that crack no matter what , but the weld material is stronger than the cast alloy , so usually the weld is more reliable.

Without knowledge of the cylinder material, heat treatments or weld metal material & associated weld heat inputs that may / will actually anneal the cylinder about the weld reworks, nor knowing if the welding has been performed correctly I’m not so sure your statement is correct ��*♂️
One thing for sure is the shrinkage stresses of the solidifying weld / welds upon a heat treated cylinder rework is akin to over tightening a con rod bolt & expecting it to still perform its role adequately, it can not.
However normalising & reheat treatments may fix these issues from welding, although then the correct weld metal filler wire would be required & I’m yet to know of a cylinder plating / repair shop to having adequate knowledge of welding to do anything other than create a soon to fail rework whilst billing the owner for the privileged of at best a rework but certainly not what I consider the meaning of the word repair is.

[Haufen]

it 's just for having some off-road fun, not to ride it at max like a pro.

Why not just leave it as it is?

I have done the exact same thing in the past and ran a cylinder with such a crack in the exhaust bridge for two seasons. It has been running with the cracks like this before for some time at the previous owner and without problems anyway. On mine, I just made sure it would keep doing it by relieving the bridge in the cracked area with some sandpaper.

After that, I put some more work into the cylinder and also had the crack repaired at the plater. I ran the cylinder for another couple of seasons without any issues afterwards. Plating and repair was done at http://www.langcourt.com in GB which is also a bit closer to where you are located. They are experienced with such kind of repairs, just tell them NOT to grind / deburr your transfer port windows after the re-plate, as they (or one of their staff) are / were usually quite generous in doing it.

[JanBros]

Why not just leave it as it is?


don't think I would feel comfortable, always thinking that at the edges of the crack the plating would start to come of.

[Condyn]

They are experienced with such kind of repairs, just tell them NOT to grind / deburr your transfer port windows after the re-plate, as they (or one of their staff) are / were usually quite generous in doing it.

I always engrave cylinders in an obvious place “plater no chamfer”. If I forget, they come back with a massively aggressive radius. Some guys are good, some are braindead. Also I would not be afraid of welding cracks. If done correctly they will not have issue. Bevel away as much as you need then repair. Bridges can be built up from nothing and be plated. Had better luck with 4043 filler not getting ruined by the stripping tank FYI, but if you are having the plater do all the labor you do not even have to know that. I would 100% go for the weld/repair/replate unless you know your plater is a hack. You could always go welded in aluminum sleeve too.

[Haufen]

don't think I would feel comfortable, always thinking that at the edges of the crack the plating would start to come of.

So was I. But I as a student, I was short of money, too :) So I worked the edges of the crack with sandpaper and used the cylinder for dynoing only, at first. But as that went perfectly well, promoted it to the real race engine, soon.

If you have it repaired at langcourt, they will weld the crack and re-shape to original shape as well.

I am not sure about the sleeve option. This seems to come with the highest cost and effort and give a compromised result (sleeved cylinder) in the end.

Maybe just getting another used cylinder would be an option, too? Are these hard to find?

[DoldGuy]

bought a KDX200 but sadly there are 2 cracks between the exhaust ports on the left. I'm in doubt as to whether have them welded and replated or have it sleeved. if welded, will they weld it through and through and not leave parts of the crack that can grow again? and if they weld it through, I'm in doubt as to if it will not harm the flow if the weld protrudes, hardly being able to correct that.
I know the downsides off sleaving, but it 's just for having some off-road fun, not to ride it at max like a pro.

also first time I've seen a raised exhaust port on a standard cylinder from the early '90ies


Janbros, as Wobbly mentioned the platers can weld these cracks. The KDX Cylinder Exhaust is very similar to the KX500 with the dual sub ports either side of the main port and notorious for cracking there in addition to the intake bridges. The repair done by most of the platers here in the states are quite remarkable and FAR better than the original casting. I’d have it repaired and replated before a ring could snag itself on that.

[JanBros]

also had a response from Jan Luyten (from Luyten import in Belgium and the son of the Luyten 125cc engine) and they say they most of the time re-crack.
gonna leave it aside for a while and see if a 200 or 220 cyl pops up somewhere.

[wobbly]

The replating process is full of pitfalls , but most are well versed in what is needed.
Yes , 4043 is the welding rod of choice , and that works very well.
The important deal is getting the cylinder up to a temp , high enough to prevent excessive stress from weld pool shrinkage , but to not destroy the heat treat.
NZ Cylinders here , heat , then weld , then run thru the bore and or grind away most of the added excess filler , then prior to final hone they do a micro piening process to reduce the localized stresses.

