ESE's works engine tuner

[wobbly]

Yes , and no ,the outer aluminum cable shield is grounded to the supply battery earth only at one end. The trigger grounds go to the separated trigger earth pins , that
have their own isolation circuitry .
I also used the same Cat 5 cable wire pairs for the servo and PJ wiring, as these also can inject ignition noise into the sensitive input pins.
Twisted signal pairs form a very high natural rejection of this power supply line " noise " that seems to be more of an issue with the P4 units having 4 CDI packed into the same box format.
But as I said , if the coil drive wiring is physically separated, and resistor plugs/caps are used , then any noise issues are largely eliminated.
The other audio amp trick of creating a common single earth ground point for the coils/case/battery and ECU power supply also eliminates circulating noisy voltage sources from affecting the super sensitive
ignition chip supply.

[SwePatrick]

Sunday.
We move along according to plan, but i dunno who´s plan... *lol*



https://youtu.be/zRTcaqloEc4

[JdG]

There are a lot of misconceptions about Ethernet cables. CAT5, CAT5e, CAT6, etc, doesn’t say anything about the shielding of the cable. It say something about the data transfer capacity of the cable. Usually this means thicker wires for for instance CAT6, compared to CAT5e.

For advice on shielding, this article is a good read: https://www.truecable.com/blogs/cable-academy/ethernet-cable-shielding-types?srsltid=AfmBOopW0U0_MecyJFkgimGzmSt5wsIMwsNH GW41QoyI4KYTh8TW75kE


Verzonden vanaf mijn iPhone met Tapatalk

[pete376403]

My dad was an old-school electrician so among the stuff left in his shed I found a 500 ft reel of screened, twisted red and black two core - 2/10/010 (2 core, 10 strands, each strand 10 thou ) I believe it was intended for wiring domestic radio receivers to an external antenna and earth point. It could be useful for ignition system wiring

[jonny quest]

Is the search function broken on this site?

Or explain to me how to use it? Or link to how to use?

Much appreciated

[husaberg]

Is the search function broken on this site?

Or explain to me how to use it? Or link to how to use?

Much appreciated

Search works fine, its just a bit fiddly
Search then on drop down "advanced search"

Use "single content type "up top left

Specify its a search by "post" rather than thread at bottom left and add in key words and preferably add user name
avoid common words.


356090356088
You can also search thread or user via images and then use that to lead to posts.
As below

356093

356092356091

You can also search using Google or another search engine but add in
Kiwibiker "ESE works engine tuner" in quotes.

[diesel pig]

I am just wondering what is the best ( this is what I think they are called) 'Truncated Cone Calculator' as I only know for sure the start diameters and some of the end diameters and what angle's I want to use or will I need to dig out Bell's Book and work out manually the templates? or do I need to bite the Bullet and buy EngMod2T so it can do most of the working out for me? and test it obviously.

[wobbly]

EngMod does not generate flattened cone dimensions, it has a basic pipe calculator in the code to get you started on a design with your input on the variables.
It is a 1D engine/pipe simulation code only.
JanBros spreadsheet calculator does the same sort of thing , for port and pipe design , but is not a simulator.
There are several apps online for doing cut cones and producing the .dxf for laser cutting.
The trickiest of these is WS Exhaust Designer , where you can manipulate a segmented pipe in 3D animation to generate the cut cones.
I use SolidWorks to cut the cones and fit them using boundary dimensions taken off the bike/kart - that will then spit out the .dxf for each segment.

[husaberg]

the pro ways are the way to make them.
An easy way to draw out simple cones is make a template out of discs the same diameter and spaced apart the distance you want.
you simply mark a start point and trace arround the arcs they roll.
You can use this to make offset cones and even transitions for round to square triangular or hexagon.


https://youtu.be/BGKOPYoM4Qo?t=245

[diesel pig]

EngMod does not generate flattened cone dimensions, it has a basic pipe calculator in the code to get you started on a design with your input on the variables.
It is a 1D engine/pipe simulation code only.
JanBros spreadsheet calculator does the same sort of thing , for port and pipe design , but is not a simulator.
There are several apps online for doing cut cones and producing the .dxf for laser cutting.
The trickiest of these is WS Exhaust Designer , where you can manipulate a segmented pipe in 3D animation to generate the cut cones.
I use SolidWorks to cut the cones and fit them using boundary dimensions taken off the bike/kart - that will then spit out the .dxf for each segment.

SolidWorks! Now I have two different projects I need that program for. I better get it. Are there different levels to the program? or do you have to get the whole thing? This is what I was ultimately wanting a way to generate .Dxf's to send to a laser cutting outfit.

[diesel pig]

EngMod does not generate flattened cone dimensions, it has a basic pipe calculator in the code to get you started on a design with your input on the variables.
It is a 1D engine/pipe simulation code only.
JanBros spreadsheet calculator does the same sort of thing , for port and pipe design , but is not a simulator.
There are several apps online for doing cut cones and producing the .dxf for laser cutting.
The trickiest of these is WS Exhaust Designer , where you can manipulate a segmented pipe in 3D animation to generate the cut cones.
I use SolidWorks to cut the cones and fit them using boundary dimensions taken off the bike/kart - that will then spit out the .dxf for each segment.

Oh. I will have a look for this "WS Exhaust Designer" It sounds like it would be very helpful in the design phase.

[jonny quest]

Husaberg, thank you for the search tips.

I still couldn't get it to work. Tried via on this site, and Google way multiple times and ways. I'm in USA, do you think region has anything to do with it? I am trying to search transfer stagger. Used Wobbly, Frits, and Jan for names.

[JanBros]

cone layout can also export .dxf files, and is a very easy to use programe to create the cones.
https://www.google.com/search?client=firefox-b-d&q=cone+layout&gl=ad
I also use solidworks to make a circumference-drawing in which I have to stay with the exhaust and create the hole pipe. than put the dimensions in cone layout and print paper versions of each segment. put them on sheet metal and cut them manualy.

[wobbly]

In SolidWorks its easy enough to create an assembly and put in boundary dimensions that the pipe has to fit within. Or another way is to create the pipes centerline sketch , and fit the middle of your
cut cones assembled onto that.
The only issue with the CAD program is that when you cut a thin revolve ( the whole cone ) you cant simply flatten that revolved part in Sheetmetal.
The angled cut will , when flattened , have two lines, depicting the inside , and the outside of the cone end.
Neither line is an accurate depiction of the angled cut pattern shape in reality - and the laser guys would have to remove one of them for the laser software to follow.
There is a workaround, by changing the OD dimensions and removing 1/2 the material thickness = the Neutral Axis or a bend factor K = 0.5 as is usual with thin sheet rolling.
Once you have cut the solid revolve , you can select the outer surface - flatten that , and create a .dxf that is exactly the correct shape to be laser cut with no extra lines.

[husaberg]

Husaberg, thank you for the search tips.

I still couldn't get it to work. Tried via on this site, and Google way multiple times and ways. I'm in USA, do you think region has anything to do with it? I am trying to search transfer stagger. Used Wobbly, Frits, and Jan for names.
Hi Jonny

Just confirm you are logged in and are following these exact steps in order they are written and using the same key words
Searches fail at times on KB as they are not single content or use too many words.

356103356108356104356109356107356106

[lodgernz]

An interesting Bucket project in Wellington
https://www.youtube.com/watch?v=dbQpYDBawEA

[SwePatrick]

YES!!!
Finally!

I finally managed to make a couple of testdrives to sort out small stuff on the Kawasaki overkill bike.
This is an old Kawasaki KX250 -96 engine with a LOT of mods done to it.

And i am all in all positivly impressed so far, it keeps somewhat together *lol*
I have only scratched the surface powerwise, i keep it 'safe' while sorting out bugs.
So far it has dynoed 67whp at 9500rpm.
I figure there are at least 5 more lurking in it.(check sparkplug in the end of video)


Setup:
Kawasaki KX250 1996 engine.
Mixmatch between years to get closest ratio gearbox.
TM racing cylinder, ported and turned 180 degrees, exhaust facing backwards
Billet head 15.5-1 compression
KTM woessner piston
Maico 490 rod
Lockup clutch(home made)
Rotary intake disc(home made, from Rotax parts)
42mm Keihin PWM
Balance shaft from Kawasaki Tecate.
Ignitech DCCDIP
Pipe made by me.

So,, for you to enjoy:


https://youtu.be/C8p8Vb4gSYw?si=hyNnt6-MY4JePBPt

[diesel pig]

An interesting Bucket project in Wellington
https://www.youtube.com/watch?v=dbQpYDBawEA

Having watched the video. I like they are not trying to reinvent the wheel and are using a Yamaha gearbox and all ready designed cylinders that are all ready good to go.

[Condyn]

Re cones.
A program called cone layout can be used as well. It is far less costly than anything else I have found. Unfortunately you need to add one material thickness to your diameters to make them correct. WS exhaust designer is intriguing, however I cannot read German and have not had time to translate the website information. I believe it is a subscription service as well which is…… blah

[wobbly]

Yea , at $600 USD/year you would have to be doing full time pipe building to justify that, way better to spend that money on EngMod as a one time cost so you can design optimized pipe and port geometry
and see the results on Hp without building anything.

[F5 Dave]

At USD600 a year, I'd want them to build the pipes and supply the materials.

They could live in the garden shed and eat what they could forage from the neighbouring gardens. And would learn the true meaning of Discipline.

Sorry. Got carried away. ;)

[katinas]

Off topic, an interesting Honda decision to integrate chain driving balancer crescent on the primary gearbox shaft of the CB 250. Has a similar scheme been used on other models?

[wobbly]

Not that I would ever presume to doubt Honda's balancing ability , when you look at the genius V5 , not so much the old 250 triple road bike, but
as the clutch primary reduction in most bikes is about 3:1 down - then that out of balance forces vector seems to bear no relationship to any forces generated at the crank.
Unless the chain drives just the balance mass at 1:1 on one end of the primary shaft , and the other end is driven by the clutch gear reduction.

