ESE's works engine tuner

[F5 Dave]

Fixed in this case is not straight line so we have our definition aligned. Fixed TZ here means fixed curve, so could be retarding like heck after 11 or 12,000 for example which is fine a dirtbike perhaps but not on road race engines.

[Tim Ey]

I am using the Czech deto device on my RS250.
But I rather test this little bugger here: http://www.bylund-automotive.com/educative/knock/index.html
Has anyone played with it before?

@Muhr:
The bellmouth test is interesting - unfortunately, they mixed tuned inlet length variation and bellmouth variation. Which causes a shift in rpm range. To get the result which bellmouth is best, you need to vary the inlet length to reach the same rpm peak (since the tube end of a bellmouth is not easy to define).

[Flettner]

<iframe width="560" height="315" src="https://www.youtube.com/embed/v5jLX4KtpXs" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>


https://youtu.be/977BWjCMC8E

https://youtu.be/mS0cyt7F9js

https://youtu.be/CLn4tsz8M1s


<iframe width="560" height="315" src="https://www.youtube.com/embed/rxc1OFcQgPM" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

Flettners flying Gibs in action:- As I understand it, these are "Fly by Wire" activated and they are part of the face of the rotary valve cover and basically open/close the normally fixed aperture in a rotary valve cover. The idle circuit is a very small reed valve about the size of your thumb nail. The idle reed valve is adjusted by a screw that limits how much it can open.

Goes on its first trail ride tomorrow, should be interesting.
Laptop all charged up. Ive mixed up 20L of E85, optimistic?
https://youtube.com/shorts/rxc1OFcQgPM?feature=share

[wobbly]

Tim , I have tested several LSU detectors , and have a 14 Point 7 one on my dyno that outputs Lambda and or 0-5V for logging and an on screen red warning.
The el cheapo Czech unit does a few things way better than anything else.
Its super simple to quickly rev your engine against some load - in gear brake on , load up with the clutch , and adjust the sensitivity to get all but the last led to light up.
Then on track the last red deto light is guaranteed to be a "real " harmful deto level.
Also the optional grounding output works perfectly with det retard on an Ignitech , and the 0-5v is simple to data log.

But , one thing to note ,only proper Lambda units like a 14 Point 7 or a Innovate LS2 do the required pre heating cycle on the Bosch 4.9 prior to applying power to the sensor.
As the unit you have shown is Arduino based then an led array and pre heat will all be possible - if the developer or someone else is competent enough to do the electronics and code.

[philou]

thanks wobbly for the connection indications

[flyonly]

Any one here had their cases scanned so you have all the relative points to be able to draw them up in 3D?


Sent from my iPhone using Tapatalk

[TZ350]

May be the fixed one was not set at the right time.
At max power both should have the same pre ignition !
At lower speed the power is the same, which should be different in favor of the Ignitech progr.
This suggests that the fixed ignition was too late.

You are right, they should both be the same at max power. But the fixed was then over advanced at lower speeds. A compromise had to be made.
Both ignitions were setup on the team ESE dyno.

[TZ350]

.
2Stroke Stuffing gets the 24/7 50cc engine running on the dyno, test run to hear the sound of it howling ...... https://youtu.be/oR_JCxyPdaQ

[Tim Ey]

Wob,

probably the link has sent you elsewhere - bylund offers knock / Lambda / NOx shields for the arduino. I was talking about the knock shield.
As I understand the el cheapo Czech knock device has a given frequency range. Sometimes you need to ignore a certain rpm range, because it shows you mechanical noise.
And that is why I would like to test the bylund devide.

Lambda is helpful, but I am still struggling with it. My RS250 had a lambda output like attached in its WOT run and was WAY too lean till 8000 rpm.
350294
So next time I will focus on my gut feeling whilst juggling jets first - and afterwards note the corresponding lambda.

[TZ350]

Lambda is helpful, but I am still struggling with it. My RS250 had a lambda output like attached in its WOT run and was WAY too lean till 8000 rpm.

Because of short circuiting in a two stroke. Lambda will always look lean and only start to come right as the engine gets up on the pipe and the trapping efficiency improves.

My EFI bike's Air/Fuel would be something like 18:1 and the reading would slowly improve until it was about 12:1 at max torque but of course in reality it was probably close to 12:1 in the cylinder all the way through even though the gauge registered lean. I think you are right to go on gut feel to get things right then use your recorded data as a development guide for later.



350295


Mine might look even leaner than yours at low RPM but the Lambda trace on your dyno graph looks pretty much what I would expect. The big lean hump where the power dip is just before coming strongly onto the pipe makes sense too.

[koenich]

Any one here had their cases scanned so you have all the relative points to be able to draw them up in 3D?
yep...it sounds tempting and an easy way forward but in reality if you are not at least an advanced CAD user it's rather useless.

Long story - I had one half of a 50cc scanned, model was 120 MB. First problem was converting it to solid: you need to heal the open surfaces to convert and while converting Catia kept crashing even on the latest workstations while Fusion only accepted smaller models. If you have the solid it won't have perfect cylindrical bearing seats nor flat surfaces where you just can place a concentric axis or planes, so some approximation is necessary. The "easier" way IMO would be to measure the necessary distances on a X-Y measuring machine, use those values to set critical dimensions and if you have a scan use that to roughly dial in the outer surfaces etc.


BTW - does anyone have a link for the Czech deto thingy? With 0-5V that could even be coupled with a datalogger (Starlane, Mychron) I suppose?

[philou]

Knock gauge Czech

http://www.knockgauge.eu/

https://www.ebay.com/itm/184413688454?hash=item2aefe99286:g:wmYAAOSw7aBVBEo m

has anyone read this book

350297

[Tim Ey]

Mine might look even leaner than yours at low RPM but the Lambda trace on your dyno graph looks pretty much what I would expect. The big lean hump where the power dip is just before coming strongly onto the pipe makes sense too.

And exactly that was my problem. I focused too much on the numbers I have expected.


Regarding 3D scanning: What koenig said. But it is useful for complex geometries and mock ups. If your CAD system can handle it.

[lohring]

I have 3D models of Zenoah and Quickdraw cases for their 26 cc engines. It took a lot of measurements, not scans.

Lohring Miller

[Frits Overmars]

Stop thinking "Lambda says lean". You all know better than that. Lambda can only say how much unused oxygen is present in the exhaust gas. It does not say anything about the presence of unused fuel. So if you keep using the words Lambda and lean in the same sentence, you may be forcing your thoughts in the wrong direction.

[TZ350]

Lambda can only say how much unused oxygen is present in the exhaust gas. It does not say anything about the presence of unused fuel. So if you keep using the words Lambda and lean in the same sentence, you may be forcing your thoughts in the wrong direction.

Yes, good advice, that paints a better picture of the situation. Thanks.

[wobbly]

The Czech gauge shows ONLY noise from the first 4 lights , so its easy to dial up the sensitivity to the max , showing only noise , by having them light up under load.
Then the red light shows ONLY deto when its happening and is independant completely of the bore.

[OopsClunkThud]

Any one here had their cases scanned so you have all the relative points to be able to draw them up in 3D?


Sent from my iPhone using Tapatalk

if I recall, Flettner set up the cases on the manual mill and then picked up the bearing locations. With that info you can do whatever you want to in CAD.

precise measurement of the section you care about.

[flyonly]

if I recall, Flettner set up the cases on the manual mill and then picked up the bearing locations. With that info you can do whatever you want to in CAD.

precise measurement of the section you care about.

That would work. I would draw it all up in CAD. Just remove the things I don’t need first e.g. kick starter. Then it would be possible to add in some of the ideas talked about in this group. Who has a mill in NZ with a DRO that has time to help out?

[SwePatrick]

Does anyone think they have the best design

https://m.youtube.com/watch?v=G8L9_XO3iCw

This is quite irrelevant to twostrokes as i have noticed that twostrokes(highrevving) can´t have too short intake.
And thereby everything that makes it longer is a failure.

[husaberg]

Does anyone think they have the best design

https://m.youtube.com/watch?v=G8L9_XO3iCw
That's a kiwi site he tries lot of interesting stuff
https://www.youtube.com/channel/UCyNujPbbQeb26dVMr5kHOhQ

He shows how to make easy bellmouths with the PVC
whilst not perfect
i would maybe use the heat gun rather than the gas

https://imgur.com/QqXkzwu
https://imgur.com/QqXkzwu
https://imgur.com/QqXkzwu

[Vannik]

Stop thinking "Lambda says lean". You all know better than that. Lambda can only say how much unused oxygen is present in the exhaust gas. It does not say anything about the presence of unused fuel. So if you keep using the words Lambda and lean in the same sentence, you may be forcing your thoughts in the wrong direction.

Frits, for full clarity of thought Lambda is defined as the AFR/AFRstochiometric, and the "Lambda" measured by the "Lambda sensor" is not a Lambda sensor but a free oxygen sensor and the name "Lambda Sensor" is a misnomer except maybe for when you are measuring a 4T running lean.

Lambda as a concept is fine and should be used to compare mixture strengths. A lambda of 0.85 on avgas ~ AFR 12.46 while a lambda of 0.85 on Q16 ~ AFR 11.33 purely because the stochiometric values are way different, then we are not talking about alcohol fuels.

[Frits Overmars]

Frits, for full clarity of thought Lambda is defined as the AFR/AFRstochiometric, and the "Lambda" measured by the "Lambda sensor" is not a Lambda sensor but a free oxygen sensor and the name "Lambda Sensor" is a misnomer except maybe for when you are measuring a 4T running lean.
Lambda as a concept is fine and should be used to compare mixture strengths. A lambda of 0.85 on avgas ~ AFR 12.46 while a lambda of 0.85 on Q16 ~ AFR 11.33 purely because the stochiometric values are way different, then we are not talking about alcohol fuels.I completely agree with you Neels. What is commonly referred to as a Lambda sensor is really just an oxygen sensor. But the name Lambda sensor has already become so well established that we encounter it everywhere, and then it is better to be aware of its limitations.

[ceci]

Good idea. I like it very much May be where I end up.
Hello TZ350.
Sorry, I'm very impatient, does the solution I indicate work?
I'm asking because I want to know if it can be injected into the crankcase with little pressure.
I'm trying to figure out how Factory Fire1 Racing's injection system works and I suspect it is low pressure injection.

[speedpro]

Does anyone think they have the best design

https://m.youtube.com/watch?v=G8L9_XO3iCw

I made the white ones, boring but seemed to work OK

[Flettner]

Actual trail ride filth, a milestone of sorts I guess.

[philou]

also uses a completely new exhaust port shape where the top edge of the main port – where it meets the cylinder – is now generously radiused. If you look at the central port it looks much higher than the sub ports either side, which would work out to much longer timing if measured conventionally, but the radius is so close to the piston that there is no real flow until the piston has travelled down as far as the tops of the sub ports.

https://scooterlab.uk/wp-content/uploads/2021/12/20211029-9601-800.jpg

https://scooterlab.uk/quattrini-adds-30-extra-power-to-his-2-stroke-kits-tuning/

[SwePatrick]

I made the white ones, boring but seemed to work OK

Small or the big ones?

My design would have been similar to the big ones, but with small changes from what i can see in the clip.

[speedpro]

both. The large ones were effectively a shorter tuned length but there was a physical length constraint. As the guy has said, you get most of the benefit of a well designed intake from a simple radius on the intake.

[Henrik Y]

Just wanted to share this channel, a guy from Finland that make his own cast iron 50cc cylinder and is now building an eddy current brake dyno.

https://www.youtube.com/user/ASoftaaja/videos

[Roflhat]

Started work on the barrel today, going alright so far. Started off as a practise barrel before moving on to another one but if this can be good enough may as well use it. Couple questions for those with more knowledge than me, is it worth drilling a hole behind the boost port? I see in some of Robs photos you’ve done it. Should I bridge the transfers? Any pros/cons to doing it or just allows different shapes?

https://i.ibb.co/Kbfcc9D/D8-DC55-EE-936-B-461-D-84-B2-03385-A2-E7-B6-A.jpg (https://ibb.co/LYcDDCr)
https://i.ibb.co/Hx5nhWW/0-C80-CB72-AAAF-4437-B267-0-A5-C60739-E72.jpg (https://ibb.co/VQf2w77)
https://i.ibb.co/NKwGNVG/B8-EB1-B9-B-73-E5-4713-8060-F2-B569-F417-EF.jpg (https://ibb.co/SBqZmsZ)

[flyonly]

The Czech gauge shows ONLY noise from the first 4 lights , so its easy to dial up the sensitivity to the max , showing only noise , by having them light up under load.
Then the red light shows ONLY deto when its happening and is independant completely of the bore.

Do these work on small bore (40mm) cylinders?


Sent from my iPhone using Tapatalk

[wobbly]

Yes , had a TZ50 ( 40mm bore ) on my dyno - worked perfectly.

[TZ350]

... is it worth drilling a hole behind the boost port? I see in some of Robs photos you’ve done it. Should I bridge the transfers?

https://i.ibb.co/Kbfcc9D/D8-DC55-EE-936-B-461-D-84-B2-03385-A2-E7-B6-A.jpg (https://ibb.co/LYcDDCr)



It is looking good.

I tried both ways but did not find any advantage on the dyno with "Bridging" in the entrance to the "A" and "B" transfer port ducts on our GP's. I would not bother doing that with the GP cylinder.

Make the "B" port as wide as possible. The angles where the ports point into the cylinder are important. Try to keep them the same as original or better yet read up on transfer port angles.

I would drill the "C" boost port. That way you get more flow area and do away with the need for that poxy hole in the piston.