One big issue may platers dont do properly is that as they VERY rough hone the bore ( for nicasil adhesion ) this removes much of the chamfer on the Exhaust port alloy timing edges.
So I have to give written instruction every time , for them to rechamfer this in the alloy prior to plating - if they dont , then as soon as I remove the chrome flash lip inside the port
then there is insufficient chrome depth within the bore to put on the required vertical chamfer.

And as all you guys on here should know by now , you dont need ANY chamfer on transfer ports - instant power loss , and no effect at all on ring life.

[koenich]

I'm still toying around with my Bidalot RF50 cylinder. Thats the best we got so far with the Bidalot pipe, w/o another pipe I doubt we hit the Dutch power figures :bye:

347951

Recently we tested several aftermarket reed cages. Is there any theory on sizing? I suppose carb area (in this case dia = 30 mm), projected area and power are the main factors? Should the carb area vs projected stay the same, decrease or increase?

[husaberg]

I'm still toying around with my Bidalot RF50 cylinder. Thats the best we got so far with the Bidalot pipe, w/o another pipe I doubt we hit the Dutch power figures :bye:

347951

Recently we tested several aftermarket reed cages. Is there any theory on sizing? I suppose carb area (in this case dia = 30 mm), projected area and power are the main factors? Should the carb area vs projected stay the same, decrease or increase?

If you are going for Dutch power levels it should not have a cage but have a spinning disc instead.

[wobbly]

This again brings up the question I am struggling with re 35cc RC boat engine design I am working on.

Assuming an engine dyno , giving sprocket Hp with a 5% factor for chain/gear friction etc.
My personal benchmark is the current TM R1 - that makes 53.3 Crank Hp at 13500 = 14.17 Bar bmep with a piston speed of 24m/s ( still not even in the ballpark of Jans rocketship ).
The 50cc graph shows 18Hp +5% = 18.9 Crank Hp at again around 13500 = 12.6 Bar at only 18m/s.
This surely isnt even remotely exciting power/rpm/bmep numbers at all , and to me means that the real potential of the 50cc isnt even close to what could be done
if you started to push the boundaries ( lets face it thats why we are here isnt it ? ) .

If it was reved to the same level as the TM with the same bmep ( this being very limited by a straight line ignition and a tiny carburetor ) the 50cc should be doing 29 Crank Hp at 18500
giving the same limited bmep of 14.17 Bar. Put it on a DynoJet and thats 25.4 Hp Rear Wheel.

What am I missing here , especially as these engines are essentially square and all the technology in the world is readily available to do sintered cylinders etc.
EDIT - in both the examples shown above we have a 50cc and a 125cc engine with the same carb @ 30mm , so maybe just one element of the 50cc is close to optimum - why ?

[lodgernz]

My Honda 50 has a bore of 39.5 and stroke of 41.4. The single Exhaust port opens at 84° for a total open period of 192°, and the A-transfers open first at 117°.
I planned to have peak power at 13,000RPM, and I guessed at 500°C for the average EGT, so that's a speed of sound of 557m/s.

With these parameters, using the pipe dimension calculations we're all now familiar with, I made a pipe with LT = 724mm. Baffle cone angle is 28°.

The engine has a 26mm OKO carb with the power jet disabled, and HPI ignition which starts at 30° advance and retards to 14° by 11,000RPM.
Compression Ratio is 14.0 (full stroke), running 98 pump fuel.

The cylinder has huge Boyesen ports and a large reed block, and lots of work has gone into smoothing or removing all sharp edges and obstructions on the intake flow to the transfers.
The exhaust duct has been extended to twice the bore and water cooled.

On the track, after much jetting etc., peak power appears to be around 11,000 and it won't rev past about 12,300. Quite good mid-range power though.

I tried various stinger nozzles from 15mm down to 13mm to try and elevate the EGT but with no improvement.

Clearly I've done something wrong. Any clues please?

[Condyn]

Diffuser too efficient for your engine? I built many sets of FOS pipes with different variations and none worked well with my single exhaust port elevator shaft transfer duct engine.

[ken seeber]

This again brings up the question I am struggling with re 35cc RC boat engine design I am working on.

Assuming an engine dyno , giving sprocket Hp with a 5% factor for chain/gear friction etc.
My personal benchmark is the current TM R1 - that makes 53.3 Crank Hp at 13500 = 14.17 Bar bmep with a piston speed of 24m/s ( still not even in the ballpark of Jans rocketship ).
The 50cc graph shows 18Hp +5% = 18.9 Crank Hp at again around 13500 = 12.6 Bar at only 18m/s.
This surely isnt even remotely exciting power/rpm/bmep numbers at all , and to me means that the real potential of the 50cc isnt even close to what could be done
if you started to push the boundaries ( lets face it thats why we are here isnt it ? ) .