[husaberg]

Off topic, an interesting Honda decision to integrate chain driving balancer crescent on the primary gearbox shaft of the CB 250. Has a similar scheme been used on other models?

Not that I would ever presume to doubt Honda's balancing ability , when you look at the genius V5 , not so much the old 250 triple road bike, but
as the clutch primary reduction in most bikes is about 3:1 down - then that out of balance forces vector seems to bear no relationship to any forces generated at the crank.
Unless the chain drives just the balance mass at 1:1 on one end of the primary shaft , and the other end is driven by the clutch gear reduction.

with that chain there I am assuming they dove it from there and used the shaft just to support it?
The CB250N def had twin chain balance shafts but diferent than that?
https://i.ebayimg.com/images/g/~EgAAOSw5S5fIITM/s-l400.jpg

I don't recall many Hondas having outrigger counter shaft bearing, so what looks like a countershaft sprocket I assume is the drive

oddly I cant find that set up in the CB250N?

356120356121



Edit found it it the CB250RS based on the XL/XR 250 the third gen after s motor but before RFVC 80-83 ish

they just use the shaft
356122356124356125

https://i.ebayimg.com/images/g/ISEAAOSwd59mMDXQ/s-l1600.webp

[jato]

i was wondering about how the balance shafts were run counter to the engine (with a chain drive) then realised the chain only runs on one side of the crank sprocket...

[husaberg]

i was wondering about how the balance shafts were run counter to the engine (with a chain drive) then realised the chain only runs on one side of the crank sprocket...

Yes
356126

you can do the same with a double sided belt.
I was going to build a single with a belt primary and drive a balance shaft off the outside.
356127356128


but to be honest a geared set up like the CRF150r with the water pump off the same shaft is neater. but harder to do with a Disc valve.
I wanted to use a belt as I was confident could get the gears centers right, the same reason the poms likely used chain primaries.

[Rudex]

There is one program called " Plate 'n' Sheet Professional " it works ok.

Regards



Yea , at $600 USD/year you would have to be doing full time pipe building to justify that, way better to spend that money on EngMod as a one time cost so you can design optimized pipe and port geometry
and see the results on Hp without building anything.

[Niels Abildgaard]

Yea , at $600 USD/year you would have to be doing full time pipe building to justify that, way better to spend that money on EngMod as a one time cost so you can design optimized pipe and port geometry
and see the results on Hp without building anything.

How well can Engmod predict a well developed 125ccm (Aprlia) in three different power situations?

[wobbly]

The RSW/RSA is very close but suffers in that there is no way of simulating the large timing radius on the Main Exhaust.
And the " real " timing of that hugely affects the sim output - if you look at the raw numbers it would seem the STA of the Transfers is about 10% better than the Exhaust port, but the radius increases the exit Cd
to very cleverly match the transfer actual flow numbers.
The RS125 road type engine is easy, and very accurate.

[jonny quest]

Transfer stagger

Honda incorporated a higher A port

RSA higher B port. I going to assume the RSA wanted a little more transfer area, if the A was raised... too much cross talk with exhaust port. So the stagger really wasn't important, just the logistics of the ports.

What made Honda work with raised A? Was it a bridged ex port that liked it?

Do the first opening transfers really not flow yet because of cylinder pressure? Is it only above a certain RPM ? Or wave tuning when pipe is working?

What about putting a powervalve into the mix? Some of these powervalve's when closed are the height of the transfers, or even lower!

I'm working on a 250cc single, CR250 triple port. I had to lower cylinder 1mm to get side exhausts lower than main port. Main port was raised .8mm.

MX application, motor needed more bottom. It gained 2hp down low, lost 2hp on top.

Going to start modifying transfers now... but don't have anymore room for error to lower cylinder if they get too high.

Now tro

[wobbly]

Transfer stagger " works " simply due to the fact that at TPO there is way more blowdown pressure pressure above the port timing edge than there is case pressure
in the ducts created by the dropping piston.
Thus there is reverse and then stalled initial flow down the duct that is opened first.
In the case of Honda using normal stagger with the A highest , this is created due to the fact that the T port outer extremities are much smaller in height than the Aux ports in a 3 port cylinder.
Thus Honda used as much A port height as they could to achieve the maximum Transfer STA within the vertical space available.

With a 3 port regime, to achieve the maximum Blowdown STA , the Aux have to be very deep , and this limits the timing height the A port can be lifted to.
Also limiting the A port height reduces the vertical short circuiting from the A into the Aux at low Transfer velocities, early in the cycle.

The added B and C chordal width total is much greater than the A alone, thus lifting that whole wider width, achieves a much higher total Transfer STA than can be achieved using normal stagger.
Lastly the natural scavenging regime of low A port reverse stagger, favors upper front side/peak and overev power.
Normal stagger scavenging that boosts the whole front side, is always used in wide band applications such as MX or more especially where there is no PV to help front side power.

I tested the two differing approaches in a KZ race engine, where I lowered a stock normal stagger engine , then ground up all the ports to replicate the Aprilia regime.
In EngMod and then on the dyno it showed a loss of around 3 Hp at 10,000 ( the usual lowest rpm on track ) and then gained around 2 Hp ( in 50 ) at the peak of 13800.
But it made an amazing 8 Hp more at 14600 - close to the max the rpm down the shute.
This setup went from 140 Km/Hr at our fastest track to an easy 145, but the serious lack of acceleration off the two slowest 2nd gear corners meant an average drop in lap time of 3/10 sec
even with shorter gearing ratios.
With a PV and a digital ignition if allowed , this reverse stagger setup would have been way faster.

[husaberg]

MX application, motor needed more bottom. It gained 2hp down low, lost 2hp on top.

Going to start modifying transfers now... but don't have anymore room for error to lower cylinder if they get too high.

Now tro
Hi Jonny with the CR250 being a mechanical PV, wouldn't you be able to fill the bottom with electronic control of the RC valve together with a Atac set up?
In some of Wobs early posts there is mention on how well it worked with the BSL.
There was also some work don't here with a different set up that allowed the valve to be closer to the pipe.
Cagiva also did combination ones on lil Jon's era bikes.
Farmaken I think?

here he used a spool valve to get it closer
https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130327391#post1130327391

Cows are dry, that means more time in the shed

Here is the latest version ; using a jaycar frequency counter/switch to drive a R1 servo motor to operate the spool valve on the header pipe

Using a DPDT switch mounted on the servo to reverse the motor - unless someone can point me at an electronic limit/polarity switch to make use of the servo`s in built potentiometer ??

In the testing I have done, the volume of the resonator chamber isnt critical, once you have reached a certain size.The best place to start is equal to the cylinder displacement, and this will "work" every time.
Fitted to a world champ ski engine, these chambers, operated by a flat, throttle slide plate,added over 30% more power at 1/2 peak rpm.
They seem to work very similar to a PV, in that the pipe effects are dramatically reduced in the area where the wave action is way out of phase with the port.
This is seen in the sim, and on the dyno, in that you can change the pipe dramatically, and it has little effect when the PV is down, or the chamber is open.


Honda obviously found out how to make these things work just as I did.
As short a connecting tube as you can get, diameter about 1/2 the header,ATAC vol about the same as the cylinder swept vol.
We had about 1/3 of the throttle plate hanging down in the header when it was open, in line with the flow direction.
By experiment you find the point where the resonating volume starts to kill power, and then go back a couple of hundred rpm, and snap it shut with a rpm driven solenoid.
Easy with the Ignitech programmable output.
There is NO advantage to ramping the closing point ie interconnecting it with the PowerValve is nowhere near as effective as a single point solenoid action.
Spencers Honda 500 Tripple had two of them on the outer pipes, and it was completely unrideable without them.
You could get even better useable band width by having a double volume system, where another plate valve opened and shut the entrance to a second bottle vol.
The two being open initially, then the second vol being shut off, creating a much smaller vol that was then shut of at a higher rpm.
But hey the simple thing works a treat on engines with no option for a PV.
.
Why would you think that? Opening the blade across the flow would have three big disadvantages. It would be much more of a disturbance to the flow, it would heat up the blade much more, and the flow colliding against the protruding half of the blade would constantly try to rotate it. As the flow direction is alternating so close to the cylinder, that would mean a constant hammering on the governing mechanism.

The spool valve allows it to get far closer

[SwePatrick]

DYNO? = !
As a dynoowner i have noticed there are a lot of misconceptions about things regarding the function and what´s what.
And also i try to give some tips and tricks, not only for the dyno owner(you should already know), the guy about to dyno his 'machine' might find it useful also.

In this episode i try to straighten out question marks to become exclamation marks instead :)

Enjoy!


https://youtu.be/qUsG0F30O0Y

[jonny quest]

Husaberg, thank you for the information.

The engine I have is a 1992 - 01 CR250. They actually incorporate a resonant chamber right in cylinder... and opened and closed by the powervalve.

Wobbly great explanation. Thank you. There has to be something a little more. Do you think high A is actually cooling exhaust gas slightly? This is reason for results of high A vs high B?

It's funny this motor was touted as being amazing back in the day. It's not. It doesn't have much bottom, a huge dip around PV opening... and just hits really hard.

I tried stiffer PV governor spring... it takes hit... but makes quite a bit less HP mid on up.

Fixing higher auxiliary exhaust ports, they were .8mm higher than main did help bottom... but still a pretty big dip in curve by PV opening.

The main PV opens first, the auxiliary ports progressively open from bottom first, which I am starting to guess might not be the best.

[wobbly]

The higher A port scenario helps front side power because its flow regime is retarded by the Blowdown backflow - thus reducing its short circuiting
tendency being the closest to the Exhaust ports depression.
The problem with a stiffer governor spring is that it absolutely helps where the PV is opening too soon , but its higher spring constant also then slows the PV opening
rate - the only solution is a servo drive from the ECU.
These were tried in the early 2000 ( along with solenoid PJ ) but the manufacturers didnt like the cable servo drives complexity and cost, even though it worked perfectly.