The disadvantage is that you have to port the cases for the "C" duct and you will break through into the gear box breather cavity. Build this area up with JB Weld epoxy first.

[Roflhat]

Cheers, will open up the B ports some more tomorrow. What sort of size do you drill the boost port? And do you have to fill the hole in the piston when opening up the casing?
Have been trying to keep the angles of the ports close to standard but will check them tomorrow again.

Also going to smooth off the intake part of the casing all the way to the air box, so many weird shapes going on in there

[TZ350]

Cheers, will open up the B ports some more tomorrow. What sort of size do you drill the boost port? And do you have to fill the hole in the piston when opening up the casing? Have been trying to keep the angles of the ports close to standard but will check them tomorrow again. Also going to smooth off the intake part of the casing all the way to the air box, so many weird shapes going on in there

Yes, the whole inlet system can use a tidy up.

350313 350315

Getting the "B" ports as wide as possible. Original "B" on the right, widened "B" port on the left.

350314

I can't remember the drill size but I think it was about the same size as the width of the original C port slot. I know you can't, but we used copper to shift heat away from high thermal load areas of the cylinder.

We did all sorts of things with the hole in the piston. Sometimes used pistons with no hole other times made the hole area much larger and angled to help flow cooling air/fuel up through the piston to cool the underside of the piston crown. Cooling is always a good thing.

350316

You can go quite extreme with the piston hole. Maybe a drilled and ported "C" boost port, big slot piston and no case porting so that all the "C" port mixture flows through the piston may be the way to go.

350317

We got to 31 RWHP on our air cooled GP125's but the inability of the cooling system to get rid of 30+ kW of waste heat eventually defeated us. 22 RWHP seemed quite reliable even without all the copper.

[TZ350]

350322

With a bit of porting gymnastics it is possible to add side exhaust ports to a GP125 cylinder. Probably possible on a 100 too.

On this cylinder. As an experiment, the main exhaust port floor was built up by screwing and gluing a alloy plate in the port floor.

Although they each added something they were so much work we did not bother to do it on our Team's race cylinders and we had hit the thermal wall anyway.

Might be worth trying on a 100 though.

[Roflhat]

Got more done today, pretty happy with the barrel the way it is now, cut the boost port in and opened up the B transfers more. Should I cut the liner behind the boost port too? Seeing some of your photos have a groove cut
Started on the casings too, a bit more to do had add some liquid metal.
Frame is all powder coated now, was getting a bit rusty with the salty air we have here
https://i.ibb.co/Vv6x6k8/3-F715-CCD-0-C64-4-D78-A5-FE-76-F037-D9-D370.jpg (https://ibb.co/hK0c0Tv)
https://i.ibb.co/M88GcCL/BACAA45-C-6-CEB-418-E-8530-A77487-EF4772.jpg (https://ibb.co/HNNxtHQ)
https://i.ibb.co/fX55Hqp/00-DB3-F3-C-8750-405-D-BFDF-52666539-EBA9.jpg (https://ibb.co/S688B5n)

[philou]

Jan Thiel Book

350329

[TZ350]

... pretty happy with the barrel the way it is now, cut the boost port in and opened up the B transfers more. Should I cut the liner behind the boost port too?

Your work is looking good.

350327

If you port the cases here for the boost port you will break through into the gear box breather cavity inside. You may be able to avoid splitting the cases.

I would now days be tempted to cut the liner in the boost port to make it one big slot with 55 deg's at the top to direct the flow up the back of the cylinder. Put a big slot in the piston and not port the cases. Its worth thinking about anyway.

[jamathi]

Jan Thiel Book

350329

For the moment in Italian.
Later Spanish, Dutch and English versions will follow,

[diesel pig]

For the moment in Italian.
Later Spanish, Dutch and English versions will follow,

That looks great Jan. I will get a English copy when it is really to go as my Dutch is no good.

[Roflhat]

Cheers

So you’d cut the liner away altogether from the boost port? And presumably smooth the open end where I drilled the C port so it’s closed again?
https://i.ibb.co/LR5Ht6H/7968627-C-9977-499-A-8-A64-80-D1505-BACE8.jpg (https://ibb.co/tKXFscF)

Would you make the hole in the piston the same width as the C port?

[TZ350]

Cheers

So you’d cut the liner away altogether from the boost port? And presumably smooth the open end where I drilled the C port so it’s closed again?
https://i.ibb.co/LR5Ht6H/7968627-C-9977-499-A-8-A64-80-D1505-BACE8.jpg (https://ibb.co/tKXFscF)

Would you make the hole in the piston the same width as the C port?

Yes match the piston to the port and elongate the hole a bit. Do you think the cylinder spigot is strong enough to cut the slot right through? You are leading the way here, it might work. All you need is the hole in the piston to line up with the slot from transfer port opening to BDC.

350330

This is what ours look like but we also heavily ported the case. You may be able to slot the cylinder all or most of the way and only lightly shape the edge of the case. Certainly worth looking to see what can be done here easily.

350331

This is a standard RGV250 cylinder. 56mm bore 50mm stroke, the same as the GP125. Because of the different thrust loading's front to rear the rear of the cylinder spigot does not have to come all the way down. The front of the RGV bore measured 110mm from top to bottom and the rear 95mm. You could copy that if it helps.

[Roflhat]

Will have to put the barrel on and get some measurements to see where the piston hole will need to be, I like the idea of the extra cooling especially for Bonneville. If I don’t have to cut the slot all the way to the base of the cylinder that would help the strength but maybe worse for flow?
First time really doing porting it’s hurting my head a bit thinking about it now.

Merry Christmas!

[Peter1962]

For the moment in Italian.
Later Spanish, Dutch and English versions will follow,

That is great news, Jan. :wings:

[Niels Abildgaard]

For the moment in Italian.
Later Spanish, Dutch and English versions will follow,

Where can it be ordered in italian?

I can make some sense from reading italian.

[philou]

Where can it be ordered in italian?



https://www.editricelamandragora.it/home/857-il-maestro-del-due-tempi-9788875866723.html

[Niels Abildgaard]

https://www.editricelamandragora.it/home/857-il-maestro-del-due-tempi-9788875866723.html

I have tried.Thank You.They only post to Italy .

[Hoebra]

Can anybody translate into english whats written to the books content? "Just" more historical, or also technical 2stroke aspects?

[Roflhat]

Here’s what I’ve gone for, opened up the piston hole to match the port and elongated it. Lengthened the slot for the C port and I’m closing up the back of it which would go to the casing, going to smooth it off so it’s a nice curved shape. Piston hole is angled up into the port
https://i.ibb.co/kxHTjdf/B4176-BAC-76-BA-4576-9464-B78-EA577234-D.jpg (https://ibb.co/6mnSzdx)
https://i.ibb.co/9VyjSm7/95-C7721-E-EF61-45-B1-9-CFF-4-C31-A5-FD942-D.jpg (https://ibb.co/NmWzbgM)

[TZ350]

Here’s what I’ve gone for, opened up the piston hole to match the port and elongated it. Lengthened the slot for the C port and I’m closing up the back of it which would go to the casing, going to smooth it off so it’s a nice curved shape. Piston hole is angled up into the port


Yes, that looks good to me, so long as the hole in the piston is fully open at TDC and BDC.

Most of the "suck" from the pipe happens around BDC.

It is the pipes suction action that moves the bulk of the mixture up from the crankcase to the cylinder.

Then the reverse pressure wave returns some spilt mixture in the header back to the cylinder. Then it plugs the exhaust port, stopping the rising piston from spilling mixture out of the Ex port. A lot more complex interactions happen too but sucking then plugging is the basics.

Cutting metal to reflect the best of two stroke tuning theory is a real challenge.

I know there is plenty more time to be spent getting the engine and bike built. But I am really looking forward to seeing the dyno results then a report on how it went on the Salt.

[F5 Dave]

Hold on. Wasn't there talk of keeping the std pipe silhouette for class rules? If so then pipe action even if hidden under a std cover will be minimal. So crankcase stuffing and as many revs as possible will be only course of action . Unless I remember that bit incorrectly. I could wade back a few pages, but it appears I'm way too lazy for that.

But back to revs. Engineering is the 2 stroke tuners 1st port of call on classic engines. You need a rod capable of crazy revs and a piston to match (air cooled suitable).

[Roflhat]

Will have to extend the hole quite a bit for it to be open at TDC, is the stock piston strong enough?
https://i.ibb.co/56YZwdW/3-F2-BF2-FF-DA5-B-40-B1-ABB3-3-E8556136-DBB.jpg (https://ibb.co/JKxZgNR)
download own photos from instagram (https://500pxdownload.com/)

Yeh running the standard exhaust with a cone welded inside it then closed up again

[TZ350]

Will have to extend the hole quite a bit for it to be open at TDC, is the stock piston strong enough?


I made a mistake. I should have said "piston hole fully exposed in the slot from TPO to BDC", transfer port opening to bottom dead center, not TDC to BDC. Sorry.

Is the stock piston strong enough, I don't know. I never used them. I favored aftermarket pistons with a single thin ring.

[F5 Dave]

Std Suzuki pistons are fine for road type revs, but grim thereafter. The heavy rings will flap, lose contact with the bore and promote overheating which on aircooled is not pretty.

Std rods are pedestrian as well. Decide what revs you need and engineer to suit.

[speedpro]

I agree with what the 2 above said. If you do end up having to use the standard piston remove the 2nd ring. If everything else is good it will be fine. Also polish all the sharp edges on the piston particularly the bit below the pin. I did that and the pistons still had to be replaced every 2 meetings due to cracks.

[Roflhat]

Cheers, will check the rules but I think I can change rod and piston. Original parts have to be engine cases, barrel, exhaust, Venturi size

[F5 Dave]

Ok so you need to see if you gut the chamber, if you build something inside it that, - will it be of any worth? May be worth choosing a bike with the biggest pipe.

Std crank and piston with peak set for 10,500 would be quite reliable, but you can push that for your purpose.

But with some decent spinning parts, the gain in revs will surpass clever porting. Obviously you want to employ every trick.

Engineer first. Tune 2nd.

Um. . . Read rules first. Engineer 2nd, etc.

. . . so, barrel must be std. . . looking.

Head? Watercool that puppy if rules allow (or dont disallow).

[TZ350]

.
The KT100 GoKart engines rod assembly with 14mm L/E pin (The same rod as an RD125 I think) may be an easy suitable conversion for the GP. We used bigger 22mm BE pins and rods from RGV's and Yamaha RD's because of the superior flat cage silver plated big end bearings that are available for them. And their 15 or 16 mm little end pin option allowed us a better choice of piston for the GP125 and to spin reliably to 14,000 RPM on occasions.

350335

We do quite a bit of work on our cranks. Big End pin bored to 22mm, std stroke for the air cooled's or de stroked for the 110's, alloy plugs in the counter balance holes, Mallory plugs for correcting the balance factor to 50% and inside faces machined back for extra crankcase volume (extra volume works best with a very sucky pipe).

[ken seeber]

I agree with what the 2 above said. If you do end up having to use the standard piston remove the 2nd ring. If everything else is good it will be fine. Also polish all the sharp edges on the piston particularly the bit below the pin. I did that and the pistons still had to be replaced every 2 meetings due to cracks.

Over here in the land of Oz, there was a kart engine called the Comer S80/SW80, which had a 2 ring piston and chrome bore. The rules stated that both rings must be in place. So, to reduce friction, some guys removed the 2nd ring and squeezed it down to a helical shape such that the ends overlapped a bit. Then hit it with some heat (oven, torch ?) such that it took on a set to the new shape. Then it was refitted, where it sat tight in the groove and not contacting the bore. I think that these were CI as the bore surface being chrome, the normal chrome plated rings could not be used.

[Roflhat]

Looking at other sub 100cc bikes available in 1980 doesn't seem many had big pipes. RM100 probably the best, 19.5hp standard

These are the rules stated for production class engines

"Use the same engines (gasoline only) originally
installed in the specific motorcycle frame at the time
of production and ensure it meets the definition set in
the ‘P’ frame class (See 3.11D). Original equipment
(OEM) shall include cylinders, cases (crankcases),
heads, and carburation or throttle body (stock venturi
size), kick-starter or electric starter. Displacement
determines the class. OEM displacement specifications
must remain stock. "

[F5 Dave]

So you need to see what P frame class means, and what gearing is ultimately useable. YZ100 used some reasonable internal bits if you can find one.

Pipe would dictate revs if it has to look the same, but not be untouched. Otherwise it might have a shorter and internal baffle cone.

[wobbly]

The rules say nothing about keeping the original pipe ?????

[husaberg]

http://bonnevillespeedtrials.com/wp-content/uploads/2014/02/2017-AMA-BonnevilleSR-FINAL.pdf

PRODUCTION (P) CLASSA “production motorcycle class” is as “produced by a recognizedmanufacturer”, and the public must be able to purchase a minimumof 500 frames through retail dealers. Production class motorcyclesshall not be modified from Original Equipment at time ofmanufacture. e.g., frame, forks, gas and oil tanks, seat, front andrear lighting, fenders, wheels, brakes, air intake box and(unmodified) exhaust system. They shall also contain the enginethat they were originally produced with. Driveline method/typemust remain stock (i.e. belt drive must remain belt drive)


12. A. PRODUCTION (P)Use the same engines (gasoline only) originally installed in thespecific motorcycle frame at the time of production and ensure itmeets the definition set in the ‘P’ frame class (See Chapter 4).Original equipment (OEM) shall include cylinders, cases(crankcases), heads, and carburation or throttle body (stock venturisize), kick-starter or electric starter. Displacement determines theclass. OEM displacement specifications must remain stock.GASOLINE ONLY. Fuel not permitted in this class. See Chapter2, paragraph 2.F.P engine class shall not run in M, MPS, A, APS or S frame classes

.