If it was reved to the same level as the TM with the same bmep ( this being very limited by a straight line ignition and a tiny carburetor ) the 50cc should be doing 29 Crank Hp at 18500
giving the same limited bmep of 14.17 Bar. Put it on a DynoJet and thats 25.4 Hp Rear Wheel.

What am I missing here , especially as these engines are essentially square and all the technology in the world is readily available to do sintered cylinders etc.
EDIT - in both the examples shown above we have a 50cc and a 125cc engine with the same carb @ 30mm , so maybe just one element of the 50cc is close to optimum - why ?

Wob,
Here’s my basic calc:
(35/125)*53.3*(18500/13500) = 20.45

[Muhr]

This surely isnt even remotely exciting power/rpm/bmep numbers at all , and to me means that the real potential of the 50cc isnt even close to what could be done
if you started to push the boundaries ( lets face it thats why we are here isnt it ? ) .


The little experience I have from 50cc, I experienced that when you set up a pipe and tried to get enough time area on the intake(rotary)
For peak around 16000k it became a hell to start and below 8000 it wants to get stuck.
I think that will be one of the biggest challenges with the engine I am working on.
Have seen here that people have worked on variable intakes but have not heard how it went.
have myself wondered if it would be possible to make some kind of centrifugal solution so you can run crazy open times.

Edit: Sorry saw that the arms were put wrong in this picture! but as long as you understand the principle

[F5 Dave]

Perhaps you could spend some time into high speed remote starter techniques? Makes warm up seem a bit unsympathetic i bet but with that range, who cares about 8000rpm?

[F5 Dave]

My Honda 50 has a bore of 39.5 and stroke of 41.4. The single Exhaust port opens at 84° for a total open period of 192°, and the A-transfers open first at 117°.
I planned to have peak power at 13,000RPM, and I guessed at 500°C for the average EGT, so that's a speed of sound of 557m/s.

With these parameters, using the pipe dimension calculations we're all now familiar with, I made a pipe with LT = 724mm. Baffle cone angle is 28°.

The engine has a 26mm OKO carb with the power jet disabled, and HPI ignition which starts at 30° advance and retards to 14° by 11,000RPM.
Compression Ratio is 14.0 (full stroke), running 98 pump fuel.

The cylinder has huge Boyesen ports and a large reed block, and lots of work has gone into smoothing or removing all sharp edges and obstructions on the intake flow to the transfers.
The exhaust duct has been extended to twice the bore and water cooled.

On the track, after much jetting etc., peak power appears to be around 11,000 and it won't rev past about 12,300. Quite good mid-range power though.

I tried various stinger nozzles from 15mm down to 13mm to try and elevate the EGT but with no improvement.

Clearly I've done something wrong. Any clues please?
Hey Roger.
If still had dyno I'd be hooking timing light up and seeing what happens at 12000rpm under load. Bet its not pretty and I'd also put a meter on the power supply to see if it browns out.

[lodgernz]

Hey Roger.
If still had dyno I'd be hooking timing light up and seeing what happens at 12000rpm under load. Bet its not pretty and I'd also put a meter on the power supply to see if it browns out.

Thanks Dave, I wish you still had the dyno.
There's no power supply: The HPI ignition is a magneto with CDI. It was working fine with my last cylinder and pipe, revving out to 15000 when required. That was a very short pipe at 678mm LT.
I'll check the timing again though.

[wobbly]

Ken , redo the calc for the 50cc we were discussing.
( 50/125 )* 53.3 * ( 18500/13500 ) = 29.2 crank Hp less 12.5 % to rear wheel on a Dynojet = 25.5 RWHp.

The 35cc reed engine ( converted from piston port ) making it similar technology as the TM , with the same proceedure
would be
( 35/125 ) * 53.3 * ( 23000/13500 ) = 25.4 Crank Hp.

24M/s piston speed is nothing unfamiliar now days , and 14 bar bmep is for sure not "easy " but again nothing unfamiliar or off the planet high.

I really am missing something here as no 35cc RC engine makes even 1/2 that on unleaded.

[Brett S]

Ken , redo the calc for the 50cc we were discussing.
( 50/125 )* 53.3 * ( 18500/13500 ) = 29.2 crank Hp less 12.5 % to rear wheel on a Dynojet = 25.5 RWHp.

The 35cc reed engine ( converted from piston port ) making it similar technology as the TM , with the same proceedure
would be
( 35/125 ) * 53.3 * ( 23000/13500 ) = 25.4 Crank Hp.