Having the Aux higher is a weird anomaly, with no discernable advantages. Kawasaki still do it in the KR150 for a road bike , with the later version having the PV servo controlled
on the very high Aux only - and this gives good low end , but due mainly to the fact the small side rotary drum valves also open and close ATAC ( KIPS ) chambers as well.

Having the Aux PV opening the same as the main blade ie from the bottom - up, works way better than the complete disaster that is the simplistic KTM setup that does the reverse.
It is impossible to get this to work seamlessly even with a servo drive.

[husaberg]

Husaberg, thank you for the information.

The engine I have is a 1992 - 01 CR250. They actually incorporate a resonant chamber right in cylinder... and opened and closed by the powervalve.

Wobbly great explanation. Thank you. There has to be something a little more. Do you think high A is actually cooling exhaust gas slightly? This is reason for results of high A vs high B?

It's funny this motor was touted as being amazing back in the day. It's not. It doesn't have much bottom, a huge dip around PV opening... and just hits really hard.

I tried stiffer PV governor spring... it takes hit... but makes quite a bit less HP mid on up.

Fixing higher auxiliary exhaust ports, they were .8mm higher than main did help bottom... but still a pretty big dip in curve by PV opening.

The main PV opens first, the auxiliary ports progressively open from bottom first, which I am starting to guess might not be the best.

funny, i thought they gave up on that inc chamber far earlier.
What are your class limits? cc

[ApolloMotoMoto]

(...)

Normal stagger scavenging that boosts the whole front side, is always used in wide band applications such as MX or more especially where there is no PV to help front side power.

(...)



How much stagger between the ports in order to achieve this effect?

What differences are seen with different "amounts" of stagger? (in terms of degrees between openings)

I currently have 1.4 degrees between opening's with a "Normal" stagger (A First), used in a VERY wide band application (single-speed, direct-drive road racing on kart tracks).

Wondering if more stagger might be a good idea?

With the help of all of this advise over the years, our little "motorized bicycles" are becomming quite the weapon on track. Taking our fastest lap times at a popular Kart track we run at, we are about 5 seconds behind the lap times of the 450cc Foul-Stroke Supermoto's, and about 10 seconds off the fastest mini-moto's that set the track record lap times. We run laps around the built Honda Grom's and its mildly hillarious to see "bicycles" out on track with leathered up racers getting the knee down.

The switch to 17" motorcycle rim's (17" moped spoked setups for most guys) and the use of the same 17" racing slicks those Supermoto's run is certainly part of this.... ;)

[wobbly]

In a fully optimized 5 port , no PV and with wide B and narrow C we have 2*/2.2* timing drop.
This seems to be alot more than in your application, and testing has shown that this setting gives the widest spread of power without hugely compromising
peak and overev too much due to lack of Transfer STA.
In this case the Blowdown and Transfer are exactly matching, and also exactly match the power capability.
One thing we have in our favor though is a carb of only 30mm bore in a 125 engine making 50 sprocket power - way smaller than would normally be the case.
Maybe this is a development path to look at in your project.
Every other aspect of the engines tune is basically unlimited , thus the very high bmep, despite the small venturi.

[ApolloMotoMoto]

In a fully optimized 5 port , no PV and with wide B and narrow C we have 2*/2.2* timing drop.
This seems to be alot more than in your application, and testing has shown that this setting gives the widest spread of power without hugely compromising
peak and overev too much due to lack of Transfer STA.
In this case the Blowdown and Transfer are exactly matching, and also exactly match the power capability.

In that case, I am bumping up my stagger from 1.4 degrees between opening's to 2.1 degree's between openings.

I, likewise, have the Blowdown STA exactly matching the Transfer STA for my entered power target in JanBros.

I will then recover the lost Transfer STA (from the additional stagger drop) by massaging them wider a few tenths of a mm here and there.



One thing we have in our favor though is a carb of only 30mm bore in a 125 engine making 50 sprocket power - way smaller than would normally be the case.
Maybe this is a development path to look at in your project.
Every other aspect of the engines tune is basically unlimited , thus the very high bmep, despite the small venturi.


I have been going back and forth on this recently, and I dont think I am going to be happy with the answer I come up with until we have these engines on a dyno.

90cc ~12+ BMEP/ 15-19 RWHP

Certainly not setting any records here.

We have run 21mm Keihin PWK clones since forever.

Recently we started playing with increasing the bore size of the carb again because we know we are making more power (2 years ago we were lucky if we were making more than 10hp out of a 70cc engine...).

24mm seems to be better everywhere. No loss in throttle response or low-end performance VS the 21mm, and it seems easier to jet with perhaps a better balanced velocity curve.

26mm is hard to tell the difference between a 24 and a 26 honestly, without a dyno I couldn't tell you which one was on the bike by feel once they are both jetted right.

28mm starts to suffer from the dreaded off-idle lean-bog if you whack the slide open too fast, but with the right jetting it all but completely goes away.

All of this is running open bore/ no filter (I know.... the shame of it...).

The last couple outings I fitted the karting airboxes I have run before to the 28mm and re-jetted it (went from a 114 main jet open bore to 90 main jet with the airbox -does this possibly suggest the air-box inlets are overly-restricting intake flow and possibly hurting powwe?)

WITH the airbox, the 28mm has better throttle response than a 21mm with an open bore, and a noticable boost in off-idle torque.

I just have not finished testing weather the airbox is restricting the top-end.

[wobbly]

It certainly sounds like the airbox Helmholtz resonant volume is wrong or the inlet tubes are too small if you have to lean down that much to get your egt back.
After reading all you have said my first reaction is to stick on a 19mm carb - again way small, but that im sure would be a jet off the bottom and you gain your peak and overev power with
inlet and pipe tuning.
That is one thing you have not mentioned - inlet tuned length from the bell mouth end to the reed tips.
You have changed carbs a few times, but what was the differences in length?

[ApolloMotoMoto]

It certainly sounds like the airbox Helmholtz resonant volume is wrong or the inlet tubes are too small if you have to lean down that much to get your egt back.

I'll measure the airbox inlets and compare the combined area to the area of the carb bores I have been running and see what I see...



After reading all you have said my first reaction is to stick on a 19mm carb - again way small, but that im sure would be a jet off the bottom and you gain your peak and overev power with
inlet and pipe tuning.
That is one thing you have not mentioned - inlet tuned length from the bell mouth end to the reed tips.
You have changed carbs a few times, but what was the differences in length?

I do have 19mm bore PWK clones in my box of carbs....

All the carb changes have been with the exact same "body" Keihin PWK Clone, just different bore sizes machined into them. Mostly through scooter tuning channels, you can get Keihin PWK clone carbs in one common "small body" size from 19mm to 32mm;

19, 21, 24, 26, 28, 30, 32

Then the body size goes up, and you are into "real" Keihin PWK's.

So I can switch carbs to adjust the bore size within that range without changing the tuned inlet length one millimeter.

Although, this is not something I have never measured or calculated. I tend to favor putting the carb as close as physically possible to the reed to attempt to eliminate any resonance effects in the inlet duct, not because its a great idea, but mostly because I have not tackled "doing it right" yet. I use a short rubber boot, the distance from the bellmouth end of the carb to the tip of the reeds is still probably going to be a good 6-7 inches. I will have to go measure...

I have been using these PWK clones for YEARS, and I have boxes of them, and even larger boxes of all tunable parts, even the ones that aren't commonly found.

I have 5-6 different emulsion tubes, but I have not gotten to testing the different styles yet, I just make sure all the ones I used have the same "standard" emulsion tube I am used to using.

I have assortments of needle jets which most people will tell you are not a tunable part in a Keihin PWK.

I have multiple slides of all cutaway sizes, and a box with needles of 3 different "series" of needle styles, with the full range for each series.

And lots of different options for the "powerjet" with multiple probe lengths, dial adjutable or jetted with single jets. (but I wont be playing with these anymore until I have the new digital CDI to shut it off with a solenoid above a set RPM; I am getting better results right now with the powerjet closed off and "just" the main jet)


I have to admit, I had not considered trying the 19mm carb's again, but that is why we ran them to begin with; better low-end response, more snap comming up off the slow corners.

[JanBros]

In that case, I am bumping up my stagger from 1.4 degrees between opening's to 2.1 degree's between openings.

I, likewise, have the Blowdown STA exactly matching the Transfer STA for my entered power target in JanBros.

I will then recover the lost Transfer STA (from the additional stagger drop) by massaging them wider a few tenths of a mm here and there.
but by dropping the cylinder to create more stagger, the bottom of the transfers won't align anymore with the piston-top in TDC ? less piston cooling and less real transfer flow (control) because it will hit the piston and disturb the flow.

can't you raise the port itself and find some extra blowdown-sta ?

[ApolloMotoMoto]

but by dropping the cylinder to create more stagger, the bottom of the transfers won't align anymore with the piston-top in TDC ? less piston cooling and less real transfer flow (control) because it will hit the piston and disturb the flow.

can't you raise the port itself and find some extra blowdown-sta ?

The as cast stock cylinder's ports are so "low" to begin with that I wont need to drop the cylinder for the extra stagger.

Transfer timing with the crown edge of the piston lined up with the bottom edge of the transfer ports is around 110-116 depending on the casting.

I have 8x cylinders for the next batch of race engines that I havent started porting yet ;)

I am finalizing the portmap template for these 8x based on the last 3x iterations of this portmap that I cut into previous cylinders, going back and forth between printed portmaps from the JanBros spreadsheet that I set inside my old cylinders to find where I can squeeze a few more tenths of a mm out of this casting. Over the iterations I have had ports a little too wide in the spreadsheet and then I find out that cutting them that wide in the cylinder breaks through into the stud bores. Each time I do it the spreadsheet portmap gets refined a little bit to more accurately represent what is actually getting cut into the cylinder.

This time I should be able to cut the portmap as entered into the JanBros spreadsheet -exactly-.