[wobbly]

OK , so its easy to cut the seams on a stock pipe , open it and rework it internaly , then reweld it back together to appear exactly as stock.
This has been done plenty of times , one example being the Stock classes in World Champ Jetskis and Karts , I have reworked many , and they are still winning titles.

[husaberg]

OK , so its easy to cut the seams on a stock pipe , open it and rework it internaly , then reweld it back together to appear exactly as stock.
This has been done plenty of times , one example being the Stock classes in World Champ Jetskis and Karts , I have reworked many , and they are still winning titles.
the way i read it its only the p class A that runs stock exhaust.....?

[F5 Dave]

"OEM displacement specifications
must remain stock. "

Hmm, trying to find something that hasn't been rebored might be a big ask.

Unmodified chassis parts. Wonder how literally they apply the position of those parts? Principally the front mudguard and suspension travel. . .
Can you find a YZ100?

[FJRider]

"OEM displacement specifications
must remain stock. "

Hmm, trying to find something that hasn't been rebored might be a big ask.



Many moons ago I got involved in racing Mini 7's ... similar regulations were applied to the class. The best (legal) gain in performance was to "Blueprint" the engine ... which is to build the engine to the exact spec's and tolerances ... the engine designer originally specified for production of the parts and assembly of the engine.

[husaberg]

"OEM displacement specifications
must remain stock. "

Hmm, trying to find something that hasn't been rebored might be a big ask.

Unmodified chassis parts. Wonder how literally they apply the position of those parts? Principally the front mudguard and suspension travel. . .
Can you find a YZ100?
later on for most vintage class's it says 50 thou overbore which is 1.25mm?
As long as it remains under class.
oem spec allows for in most cases 1mm.
That said, a MB100 is over the allowable size on a .25mm overbore

[Roflhat]

Rules are fairly limiting, allowed to change tires, handlebars within reason and airbox element. I've already had the exhaust apart and welded in a cone then covered up again. Changing the exhaust will change the frame class
Also took the foam out of the seat and replaced with softer stuff, so it looks stock but when I sit on it I'll be about 1.5" lower :cool:

[pete376403]

Many moons ago I got involved in racing Mini 7's ... similar regulations were applied to the class. The best (legal) gain in performance was to "Blueprint" the engine ... which is to build the engine to the exact spec's and tolerances ... the engine designer originally specified for production of the parts and assembly of the engine.
I assisted a guy with his 7 way back when as well. There were blueprinted engines and there were "blueprinted" engines. A bit like paraphrasing George Orwell - "all engines are equal, but some engines are more equal than others". A good reason for the AMA claiming rule, that has been applied to other classes as well. Up to 30 minutes after the end of a race, any competitor in that race can claim the winners engine for a predetermined sum - deters people from spending astronomical sums on an engine that might end up going to someone else for 10 grand or something.

[Frits Overmars]

We do quite a bit of work on our cranks. Big End pin bored to 22mm, std stroke for the air cooled's or de stroked for the 110's, alloy plugs in the counter balance holes, Mallory plugs for correcting the balance factor to 50% and inside faces machined back for extra crankcase volume (extra volume works best with a very sucky pipe).
Apart from enlarging the crankcase volume, which indeed requires a sucky pipe to make the most of it, machining the inside faces back for extra crankcase volume has yet another advantage: it improves lubricating and cooling of the big end bearing.

I noticed a couple of things in your crankshaft picture though. As a rule of thumb you'll need at least half the big end pin's diameter worth of material around the pin bore for a firm grip on the pin. My MS-Paint analysis may not be exact, but 7 millimeter of material around the bore doesn't look bulletproof to me...
350337
The Mallory balance plug will need a small amount of shrinkage fitting, which brings a tension load in the material around the bore. And when you rev it, centrifugal force will increase this load. Again my analysis may not be exact, but only 1,5 millimeter of material around the bore doesn't look bulletproof either...


The rules say nothing about keeping the original pipe ?????
PRODUCTION (P) CLASSA “production motorcycle class” is as “produced by a recognizedmanufacturer”, and the public must be able to purchase a minimumof 500 frames through retail dealers. Production class motorcyclesshall not be modified from Original Equipment at time ofmanufacture. e.g., frame, forks, gas and oil tanks, seat, front andrear lighting, fenders, wheels, brakes, air intake box and(unmodified) exhaust system.
OK , so its easy to cut the seams on a stock pipe , open it and rework it internaly , then reweld it back together to appear exactly as stock.That's called cheating Wob. After a lifetime of composing rulebooks and dodging other people's rules, let me tell you how to read them. You'll need an unmodified exhaust system. OK. But if it doesn't say from which bike, you could use an RSA pipe if it happened to fit the bike without modifying, and if you could find and afford one. Simple as that.

And while I'm here: Happy New Year everybody :niceone:

[andreas]

Right back, Frits

[FJRider]

I assisted a guy with his 7 way back when as well. There were blueprinted engines and there were "blueprinted" engines. A bit like paraphrasing George Orwell - "all engines are equal, but some engines are more equal than others". A good reason for the AMA claiming rule, that has been applied to other classes as well. Up to 30 minutes after the end of a race, any competitor in that race can claim the winners engine for a predetermined sum - deters people from spending astronomical sums on an engine that might end up going to someone else for 10 grand or something.

There were a few that spent money that was beyond the usual ... I think to compensate for their lack of ability in the drivers seat.

Those were times mini when engines were in abundance. We didn't have the money for constant expensive (to us) rebuilds.

We won a few races ... and had a bloody lot of fun. The actual base reason for these types of racing to have started.

On a few occasions ... I gave a whole different meaning to the term "Angle Parking" ... :innocent:

[Ocean1]

Many moons ago I got involved in racing Mini 7's ... similar regulations were applied to the class. The best (legal) gain in performance was to "Blueprint" the engine ... which is to build the engine to the exact spec's and tolerances ... the engine designer originally specified for production of the parts and assembly of the engine.

Of note with the final iteration of those reg's was the simple expediency of defining what you WERE allowed to do.

I recall previous attempts, particularly banning grinding off the massive vertical body seams and welding the joints up properly.

[FJRider]

Of note with the final iteration of those reg's was the simple expediency of defining what you WERE allowed to do.

I recall previous attempts, particularly banning grinding off the massive vertical body seams and welding the joints up properly.

The cheaper course of action was using superior driving skills ... or taking advantage of the other drivers lack of skill.


Or as in most cases (when getting a win) ... just hope you get lucky.

[TZ350]

350345

We started with the original Suzuki GP125 air cooled cylinders and by taking the exhaust port timing and port width to extreme's.
We managed 31 RWHP on our best dyno day. But the engine faded with heat stroke quite quickly on the track. So we looked to water cooling.
Class rules required reduced capacity for water cooled engines.

350346

Suzuki GP100 with replated NSR water cooled cylinder and de stroked crank for 110cc.

Standard NSR cylinders gave about 26 - 28 RWHP and a heavily ported one to the air cooled specs was 29 - 30 RWHP.
Disappointing results from the NSR cylinders that have lots of lovely ports that look pretty much like the Honda NF4 RS125 race cylinder.
We were clearly getting better transfer and trapping efficiency with the ported air cooled Suzuki GP125 cylinders than we could manage with the Honda NSR one's.

The take away here is that the pretty looking ports of the NSR cylinders did not translate to better performance.

350347

In reality NF4's make way more power than our GP's. So something is wrong. We got hold of a NF4 engine to take a quick look at the port timings.

350348 350349 NF4.

NF4
Ex opens nominally 84 ATDC for 192 degrees duration.
A Transfers open 115 ATDC for 130 duration.
B Transfers open 117 ATDC for 126 duration.
C Transfer opens 122 ATDC for 116 duration.

30 RWHP Air Cooled GP125 cylinder.
Ex opens nominally 80 ATDC for 200 degrees duration and 72% bore width.
A Transfers open 114 ATDC for 132 duration.
B Transfers open 114 ATDC for 132 duration.
C Transfer opens 114 ATDC for 132 duration.

The Exhaust port time area shape is a little more generous on the NF4 cylinder than the NSR one but other wise pretty much the same timing.

The interesting difference is between the more powerful NF4 Ex at 192 duration and the single Exhaust port 30 RWHP Suzuki GP at 200 degrees duration.

The shorter NF4 exhaust duration of 192 has expansion chamber resonance benefits.

I think we may have been over porting our NSR cylinders by making them similar timing to our best air cooled cylinders. Looks like we should try one made to more closely replicate the NF4 cylinder. Match the NSR's blow down time area to the Suzuki air cooled cylinder.

By being lees ambitious with the NSR's Exhaust duration we may get better results with improved pipe resonance.

[wobbly]

The NF4 MX bike case based cylinders have been hugely surpassed in performance with dozens of updates from the factory as well as examples from other manufactureres, using 54.5/54
The transfer stagger numbers are super old school and can be easily updated to something more modern that would make way more power everywhere.
My first thought that needs an STA check of course would be near 114-116-117 with an Ex around 83 to 82.5 as later customer engines came with..
And as for having all the aircooled transfers @ 114 , that is simply Hp suicide from mid last century as conventional stagger is super effective in widening the powerband in non PV cylinders.

[TZ350]

My first thought that needs an STA check of course would be near 114-116-117 with an Ex around 83 to 82.5

Thanks Wob. I just need to check. Is that 114-116-117 port A-B-C in that order.

[wobbly]

Sure is , with A maybe a little lower and C a little higher as the trend seems to be less stagger differential on the C , than that of the A/B delta.
But as always its getting the Blowdown and Transfer STA to match that is all important.

[philou]

I am curious to try my new 45 degree contra-angle

I think it must be practical for working the vertical angle of the port.

[wobbly]

I posted this chart on my Wobblypipes FB page and was asked several times if the idea works for any racing twostroke .
The anwer is yes.
The method starts with first finding the best power egt just short of deto with a specific weather . I do it on the dyno , but a first data point can be gained at the track , where you lean it down to the point where
the next smaller jet does not give any rise in egt ie the deto limit.In my specific case of Dellorto jets on a TM KZ engine I would expect to see a 20°C rise in EGT when using the usual jet size split ie dropping from a 160 to a 158 size, as long as the jets are
pinned as accurate. Any less than this EGT increase and we are on the deto limit. Once you
have created a set of pinned jets in one size increments ie 160 down to 159 the EGT
increase should be 10°C per size. This enables very accurate and safe tuning during the day
to stay bang on the desired best power numbers.

Then you would need another couple of weather/jet points ( gained from a RAD app on your phone accessing the nearest airport weather station ) where you hit the same egt on the day.
Once you have 3 points you can draw the reference line thu them.

The scale of jet size along the bottom can be whatever the carb uses - but for it to be reliable the jets must be guaranteed accurate by being flow/time tested or using a jet pin diameter set.

EDIT - added temp rise targets for egt.

I did the first chart over 10 years ago , but have used the same reference line ever since , with different engine versions /mods and tune , the lines are always parallel for the Dellorto jets I use.
In this kart chart the top line is a TM KZ10C in OZ on 100 octane race fuel.
The middle reference line is an older KZ10B on 98 pump gas in NZ
And the bottom line is a TM R1 on C12 110 octane in USA - the only difference is the combination of tune and fuel quality.

Once I have the tune line I can go to any track , dial up the weather combination on my phone , and fit the perfect jet for that RAD on the day.
Usually I would change jets 3-5 times during the day , simply keeping the same egt - tracking any weather changes in temp , pressure , or humidity.
I use Density Altitude as it has an expanded scale over RAD.

All this is doing is maintaining the optimum bsfc for the engine/fuel ie - less air density = less fuel needed = less power generated = smaller jet.

[Roflhat]

Interesting with the graphs and a clever solution. Do you find that at higher temperatures/altitude you may need a larger main jet to aid cooling? Been reading up about it for Bonneville, most folk say the change in jetting in reality is much smaller than the calculations would suggest

[wobbly]

The thing is these data points are not calculations , each is taken from hitting the optimum egt at a specific Density Altitude,
Most of the KZ10B was done at sea level , the Vegas R1 altitude is 650M , but Density Altitude uses Temp , Air Density and Humidity for the data points and as actual altitude
affects the Air Density the airport calibrated weather station sends out by default.

[Roflhat]

I like the idea a lot, might try do the same for mine.

Got my suzuki running today, definitely feels like it has more power but it's quite intermittent. Going to change plug and try again, used plenty 2 stroke during engine assembly. What sort of jetting would you expect for this? GP100 with tranfers opened up as per Rob's recipe, standard carb and exhaust (with cone welded inside). Currently 107.5 main. Will get it on the dyno soon once the ignition setup arrives but would be nice to have a rough idea

[TZ350]

I like the idea a lot, might try do the same for mine.

Got my suzuki running today, definitely feels like it has more power but it's quite intermittent. What sort of jetting would you expect for this? GP100 Currently 107.5 main.

For our GP125's running 24mm carb's we were around 135mj.

For the 100 with its 22mm carb. Maybe 120ish would be my guess but take as many different main jets of all sizes as you can get hold of.

On the dyno, take big steps, high and low to find the likely area to zero in on. Start with going high first.

Adjusting the needle clip may be required with changes in main jet. Ie a much bigger main jet may require lowering the needle to keep things throttling well.

[F5 Dave]

So have you calculated your peak power revs with the modified pipe?

What was ignition? Not worth wasting your time on dyno if left std unless revs are real low, and that would be a waste of power anyway.