24M/s piston speed is nothing unfamiliar now days , and 14 bar bmep is for sure not "easy " but again nothing unfamiliar or off the planet high.

I really am missing something here as no 35cc RC engine makes even 1/2 that on unleaded.


Is it just the fact that these engines are used as direct drives and require a flatter/broader power curve?
If they cannot have enough power down low they may not gain enough rev's to get onto the pipe?

[dutchpower]

Working now on Nico Claasen 50cc twin
On the left hand the Sim 17.3 hp and the right hand dyno
We find every 2 weeks 0.5 hp this moment we have 14 pk 25 cc

[koenich]

it's HP at the wheel. but nevertheless far off what could be done/seems possible, however currently within my capabilities :violin:

Let's see if I can figure out a better pipe...anyone reg carb size vs reed cage inlet size vs projected area?

[Niels Abildgaard]

Working now on Nico Claasen 50cc twin
On the left hand the Sim 17.3 hp and the right hand dyno
We find every 2 weeks 0.5 hp this moment we have 14 pk 25 cc

The ultimate limit to power is timearea.
A 125 ccm can be modelled into a 25 ccm by making all dimensions smaller by a factor of cuberoot of five(125 divided by 25) that is 1.71.
The port areas will be linear scalefactor (here 1.71) squared ie 2.92 times smaller.
A 25 ccm model of Aprillia 125 that gave 55 horseplower will thus make 55 divided by 2.92 equal to 18.8 hosepower, if you are as capable as mr Thiel and there was no extra thermal loses due to the changed relation between volume that do the work and surface that puts heat in and out of working medium at the wrong time.
A V twin 50 cubic giving 35 horsepower will be quite interesting

[lohring]

As I've posted before, we only got a little under 12 hp from our 35 cc engine. It was rpm limited by mechanical issues as well. I would hope that you could seriously improve this with a modern design. I wouldn't think that reed valves be much of an improvement over a piston port for a boat engine. We need peak power over a narrow rpm range. We run all races at wide open throttle after the start. Disk valves should be better, though BZM makes a reed engine (https://www.novarossi.us/products/bzm-27cc-gas-rc-engine-bizetamotor-bizeta-motors) that some people feel is good. I would like to see a dyno comparison with a similar, piston ported Quickdraw (http://www.quickdrawengines.com/Page_261.html). Quickdraw does post dyno results (http://www.quickdrawengines.com/Page_264.html) and their brake dyno results were very similar to our inertial dyno results on the same engine. Both engines are a more modern design, but could be improved.

The factor that people miss is the overwhelming importance of friction as engines get smaller. Ringless pistons have been tried, but failed in the 35 cc CMB engine. They do work in 15 cc engines. Again, I think a more careful design and manufacturing process might succeed. After all, we seized a ringed piston in a sleeve that was out of round just above the exhaust port. We seized all the stock ringless piston and liner combinations we tried despite high castor lubes and a careful break in procedure. You need to match the expansion of the hot piston to a cooler cylinder. The cylinder needs to taper from a huge clearance at BDC to no clearance at TDC. One builder compared his fit to a glass stopper in a flask. That is the piston taper matched the cylinder with no clearance at TDC. Our 35 cc ringless piston and liner sets were nothing like this good.

Lohring Miller

[Niels Abildgaard]

Further to limit of power thinking.
A gentleman showed some very nice pictures of a worldbeating 2.5ccm model areo engine and claimed 2.5 horsepower dyno.
An eqvivalent 6.5 state of art gives 5.
He got angry and removed all his writings and pictures but I did the same area,cube thing calculation.

https://www.model-engineer.co.uk/forums/postings.asp?th=165845&p=1

[andreas]

My Honda 50 has a bore of 39.5 and stroke of 41.4. The single Exhaust port opens at 84° for a total open period of 192°, and the A-transfers open first at 117°.
I planned to have peak power at 13,000RPM, and I guessed at 500°C for the average EGT, so that's a speed of sound of 557m/s.

With these parameters, using the pipe dimension calculations we're all now familiar with, I made a pipe with LT = 724mm. Baffle cone angle is 28°.

The engine has a 26mm OKO carb with the power jet disabled, and HPI ignition which starts at 30° advance and retards to 14° by 11,000RPM.
Compression Ratio is 14.0 (full stroke), running 98 pump fuel.

The cylinder has huge Boyesen ports and a large reed block, and lots of work has gone into smoothing or removing all sharp edges and obstructions on the intake flow to the transfers.
The exhaust duct has been extended to twice the bore and water cooled.

On the track, after much jetting etc., peak power appears to be around 11,000 and it won't rev past about 12,300. Quite good mid-range power though.