While I am spending the time doing this refining, I usually have some element of the portmap I want to try and "improve" from a scavenging/blowdown efficiency standpoint so I will post a theory question here to try and get some guidance from the "brain trust".

And you all never dissapoint!

Thanks again!

[ApolloMotoMoto]

can't you (...) find some extra blowdown-sta ?

Thats what SHE said... :lol:

Single exhaust port cylinder, 71% bore diameter width, using the FOS multi-radius shape.

Timing currently at 194 exhaust over 123 A Transfer

If you can find me some extra blowdown-sta without lifting the port any higher I am all ears :D

[JanBros]

I didn't realise it was all still theoretical ;-)

[ApolloMotoMoto]

I tested the two differing approaches in a KZ race engine, where I lowered a stock normal stagger engine , then ground up all the ports to replicate the Aprilia regime.
In EngMod and then on the dyno it showed a loss of around 3 Hp at 10,000 ( the usual lowest rpm on track ) and then gained around 2 Hp ( in 50 ) at the peak of 13800.
But it made an amazing 8 Hp more at 14600 - close to the max the rpm down the shute.
This setup went from 140 Km/Hr at our fastest track to an easy 145, but the serious lack of acceleration off the two slowest 2nd gear corners meant an average drop in lap time of 3/10 sec
even with shorter gearing ratios.
With a PV and a digital ignition if allowed , this reverse stagger setup would have been way faster.

This sounds quite familiar to me...

I feel like I read the same story from Frits Overmars, although the engine in question is not directly referenced...



Direct-drive engines are a very special case. When I first encountered such an engine, I thought it was horrible and I was convinced I could do better. The first thing I did was make a new exhaust pipe for it. With this pipe, with a much narrower, tapered header, 'my' kart could overtake two or three competitors every time it went onto the main straight.
Small problem: it would be overtaken by two or three competitors at every corner exit. And all circuits have more corners than straights...

(...)

Below is the power graph of a world champion direct-drive kart engine. You can see that it is willing to rev to the moon, which allows the rider to fit a short gearing that will help with accelerating out of the corners. The maximum power is nothing special, but the power range is.

Conclusion: I hesitate to give any advice regarding your exhaust. You may think, as did I, that the exhaust systems of these direct-drive engines are not very effective, but bear in mind that they are the result of many fine technicians trying everything to improve them over many years.

PS: if the rulebook allows it, you can gain a lot with a programmable ignition.....



The reason this piques my interest so much is my own Single-Speed Direct-Drive application wherin I DO NOT have access to power-valve cylinders (yet....), but I do have access to programmable ignition curves.

I am also currently in the position where I am not YET ready to start making pipes, so we are simply "stealing" pipes from other engines and using what gets the best results so far, which happens to be literally any manufacturers 80-85cc "motocross" pipes. No one has yet tried -ANY- 100cc Kart pipes on our engines.

The "feature" of Frits' world champion direct drive kart engine that interests me DEEPLY is the "plateau" of power in the over-rev after an initial drop-off of power from the peak.

Attached is Frits' dyno chart as well as a much more modern reed valved 100cc single-speed direct-drive karting engine, the IAME KA100, which also exhibits this over-rev power-plateau effect. (along with screenshots from the KA100 homologation fische)

How do you create this plateau?
-I have read from Wayne that part of it is the internally perforated baffle cone that is not clearly visibly until you cut one of their pipes open, or examine the homologation fische
-I further understand that this is being achieved with a FLAT ignition curve as mandated by all top-level Karting series

Given the imposed limitation of my case of "no powervalve" and also considering the availablity of fully programmable digital ignition;

What features of the engine would be required in order to achieve this over-rev power-plateau without negatively impacting the net-net "power range" by hurting the 'front side' part of the power curve?

As noted, I have a suspicion that its mostly the pipe; and I would like to hear anything anyone has to share about what needs to happen to the pipe in order to achieve this effect....

But, I am also very curious how the other elements of the engines design must be tailored to suite this goal.

[wobbly]

The answer to your question regarding power range in the direct drive kart engine application is surprisingly simple.
Its the perforated rear cone surrounded by a resonant volume, ending in a flat plate end that also just happens to have the stinger in it.
Neels finally nailed down the sim operating mechanism, after alot of email back and forth and hair tearing out.

I discovered the effectiveness of each element in the design many years ago, after doing nothing but build and dyno testing pipes for our classes of the KT100 Yamaha.
This was a solid 6 months of doing nothing else by trial and error.

The mechanism is straight forward, at low rpms the perforated rear cone, and the non resonance of the " muffler " volume, allows most of the advancing wave front
from the diffuser to pass thru almost unhindered.
This wave is then bounced off the end plate, at a much longer tuned length than that of the rear cones.
As rpm increases, the rear volume gradually begins to resonate , and eventually the " holes" almost disappear and the rear cone starts to work in its effective tuned length range.

I tested every single 100cc direct drive pipe available on the planet , as the pipe and header was open in our KT100 classes.
The pipe I finally developed was far superior in every part of the powerband, from around 6000 to 16,000 rpm
It had a fully tapered header, with 3 diffuser cones ( the first being the steepest ) and a two part rear cone , the first one had no perforations.
I hand cut and built around 2000 of those things , winning every class title available for over 10 years.

The Yamaha class is redundant now , so there will be pipes lying around doing nothing under benches - I dont have the .dxf pattern files I eventually drew up, long gone on an old Win 7 hard drive.
I am sure the laser guys will still have the files , but getting a sample should be easy.

Edit - re the intake length , there is no such thing as too short - the 30mm carb on the TM125 KZ has the manifold recessed into the reed block , just to loose 3mm.

[ApolloMotoMoto]

(...)

I discovered the effectiveness of each element in the design many years ago, after doing nothing but build and dyno testing pipes for our classes of the KT100 Yamaha.
This was a solid 6 months of doing nothing else by trial and error.

(...)

I tested every single 100cc direct drive pipe available on the planet , as the pipe and header was open in our KT100 classes.
The pipe I finally developed was far superior in every part of the powerband, from around 6000 to 16,000 rpm
It had a fully tapered header, with 3 diffuser cones ( the first being the steepest ) and a two part rear cone , the first one had no perforations.
I hand cut and built around 2000 of those things , winning every class title available for over 10 years.

The Yamaha class is redundant now , so there will be pipes lying around doing nothing under benches - I dont have the .dxf pattern files I eventually drew up, long gone on an old Win 7 hard drive.
I am sure the laser guys will still have the files , but getting a sample should be easy.


I dont suppose you had a "name designation" for this pipe you came up with so I can search for it?

I just started looking around at KT100 pipes, and well, damn. There are a LOT of them.

I have been thinking about it for a while, but the itch to slap a KT100 pipe on our Motorized Bicycle engines is getting stronger.

At some point in the not-to-distant future I will begin using EngMod2T to develop this package even further. When that time comes I will have a lot of technical questions about how to design a pipe to achieve this effect.

Until that day comes, I would love to try the pipe you came up with :D

[wobbly]

The pipe was sold world wide thru my Wobblypipes company name , but mostly in NZ.
The name for it became " Wobbly 3 Cone".
You have to be careful as many classes used centrifugal clutches - a very different animal altogether.
I will ask around the kart guys and see if I can find one hiding in a corner.

[crbbt]

I am guessing there too many other approaches available on a GP bike to use a perforated rear cone?

[katinas]

Interesting comparison of flow direction through different A, B and C. Experiments with Vector tester developed by Dr. Jaros in mid 90, from Brno University of Technology. Wobbly often mentioned, that they helped to develop Yamaha GP cylinders.
Flow from very narrow A, boost short circuiting.
Less steeper flow from C makes "saltos" and goes longer way.

[wobbly]

crbbt - the perf rear cone setup is only suitable for direct drive single gear applications. It has a huge power range capability , all generated at the expense of power numbers around peak Hp
Not needed at all in classes with a gearbox.

[diesel pig]

crbbt - the perf rear cone setup is only suitable for direct drive single gear applications. It has a huge power range capability , all generated at the expense of power numbers around peak Hp
Not needed at all in classes with a gearbox.

So you wouldn't do a perf rear cone set up on a engine set up for a Enduro Dirt Bike?

[SwePatrick]

I hate beeing out of control, so let´s take control!
I install a laser height sensor on my Maxxecu controlled Yamaha TZR250 '100whp' engine.

This little device will help me control the engines performance in the important first 60ft on the 1/8 mile.

Why?
The bike´s dryweight is only 68kg´s and with almost 100whp it might rise so fast you can´t control it, electronics are faster in reaction than the human brain :D

https://youtu.be/-VSn3YosP0k


https://youtu.be/-VSn3YosP0k

[wobbly]

Mr Pig , the Enduro engines are easily setup with a " normal " pipe to operate perfectly for that application.
Very hard I would imagine to fit the large diameter long muffler " tube " onto a bike chassis.

[diesel pig]

Mr Pig , the Enduro engines are easily setup with a " normal " pipe to operate perfectly for that application.
Very hard I would imagine to fit the large diameter long muffler " tube " onto a bike chassis.

Fair enough, I was just trying to think of something 2 stroke related that would benefit from a wider rev range. I am sure I read somewhere that 2S enduro bike's benefited more from the induction of exhaust power valves more than 2S MX bikes.

[Pagi]

Interesting comparison of flow direction through different A, B and C. Experiments with Vector tester developed by Dr. Jaros in mid 90, from Brno University of Technology. Wobbly often mentioned, that they helped to develop Yamaha GP cylinders.
Flow from very narrow A, boost short circuiting.
Less steeper flow from C makes "saltos" and goes longer way.

Woobly,

Can you give us your opinion, comments, advice on these drawings?...............

[wobbly]

I have spent literally hundreds of hours studying the flow vector patterns from a Czech CNC flow visualization rig.
And I think I have made the point that the Japanese head race team engineer said to me in 2000 ( where his 250,s blitzed the GP championship ) that he didnt
need a dyno anymore as the flow patterns told him all he needed to know in predicting the power band shape and efficiency.