[Roflhat]

Cheers, have ordered a big pile of jets so I'll have 105 up to 135.
Pipe is designed for ~10k rpm. Currently using the electronic ignition kit, Rob is very kindly sending me a setup so once that's on will get it over to the dyno

[Roflhat]

Was playing with some free programs for pipes, I think mine is not too far away from these given the restrictions for class
https://i.ibb.co/wJ17NxS/Screenshot-2022-01-06-at-16-47-18.png (https://ibb.co/XyTDZv7)
Drew them up in Rhino quickly
https://i.ibb.co/bmyJh89/Screenshot-2022-01-06-at-10-59-25.png (https://ibb.co/tKNXfWr)

I've got a file for a carb housing spacer if anybody wants too, I 3D printed mine

[F5 Dave]

Any curve he sends you will be geared towards significantly more revs. That will keep the power quite modest. Maybe within class limits that will be competitive. I wonder for top speed if a pwm power jet project would increase revs/spread and be worth pursuing as a high priority.

[Roflhat]

I've got another standard exhaust sitting in the shed, I can cut it up and put a cone further up inside so it'll be suited for more RPM. I have to run the standard carb, unless you mean adding a power jet to the standard carb?

[husaberg]

I've got another standard exhaust sitting in the shed, I can cut it up and put a cone further up inside so it'll be suited for more RPM. I have to run the standard carb, unless you mean adding a power jet to the standard carb?
Come countries had the same exhaust for the GP100 and GP125.
might be worth investigating if the GP125 one is bigger dia
https://www.cmsnl.com/suzuki-gp125-1981-x-e02-e04-e17-e18-e21-e22-e41_model13396/muffler-assy_1430139671/

looks like the early Gp125 and the later GP 125 headers are potentally different sizes as well judging by the parts numbers although it might be materials

https://www.cmsnl.com/suzuki-gp125-1978-c-e01-e02-e04-e06-e13-e17-e18-e21-e22-e24-e30_model13390/gasket-exhaust-pipe-nas_1418111010/

https://www.cmsnl.com/suzuki-gp125u-1981-x-sweden-greece-e17-e41_model13395/gasket-exhaust-pipe-nas_1418111020/
gasket same part as a RGV250.
I would bet the Header is double skinned or at least the later one might be.

[F5 Dave]

I've got another standard exhaust sitting in the shed, I can cut it up and put a cone further up inside so it'll be suited for more RPM. I have to run the standard carb, unless you mean adding a power jet to the standard carb?
Adding a power jet with a solenoid, perhaps like Robs experiment a few pages back. I made one from parts from a KX 125 carb which was fitted std when I couldn't get the carb to fit in the space. Had other things to chase so never had it working properly in anger. But being able to control turning it off should extend your rev range.

At some point working with std pipe the header/diffuser will be quite long compared to the length of the pipe required for say 13,000rpm you would prefer to spin. Find someone to model in engmod might save you going in wrong path given such restrictions.

[Condyn]

I am curious if somebody could please point me in the correct direction, regarding the best possible coolant path in a 2 stroke. I know I have stumbled across some info on this, but I cannot find it now. Thank you.

[wobbly]

The best setup is to have the cold water enter the cylinder above or each side of the boost port, this cold flow runs directly across the transfer tops toward the hot Exhaust area.
This hot flow then enters the head above the Exhaust port , crosses the head and exits at the rear , the highest point.
Bleed holes for trapped air need to be added at the cylinder highest point, and if the case is cooled between the gearbox and case , then small bleed holes can cool the Ex underside.

In say an RD/LC/TZ a gasket plate of some sort is needed to prevent the cylinder entry flow from rising directly into the head.

[husaberg]

The best setup is to have the cold water enter the cylinder above or each side of the boost port, this cold flow runs directly across the transfer tops toward the hot Exhaust area.
This hot flow then enters the head above the Exhaust port , crosses the head and exits at the rear , the highest point.
Bleed holes for trapped air need to be added at the cylinder highest point, and if the case is cooled between the gearbox and case , then small bleed holes can cool the Ex underside.

In say an RD/LC/TZ a gasket plate of some sort is needed to prevent the cylinder entry flow from rising directly into the head.
i was looking up something the other day and seen this
i cant be arsed redig them agin but one has the bit with the pockets

https://www.cycleworld.com/story/blogs/ask-kevin/motorcycle-engine-cooling-explained/
https://www.cycleworld.com/story/blogs/ask-kevin/engine-cooling-and-horsepower/
https://vintagebikemagazine.com/technical-articles/engines-and-heat-by-kevin-cameron/

[porttiming124]

Hello everyone.
I'm helping a friend to try and gain power on an old 440cc 2 cylinder snowmobile engine (1979) for racing on an oval track.
This type of engine develops approximately 110 hp at 9800 rpm.
The intake is controlled by a rotary valve.
I am wondering about the shape of the port of admission.
The carburetors are mikuni vm 44 and the port is well round (44mm) all the way to the entry of the crankcase.
Is there an advantage of having a port like the aprilia rsa-rsw (square with rounded corners) for the same area in mm2 compared to a round port?
350378

[husaberg]

Hello everyone.
I'm helping a friend to try and gain power on an old 440cc 2 cylinder snowmobile engine (1979) for racing on an oval track.
This type of engine develops approximately 110 hp at 9800 rpm.
The intake is controlled by a rotary valve.
I am wondering about the shape of the port of admission.
The carburetors are mikuni vm 44 and the port is well round (44mm) all the way to the entry of the crankcase.
Is there an advantage of having a port like the aprilia rsa-rsw (square with rounded corners) for the same area in mm2 compared to a round port?
350378

if you go to part one and two of the ask Jan and Frits about the RSA thread on Pitlane .fr
you will find some discussion about this sort of engine if memory serves.

[wobbly]

The Aprilia RSA later model port was oval shaped with the largest dimension on the RV centerline ie 90* to the RSW.
This narrows the port , and thus reduces the time the valve is sweeping across the port , given the same timings.

[Roflhat]

Measured the exhausts some more, current one is designed to peak at 9.4k, this new one I’m working on should be 10.8k. That’s as high as I can get it with having the standard exhaust fit over it
https://i.ibb.co/mNjf705/1-FF3-FDD2-00-CE-4669-95-D8-756075-AF023-E.jpg (https://ibb.co/Vw1f8xY)
https://i.ibb.co/Kw1kPct/3-A5064-FA-F500-4902-94-AF-7-E0-B6473-A675.jpg (https://ibb.co/0twS7p0)

[Frits Overmars]

if you go to part one and two of the ask Jan and Frits about the RSA thread on Pitlane .fr you will find some discussion about this sort of engine if memory serves.Thank you for the free advertising Husa. However, googling Pitlane.fr will give the scary result "The domain Pitlane.fr may be for sale...".
You might want to try http://www.pit-lane.biz/t117p246-gp125-all-that-you-wanted-to-know-on-aprilia-rsa-125-and-more-by-mr-jan-thiel-and-mr-frits-overmars-part-1-locked
It may be necessary to register (free) in order to see all the images. And don't be put off by the French language; the RSA thread is mainly English-spoken.

[Roflhat]

Got the pipe finished off, stuck a 115 main jet it the carb. Goes like the absolute clappers now!
Very happy with it, just need to quieten it down a lot. Will put the standard exhaust shell back over it and the stock baffle trimmed down. Hopefully quiet enough, pulled a huge pile of baffles and sound deadening out of the standard pipe
https://i.ibb.co/sQKs4YN/0540-C005-6764-49-F9-A02-A-8-F1-CD8131512.jpg (https://ibb.co/Xp7FPRK)
https://i.ibb.co/wCcP6cj/F41-AF663-EBA3-4-EAD-A56-A-00-E219-DF839-B.jpg (https://ibb.co/3WRjhRQ)

[jfn2]

Frits
On your scavenging concept drawing, you are using a cylinder with 5 transfer ports. Would you change any of the angles for either direction or position and your axial angle formula for a 4 port ( A and B ports and no D port) cylinders? And how about a 2 port ( just A ports and no D port) cylinder, as in some chainsaws? Thank you, Jeff.

[porttiming124]

if you go to part one and two of the ask Jan and Frits about the RSA thread on Pitlane .fr
you will find some discussion about this sort of engine if memory serves.

ok thank you

[Frits Overmars]

Frits
On your scavenging concept drawing, you are using a cylinder with 5 transfer ports. Would you change any of the angles for either direction or position and your axial angle formula for a 4 port ( A and B ports and no D port) cylinders? And how about a 2 port ( just A ports and no D port) cylinder, as in some chainsaws? Thank you, Jeff.Jeff, this is one of those simple questions for which there is no simple answer.
To start with, I have zero information about the cylinder you have in mind, so I will have to assume that you want to derive it from a cylinder with angles as shown in my scavenging concept, below.
If you omit the C-port opposite the exhaust, I would leave the A-ports as they are, increase the B-ports' trailing position angle from 160° to 165°, increase their trailing direction angle from 132° to 137° and increase their axial angle from 10° to 15°, always assuming that there is sufficient material to do so.

If you want the best solution with only the A-ports, my first reaction would be: "You want to know how much 2 x 2 is, but you don't want the answer to be 4".
There is no way you can approach the scavenging quality of a 5-port layout with just 2 ports. You might increase the A-ports' trailing position angle from 100° to 140° and their trailing direction angle from 65° to 90°, always assuming that there is sufficient material, and decrease their axial angle from 25° to 20°.
But the lack of flow guidance in just two ultra-wide A-ports would not do any good. Besides, the piston ring would object to making the total port width of those 2 ports equal to the total port width of a 5-port scavenging layout.
350392

[philou]

anyone using "Ice" two stroke engine simulator?

http://www.jhis.co.uk/ICE/

I have had the program for a long time and it cannot be installed on the computer. the author cannot solve my problem.

it offers neither the precision and the possibilities of engmod2t.
it only costs £ 25

[jfn2]

Hello Frits;
Thank you for your reply. I did not give you any engine specifics for a reason, I did not want a specific answer. You answered both of my questions exactly as I hoped you would. Thank you.
As to your comment, " You want to (know) how much 2 x 2 is, but you don't want the answer to be 4". I asked my son this question and he, in turn, asked me if it was asked verbally or written down? I answered, written down. He right away, took a piece of paper and wrote, the answer could be 0100. Then he said to me, " The answer is still 4".

[Frits Overmars]

Hello Frits;
Thank you for your reply. I did not give you any engine specifics for a reason, I did not want a specific answer. You answered both of my questions exactly as I hoped you would. Thank you.
As to your comment, " You want to (know) how much 2 x 2 is, but you don't want the answer to be 4". I asked my son this question and he, in turn, asked me if it was asked verbally or written down? I answered, written down. He right away, took a piece of paper and wrote, the answer could be 0100. Then he said to me, " The answer is still 4"..........:clap:

[tdc211]

Jeff, this is one of those simple questions for which there is no simple answer.
To start with, I have zero information about the cylinder you have in mind, so I will have to assume that you want to derive it from a cylinder with angles as shown in my scavenging concept, below.
If you omit the C-port opposite the exhaust, I would leave the A-ports as they are, increase the B-ports' trailing position angle from 160° to 165°, increase their trailing direction angle from 132° to 137° and increase their axial angle from 10° to 15°, always assuming that there is sufficient material to do so.

If you want the best solution with only the A-ports, my first reaction would be: "You want to know how much 2 x 2 is, but you don't want the answer to be 4".
There is no way you can approach the scavenging quality of a 5-port layout with just 2 ports. You might increase the A-ports' trailing position angle from 100° to 140° and their trailing direction angle from 65° to 90°, always assuming that there is sufficient material, and decrease their axial angle from 25° to 20°.
But the lack of flow guidance in just two ultra-wide A-ports would not do any good. Besides, the piston ring would object to making the total port width of those 2 ports equal to the total port width of a 5-port scavenging layout.
350392


Frits. How's that inner radius below the case deck work?
New yz85 is like this. I didn't know what to think about it.

[husaberg]

Frits. How's that inner radius below the case deck work?
New yz85 is like this. I didn't know what to think about it.


Hi i am confused Nearly every case i have seen short of a 1960 old villers/ greeves is radius below the casedeck?
350411350412350413350414

[Vannik]

Hi i am confused Nearly every case i have seen short of a 1960 old villers/ greeves is radius below the casedeck?

Interesting - I saw the inner radius of the transfer port as the radius on the sleeve side of the port?

[husaberg]

Interesting - I saw the inner radius of the transfer port as the radius on the sleeve side of the port?


oh i get it (only after he actually looks at Frits pic again)

Still fairly common


https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSdu9MuZA2OvBszn3m6aR1sDLkka0qQw wXQsQ&usqp=CAU

cagiva
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=338907&d=1536917354

YZR500
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=337852&d=1532951074

NSR500
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=316037&d=1443001389

Cant remember what this one was later oh KR3
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=337830&d=1532918336



NSR or RS cant recalll
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=300509&d=1409560182

when we were sharpening septums to razor shapeness that inner area got a radius as well :)
Just like we were taught from looking at pictures in robinsons, book the sharp point kept them cool at Mach 3

i cant remember where i seen it but there is an odd looking bump in the unmentionable RSW500.

[Frits Overmars]

Frits. How's that inner radius below the case deck work?
New yz85 is like this. I didn't know what to think about it.I'm not sure I understand your question. Do you mean the radius indicated in the picture below?
350415

[husaberg]

I'm not sure I understand your question. Do you mean the radius indicated in the picture below?
350415
Yes i think he means this bit Frits with the inner radus continues lower than the machined deck height of the cylinder. (Thanks for correcting me Neels)
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=349796&d=1633762622https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=337828&d=1532914973
Now i am going to spend an hour looking for that the weird looking protrusion on a RSW500.

okay 27 minutes
Any ideas re the shapes of this
It looks nothing like any of the other Aprila or Rotax tranfers in design
it almost looks like a different guy did designed the inner side than the outer sider?