I tried various stinger nozzles from 15mm down to 13mm to try and elevate the EGT but with no improvement.

Clearly I've done something wrong. Any clues please?

Well, there are numbers given by Frits as to how much time-area is needed in any application, I think the blow-down is 8,72mm2 x cc x rpm to be rsa equivalent (I or someone else has the correct furmulas if needed) Just looking, 192*, even for 50cc isn't much, and possibly 500* is a too high estimaton.

[Niels Abildgaard]

it is interesting for me at least to make a simple ultimate two stroke power as function of cylindersize.
First assumption:
54 dyno crank horsepower from a 125 ccm is very close to limit found by lots of trial and error.
Second assumption:
Ultimate power depends on Blow Down Time area.
The formula will then be:
Power from a 50ccm cylinder can max be 54 *(50/125)**0.66666= 29.3 shp.
for a 35ccm likewise: 54*(35/125)**0.66666=23.1 shp
for a 6.5 54*(6.5/125)**.66666= 7.5
and a 2.5 ccm 54*(2.5/125)**.66666=3.9 horsepower
When cylinder gets smaller mr Lohring tells us that unwanted heat losses and friction grow.
This can explain that state of art aircraft model engines of 2.5 ccm can reach 2.5 shp and for a 6.5 ccm engine it is 5 shp.
The 2.5ccm engine only give 2.5 of 3.9 according to the Thiel /Frits law or a minus of 36%.
The 6.5ccm is give 5 of 7.5 predicted by the law or a minus of say33%.
An estimate of a 25ccm cylinder is
According to Thiel/Frits 54*(25/125)**.6666= 18.5shp that shal be reduced with something between 36 and 0% due to extra friction and thermic losses.
Let me asume 20% for a 25ccm cylinder and we can reasonably realistic expext ca 15shp from a Thiel/Frits equal 25ccm cylinder.

[wobbly]

Several points to answer.

BrettS - you are right about having enough mid power to even get the boat up on the plane.
I did simulations of piston port and RV , and against the reed version they made way less mid power , when configured to achieve identical peak and overev power.
So having the reed conversion , then allows me to tune other elements alot more radically , and still have more power than previously using the piston port.

Dutch - purely by my eye dyno the cylinder Exhaust duct exit looks very big. And if its a T port , it should be oval like a Honda, and if a 3 port it should have Aux eye ducts down the side, like an Aprilia.

Re the relationship of carb size to reed block port area. I have found both on the dyno and in the sim , that having the block port area slightly smaller is compensated for by the reed petals staying open longer.
The smaller block always seems to have better mid , and looses nothing up top.
Best example I have would be the 400cc Banshee based CPI cylinder that was designed for a CR250 reed block.
When up at 100 RWHp using a CR125 block ( VeeForce ) it makes more power everywhere , than the original much bigger CR250.
Part of this is also due to the fact that to fit the CR250 block in place meant that the petal exits were off bore center by 6mm - the CR125 is 6mm narrower , so it can be put back on center with an adapter plate
then a stuffer plate fitted down one side.

So one lesson I learned is that asymetric intake regimes loose power - be it an offset block or even worse sideways angled manifolds.

Edit - you would think that the 30mm carb in the TM connected to a huge reed block would be the weakest link in making serious power. But once again the devil is in the detail.
By having a 28mm venturi inside the block as part of the stuffer makes about 0.5 Hp to 0.75 Hp , I believe by increasing the velocity of the flow within the block , thus opening the petals quicker and further.

And yes I agree completely about the friction in small engines when up at 20,000 rpm + , but this factor simply cant explain why the theoretical numbers , using well established benchmarks , is hugely higher
than what is actually being achieved currently.

[F5 Dave]

Thanks Dave, I wish you still had the dyno.
There's no power supply: The HPI ignition is a magneto with CDI. It was working fine with my last cylinder and pipe, revving out to 15000 when required. That was a very short pipe at 678mm LT.
I'll check the timing again though.

Charge coil might now be breaking down? Muffler hasn't partially collapsed? Needle doesn't obstruct at WO? Remove main and it must bog when blipped to wide open, maybe without pj it can't?

Try scribe timing lines and see timing light isn't breaking up or going silly. Better with load but needs must.

[teriks]

<snip>
And yes I agree completely about the friction in small engines when up at 20,000 rpm + , but this factor simply cant explain why the theoretical numbers , using well established benchmarks , is hugely higher
than what is actually being achieved currently.
I can easily have a huge increase of power in my MB Profi 6.65cc engines, simply by changing from glow to spark ignition and a decent ignition curve, in the sim.
Unfortunately not so easy in real life, there aren't even spark plugs that work... that I'm aware of.
Not to mention ignition systems coping with 30+krpm and 20%castor oil that are small and light enough to fit onboard a plane.
-Yes, fuel is stipulated by the rule book, 80% methanol, 20% castor oil.