The first point is that this cylinder has normal stagger , but this testing method is only showing the raw result of flow at BDC with a depression at the Exhaust port.
No account is being taken of the flow reversion happening at TPO, that helps to separate the flow columns in the time domain and thus helping to maintain the individual flow column coherency.
Lastly showing each port individually is helpful but again this neglects the interaction effects of each column with another's.

The first LH ( MOD ) flow column is much more coherent, and would be very efficient at scavenging Exhaust residuals in the area in front of the Exhaust port.
But this positive effect is offset by the large amount of direct short circuiting taking place.
In my opinion this port needs angling backward and upward more thus scavenging higher up the wall area above the Exhaust port - with the inherent advantage of also reducing the short circuiting.

The second ( Middle ) stock column coherence is absolute crap , but this is the only regime with any scavenging of the dome residuals.
This deficiency is somewhat helped by the RH ( MOD ) boost flow in this example. The middle MOD roof should be flatter to help prevent disturbing the Boost scavenging of the cylinder upper and head dome area.

Lastly the boost ( MOD ) roof angle should be angled slightly more upward , as it has some good upper cylinder scavenging, but although the 360* loop will dramatically increase the loop time period, before entering the Exhaust
this flow across the head is " backwards ". Good head scavenging is seen dramatically in engines with a Toroid chamber. The flow attached to the rear wall then turns directly across the chamber,
and this is then masked by the low plugs downward intrusion into its path. This shows as a shadow of dark burnt on oil from the plug, out to the wall above the Exhaust. This negative effect can be ameliorated
by using small 10mm race plugs , and this has been proven to make more power in Snow Ski World Champ engines.

I think that all my comments would point toward this cylinder needs modifying in the axial and radial angles to conform more to that developed by Jan with the RSW/RSA - even aside from the stagger.
But although Jan has made the comment that he didnt see any advantages in using the vector flow visualization method , I think Yamaha , and by extension Bud Askland who's work on Raineys multi champ winning
cylinders for Team Roberts would agree to disagree.

[Pagi]

I have spent literally hundreds of hours studying the flow vector patterns from a Czech CNC flow visualization rig.
And I think I have made the point that the Japanese head race team engineer said to me in 2000 ( where his 250,s blitzed the GP championship ) that he didnt
need a dyno anymore as the flow patterns told him all he needed to know in predicting the power band shape and efficiency.

The first point is that this cylinder has normal stagger , but this testing method is only showing the raw result of flow at BDC with a depression at the Exhaust port.
No account is being taken of the flow reversion happening at TPO, that helps to separate the flow columns in the time domain and thus helping to maintain the individual flow column coherency.
Lastly showing each port individually is helpful but again this neglects the interaction effects of each column with another's.

The first LH ( MOD ) flow column is much more coherent, and would be very efficient at scavenging Exhaust residuals in the area in front of the Exhaust port.
But this positive effect is offset by the large amount of direct short circuiting taking place.
In my opinion this port needs angling backward and upward more thus scavenging higher up the wall area above the Exhaust port - with the inherent advantage of also reducing the short circuiting.

The second ( Middle ) stock column coherence is absolute crap , but this is the only regime with any scavenging of the dome residuals.
This deficiency is somewhat helped by the RH ( MOD ) boost flow in this example. The middle MOD roof should be flatter to help prevent disturbing the Boost scavenging of the cylinder upper and head dome area.

Lastly the boost ( MOD ) roof angle should be angled slightly more upward , as it has some good upper cylinder scavenging, but although the 360* loop will dramatically increase the loop time period, before entering the Exhaust
this flow across the head is " backwards ". Good head scavenging is seen dramatically in engines with a Toroid chamber. The flow attached to the rear wall then turns directly across the chamber,
and this is then masked by the low plugs downward intrusion into its path. This shows as a shadow of dark burnt on oil from the plug, out to the wall above the Exhaust. This negative effect can be ameliorated
by using small 10mm race plugs , and this has been proven to make more power in Snow Ski World Champ engines.

I think that all my comments would point toward this cylinder needs modifying in the axial and radial angles to conform more to that developed by Jan with the RSW/RSA - even aside from the stagger.
But although Jan has made the comment that he didnt see any advantages in using the vector flow visualization method , I think Yamaha , and by extension Bud Askland who's work on Raineys multi champ winning
cylinders for Team Roberts would agree to disagree.


Wobbly, Thank you for all this information.

[TZ350]

.
Two Stroke Stuffing

https://youtu.be/kIcb7x7NytQ?si=sGmQArawZSWfqeqW

Supercharged Nitro 50cc two stroke startup running.

[SwePatrick]

Everone want´s more speed...
So, go the easy way with boost!!
Shuuututututututuuu!!!

A VERY simplified guide:


https://youtu.be/cbmLJgYSv3k

[ken seeber]

Surely this is the go....high power , low emissions , no expansion chambers....dyno proven...

And here it is: https://www.youtube.com/watch?v=5czHDU6pK8E

Lots of other 2 stroke stuff on youtube under "driving4answers" 2 strokes

[lohring]

As I posted earlier, most of the problems with two strokes were solved a long time ago. The Junkers opposed piston aircraft two strokes were reasonably successful both with their weight and especially with their fuel economy. If you replace the blower with a modern electric turbocharger (https://www.garrettmotion.com/emission-reduction/garrett-e-turbo/) you get even better power, weight, and economy.

Lohring Miller

[lohring]

A friend built an inertial dyno based on our very successful small engine dyno. Though we had maybe thousands of trouble free runs, he has had issues. Pictures of both dynos are below. Ours is on the bench with the shield.



His problems have been:

Constant failures of the square key connecting the engine to the dyno

Failures of the round shaft he replaced the square shaft with

Slip of the shaft Locktited into the flywheel



The only difference between his dyno and ours is the position of the clutch and the Lovejoy coupling. We have the coupling before the clutch and he has the clutch before the coupling. My thought is that the clutch is a solid connection and in our design the coupling insulates the engine's torque fluctuations from the flywheel's constant inertia better. We never did more than twist the square key. Others with dynos we copied never had any of these problems either.



What are your thoughts?

Lohring Miller

356303356304

[wobbly]

The only suggestion I have is it seems the failures are all related to torsional harmonic twisting between the crank and the inertial mass.
Those Lovejoy type slotted couplings with varying grades of what is probably urethane pads on the force faces , have to be very hard, or they distort and fail.
Lovejoy also make what are called donut couplings as are used in racecar rear axle assemblies like Formula Ford etc - but I doubt they have something small enough.

Maybe suppliers of mechatronic components for robots etc have a small donut drive coupling , that not only can take axial misalignment, but the rubber coupling itself dampens
torsional harmonics really well.

The other way of doing this is the camshaft drive torsional damper that was invented at Cosworth for the DFV - this has a set of small radial leaf springs that bend back and forth
to insulate the cam drive from crank harmonics.

[husaberg]

The only suggestion I have is it seems the failures are all related to torsional harmonic twisting between the crank and the inertial mass.
Those Lovejoy type slotted couplings with varying grades of what is probably urethane pads on the force faces , have to be very hard, or they distort and fail.
Lovejoy also make what are called donut couplings as are used in racecar rear axle assemblies like Formula Ford etc - but I doubt they have something small enough.

Maybe suppliers of mechatronic components for robots etc have a small donut drive coupling , that not only can take axial misalignment, but the rubber coupling itself dampens
torsional harmonics really well.

The other way of doing this is the camshaft drive torsional damper that was invented at Cosworth for the DFV - this has a set of small radial leaf springs that bend back and forth
to insulate the cam drive from crank harmonics.
as seen on the
356324
Mark IV cortina propshaft:innocent: up to and likely beyond the seira

Cosworth also used a quill drive on both he v8 and the Norton twin
https://www.f1technical.net/forum/viewtopic.php?t=26642

I think some even used a hollow shaft as Torsion bar
Triumph BSA used one on the points drive on the F750 tripple as the crankshaft tended to whip up and down.

[pete376403]

as seen on the
356324
Mark IV cortina propshaft:innocent: up to and likely beyond the seira

Cosworth also used a quill drive on both he v8 and the Norton twin


I think some even used a hollow shaft as Torsion bar
Triumph BSA used one on the points drive on the F750 tripple as the crankshaft tended to whip up and down.

Also used for Hillman Imp gearbox to driveshaft joints. AKA Rotoflex coupling

[Pursang]

Surely this is the go....high power , low emissions , no expansion chambers....dyno proven...

And here it is: https://www.youtube.com/watch?v=5czHDU6pK8E

Lots of other 2 stroke stuff on youtube under "driving4answers" 2 strokes

Many of these get posted in the Oddballs and Prototypes thread.

And it looks like our favorite 2 stroke Stuffer has some thoughts about the "Prior Art"!


https://www.youtube.com/watch?v=MC3wNFApaKE

[lohring]

Re the dynos; It was pointed out to me that our dyno had a very much thicker motor mount. I think it's possible that the engine is moving a lot more with the thin mount and that's what is causing the problem.

Lohring Miller

[Frits Overmars]

................
356340

[Peter1962]

Gelukkige verjaardag, Jan !

Happy birthday

[bad'rule]

Oh how fast time goes by,and already another Happy birthday to our Mr.Jan. Wishing you good health through the year Jan


Sent from my RMX1911 using Tapatalk

[TZ350]

.
356342356343356344356345356346

Unusual damage to the thrust side of one of the NF4 Honda RS125 pistons that we use in our Suzuki GP110's.

I think it might be that the squish was too tight (< 0,6mm) and the piston was hitting the head while the crank was still trying to go up. There by applying severe leveraging pressure on the piston skirt.

Would be happy to hear other ideas.

[TZ350]

.
356347

Could the tongue on the NSR250 cylinder have caused this, as the piston is rocking over from bottom dead center? Has this been a problem with Honda RS125's? Ideas?