Was it just as they tried to use the skinny 250 case?
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=257931&d=1329599653

[sniemisto]

While were at it, I’m curious about this double radius:
https://uploads.tapatalk-cdn.com/20220114/3694ee6edd584ad774a9bfea9dad5762.jpg
What is the reason for “step” and radius change at case deck?

[Frits Overmars]

Now i am going to spend an hour looking for that the weird looking protrusion on a RSW500. okay 27 minutes
It looks nothing like any of the other Aprilia or Rotax transfers in design. it almost looks like a different guy did designed the inner side than the outer side? Was it just as they tried to use the skinny 250 case?
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=257931&d=1329599653You're spot-on about a 'different guy' Husa.
The RSW500 was the brainchild of Aprilia's then-technical director Jan Witteveen. It was an extremely-short stroke engine and Jan Thiel did not want anything to do with it.

[Frits Overmars]

While were at it, I’m curious about this double radius:
https://uploads.tapatalk-cdn.com/20220114/3694ee6edd584ad774a9bfea9dad5762.jpg
What is the reason for “step” and radius change at case deck?This was a case of mutilating a new cylinder design because it had to fit old-type crankcases. You also see it quite a lot on aftermarket big-bore cylinders.

[tdc211]

Piston at bdc. ktm cylinder next to it

[jamathi]

This was a case of mutilating a new cylinder design because it had to fit old-type crankcases. You also see it quite a lot on aftermarket big-bore cylinders.

This is particularly bad...
This is the main cause why big-bore cylinders usually give diappointing power....
The transfers become too small!!

[jamathi]

I'm not sure I understand your question. Do you mean the radius indicated in the picture below?
350415

This radius gave about 0.4HP more...

[jamathi]

Yes i think he means this bit Frits with the inner radus continues lower than the machined deck height of the cylinder. (Thanks for correcting me Neels)
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=349796&d=1633762622https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=337828&d=1532914973
Now i am going to spend an hour looking for that the weird looking protrusion on a RSW500.

okay 27 minutes
Any ideas re the shapes of this
It looks nothing like any of the other Aprila or Rotax tranfers in design
it almost looks like a different guy did designed the inner side than the outer sider?

Was it just as they tried to use the skinny 250 case?
https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=257931&d=1329599653

This engine was a complete failure, best power was, of course, reached when it was finally enlarged to 500cc....
I still don't understand why they needed 5 years to discover it....................
It just shows how little they understood about engines!

[jamathi]

You're spot-on about a 'different guy' Husa.
The RSW500 was the brainchild of Aprilia's then-technical director Jan Witteveen. It was an extremely-short stroke engine and Jan Thiel did not want anything to do with it.

Enlarging a 250cc engine proved to be a totally wrong idea....
Of course the short stroke engine was always short of power.
And when it was finally enlarged to 500cc the gearbox broke....
Small wonder, as it was basically made for a 125
The 250cc tandem used already the 125 gearbox, sometimes broke..
I still think a well-made 500/2 could have won!!!!

[husaberg]

You're spot-on about a 'different guy' Husa.
The RSW500 was the brainchild of Aprilia's then-technical director Jan Witteveen. It was an extremely-short stroke engine and Jan Thiel did not want anything to do with it.


Enlarging a 250cc engine proved to be a totally wrong idea....
Of course the short stroke engine was always short of power.
And when it was finally enlarged to 500cc the gearbox broke....
Small wonder, as it was basically made for a 125
The 250cc tandem used already the 125 gearbox, sometimes broke..
I still think a well-made 500/2 could have won!!!!


Cheers Frits and Jan


https://www.honda.co.uk/engineroom/world/mick-doohan-and-the-honda-nsr/

I read this today on Hondas own page
Now i never worked at HRC
But i do know the RS500 never had two cranks or Disc valves.
350419350420350421

Nor did the Switch to unleaded make it needed to be switch back to 180 crank.
350424
One often over looked advantages of the 3 was it had a lot f room for wide swept transfers as well as full width cadges as did the Single cranked NSR500.
Of course the Tandem and the cranked tandem Aprilia had this room as well.
350423350422

I seems Honda has forgotten.

[F5 Dave]

Always thought a 500VTwin would make a cracking roadbike in the 90s. . . . If only someone made one. . . . ;)

[Flettner]

It's here, just waiting on a suitable gearbox.
Wayne Blackwood has an R1 gearbox lined up.
A 700 twin, start looking for R1 gearboxes, if you want one.

[Frits Overmars]

The V4 engine employed a single crankshaft, instead of the dual-crankshaft arrangement of the three-cylinder unit in the previous NS500.

To take the greatest possible advantage of the four-cylinder engine's increased power over its three-cylinder predecessor, the V4 was fitted with a single crankshaft instead of dual counter-rotating crankshafts which minimised losses due to friction. Another innovation was the engine's reed valve input system which was introduced to replace the rotary valves that had been used up until then.

An Auto-controlled Torque Amplification Chamber (ATAC), which is a valve system in the exhaust designed to optimise gas flow, was also introduced to further improve the engine's performance.

In 1990, engineers went yet another step further by deciding to change the engine's ignition timing to allow the pistons to deliver power all at once or in a distributed manner. They achieved this by coming up with an engine design where the two sets of two pistons were at 180-degree angles, and because of the unique sound it made, this engine became known as the "Screamer."
I read this today on Hondas own page. Now I never worked at HRC but I do know the RS500 never had two cranks or Disc valves.
Yep, it's an incredibly ill-informed article. BS about dual crankshafts, rotary valves, ATAC (introduced years before on the NS500 triple but never used on the NSR500), 180°-firing screamer (the real screamer had 90°-firing), and so on; hard to believe that Honda published it on their own pages.

[katinas]

Indeed very strange, but except about rotary rotary valve, maybe it could be explained by wrong translation.

NS500 engine, like first 1984 "bottom tank" NSR500, was counter rotating, with additional shaft between crank and clutch basket "instead of the dual-crankshaft arrangement of the three-cylinder unit in the previous NS500",

With new 1985 1986 NSR 500 under engine exhaust concept, that required more space under engine for four exhaust, intermediate shaft was removed . Because of that, forward rotating crank connected directly to clutch gear and looks like this was widest NSR engine "the V4 was fitted with a single crankshaft instead of dual counter-rotating crankshafts which minimized losses due to friction".

ATAC was used on NSR500 until 1986.

From 1987 intermediate shaft again was added, because rear cylinders exhaust arranged under seat and more free space under engine was available.

Inline double crankshaft was used from 1992 to the end, together with shorter intermediate shaft, with gears positioned in the center. This reduce crankshaft twisting angle, with more accurate ignition timing for 1 and 2 cylinders in comparisons to previous single peace crank

[Peter1962]

It's here, just waiting on a suitable gearbox.
Wayne Blackwood has an R1 gearbox lined up.
A 700 twin, start looking for R1 gearboxes, if you want one.

Neil, i suppose this is your homemade twin 700 that you made for the autogyro ? For that specific usage, do you still think that a 2 stroke is a viable option for a gyro or an ULM, or would you also opt in for the 4 stroke subaru or the inevitablel rotax 912-914 ?

Back over here in Belgium, it is all Rotax... I live at a couple of kilometers of the Airport-Amougies ULM base. Every ULM has a Rotax 4 stroke... Not one 582 or 503 has lasted. All gone. :(

[F5 Dave]

It's here, just waiting on a suitable gearbox.
Wayne Blackwood has an R1 gearbox lined up.
A 700 twin, start looking for R1 gearboxes, if you want one.
R1 gearbox are known to be a bit fragile in 2nd at least.

[Ns1Montesa]

Always thought a 500VTwin would make a cracking roadbike in the 90s. . . . If only someone made one. . . . ;)

https://en.m.wikipedia.org/wiki/Bimota_V_Due

The Bimota V due is a 500V Roadbike. Dont know the whole story, but seems like they had some problems with fuel injection and reliability.

[Flettner]

Neil, i suppose this is your homemade twin 700 that you made for the autogyro ? For that specific usage, do you still think that a 2 stroke is a viable option for a gyro or an ULM, or would you also opt in for the 4 stroke subaru or the inevitablel rotax 912-914 ?

Back over here in Belgium, it is all Rotax... I live at a couple of kilometers of the Airport-Amougies ULM base. Every ULM has a Rotax 4 stroke... Not one 582 or 503 has lasted. All gone. :(

Rotax dont support the twostroke now. 503 gone, 582 shortly.
My 700 twin I think is a great engine (I would say that) smooth with the balance shaft and powerful.
Reliable? In 30 flying hours its stopped three times with three different pilot's, me being one of them. These problems all solved now. Its an ideal gyro engine, light, powerful, smooth and compact with a built in pre rotator output, in my small single seater its a rocket.
Yet all I hear is 'it sounds like a scooter'. Aviation people are not engine people, they tend to have deep Rotax pockets also. The Rotax fourstroke is not a particularly good engine but it has millons of flight hours history.

Ive had zero interest in the 700 twin but then I havent really advertised it. Im just happy burning off some hours myself, it needs more flight time before Im comfortable to let anyone else have one. Its a circuits only or at least only fly over what you can land on engine still at the moment.

[Peter1962]

Rotax dont support the twostroke now. 503 gone, 582 shortly.
My 700 twin I think is a great engine (I would say that) smooth with the balance shaft and powerful.
Reliable? In 30 flying hours its stopped three times with three different pilot's, me being one of them. These problems all solved now. Its an ideal gyro engine, light, powerful, smooth and compact with a built in pre rotator output, in my small single seater its a rocket.
Yet all I hear is 'it sounds like a scooter'. Aviation people are not engine people, they tend to have deep Rotax pockets also. The Rotax fourstroke is not a particularly good engine but it has millons of flight hours history.


Yes, all that matters is Rotax...
But it is also very sad that the few two stroke engine builders for the aero market did not innovate more.

Take Hirth for example, they are still producing the same engines like 20 years ago.

Not one brand ever made a twin with a counter balancer...

I would say that 'the competition' made it verry easy for Rotax to dominate the market with their overpriced 912-914's...

[Peter1962]

Rotax dont support the twostroke now. 503 gone, 582 shortly.
My 700 twin I think is a great engine (I would say that) smooth with the balance shaft and powerful.
Reliable? In 30 flying hours its stopped three times with three different pilot's, me being one of them. These problems all solved now. Its an ideal gyro engine, light, powerful, smooth and compact with a built in pre rotator output, in my small single seater its a rocket.
Yet all I hear is 'it sounds like a scooter'. Aviation people are not engine people, they tend to have deep Rotax pockets also. The Rotax fourstroke is not a particularly good engine but it has millons of flight hours history.

Ive had zero interest in the 700 twin but then I havent really advertised it. Im just happy burning off some hours myself, it needs more flight time before Im comfortable to let anyone else have one. Its a circuits only or at least only fly over what you can land on engine still at the moment.


My favorite of all times : the Monarch butterfly
https://www.youtube.com/watch?v=k7A3pobLMfU

[Flettner]

Yes, all that matters is Rotax...
But it is also very sad that the few two stroke engine builders for the aero market did not innovate more.

Take Hirth for example, they are still producing the same engines like 20 years ago.

Not one brand ever made a twin with a counter balancer...

I would say that 'the competition' made it verry easy for Rotax to dominate the market with their overpriced 912-914's...

I would say you are totally on the money.

I fly my two seat a lot, with the Subaru EA81 engine. Its got the SUB4 four port heads, turbocharged. The SUB4 heads are no longer availabe so Im re making the molds now. NA these engines with the four port heads will produce 130HP at the prop flange for 90kg dry, including reduction gearbox. Not to shabby in my book.
But once again a small market. In saying that I have a number pre sold aready (with a camshaft). These engines/heads have a long history now and finally are seen as desirable and dont sound like a scooter.
https://youtu.be/6Az42nw0Hx8

[Flettner]

R1 gearbox are known to be a bit fragile in 2nd at least.

I don't think we will be pushing ithe gearbox as hard as an R1.

[F5 Dave]

Yeah but 2nd hand ones may be hard to find as a result.

[F5 Dave]

https://en.m.wikipedia.org/wiki/Bimota_V_Due

The Bimota V due is a 500V Roadbike. Dont know the whole story, but seems like they had some problems with fuel injection and reliability.

That bike was really the subject of my slightly surreptitious post
Or was I being forseafish? :laugh:

[Flettner]

My favorite of all times : the Monarch butterfly
https://www.youtube.com/watch?v=k7A3pobLMfU

Imagine it with a decient engine.

[Flettner]

Yeah but 2nd hand ones may be hard to find as a result.

Or easier, lots of broken R1's about. Second gear is easy enough to get, for Blackwood Yamaha.
Or probably even easy enough to manufacture a new second gear set if I have to.
If Wayne turns up with an R1 gearbox, it will have an R1 gearbox.

[Grumph]

Remember I've got a heap of Z1 gearbox bits here that apparently no-one wants. Reasonably close ratio 5 speed - and rugged.
Drag guys have put huge HP through these boxes.
Pay freight and they're all yours. One complete and one with no selector drum.

[Flettner]

Remember I've got a heap of Z1 gearbox bits here that apparently no-one wants. Reasonably close ratio 5 speed - and rugged.
Drag guys have put huge HP through these boxes.
Pay freight and they're all yours. One complete and one with no selector drum.

Send me a $ figure and a bank account number and you are on.
To Hamilton depot only.
Dont suppose you have the cases, to measure up?