Re. the small model SI engines, Id guess they are simply not very developed. Im sure you can improve a lot on those.

[wobbly]

Just love it when you finally get the right gear to do a job properly , and it does.
Rule says no part of the BODY to protrude into the chamber .
Now , dyno time , to test this and the cylinder water jacket cooling .
Watch this space.

[husaberg]

Just love it when you finally get the right gear to do a job properly , and it does.
Rule says no part of the BODY to protrude into the chamber .
Now , dyno time , to test this and the cylinder water jacket cooling .
Watch this space.

Shit that's an extreme. i thought that's going to be hard on the heatrange
but of course the colder longer the internal inside path the shorter the outside path...........
https://www.ngkspark.co.nz/wp-content/uploads/2016/11/heat-range-image-for-website.jpg
how much cc is inside a plug? 1-1.5?

[wobbly]

The race plug I use is a 10.5 heat range , and as you can see the insulator is super short.
All I have done is move the spark gap , 3mm closer to the middle of the combustion space - but kept the body flush to the roof as per the rules.
Same deal as using a toroidal chamber roof - but the tech rules for measuring the chamber volume wont allow a toroid as it traps air.
The difference in actual trapped chamber cc will be tiny - but a normal 10.5 race plug has 0.15cc of added volume between the body inner and the insulator.

[husaberg]

The difference in actual trapped chamber cc will be tiny - but a normal 10.5 race plug has 0.15cc of added volume between the body inner and the insulator.

Shit here was me already making a pig of myself only to be told there is no free lunch.
my eye-ometer was thinking a cc of volume not being fully utilised there.
Have you milled that in situ?

[koenich]

Thanks!

Reg the availability of 35cc/50cc engines with close to optimal power output - likely just no one had a real go at it. At least for 50cc I'm pretty certain that even Bidalot was surprised how many cylinders they can sell.

[dutchpower]

Dutch - purely by my eye dyno the cylinder Exhaust duct exit looks very big. And if its a T port , it should be oval like a Honda, and if a 3 port it should have Aux eye ducts down the side, like an Aprilia.


Wobb

This are the cil. Nico made in the beginning 4 jears ago some are compleet scaled copies of the aprilia all give 10 hp
Duct exit now is 21.15
His last cil. had nice inner cirkle of the transfers resulting in 2 hp lost !!!!!!

[lodgernz]

Well, there are numbers given by Frits as to how much time-area is needed in any application, I think the blow-down is 8,72mm2 x cc x rpm to be rsa equivalent (I or someone else has the correct furmulas if needed) Just looking, 192*, even for 50cc isn't much, and possibly 500* is a too high estimaton.

Thanks Andreas, I do use that formula from Frits, and I know how crap my setup is. I think you are right about my EGT estimate being too low, so I will make a new pipe.

Thanks also to Dave and others who have helped. I'll be checking all your suggestions.

[wobbly]

Lodger - couple of things.
If I put in 13,000 / 84* / bulk temp av =580* ( very average to lower guess ) into EngMod then Lt = 725.
But then you say the ignition is 14* at 11,000.
It should be 15* at 13000 ( your calculation peak ) if everything else is correct.
What egt in the header were you seeing , something basic is not right .

[dutchpower]

According to Thiel/Frits 54*(25/125)**.6666= 18.5shp that shal be reduced with something between 36 and 0% due to extra friction and thermic losses.
Let me asume 20% for a 25ccm cylinder and we can reasonably realistic expext ca 15shp from a Thiel/Frits equal 25ccm cylinder.


Did you ever measure that we did com not even close

[wobbly]

Dutch - no is the answer but if you look at the Quickdraw website they say the "best " gas ( petrol I assume ) engine is the Pioneer 30.5 " stroker " engine , that has a dyno sheet making 8. 75 Hp @ 16250 with power out past 20,000 -
but considerably less.
As I keep saying that level of bmep ( the baseline measure for outright engine efficiency in any displacement ) and piston speed , to my way of thinking is a technical joke in 2T tuning terms.
Unless what Im underestimating hugely is the disparity in friction losses as the rpm goes stratospheric , or something else completely.
I really am in the dark here , as im trying to make a full effort , cost no object race engine of 35cc on unleaded race gas , but as far as I can ascertain no one is even remotely close to the numbers
given by " normal " bmep and piston speeds already fully proven elsewhere.
WHY.