[wobbly]

That piston markup on the dome is all the way round, the width of the squish , so that isnt deto, its been smacking the head big time.
I would say that the crank is flexing - is it a hollow pin or solid - Jan has said that the Aprilia would not hit the head at 14,000 with 0.4 squish.

And no, Honda have used the tongue idea for ever with no issues - and that hole in the piston skirt starts well above the tongue at BDC.
At 0.6 squish depth, and that very wide squish width, what is the MSV in EngMod.

[TZ350]

That piston markup on the dome is all the way round, the width of the squish , so that isnt deto, its been smacking the head big time.
I would say that the crank is flexing - is it a hollow pin or solid - Jan has said that the Aprilia would not hit the head at 14,000 with 0.4 squish. And no, Honda have used the tongue idea for ever with no issues - and that hole in the piston skirt starts well above the tongue at BDC. At 0.6 squish depth, and that very wide squish width, what is the MSV in EngMod.

Hollow Pin and 37.5 MSV

356348

[jonny quest]

Is the ring pinched in the piston?

[wobbly]

Squish looks wider than 6.9mm in the pics is only reason I asked.

[husaberg]

Is the ring pinched in the piston?
When I zoomed the pic way in it looked that way. just by the ring not poking out but the land groove appears to have gap?
I couldn't imagine it whacking the head hard without it doing this either...
356349
looking at the pic though is it pinned at 7am or where the ring is?
is 7am debris?

Also Hey Rob is that the strort stroke engine with NSR top end if so its not impossible for that cylinder to catch due to the dimensional changes you made taking 6mm? off the stroke?

[ken seeber]

Looking at Hooser's pic, the crown damage/ring jamming is obviously due to shrapnel from the busted out bit. However, as there is no other longitudinal skirt damage that might have caused the "punched out" bit, I reckon it started with the small crack from the bottom which progressed upwards and you can see is aligned with the LHS of the hole. Then, being on the thrust face, this allowed the area to flex = fatigue = breakage = failure.

As to why the small crack got there in the first place is a guess. I'm sure TeeZee doesn't hammer his pistons too much.

Surprised that there wasn't much more destruction.

[husaberg]

TZ
Following what Ken has said, whats at 9 oclock have you moved the pin and its pinned through at the top? or is it like a casting or makers mark?
becasue if that is sticking out of the top of the piston? why is that not hitting the head?
356350356351

[Condyn]

Both times that I have seen cast pistons hit the head, the force damages the ring land and the crack propagates from the ring land down to the wrist pin bore. In your case it almost looks like the problem started in skirt. Does the shrapnel appear to have gone outward or in towards the rod? Maybe something was ingested and got between the rod and the piston skirt?

[TZ350]

.

When I zoomed the pic way in it looked that way. just by the ring not poking out but the land groove appears to have gap?
I couldn't imagine it whacking the head hard without it doing this either...
356349
looking at the pic though is it pinned at 7am or where the ring is? is 7am debris? Also Hey Rob is that the short stroke engine with NSR top end if so its not impossible for that cylinder to catch due to the dimensional changes you made taking 6mm? off the stroke?

Ring jammed. The apparent side gap is just an optical illusion because of the slight ring groove chamfer. Yes 45mm stroke NSR250 cylinder on a short 48mm stroke bottom end with a long rod. Cylinder shortened, plus head insert inserts down into the cylinder. BDC for the piston is not go all the way down like the original NSR.


TZ
Following what Ken has said what's at 9 o'clock have you moved the pin and its pinned through at the top? or is it like a casting or makers mark?
because if that is sticking out of the top of the piston? why is that not hitting the head?
356350356351


356355 356356

Original Honda RS125 pistons have the ring pegged at 7 o'clock so that the ring ends run up the cylinder wall between the B and C ports. Works the same on the NSR cylinders that we use for the 110cc engines.

Piston crown definitely crushed down trapping the ring.

[TZ350]

Squish looks wider than 6.9mm in the pics is only reason I asked.

356357

Squish band 9mm wide so 55% not the 45% Engine mode was told. I do find it challenging to cut metal to match the plan.

The squish gap would probably have been fine if it was not for the debris getting jammed in the squish gap. Although I have opened it up a bit for this rebuild.

[diesel pig]

. Yes 45mm stroke NSR250 cylinder on a short 48mm stroke bottom end with a long rod.

Sorry to be pedantic. But don't you mean 54mm bore on a NSR250?

[TZ350]

Sorry to be pedantic. But don't you mean 54mm bore on a NSR250?

Yes you are right. 54mm bore, 48mm stroke.

356358

Also it came to me in a dream last night. I had over tightened the piston in the mill vice and cracked it. We have to take a bit off the pin boses to get the piston to fit over the little end of the RD400 rods we use.

[husaberg]

Yes you are right. 54mm bore, 48mm stroke.

356358

Also it came to me in a dream last night. I had over tightened the piston in the mill vice and cracked it. We have to take a bit off the pin boses to get the piston to fit over the little end of the RD400 rods we use.


My dreams seem to be a bit more exciting than yours Rob.......
Oddly though they both seem to involve vice and short tight skirts....:bleh:

[lodgernz]

My dreams seem to be a bit more exciting than yours Rob.......
Oddly though they both seem to involve vice and short tight skirts....:bleh:

Gold !!!!!!

[wobbly]

Especially short tight skirts with splits in them.

[TZ350]

.
356359

Maybe not a split but at least a tight skirt, I think it is the girl my grandson is with .......

[wobbly]

Im pretty sure I shagged her mum in a dream the other night.

[TZ350]

Im pretty sure I shagged her mum in a dream the other night.

Your dream :sleep: would have had to take you to Vladivostok.........

[Vannik]

As we do not read Help files except as a last resort I thought it a good idea to create a YouTube channel to release some videos. Somewhere along the road the idea is to also convince Wobbly to add a video or two :innocent:

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

[wobbly]

Shit I will have to get a haircut, the missus reckons I look like a homeless man.
I thought the Albert hair with the GiGi goaty was quite sporting.
Better idea is just to do a screen shot video with my audio over, seeing me wont add anything except rabid derision - especially if I do a TikToc and get my tits out for you.
EngMod 2T Only Friends.
Now you know what the 2T stands for.

[Frits Overmars]

As we do not read Help files except as a last resort I thought it a good idea to create a YouTube channel to release some videos. Somewhere along the road the idea is to also convince Wobbly to add a video or two :innocent:
https://www.youtube.com/watch?v=jUSGpqikWtEExcellent initiative Neels ! :niceone:

[Frits Overmars]

seeing me wont add anything except rabid derision - especially if I do a TikToc and get my tits out for you.
EngMod 2T Only Friends. Now you know what the 2T stands for.God help us, I'd rather start grinding camshafts :brick:

[Condyn]

Your on camera skills are quite pleasant Neels. If you second guess that like I would, please do not. Bravo. When you get to the post 2t phase, many of us novice users who have not invested enough time would really enjoy diving into depth on how to investigate certain situations, and how to better utilize the information available for developing pipes etc. If I am not mistaken, similar information was in the “overview” write up that I may have received when purchasing the suite. I enjoyed that type of thing. Great job Neels!

[wobbly]

OK Frits , in the spirit of endeavoring to keep your sanity intact, I will promise to keep my blouse on at all times on the big screen.

[diesel pig]

Yes , and no ,the outer aluminum cable shield is grounded to the supply battery earth only at one end. The trigger grounds go to the separated trigger earth pins , that
have their own isolation circuitry .
I also used the same Cat 5 cable wire pairs for the servo and PJ wiring, as these also can inject ignition noise into the sensitive input pins.
Twisted signal pairs form a very high natural rejection of this power supply line " noise " that seems to be more of an issue with the P4 units having 4 CDI packed into the same box format.
But as I said , if the coil drive wiring is physically separated, and resistor plugs/caps are used , then any noise issues are largely eliminated.
The other audio amp trick of creating a common single earth ground point for the coils/case/battery and ECU power supply also eliminates circulating noisy voltage sources from affecting the super sensitive
ignition chip supply.

I have watched some boy racer videos on earthing there shielded cables. Are they doing the same thing? I have ever done this before and I want to get it right.

Also, after watching 2strokestuffing new video. I am wondering have I missed a video of him explaining the cooling circuit on his 50cc? As the way it appears in the video the cooling would go in the back of the cylinder and straight out the head. unless there is the plates in the cooling jacket redirecting the flow of the coolant.

[wobbly]

Mr Pig , the best physical way to reduce radiated EMI is a twisted pair with a shield grounded at one end, but with an Ignitech I have never needed to use this as long as the coil drive wires
and the trigger/input wires are physically separated down each side of the bike.
Those wires are at each end of the loom plug for a reason.
I have some CAT6 lying around and use it when wiring carbs with TPS and solenoid PJ , as its tidy and convenient all in one cable loom.

Re Alex's water - the best cooling circuit is as I have described many times - cold water in above the boost port , with a separation plate between the cylinder or head that only has water holes
allowing water to enter the front of the head above the Exhaust port.
Thus cold water is forced forward over the transfers toward the Exhaust duct, and only then is allowed into the head.
This warmer water then crosses the head and exits above the boost.
An additional plus is if there is water in the case below the Exhaust duct, then a couple of 3mm holes from the case up under the duct helps cool that with extra cold flow.
Also if the cylinder is angled forward, this means air can be trapped above the boost in the cylinder, so a small air lock bleed is needed at that high point directly under the exit spigot as well.
I have tested this with great results in KZ as well as the TZ/Banshee style engines used for various projects.

EDIT - the separation can be as simple a plain copper gasket with only the bore, the clamp bolts and a pair of water holes each side of the Exhaust duct.
This worked well on several LC racebikes that had a gasket anyway ( full of holes and slots ).

[SwePatrick]

Hey!
Finally i got my fingers out!
Testdrive of my molested SGM GA207 Kartengine.