[speedpro]

3rd gear is only good for about 180hp, evidently

[husaberg]

Hi Neil
If i was going to the trouble to clock the case and do a production run, i would use a Oil air GSXr transmission they are good or over 200HP for the 5 and available in a wide variety of years and 5 and 6 speed 750/1100. Suzukis of that era were the best shifting bikes.
Either that or a VF750 as they are narrow as none of those lasted long enough to blow a gearbox. Pretty sure they are available in 5 or 6 as well

[Flettner]

Are they free, or seriously cheap?
I only want two gearboxes, one for me and one for Wayne.
I kind of doubt anyone else would want a 700cc twin twostroke road bike engine.

[andreas]

What is the anticipated price for such engine?

[husaberg]

Are they free, or seriously cheap?
I only want two gearboxes, one for me and one for Wayne.
I kind of doubt anyone else would want a 700cc twin twostroke road bike engine.

Well They are not as cheap as free. :) $300-500 landed by the looks of it on fleecebay . if you are only doing two go with Grumps

[philou]

I kind of doubt anyone else would want a 700cc twin twostroke road bike engine.

it will be complicated to place the exhausts on the bike.
but it will be fun

[husaberg]

350429350430350431350432350433
Just saying
From memory Alfred Scott invented the Kickstarter
with 700cc you can giveaway a few HP

[F5 Dave]

it will be complicated to place the exhausts on the bike.
but it will be fun

Well if you style the bike as a Cruiser cornering clearance can be used to house the pipes.

Hello? Hello? I seem to have been cut off? :weird:

[speedpro]

I 2nd the comment about shifting. The Zs were horrible. Yamaha bikes of a similar vintage were heaps better and my GSX11 was simply the best. Other riders of that vintage bike were saying similar things, suzuki boxes were the best to use. The benefit of a Z was the straight cut primary gears. The helical cut primary gears on the Suzukis were rubbish but there are fixes for that which I'm sure Neil could sort easily. I seem to recall the Suzuki clutches were a bit less than optimal but later on with the Z clutch I did end up doing significant mods but the engine was pretty excessive on that.

[jato]

Re gearboxes, i believe inline fours with equal firing intervals give gearboxes a fairly easy life, with peak torque values only of whatever a 250 fourstroke can manage ( including inertia torque of 2 rising pistons at high revs ). if one of those gearboxes has a known weakness a powerful two stroke single/twin will soon find that weakness thanks to those new higher torque pulses.

[DoldGuy]

Are they free, or seriously cheap?
I only want two gearboxes, one for me and one for Wayne.
I kind of doubt anyone else would want a 700cc twin twostroke road bike engine.

Flettner, you might be surprised...

[Flettner]

Flettner, you might be surprised...

Ive shown the 700 twin to a number of aviation people, zero intetest, which surprises me as its not some pie in the sky digital solid model, its real, doing the business, in the air. With CNC programs/cut paths and casting patterns.
People say a lot but when it comes time to put cash down, its crickets.
Ill build a couple for me and Wayne, and we can see what happens from there.
Sounds negative I know, when did I become such a cranky old man?
NO, not a crusier F5.

[husaberg]

Ive shown the 700 twin to a number of aviation people, zero intetest, which surprises me as its not some pie in the sky digital solid model, its real, doing the business, in the air. With CNC programs/cut paths and casting patterns.
People say a lot but when it comes time to put cash down, its crickets.
Ill build a couple for me and Wayne, and we can see what happens from there.
Sounds negative I know, when did I become such a cranky old man?
NO, not a crusier F5.
https://qph.fs.quoracdn.net/main-qimg-6b6bde8ee992738e5a93622c5ee5518d-lq

[Brett S]

BRC is doing a 600 parallel twin project using the CBR600 gearbox.
They must be pretty confident the gearbox will handle the extra 2 stroke loads to be so far along with the project?
Hopefully their new cylinders suits a ktm base gasket mounting..

You may have to change primary drive ratio to clear the crank due to the 4 strokes having a tiny stroke?
This may suit your lower rpms anyway?

[jato]

Changing the primary drive to a higher ratio (speeding up the gearbox) is a good way to lower the gearbox loads up to a point when speeds start getting excessive . too high and selecting first from neutral becomes risky and the fast spinning parts ad excessive flywheel effect. Engineering and compromises ...

[husaberg]

Ducati Gearbox's are pretty inexpensive secondhand made for twins so are reasonable robost and narrow and have big clutch's.
from what was said in the 90's by cramp though they have odd tooth profiles so you will need to use their own primary or make your own clutch.
I don't ever recall anyone having much trouble with the gearbox's

[wobbly]

The 2T 500 twin project Dr Jeff and I are doing is built around the CBR600 gearcluster like the BRC - as was used in
Moto2 for years with no issues..
This was chosen purely based on the normalised gear ratios , its power handling ability and readily availablity.
The ratios are all but identical to the TZ500 , and that gearset was used in the BSL500 tripple for the ratio reason as well.
Pipes for a 700 twin are going to be a mile long / fat as hell, and looking at the Tularis that had a Polaris 700 twin in it ,its reversed cylinder pipes hung out well past the rear wheel ( making it illegal for any form of racing )
and this problem isnt going away even with ugly looking U bend stingers like the Bimota 500 used.

[Flettner]

The 2T 500 twin project Dr Jeff and I are doing is built around the CBR600 gearcluster like the BRC - as was used in
Moto2 for years with no issues..
This was chosen purely based on the normalised gear ratios , its power handling ability and readily availablity.
The ratios are all but identical to the TZ500 , and that gearset was used in the BSL500 tripple for the ratio reason as well.
Pipes for a 700 twin are going to be a mile long / fat as hell, and looking at the Tularis that had a Polaris 700 twin in it ,its reversed cylinder pipes hung out well past the rear wheel ( making it illegal for any form of racing )
and this problem isnt going away even with ugly looking U bend stingers like the Bimota 500 used.

Could it be any worse than the four cylinder 500's , four of the buggers to house.
Dont worry, Ill make them fit.

[speedpro]

Re gearboxes, i believe inline fours with equal firing intervals give gearboxes a fairly easy life, with peak torque values only of whatever a 250 fourstroke can manage ( including inertia torque of 2 rising pistons at high revs ). if one of those gearboxes has a known weakness a powerful two stroke single/twin will soon find that weakness thanks to those new higher torque pulses.
Z gearboxes in that regard were well over-engineered as were the majority of similar vintage models. There were weaknesses, I found a few, but the cogs themselves were generally pretty good

[speedpro]

It's a bit of a compromise but you could take the stingers from the belly of the chamber. Added bonus - it reduces noise

[wobbly]

Yea Neil , but in the 500x4 , two fitted under the bike and 2 fitted under the seat easily as they were only 750 ish long.

[speedpro]

I've thought about it a bit more. Get a decent gearbox. You are going to all this trouble to build an engine and then considering archaic components when newer better ones are available. The other thing is, depending on engine characteristics, would a 5 or 6 speed box actually be better?

I have FZR250 gearboxes spare. These engines are high revving and lowish torque but looking at the boxes they aren't too bad and have huge clutches and primary drives cogs behind the clutch. They shift beautifully. I have engine cases you could have to measure up as well and clutches. I even have crankshafts you could cut up to get the primary drive cog if that could be used instead of making one.

[speedpro]

Thought. As your engine is unlikely to ever do 18,000rpm you could use a lot bigger crankshaft primary drive sprocket than the standard one. Possibly twice the tooth count?

[lodgernz]

If my bike runs nicely on 98 unleaded pump petrol, is switching to 100 octane unleaded pump petrol likely to have any negative effects?
I don't any pre-ignition or deto issues on 98. Will I need to advance the ignition a little to get the best from 100?

[wobbly]

The difference between 98 and 100 unleaded comes down to how they raised the octane level.
The other issue to be aware of is how good is the 98 pump gas , Vs is the 100 stored and sold in 20L or 200L tins.
Many times the 98 has been sitting in the stations tank forever , as its not that popular , and its Reid Vapor Pressure is non existant.
But my opinion would be if you have optimised the ignition already , then if the 100 is truly " better " this will mean you can safely run leaner without deto.
ie Leave the ignition alone.

[lodgernz]

Thank you Wobbly.

[Flettner]

Yea Neil , but in the 500x4 , two fitted under the bike and 2 fitted under the seat easily as they were only 750 ish long.

Maybe Ill be running one underneath and one out the back, I can make them fit.

[Vannik]

There are people in this world that uses an Excel spreadsheet and acoustic theory to create what they claim is a simulator that calculates what your exhaust pipe should look like. They publish this mostly on Farcebook so I thought it would be a good idea to add another installment on gasdynamics. Please give comments so I can improve this.

350438

[Frits Overmars]

Maybe Ill be running one underneath and one out the back, I can make them fit.It's not your parallel-twin (it's the Dutch Rimar 600V2) but it might give you some pipe-fitting ideas.
350439 350440 350441 350442

[Frits Overmars]

There are people in this world that uses an Excel spreadsheet and acoustic theory to create what they claim is a simulator that calculates what your exhaust pipe should look like.
They publish this mostly on Farcebook so I thought it would be a good idea to add another installment on gasdynamics.
Please give comments so I can improve this.I am terribly sorry to have to say this, Neels, but your dissertation CAN'T be improved :msn-wink:.
Well okay, one minor misspelling: "Typical pressure pulses in an engine has amplitudes..." should read '..HAVE amplitudes...".
Did you have one particular Fakebook contributor in mind (Michael Forrest) or are you dedicating your treatise to all the Dunning-Kruger cases over there?
https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

(https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect) Neels, would you kindly allow me to share your Gasdynamics 101 ?

[Vannik]

Neels, would you kindly allow me to share your Gasdynamics 101 ?

Frits, please feel free to share wherever you like.
I might later fix the grammar error but not now.
And yes, you know exactly who it is aimed at.

[Condyn]

I have never seen somebody promote propaganda quite like “ he who must not be named “

[philou]

Facebook the worst time waster. everyone is an engineer, doctor, economist, tuning engine

the easier access to knowledge, the more people seek and choose the easiest even if it is false. which increases the spread of stupidity.

[OopsClunkThud]

Other than the impracticality of packaging, is there any reason the intake can't be placed on the exhaust side of the cylinder?

The thought came while working on the base of the transfer ports and I just kept looking at all that unused real estate below the exhaust.

350443

[Condyn]

350444
Arctic Cat ( Suzuki ) engines have case reeds on the exhaust side. They tilt way back in the chassis, giving them the nickname “ laydown “ engines.

[husaberg]

It's not your parallel-twin (it's the Dutch Rimar 600V2) but it might give you some pipe-fitting ideas.
350439 350440 350441 350442

Pretty sure fletner did a tornado chamber for one of the creations already
plus with 700cc he can give away a few HP

Whilst not as Shinny but very petite Mr Mike Green's earlier chamber. off the web
350445350446350447350448

Scooters also use some lever tricks for packaging

[Tim Ey]

On behalf of the gearbox for the 700cc: It seems it was done before.
https://grabcad.com/library/gearbox-for-a-rotax-600-engine-installed-on-kart-1

Regarding the piping in a 700cc twin: you can always go the 2in1 way. Otherwise making the pipes thinner should not kill all the power if done proper.

And regarding packaging in the most complex ways, have a look at the vespa scene:
https://falk-r.de/
http://pipedesign.de/home.html

[Flettner]

I have managed this reverse pipe ok. Single cylinder 360cc, YZ 250X gearbox. Just double it up.

[husaberg]

https://www.cycleworld.com/2016/02/28/rocket-science-professor-robin-tuluie-tul-aris-prototype-racebike-cycle-world-classics/


Powering the Tul-Aris is a highly modified Polaris snowmobile engine. The two-stroke Twin has been enlarged to 780cc with hop-up components intended for snowmobile competition, though the straight-shot expansion chambers actually allow it to make more power than in a sled–165 crankshaft horsepower. The engine breathes through twin carburetors and reed valves at the front.
350454350455

And smart enough to mount the water pump real low.

[TZ350]

<iframe width="560" height="315" src="https://www.youtube.com/embed/pJwiAO-8Wgc" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

Living the dream........ quitting regular work for a life of following his passion. I take my hat off to everyone who has done that.

350460

[Flettner]

So I guess we make the 700 twin fit an R1 chassis, as we have one.
Im not a fan of bolting everything to the engine, as a stressed member.
Or for my own road bike, make my own frame, twin shock, more room for stuff to fit.

[Pursang]

...
Down the page from Tim's link to the Rotax gearbox
https://grabcad.com/library/gearbox-...lled-on-kart-1
was this pic of a pair of pipes neatly arranged on the side of the machine.

https://d2t1xqejof9utc.cloudfront.net/screenshots/pics/cefed73abf17b704af08784e60a0a096/original.jpg

Obviously, for a motorcycle, you would need to put a saddle on top,
https://media0.giphy.com/media/5eM4x8fxZNzPO/giphy.gif?cid=ecf05e47vn9nsobx6cgpn5j3ufdll64d90yx rzfir924b7v5&rid=giphy.gif&ct=g
Cheers, Daryl.

[andreas]

So I guess we make the 700 twin fit an R1 chassis, as we have one.
Im not a fan of bolting everything to the engine, as a stressed member.
Or for my own road bike, make my own frame, twin shock, more room for stuff to fit.

Those are all good ideas, be interesting to follow either one.

[Javier Ruda]

There are people in this world that uses an Excel spreadsheet and acoustic theory to create what they claim is a simulator that calculates what your exhaust pipe should look like. They publish this mostly on Farcebook so I thought it would be a good idea to add another installment on gasdynamics. Please give comments so I can improve this.