[Niels Abildgaard]

According to Thiel/Frits 54*(25/125)**.6666= 18.5shp that shal be reduced with something between 36 and 0% due to extra friction and thermic losses.
Let me asume 20% for a 25ccm cylinder and we can reasonably realistic expext ca 15shp from a Thiel/Frits equal 25ccm cylinder.


Did you ever measure that we did com not even close

It indicates that Aprilia/Thiel/Frits have not been in that country yet.
Enjoy the journey.

[lodgernz]

Lodger - couple of things.
If I put in 13,000 / 84* / bulk temp av =580* ( very average to lower guess ) into EngMod then Lt = 725.
But then you say the ignition is 14* at 11,000.
It should be 15* at 13000 ( your calculation peak ) if everything else is correct.
What egt in the header were you seeing , something basic is not right .

Thanks for your input Wobbly. I don't have an EGT sensor, so I don't know the EGT.
Here are the two curves for the HPI ignition. As you can see, I misquoted the numbers.
347960

[Brett S]

Just love it when you finally get the right gear to do a job properly , and it does.
Rule says no part of the BODY to protrude into the chamber .
Now , dyno time , to test this and the cylinder water jacket cooling .
Watch this space.


Most karting rules have a minimum length of spark plug thread to stop people doing things like this.

[wobbly]

The spark plug and the head insert thread length are identical to the stock parts.
In what way is this plug ground electrode any different to the huge thing hanging off a B10 EGV or EIX.

[dutchpower]

It indicates that Aprilia/Thiel/Frits have not been in that country yet.
Enjoy the journey.


I wonder why is that 54 without friction and thermic losses !!!!!!!

[Niels Abildgaard]

I wonder why is that 54 without friction and thermic losses !!!!!!!

Nobody claims that a 125 can give 54 without friction and thermic losses.
Try if You can to plot a max shaft power curve for known good cylinders versus cubic capacity of one cylinder.
We have at least three state of art points

125 aprilia 54 hp
2.5 ccm aeromodel 2.5 hp
6.5 ccm aeromodel 5 hp

all made after many failures and dead ends

The problem Wobbly and You have with 35 and 25 ccm cylinders is ,I think, internal air/fuel charge resistance in the crank chamber.
Try and compare a weed hacker engine with the 2.5 aeromodel.
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=347808&d=1606384149

How much was the ultimate 50ccm Kreidler cylinder able to give

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/WORNBXGpEVM" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

[dutchpower]

Nobody claims that a 125 can give 54 without friction and thermic losses.
Try if You can to plot a max shaft power curve for known good cylinders versus cubic capacity of one cylinder.
We have at least three state of art points

125 aprilia 54 hp
2.5 ccm aeromodel 2.5 hp
6.5 ccm aeromodel 5 hp

all made after many failures and dead ends

The problem Wobbly and You have with 35 and 25 ccm cylinders is ,I think, internal air/fuel charge resistance in the crank chamber.
Try and compare a weed hacker engine with the 2.5 aeromodel.
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=347808&d=1606384149

How much was the ultimate 50ccm Kreidler cylinder able to give

Nico and I start this project years ago
I wanted to make it at the same level as Jans baby the RSW/RSA
Nico copie scale the RSW/RSA
Nico had big friend Jan de Vries always there
Last sommer we had contact to start his project
From 10 hp we went to 12 hp Oh said Jan de Vr. there I start whit in the early days and ended 19 hp
Thats what I have now Jan !!!


That was a big stap yes ( internal air/fuel charge resistance in the crank chamber )

[Frits Overmars]

Try if you can to plot a max shaft power curve for known good cylinders versus cubic capacity of one cylinder.
We have at least three state of art points
125 aprilia 54 hp
2.5 ccm aeromodel 2.5 hp
6.5 ccm aeromodel 5 hpApples and oranges, Niels.
The Aprilia power is measured at the gearbox exit; it would be about 57 hp at the crankshaft. It burns unleaded petrol with 5% oil and has spark plug ignition.
Both aeromodel engines have their power measured at the crankshaft. The 6,5cc engine burns methanol with 20% oil. The 2,5 cc engine fuel probably carries a noticeable percentage of nitro. Both have glow plug ignition.
The fuel will make an obvious difference. But the ignition system may make an even bigger difference.
For maximum power, a glow plug engine needs to have the same ignition timing as a spark-ignited engine. But practice has shown time and again that this is too critical for a glow plug: one missed combustion will kill the engine completely. For a glow plug to function reliably its ignition timing must be about 30° earlier than the max.power timing. And that will cost an estimated 30% of power.

In addition, I agree with Wobbly that the development of smaller engines is seriously lagging behind the development of Jan Thiel's 125cc RSA: we do not have three state of the art points.