Setup:
Ported.
144cc (Woessner piston)
42mm Keihin PWM
E85 fuel
18-1 compression ratio(total)
Homemade billet head


https://youtu.be/tDVBGh_TMLM?si=kdwW7NIpWui_M1Im

[Storbeck]

Wobbly

I'm interested in how this scheme might be modified for a watercraft engine (jet ski) where the water traditionally enters first into an exhaust manifold and into the cylinder through water jackets around the exhaust port.

The most obvious answer might be to block off the passages between the exhaust manifold and the cylinder then modify the cylinder to flow exactly as you have described (so maybe I already have the answer), but interested if there is anything that the watercraft allows that is different than something that has a radiator. I have a virtually unlimited supply of cooling water at ~80 deg F (a lake) and the flow is very small and thus the lines are very small, so I have the freedom to run cooling circuits every which way if so desired. I could isolate the head from the cylinder with it's own cooling circuit or specifically cool the exhaust port or the crankcase or whatever.

Also, conventional wisdom for water cooling an exhaust chamber on a watercraft is as little water and as hot as possible (which is still not that hot, ~190F maybe), but I'm not sure if the manifold portion of the exhaust would be best to keep as cold as possible, or to restrict cooling flow to get as hot as possible. Intuitively I feel like I want the exhaust port in the cylinder as cool as possible, but the manifold (starting maybe 2" or so away from the cylinder wall) to be as hot as possible (again hot is relative here because we're talking about water jacketed aluminum and silicone hoses).






Mr Pig , the best physical way to reduce radiated EMI is a twisted pair with a shield grounded at one end, but with an Ignitech I have never needed to use this as long as the coil drive wires
and the trigger/input wires are physically separated down each side of the bike.
Those wires are at each end of the loom plug for a reason.
I have some CAT6 lying around and use it when wiring carbs with TPS and solenoid PJ , as its tidy and convenient all in one cable loom.

Re Alex's water - the best cooling circuit is as I have described many times - cold water in above the boost port , with a separation plate between the cylinder or head that only has water holes
allowing water to enter the front of the head above the Exhaust port.
Thus cold water is forced forward over the transfers toward the Exhaust duct, and only then is allowed into the head.
This warmer water then crosses the head and exits above the boost.
An additional plus is if there is water in the case below the Exhaust duct, then a couple of 3mm holes from the case up under the duct helps cool that with extra cold flow.
Also if the cylinder is angled forward, this means air can be trapped above the boost in the cylinder, so a small air lock bleed is needed at that high point directly under the exit spigot as well.
I have tested this with great results in KZ as well as the TZ/Banshee style engines used for various projects.

EDIT - the separation can be as simple a plain copper gasket with only the bore, the clamp bolts and a pair of water holes each side of the Exhaust duct.
This worked well on several LC racebikes that had a gasket anyway ( full of holes and slots ).

[katinas]

Konig outboard cylinder with cooling passages between inside transfers wall and liner, similar like on Aprilia GP and KR3 500 cylinders.

[Storbeck]

Konig outboard cylinder with cooling passages between inside transfers wall and liner, similar like on Aprilia GP and KR3 500 cylinders.

Cool stuff, but unfortunately the motors I play with are parallel twins with relatively small center to center distance so the transfer ports are squished together, the classic "elevator shaft" transfers, so there is no chance to put cooling passages between the transfers and the bore, or around the outside for that matter either, over the top is how they already are designed, although not in the way that Wobbly described. Wouldn't be hard to modify them to be that way though.

[wobbly]

Jetski's give you the opportunity to really do some great things with the cooling circuits.
In the 1100cc SeaDoo world champ engines , they had water jacketed pipes. This meant I could double the
cold length of the Exhaust duct, with hot water on the other side - this gave way less deto level from hot A/F being shoved back past the piston.
The head was a completely different circuit, with hot water taken from the pipe to reduce the temp delta between the combustion chamber wall and the expanding hot gasses.

On the dyno it was found that what I thought was a good cylinder exit temp, was way too cold.
We ran big clearances , but there was more power to be had with the exit temp up at 70*C due to bore friction I think, than down at 50*C to over cool the incoming transfer charge.

The cylinders with close bore centers like all the RD/LC/TZ/YPVS/Banshee's respond real well to the cold transfer tops, that in stock form had a completely random " water everywhere " approach.

[Storbeck]

Great info but I'm a little unclear on some things:




Jetski's give you the opportunity to really do some great things with the cooling circuits.
In the 1100cc SeaDoo world champ engines , they had water jacketed pipes. This meant I could double the
cold length of the Exhaust duct,

What length is being doubled? The "Wobbly on exhaust port design" doc says 1.5*bore for length of exhaust port, so double that? OR do you mean like double whatever i was before you modified it?

with hot water on the other side -

Hot water on the other side of what? You mean the exhaust port portion was kept very cold then the rest of the manifold/exhaust was much hotter?

this gave way less deto level from hot A/F being shoved back past the piston.
The head was a completely different circuit, with hot water taken from the pipe to reduce the temp delta between the combustion chamber wall and the expanding hot gasses.

How hot did you run the head? So you did this by blocking off coolant flow from cylinder to head and running water from the exhaust water jacket to get the head hotter than the cylinder?

On the dyno it was found that what I thought was a good cylinder exit temp, was way too cold.
We ran big clearances , but there was more power to be had with the exit temp up at 70*C due to bore friction I think, than down at 50*C to over cool the incoming transfer charge.

Super interesting. I have a couple of engines currently running around 120 degrees F (~50 C) on a heat tape stuck on the head (so I assume water temp is about that). Sounds like I should be trying to get that a little warmer, and the head even warmer yet. My thinking was cooler = better, or at least I didn't think 120F was too cool.

The cylinders with close bore centers like all the RD/LC/TZ/YPVS/Banshee's respond real well to the cold transfer tops, that in stock form had a completely random " water everywhere " approach.

So one approach might be to isolate head from cylinder, run water in the top of the cylinder water jacket from the intake side, let it flow past transfers and down around the exhaust port and into the first part of the exhaust manifold and out, so the intake side of the cylinder and top of the transfer ports is coolest. Then run hot water from the exhaust into then out of the head.

[wobbly]

JetSki's typically have super short Exhaust ducts , the big oversquare ones would be lucky if its length equals the bore.
In the case of the Seadoo I doubled the duct length as part of the pipe header, and there was a separator plate between that and the hot pipe water jacket.
The duct plus the bolt on manifold extension had cold water supplied thru the flange face as is normal in those engines.
There was no flow at all from the cylinder to the head, it had a plain copper gasket with no holes, O rings on both sides.
The head inflow was from the Exhaust jacket , yes.
Thus the cylinder exit temp was controlled by jets, as was the head exit flow , with completely separated supplies and exit jets.

The cylinder made best power at 70*C - honestly, cant remember how hot the head was - but it was well over 100 though.
But I did drill a radial series of holes just outside the bore O ring to allow the colder cylinder water to cool the alloy head insert right next to the squish band.
Those engines were very deto resistant in the config with squish band and extended duct cooling - enabling much higher com than we had previously maxed out at.
The thing was a raped ape to the first buoy.
Keeping the back of the combustion chamber hot, has no effect on deto , but helps prevent combustion energy simply being dumped into the coolant for no reason.

[koba]

If you are going to actually build a pipe at some stage I dont get why you are even considering using a design that is so obviously flawed.
The only reason it would be " insensitive " is because the engine is making bugger all power.
Post the .pack file on the site and I will help with something a bit cleverer.

It took ages.
The model is basic and probably flawed.

356379

[TZ350]

I have been playing with rotary valves tonight.

356380 70cc sports cylinder on a RG50 converted to rotary valve.

356381 Blue line 356382 Red line.

Interestingly it still idles pretty well with the radical rotary valve. I think that with a bit of jetting and ignition work the red line will be a good 25RWHP.

The next move is to turbo it. So maybe 30RWHP may be possible.

[wobbly]

TeeZee, just remember that the RSA made over 16Bar BMEP @ 13,000 ( crank ) with a valve timing of around 140/90 - and going much over 140* makes front side jetting a nightmare.
I dont understand why you and many others are running these small stroke engines at well below the accepted mechanical limits of piston speed, as Hp = T X RPM so if
you engineer the overall efficiency to hold up the torque , then going from 13,000 to say 15,000 will increase power by 15% - and you wont need " radical " anything to achieve that
level of performance.

[F5 Dave]

I was well guilty of that sin. However I started on MB50s where the ring tips would fly off if revved to 12000 (even the 100s were more tolerant.
Then onto RG50s where the cranks didn't tolerate 13000 for any time plus the rings were thick enough to lose seal above 12000.
I thought the next stage with TZR crank parts and Kx pistons at 13000 were bone reliable. So I could have pushed higher but was reluctant due to earlier (regular) mishaps.
Commuter bikes had hard limits.

[Flettner]

The water cooled, powervalve AG out and about at a local maize paddock day, blends in well. An opportunity to tune the powervalve settings, very worthwhile. I have re fitted the boost bottle, power now is much like any modern powervalve engine with smooth delivery, the 6000 to 7000 dip is gone (as I'd expect) and also the surging that used to happen .... completely gone.
No change to jetting, since the original air cooled cylinder.
My next cylinder will most certainly be twin exhaust port but 54 x54 , not this rubbish 48 x 58 I have now.
It's surprisingly good fun to ride now, cant wait for the new Vinduro / VMX season 👍

[Vannik]

It took ages.
The model is basic and probably flawed.

I unpacked the model and had a quick scan through and ran it - looks well done. Will be interesting to see what Wobbly says.

[Flettner]

The cylinder in this also has a 4mm exhaust dam, on 48 stroke.

[TZ350]

.

TeeZee, just remember that the RSA made over 16Bar BMEP @ 13,000 ( crank ) with a valve timing of around 140/90 - and going much over 140* makes front side jetting a nightmare.

This disk rotates anticlockwise.

356387 inlet opens 170 before TDC.

Oooops a little wild 170/88.