350438

Thank you Neels for sharing this knowledge, so far my understanding was “sound waves type” :innocent:.

Now I am modifying a Rotax 122 cylinder, and I need to increase blowdown sta. For not increasing exhaust timing, my intention was to make the auxiliary ducts taller, but after reading the gas dynamics article now I think there is possibility of contributing to a shock wave that looses energy as heat.

For increasing peak power, Is there a rule of thumb for auxiliary vs. main exhaust port timing?

[andreas]

If it's a rule of thumb, I think 3-5* delay ie. double total, for the aux goes.

[Javier Ruda]

If it's a rule of thumb, I think 3-5* delay ie. double total, for the aux goes.

Thank you andreas. That is around 2 mm, then I still have a bit of margin.

[lohring]

That's no where as bad a mistake as filling the tank with gasoline only, no oil mix. That's really hard on an engine at 15,000 rpm or so when the piston seizes.

Lohring Miller


<iframe width="560" height="315" src="https://www.youtube.com/embed/pJwiAO-8Wgc" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen=""></iframe>

Living the dream........ quitting regular work for a life of following his passion. I take my hat off to everyone who has done that.

350460

[philou]

expand boosters to increase blowdown

quick superimposition with photoshop of the pvp cylinder (Aprilia copy) portmap with that of the 122 cylinder the setting of the port heights is not respected.

It gives you an idea for the shape of the ports.

350461

[Javier Ruda]

expand boosters to increase blowdown

quick superimposition with photoshop of the pvp cylinder (Aprilia copy) portmap with that of the 122 cylinder the setting of the port heights is not respected.



Merci philou!

That will be a good inspiration. I am limited by a piston pin without plugs, but there is plenty of mm2 there.

[philou]

I did not raise the engine myself or create the engmod2t file. so to check on a cylinder in real life.

data on transfers and TA values of the stock cylinder.

a lot of work on the transfer ports. widen the B backwards and angle upwards for A and B



350462

[Javier Ruda]

a lot of work on the transfer ports. widen the B backwards and angle upwards for A and B



Merci philou!

My plan is to raise transfers 0.6 mm and I will try to do the angle upwards too. With the tools I have, I can widen the B transfer only a bit. Do you know if there is a benefit on widen C transfer too?

[philou]

the C is already too wide

the B deserves to be widened to a close to the C

on the file the B (12°) has an upward angle greater than the A (5°).
it has to be the other way around.

why do you say you don't have enough blowdown?

[Javier Ruda]

the C is already too wide

the B deserves to be widened to a close to the C

on the file the B (12°) has an upward angle greater than the A (5°).
it has to be the other way around.

why do you say you don't have enough blowdown?

Merci philou, I will not touch C then, and will work on B as much as I can. I need the blowdown for matching the transfer sta increase. I did some calculations with Janbros spreadsheet and that was output.

[andreas]

Merci philou!

My plan is to raise transfers 0.6 mm and I will try to do the angle upwards too. With the tools I have, I can widen the B transfer only a bit. Do you know if there is a benefit on widen C transfer too?

You want to have as much area as possible. If the rings are to stay in the same location, naturally there is a potential benefit from widening the c an b port respectively.

[philou]

to choose in my opinion, it is better to work on the efficiency of scavening even if it means losing a bit of surface.

enlarge the C even more, will decrease its effectiveness

[JanBros]

the greater the angle of a port, the smaller it's effective flow area.
so widening the C-port (for example 4mm) by the same amount as widening the sum of the B-ports (for example eacht B-port 2mm) generates less extra TA than widening the B's,
and keep an eye an the angle of the scavenging column while changing the ports so that you do not end up with a crzay angle.
and don't mkae the angle of the A's to big, as the higher if flow's , the easier it can flow straight out the exhaust.

[andreas]

Obviously this is the case, but it didnt seem like he was about to change the ring-pegs locations.

[HenkS]

I did not raise the engine myself or create the engmod2t file. so to check on a cylinder in real life.

data on transfers and TA values of the stock cylinder.

a lot of work on the transfer ports. widen the B backwards and angle upwards for A and B



350462

I believe some numbers in your calculation are not right.

Total Port Transfer area sum = 834.91 (not 940.14).
Eff. dia area 852.13 = 32.94 (not 34.85).
Eff. dia area 1019 = 36.02 (not 37.78).
Eff. dia area 132.62 = 12.99 (not 17.16).


In that case results as 10.500 rpm also can't be right, or am I wrong?

[philou]

unfortunately when there is an image, people don't read the text.

it is a file found on the internet. I insist on checking on a real cylinder that the data is correct.


http://adardaine.free.fr/file/Aprilia_RS125.zip

[HenkS]

unfortunately when there is an image, people don't read the text.

it is a file found on the internet. I insist on checking on a real cylinder that the data is correct.


http://adardaine.free.fr/file/Aprilia_RS125.zip

Ok, I understand.
But the warning about these wrong numbers was right, so be carefull.
It seems they come from a program which didnot work right.
You call it an Engmod2t file, but I can't imagine that's right ?

[Javier Ruda]

Total Port Transfer area sum = 834.91 (not 940.14).
Eff. dia area 852.13 = 32.94 (not 34.85).
Eff. dia area 1019 = 36.02 (not 37.78).
Eff. dia area 132.62 = 12.99 (not 17.16).


Thank you HenkS and philou, in my opinion the file could be a modified Rotax.

My measurements, with 0.5 mm cylinder gasket would give this sta numbers:
Blowdown: 0.00116 s/m
Transfer: 0.00860 s/m
Exhaust: 0.01448 s/m

[Javier Ruda]

You want to have as much area as possible. If the rings are to stay in the same location, naturally there is a potential benefit from widening the c an b port respectively.

Thank you for noticing that. I will not move the ring pegs.

Now the pegs pass exactly in the middle between B and C and they are separated 8 mm in circumference. If I reduce the gap for pegs from 8 to 4 mm, then there is potential to enlarge 2 mm B and 2 mm C each side.

[Javier Ruda]

to choose in my opinion, it is better to work on the efficiency of scavening even if it means losing a bit of surface.

enlarge the C even more, will decrease its effectiveness

Merci Philou, I think you are right. As Janbros pointed out, because of the axial angle the flow from C is much weaker than from B.

So there is small potential benefit and danger of decreasing scavenging quality as you mentioned.

[Javier Ruda]

the greater the angle of a port, the smaller it's effective flow area.
so widening the C-port (for example 4mm) by the same amount as widening the sum of the B-ports (for example eacht B-port 2mm) generates less extra TA than widening the B's,
and keep an eye an the angle of the scavenging column while changing the ports so that you do not end up with a crzay angle.
and don't mkae the angle of the A's to big, as the higher if flow's , the easier it can flow straight out the exhaust.

Thank you Janbros for noticing that. I did the check using you wonderful spreadsheet (thank you again!) and +1 mm on B width generates +0.00018 s/m while only 0.00007 s/m on C. That is more than double.

The original column is 80º and the new one could be 83º-84º, keeping the same roof angles (I measured around 20º on both A/B and 50º on C).

[philou]

I never touch C port. just clean and sometimes touch up the angle of the roof.

it would be nice if you post some data of your cylinder. not all of them know him. and what they find can be misleading.

for Axial angles I have this, rotax 123 Aprilia RS.
but again it was not me who measured

350463




My measurements, with 0.5 mm cylinder gasket would give this sta numbers:
Blowdown: 0.00116 s/m
Transfer: 0.00860 s/m
Exhaust: 0.01448 s/m

your results are not very far from those of the file

Blowdown : 0,001440
Transfert : 0,008637

[wobbly]

Its way more important how you generate the STA numbers , than just looking at the result.
You say the Rotax axials are 12-5-50 , but later you say the A,B are both 20*.
Either way those numbers are so far wrong it wouldnt matter what the calculated STA is , the scavenging regime is seriously wrong and thus would never work correctly to produce the predicted STA power.
Yes , the C port is way too wide already ( RSA/PVP is 15mm , its easy to narrow this with epoxy ) and to get anything like the RSA scavenging the B,C need to be around 0.4mm higher than A , with the axials up around 28,7,52.

With its shallow axial and its high timing , any extra width on the B is always going to achieve the greatest return.
I would narrow the C , put the ring pin over the boost and widen the B fully - but as to what timings to use , this depends on how much Blowdown STA can be generated.
The final Exhaust STA is irrelevant , but dont try lifting the floor above BDC , as this only works if the full Aux Blowdown capability is used.

There are plenty of single ring , center pinned pistons you can use in this engine - so you dont have to suffer brain damage moving the pin.

[Javier Ruda]

it would be nice if you post some data of your cylinder. not all of them know him. and what they find can be misleading

Bien sure philou, I did some measurements for using the spreadsheet, but the accuracy on angles was very poor. Now the cylinder is on the motorbike though. I will think on how to get a better measurement.

[Javier Ruda]

... to get anything like the RSA scavenging the B,C need to be around 0.4mm higher than A , with the axials up around 28,7,52.

With its shallow axial and its high timing , any extra width on the B is always going to achieve the greatest return.

Thank you wobbly. I measured the axials very poorly. I extended the roof to the opposite wall and did some trigonometry. I got 19° for both A and B but I do not dare to use 2 significant digits so let’s say they are 20°ish.

I think I could leave A port as it is, raise B and C 0.4 mm, widen B 2 mm, and flatten B roof. Of course making that transfer and blowdown have matching bmep numbers. And in a 2nd step, a center pinned piston with maximum B width.

[wobbly]

You could drop the cylinder to get enough material above the A port for more axial angle , but then all the ports BDC edges will be low - and alot of extra grinding needed to restore the other ports.
Better to epoxy the A roof with increasing thickness of fill as it goes around the outer radius - this will keep the timing as needed but give you a proven axial scavenging pattern.
You dont need to go to Italy to see the Leaning Tower , we can all have one in our workshop.

[HenkS]

unfortunately when there is an image, people don't read the text.

it is a file found on the internet. I insist on checking on a real cylinder that the data is correct.


http://adardaine.free.fr/file/Aprilia_RS125.zip


Thank you HenkS and philou, in my opinion the file could be a modified Rotax.



For me it was not about which engine the data is for, but about the errors and in which program.
Philou wrote Engmod2t, was that correct?

[Vannik]

For me it was not about which engine the data is for, but about the errors and in which program.
Philou wrote Engmod2t, was that correct?

That is from a very old version of the EngMod2T preprocessor, Dat2T and is probably about 15 years old.

[philou]

Philou wrote Engmod2t, was that correct?

No.

I did not design the engmod2t software, Vannik designed and developed it.

I didn't make the file either.

as no information was communicated by the applicant.
I looked for data on the internet to be able to reflect and help him in his request.

[Javier Ruda]

Better to epoxy the A roof with increasing thickness of fill as it goes around the outer radius - this will keep the timing as needed but give you a proven axial scavenging pattern.
You dont need to go to Italy to see the Leaning Tower , we can all have one in our workshop.

😂 thank you wobbly, I will try to keep the tower on the right side!

[Javier Ruda]

I looked for data on the internet to be able to reflect and help him in his request.

:niceone: And It was useful indeed, to imagine where to add mm2. However it may be from another version of Rotax 122 cylinder. Mine is 220H, part number 223618, and the exhaust port is 29.5 mm tall in example.

[andreas]

Rotax 122

On the Rotax 122 the cylinder with the number 223618 (220H) is installed. Again, there are inscriptions “Gilardoni 1” and “Gilardoni 2”, now on the side of the reed valve case, but the cylinders are identical. The cylinder is also available without the milled slot for the power valve.

Support Channel (Gilardoni 2)
Support Channel (Gilardoni 1)

Cylinder 223618 220H aprilia with support channel

Doesn't help much but it's a portmap.

[Javier Ruda]

Doesn't help much but it's a portmap.

Thank you andreas. Very interesting. My cylinder has B and C top edges at same height though.

[HenkS]

That is from a very old version of the EngMod2T preprocessor, Dat2T and is probably about 15 years old.


No.

I did not design the engmod2t software, Vannik designed and developed it.

I didn't make the file either.

as no information was communicated by the applicant.
I looked for data on the internet to be able to reflect and help him in his request.

For me, it's about trusting data from any program. Not every program can be trusted blindly, and simple mistakes, such as in this example, can easily be made and can have major consequences.
This old Engmod2t, is an example of this. Old version or not but add numbers must still be correct and a diameter calculation must still be equal to the area in mm2.

[TZ350]

350465 350466

Having ruined the last RG50 cylinder and head insert. I figured I would make my own insert with some added features.

As the new cylinder is going to be razed 2mm with a packer to get the port timing right. Instead of trimming the top of the cylinder I plan on spigotting the insert into the cylinder. I have heard that using a spigot has a beneficial effect on over rev detonation.

And instead of a smooth combustion chamber water jacket wall I thought I will add fining to help with waste heat transfer from the combustion chamber and plug area to the cooling water. Does the fining look like a good idea or waste of time or worse, likely to cause problems? Comments welcome. I would love to hear from anyone who has tried this.

[Vannik]

For me, it's about trusting data from any program. Not every program can be trusted blindly, and simple mistakes, such as in this example, can easily be made and can have major consequences.
This old Engmod2t, is an example of this. Old version or not but add numbers must still be correct and a diameter calculation must still be equal to the area in mm2.

I agree, the EngMod2T numbers will not change if the input is the same, the later version gives a lot more data. If the data is not right that was used as input I cannot help.

[philou]

Old version or not but add numbers must still be correct and a diameter calculation must still be equal to the area in mm2.