[koenich]

this just comes down to $$$...how much dev money and manpower went into the RSW/RSA? and who's pouring money nowadays into 50cc or below? At some point obviously no ROI. the enthusiast/single tuner can come pretty far and reach impressive results (cheers Wob and Dutch) but at some point the required effort will rise exponentially for small gains...

[Niels Abildgaard]

Honda ended up with a fourcylinder 500ccm and a twocylinder 500 ccm.
Are there some thrustworthy horsepower figures for these?
If we guesstimate 52hp for the 125ccm cylinders we can try to estimate the 250 cylinder power.

52*(250/125)** 0.66666= 83 hp

In the ballpark?

[Frits Overmars]

this just comes down to $$$...how much dev money and manpower went into the RSW/RSA? and who's pouring money nowadays into 50cc or below? At some point obviously no ROI. the enthusiast/single tuner can come pretty far and reach impressive results (cheers Wob and Dutch) but at some point the required effort will rise exponentially for small gains...That sounds sensible, Koenich, except.... The pictures below show Dutchman Paul Lodewijkx chasing and beating Hans-Georg Anscheidt at the 1986 Dutch TT. 50cc world champion Anscheidt was riding the twin-cylinder 14-speed Suzuki works machine, Lodewijkx rode a home-built single-cylinder bike, designed and built by the man with the glasses: Jan Thiel. His budget: what he earned as a moped repair mechnanic, i.e. close to zero. His gains: just enough to buy petrol and make it to the next GP.
It was not Aprilia-money that made the Aprilia engines the strongest; Honda spent a whole lot more but did not succeed. I consider myself fortunate that I got to know Jan Thiel with his unbridled commitment as a friend. And whenever a task seems impossible, I say to myself: Jan could do it....
347966 347965 347964 347963

[Niels Abildgaard]

Apples and oranges, Niels.
The Aprilia power is measured at the gearbox exit; it would be about 57 hp at the crankshaft. It burns unleaded petrol with 5% oil and has spark plug ignition.
Both aeromodel engines have their power measured at the crankshaft. The 6,5cc engine burns methanol with 20% oil. The 2,5 cc engine fuel probably carries a noticeable percentage of nitro. Both have glow plug ignition.
The fuel will make an obvious difference. But the ignition system may make an even bigger difference.
For maximum power, a glow plug engine needs to have the same ignition timing as a spark-ignited engine. But practice has shown time and again that this is too critical for a glow plug: one missed combustion will kill the engine completely. For a glow plug to function reliably its ignition timing must be about 30° earlier than the max.power timing. And that will cost an estimated 30% of power.

In addition, I agree with Wobbly that the development of smaller engines is seriously lagging behind the development of Jan Thiel's 125cc RSA: we do not have three state of the art points.

Are there some model aircraft/boat classes where both spark ignited and glow engines compete?
The 2.5 and 6.5ccm engines have a ringless pistons and that can help produce as much power as they do
Has it ever been tried to modify a weedhacker engine with glow ignition and ringless pistons?

[Niels Abildgaard]

That sounds sensible, Koenich, except.... The pictures below show Dutchman Paul Lodewijkx chasing and beating Hans-Georg Anscheidt at the 1986 Dutch TT. 50cc world champion Anscheidt was riding the twin-cylinder 14-speed Suzuki works machine, Lodewijkx rode a home-built single-cylinder bike, designed and built by the man with the glasses. His name: Jan Thiel. His budget: what he earned as a moped repair mechnanic, i.e. close to zero. His gains: just enough to buy petrol and make it to the next GP.
It was not Aprilia-money that made the Aprilia engines the strongest; Honda spent a whole lot more but did not succeed. I consider myself fortunate that I got to know Jan Thiel with his unbridled commitment as a friend. And whenever a task seems impossible, I say to myself: Jan could do it....
347966 347965 347964 347963

Are there pictures of the two cylinder Suzuki somewhere?

[Frits Overmars]

Honda ended up with a fourcylinder 500ccm and a twocylinder 500 ccm. Are there some thrustworthy horsepower figures for these?
If we guesstimate 52hp for the 125ccm cylinders we can try to estimate the 250 cylinder power.
52*(250/125)** 0.66666= 83 hp. In the ballpark?Not even in the same time zone, Niels :msn-wink:. The 125cc Honda works cylinders of that era made about 44 hp at the gearbox exit which, according to your calculation method, would give their NSR500V 2x70 hp, a value that is not too far from their manufacturer's specification: 136 hp.



Are there pictures of the two cylinder Suzuki somewhere?Hundreds. Any specific wishes?