I never paid attention to this given in engmod.
This calculated surface may be the surface corrected by the angles. giving an effective surface and not a geometric one.

which would seem false, whereas it is what interests us mainly

[husaberg]

I have managed this reverse pipe ok. Single cylinder 360cc, YZ 250X gearbox. Just double it up.
doz piss

the cams will be melted choc but the engine will not have lasted long enough to wear the gears.
350470

[HenkS]

I agree, the EngMod2T numbers will not change if the input is the same, the later version gives a lot more data. If the data is not right that was used as input I cannot help.


I never paid attention to this given in engmod.
This calculated surface may be the surface corrected by the angles. giving an effective surface and not a geometric one.
which would seem false, whereas it is what interests us mainly

It looks like you both don't understand what I mean, but I will try it again.
They are simply conversion errors from surface to diameter.
At the underside of the EngMod2T picture of philou.

EXHAUST PORT.
main port eff.dia 34.85 = Area 852.13 is wrong.
auxillery eff.dia 14.58 = Area 166.87 is right
total port eff.dia 37.78 = Area 1019.00 is wrong.

TRANSFER PORT.
Port 1 eff.dia 24.99 = Area 488.58 is right.
Port 2 eff.dia 16.68 = Area 213.71 is right.
Port 3 eff.dia 17.16 = Area 132.62 is wrong.
Total Port Area = 940.14 is wrong..


All together 3 eff.dia's are right and 3 are wrong.
Total transfer area is also wrong.

It has nothing to do with corner corrections or with the input.

[andreas]

It looks like you both don't understand what I mean, but I will try it again.
At the underside of the EngMod2T picture of philou.

EXHAUST PORT.
main port eff.dia 34.85 = Area 852.13 is wrong.
auxillery eff.dia 14.58 = Area 166.87 is right
total port eff.dia 37.78 = Area 1019.00 is wrong.

TRANSFER PORT.
Port 1 eff.dia 24.99 = Area 488.58 is right.
Port 2 eff.dia 16.68 = Area 213.71 is right.
Port 3 eff.dia 17.16 = Area 132.62 is wrong.
Total Port Area = 940.14 is wrong..


All together 3 eff.dia's are right and 3 are wrong.
Total transfer area is also wrong.

It has nothing to do with corner corrections or with the input.

Maybe the area of the main exhaust port represent it's blow down area, and is it not possible that the third transfer port is corrected for the entry angle, as Philou suggests?

[TZ350]

TRANSFER PORT.
Port 3 eff.dia 17.16 = Area 132.62 is wrong.
It has nothing to do with corner corrections or with the input.


Is the angle of entry to the cylinder influencing the eff.dia calculation compared to the measured area at the face of the port? In your example, Port eff.dia and Area, they could both be right.

[wobbly]

TZ350 - dont spigot , unless the material extending into the bore is a press fit , the edge of the squish step will overheat and create deto.
Even then, if the bore is chromed you have another heat flow barrier surface.
The basic idea is to find a way to keep the plug threads and the area above the squishband cool - but keep the back of the combustion chamber hot.
TM have the chamber back enclosed in a solid step , that presses into the cover - but this keeps water away from the threads as well , unless you do some jiggery to have water flow accessing just in that area..
Its very easy to have the inner surface of just the bowl ceramic coated to reflect combustion heat back into the gas and not wasted by disappearing into the water system.

Edit - fins on the back of the chamber is just simply not right - the marketing gobbledygook " coolhead " comes to mind as plain old masturbation.
\.
Edit - port areas must always be quoted as the geometric area X the Cosine of the up or down angle - EngMod does this as should any port calculator.

[Frits Overmars]

As the new cylinder is going to be razed 2mm with a packer to get the port timing right. Instead of trimming the top of the cylinder I plan on spigotting the insert into the cylinder. I have heard that using a spigot has a beneficial effect on over rev detonation.

TZ350 - dont spigot , unless the material extending into the bore is a press fit , the edge of the squish step will overheat and create deto.Wob is right. And it will be even worse if the outer edge of the squish band is shaped to cooperate with a radiused piston timing edge. My solution is to spigot the head insert alright, but in a bigger diameter bore. This way the insert won't have a sharp outer edge.
350472 350473

[Flettner]

TZ350 - dont spigot , unless the material extending into the bore is a press fit , the edge of the squish step will overheat and create deto.
Even then, if the bore is chromed you have another heat flow barrier surface.
The basic idea is to find a way to keep the plug threads and the area above the squishband cool - but keep the back of the combustion chamber hot.
TM have the chamber back enclosed in a solid step , that presses into the cover - but this keeps water away from the threads as well , unless you do some jiggery to have water flow accessing just in that area..
Its very easy to have the inner surface of just the bowl ceramic coated to reflect combustion heat back into the gas and not wasted by disappearing into the water system.

Edit - fins on the back of the chamber is just simply not right - the marketing gobbledygook " coolhead " comes to mind as plain old masturbation.
\.
Edit - port areas must always be quoted as the geometric area X the Cosine of the up or down angle - EngMod does this as should any port calculator.

Kinda like this? Next time I have it apart Ill machine fins around the sparkplug root. The top cover acts like a gate and forces all the water through these grooves, machined just above the squish area.

[DoldGuy]

Wob is right. And it will be even worse if the outer edge of the squish band is shaped to cooperate with a radiused piston timing edge. My solution is to spigot the head insert alright, but in a bigger diameter bore. This way the insert won't have a sharp outer edge.
350472 350473


Frits/Wobbly,

The previous GasGas design used the “Spigot” design, are they also prone to detonation? I hate to assume, but the detonation mentioned is caused by end gases escaping between the head and cylinder bore? If memory serves the Wiwa also used this design.:scratch:

50E33258-93F2-4CD8-B9B0-9112D6D8239B.jpeg (182.9 KB)

[F5 Dave]

But the BMEP of a gaser isn't particularly high, or the revs for that matter.

Actually on old gas (quite common on a lesser used dirtbike) I do get a few knocks up steep hills.

300 is an awesome engine for intended purpose.

[Frank S.]

Its very easy to have the inner surface of just the bowl ceramic coated to reflect combustion heat back into the gas and not wasted by disappearing into the water system.


Hi Wobbly,
I have some questions about the ceramic coating.
What kind of coating works here? Can I just anodise the aluminium to get an AL²O³ coat? This could be done by DIY.
Or do we have to apply extra ceramic material?

Greetings from Germany

[teriks]

Hi Wobbly,
Can I just anodise the aluminium to get an AL²O³ coat? This could be done by DIY.
Greetings from Germany
That would actully increase the heat transfer, at least for thin layers where insulating properties are of less importance.
-The emissivity of anodized al is ~0.8, while a polished al surface is only ~0.04! In terms of radiation, a clean polished surface is the clear winner.

[Frank S.]

I agree about radiation.
So the coating needs a certain thickness for insulating. And the best would be a polished coating.

[Flettner]

I agree about radiation.
So the coating needs a certain thickness for insulating. And the best would be a polished coating.

Too thick and the surface itself gets hot and becomes an ignition source. I tried a ceramic coat years ago to pistons, just created detonation. Surface was approx 0.5mm thick.

[Larry Wiechman]

I really like that design. How does the coolant exit spigot attach/seal?

https://www.kiwibiker.co.nz/forums/attachment.php?attachmentid=350474&d=1643275156

[Frits Overmars]

Too thick and the surface itself gets hot and becomes an ignition source. I tried a ceramic coat years ago to pistons, just created detonation. Surface was approx 0.5mm thick.Same here.

[wobbly]

I use a company called HPC , they have a Thermal Barrier coating specifically designed to prevent heat going thru to the substrate material. Its used on 4T pistons and valve faces and is very thin.
If you coat the chamber inner only , NOT the squishband , this reflects heat back into the combustion gas , rather than the water ,and doesnt cause deto.
I use Mothers Mag Wheel alloy polish on the piston surface.

[flyonly]

If I wanted to run an O2 sensor in my expansion chamber. Where should it be located?


Sent from my iPhone using Tapatalk

[husaberg]

If I wanted to run an O2 sensor in my expansion chamber. Where should it be located?


Sent from my iPhone using Tapatalk

on exhaust pipe of the car you use to tow the bike to the races...;)

Okay here is Wobs posts



Hi David, yes I got the PM with your home address, but not an email.

The Lambda I use is from Innovate Motorsports with a Bosch heated wideband, and it can read out in various formats.
It will convert directly to A/F ratio, Lambda Number, or 0-5V, I use the A/F ratio as an input direct to the dyno datalogger so as to see
the power overlayed with A/F as well as deto etc.
The probe is in the front of the muffler,with a threaded insert that sits right on top of the perf tube.
It has a gauge reading out A/F, but you for sure havnt time to watch that when doing a dyno run.

One take on the dam idea affecting the top end so much, is that is exactly the effect you see by putting a 75% nozzle in the duct exit when running a sim.
This is why I thought the next step should be to extend the floor right out the flange face.
Gaining all that top end means you have an option to redesign the pipe for better mid, or use the overev capability and use the pipe to make even more power up top.

The Ryger homologation is due to be published publicly by the CIK on the 1st Jan.
I will be onto the site all day looking for the info we all are screaming for.


Re Vegas - here is some cut and paste from a report on the result I did.


We were top 3 fastest thru all the sessions, but the engine guy for the team we race for didnt tighten the new sparkplug prior to qualifying.
Of course it wound almost all the way out and our pace dropped by 3/10s, enough only for 6th.
In the first heat we were up to 4th pulling in the top 3 easily within 2 laps when the 3rd place missed a gear mid bend under big pressure and spun
right in our karts path - DNF.
Means we went into the final from 12 on the grid, got to 5th place and ran out of time - track position is everything when only a few 1/10ths cover the top 5 pace.

I took the deto gauge off the dyno and ran the 0-5V output into the Pi datalogger, and was very surprised to find that after leaning down enough to get hits, that the only place
it deto'ed was the acceleration phase after 2nd, 3rd, 4th gearchanges, when dropping back to near peak power after overeving to 12200.
The 5th to 6th change stayed above peak power and didnt deto at all down into the shute.
So I fitted the new header with the deto button installed and the gearchange deto dissapeared completely.
That allowed another 3 jets leaner before it started again.

Get this - the egt at that level was 1390* F with no sign of deto or piston heat stress.
This is due to the fuel octane being too high for the com, and the fact that the SKUSA advance restrictor plate doesnt allow us to add enough static timing to create more power - only pipe heat.

I think I have worked the logic of the deto button - it creates turbulence in the top 1/2 of the duct, allowing the smooth flow along the floor to return easily up the duct and be aimed upward off
the ski jump at the closing Ex port.
This came from finding that having the floor of the oval/round transition spigot co linear with the duct floor, and all of the transition angle in the roof made best power.

So here is the jetting chart prior to adding the new header, based on safe deto level, not egt as I would usually use.
The Lambda ( in the muffler ) showed the kart was fastest at 13.8 :1 ( and it hardly varied anywhere within the usable power band ), going leaner or richer was slower on track.
We tested both VP C12 ( 108 octane ) and VP98, the 98 being both faster and easier to tune to the edge.

[koenich]

I agree about radiation.
So the coating needs a certain thickness for insulating. And the best would be a polished coating.
So you want to again win Liedolsheim with knowledge from here? :-P

Reg coating - total heat transfer at combustion temps is partially depending on thermal radiation. If you can stop that quite a bit is already maintained in the bowl.

[Frank S.]

So you want to again win Liedolsheim with knowledge from here? :-P
.

Yes, the 3rd win would be nice😎
Let's hope it will take place this year.

[lohring]

We ran a stinger lambda sensor. This was for test purposes only.

Lohring Miller

350493 350492

[wobbly]

In the front of the muffler has proven to be the best spot for Lambda imho - the need for Lambda is another story.

[Javier Ruda]

In the Rotax 122, I did some modification for making shorter and easier the flow from reed case to crankcase. Not sure if it helps or not because I cannot measure the effect accurately.

Does it make sense to copy that cut to the bottom of the piston skirt, and matching the cut edges at BDC?

I read from wobbly that the reeds open at some point between BDC and TPC because of the crankcase pressure becoming lower than intake pressure, but I cannot imagine if the piston cut would help on that process, or the collateral effect on the cylinder intake hole.

[philou]

if the transfer ports and the blowdown are not granted, there is no point in enlarging the admission.

for admission, I am inspired by the kart rotax max cylinder.

[Javier Ruda]

for admission, I am inspired by the kart rotax max cylinder.

I see. Bigger Boyessen ports with a “sky jump” down to the crankcase. I seems doable.

[philou]

cdi ignitech on SEM ignition for rotax 122 Aprilia RS.

the pick-up is inside the flywheel and triggers on 2 magnets side by side.

the oscilloscope gives 2 sinusoids for the top sensor.

ignitech indicates that their cdi works on this ignition. without further indications.

now the bike starts. but can't find a configuration that works.
the cdi is a P2-race.

do you have an idea of configuration?

350500

[Javier Ruda]

the cdi is a P2-race

From IGNITECH website, P2 is for 2 cylinders. It seems the pick up is “reading” the 2 magnets.

I have Zeeltronic, and you have to input there the static advance angle. That is the position of the pick up vs tdc.

Edit: original pick up on Rotax 122 is 36° before TDC and Zeeltronic has a “compensation” of 30 us (microseconds). Compensation is like a fixed delay.

[philou]

several configurations have been tested.

ignition is erratic. clearly visible under the strobe light.

spark plug and cap with resistor.

ignition of the 123 is different from the 122

https://transmic.fr/wp-content/sem/flywheel.jpg

https://transmic.fr/wp-content/sem/stator.jpg