356388 Inlet closing, looks to be on the money at 88 after TDC.

Next move is to cut another disk.

356389 140/90

Yep this one looks more sensible.

356390 F8 356392 RG500 356391 RSW250

Some other pictures of rotary valves.

[wobbly]

The angled closing edge of that RSA picture really helps the wear issue of inlet ram pushing the valve hard against the case.
When the Rotax 256 was starting to be used in 250 Superkarts , I was on the dyno day and night at ZipKarts, and tried every valve shape and timings possible.
Full radius open/close shapes, sharp straight valve edges., corner rad's, triangle shaped inlets etc.
The dead straight opening, and sharply angled valve closing always made max power.

But with the power available initially from the ports/pipes/ignition the best setup was 135/85 , later, better pipes/ports made alot more power with 138/88.
That setup won several 250 Superkart World and Euro titles for Martin Hines.

140/90 or a little more was only ever used on the factory Aprilia, and copies made by FPE/PVP for Superkarts that easily rev'd past 14,000 all day.
The sharply angled closing edge made no difference to power with the same timing, but helped the case wear immensely.

[Vannik]

I unpacked the model and had a quick scan through and ran it - looks well done. Will be interesting to see what Wobbly says.

I found one issue - you specify 0.42mm thickness for the reed petal which is a typical glass fiber petal but specify density and Youngs modulus for steel, resulting in a very stiff petal.

[koba]

I found one issue - you specify 0.42mm thickness for the reed petal which is a typical glass fiber petal but specify density and Youngs modulus for steel, resulting in a very stiff petal.

Ahh, that oversight explains a lot; basically why the reed portion never made sense.
I modelled it as a piston port too, and that was a lot more predictable.

Shit in = Shit out, eh!

Even with that in the mix, I'm stoked (joyous?) at the results, even if they aren't super-dupa, they are at least dupa.

[koba]

I was well guilty of that sin. However I started on MB50s where the ring tips would fly off if revved to 12000 (even the 100s were more tolerant.
Then onto RG50s where the cranks didn't tolerate 13000 for any time plus the rings were thick enough to lose seal above 12000.
I thought the next stage with TZR crank parts and Kx pistons at 13000 were bone reliable. So I could have pushed higher but was reluctant due to earlier (regular) mishaps.
Commuter bikes had hard limits.

Fear of revs is a big part of it, eh.

Sometimes it is fear, other times it's practical.

My old nail still runs an original style (road tune) piston, I dropped one of the rings but it's still, well, rather "plump".
That seems to be the rev limit.

For the MB100 as a platform, to do a 12.5k redline kinda deal is about 20% of the resources of going above that, from what I've done anyway.
Some of that will be a lack of experience and wisdom, but mostly it's diminishing returns in a sport where power is cool but the main reason I turn(ed?) up was basically social.

[wobbly]

Re the TF125 .pack info. I thought I would do a couple of pages at a time and suggest changes as needed.
First, engine geometry.

The MSV with a 0.9 squish gap is way, way low. Changing the width back to 50% and going to 0.65mm gap gives 39M/s which is close to the recommended start point of 40M/s
for most applications.
With this very short stroke, that depth will be nowhere near the piston clipping in the overev.

The CCR - if you add the Transfer volume , found on the transfer page we get 566cc with those ducts added in. This equals a CCR of 1.278, is this what you actually measured as it is quite big
for a piston port , and well big for a reed engine.
I automatically put the Exhaust Transducer at the duct length - to measure what the Mach is at that point later in the sim optimization, so I put in 72mm.

Moving onto the Exhaust Port.

The corner rads are OK, but the top and bottom timing edges are way too flat.
Using the FOS guidelines we get 4.5mm for the top corners and a center radius of 75% of bore = 42mm.
The bottom corner should extend up to around TPO , to reduce short circuiting, so I put in 10mm
This reduces the Blowdown STA, so I simply widened the port out to 40mm = 71%, so safe, and that got us back to the 24Hp Blowdown STA needed.

The duct exit is enormous, as the original 36mm = 127% of the port area, using the software radio button gives us a 30.4mm exit = 90%.
This should be easy to do by counterboring the duct and pushing in an insert, then grinding and blending the shape.

So there is the first set of changes I recommend.

[TZ350]

.
356395 356394 170/88 ... Red Line on graph.

I recall someone talking about dyno testing a rotary valve two stroke. Where the valve seized in the fully open position at WOT and max RPM. With the sympathetic inlet resonance it apparently still made the same power but it did not pick up again once the throttle was closed. Probably explains how maximum powerwise I got away with crazy ass timing. Looks like more subdued timing is required if I want to ride the thing.

[husaberg]

.
356395 356394 170/88 ... Red Line on graph.

I recall someone talking about dyno testing a rotary valve two stroke. Where the valve seized in the fully open position at WOT and max RPM. With the sympathetic inlet resonance it apparently still made the same power but it did not pick up again once the throttle was closed. Probably explains how maximum powerwise I got away with crazy ass timing. Looks like more subdued timing is required if I want to ride the thing.

Pretty sure Frits or Jan wrote something similar to that about one doing that in practice or a race. ran good but refused to start again
Pretty sure piston ports get harder to start as the inlet duration gets extreme as well.

What would change if Rob contoured the leading edge and trailing of the disc to the same shape as the round ish port.
not meaning duration more so time area and intake pulse?

TBH I thought that port would be squarer.

[wobbly]

The RSW is a slightly oval inlet port horizontally, the RSA is slightly oval vertically on the disc axis.
The RSA is better in that the narrower the port for the same timings, the less time the disc covers the port shape.
Having rounded disc leading or trailing edges , with the same timings, does NOT make more power.
That was the first test I did at Zip when the 256 engine was introduced.
Having a slightly triangular port with straighter angled sides, is better than a round port, but always has bad wear issues, the RSA vertical oval is easily the best.
All dyno proven reality.

[koba]

Re the TF125 .pack info. I thought I would do a couple of pages at a time and suggest changes as needed.


Thank you, certainly appreciate the input!



The MSV with a 0.9 squish gap is way, way low. Changing the width back to 50% and going to 0.65mm gap gives 39M/s which is close to the recommended start point of 40M/s
for most applications.
With this very short stroke, that depth will be nowhere near the piston clipping in the overev.


Good to know, my target was around 0.6mm but I chickened out with the compression ratio getting so high. As it was I decided to file the piston down to reduce that, until I chickened out on the piston crown thickness.
The head had already been skimmed, that and the slugs for the crank balance were the only uses of machine tools in this project.
(The objective being minimal input to get to a good starting point).



The CCR - if you add the Transfer volume , found on the transfer page we get 566cc with those ducts added in. This equals a CCR of 1.278, is this what you actually measured as it is quite big
for a piston port , and well big for a reed engine.


I've probably stuffed that up, the transfer data was from measured sizes and the crankcase volume (including transfers) from a liquid measurement. (a holey piston). I'm pretty sure there were a number of 330ml liquid measurements being made that night too, so yeah, likely a cockup. I'll see if I can convince someone to check my working...



I automatically put the Exhaust Transducer at the duct length - to measure what the Mach is at that point later in the sim optimization, so I put in 72mm.


That's another oversight on my part, I noted your earlier advice on that and missed it here.



Moving onto the Exhaust Port.

The corner rads are OK, but the top and bottom timing edges are way too flat.
Using the FOS guidelines we get 4.5mm for the top corners and a center radius of 75% of bore = 42mm.
The bottom corner should extend up to around TPO , to reduce short circuiting, so I put in 10mm
This reduces the Blowdown STA, so I simply widened the port out to 40mm = 71%, so safe, and that got us back to the 24Hp Blowdown STA needed.


Awesome!



The duct exit is enormous, as the original 36mm = 127% of the port area, using the software radio button gives us a 30.4mm exit = 90%.
This should be easy to do by counterboring the duct and pushing in an insert, then grinding and blending the shape.

It's a bleeding whopper eh!
I do wonder about that as bikes of that design period all seem to approach it with this rapid increase in cross section, I do wonder if there was some rationale at the time or if it's just the way it ended up.

Either way, given project parameters the insert was not an option for this build. I did consider it, and also thought a smaller engine that is allowed water cooling, might even be able to get some cooling water in there.

However, if I ever do another one I will try following this, thanks!



So there is the first set of changes I recommend.


Thank you!

I was going to ask your opinion on which would be more worthwhile, between a better optimised head and a better optimised exhaust duct.
I'm still interested, but of course we are talking about an engine simulator, I can also model it and see!

I know the whole thing is a system and that optimising it all to work together is the best option but I'm also always interested in working out what step to take next, I guess this comes from me building bikes up that I am still racing each month, rather than building something up to a given spec from day one.

[koba]

I know the whole thing is a system and that optimising it all to work together is the best option but I'm also always interested in working out what step to take next, I guess this comes from me building bikes up that I am still racing each month, rather than building something up to a given spec from day one.

A quick run with the duct and head changes made...
(I haven't yet corrected the exhaust port window).

I'm guessing the minimal change from the head would be because combustion efficiency parameters are dealt with elsewhere.
I set it at 0.8 as a bit of a guess, I'll try another run with a higher number to gauge the effect of an increase here.

I also note I have it set to 95 octane where the engine actually runs on Av-gas.
356408

Yep, from .80 to .85...

356409

So, conclusion: both will be good, ideally do both at once!

I should also note, the model used with these graphs is straight line in the ignition, so there is power to be found above and below peak in setting that up well.
My way of approaching this has been to keep ignition timing as a relatively static variable for these calcs, (14 de BTDC).
Then I dial it in on the track, upping the advance under peak and tapering it off over peak, it makes a massive difference.
I've only done this with rudematary instrumentation (RPM and EGT), maybe oneday it would be good to get some knock stuff in there.
(Acually, one bike has the knock stuff thanks to F5dave)

[wobbly]

So running AvGas and a properly working squish, with a digital advance curve I will be putting in a CE of 0.9 and a com of 17:1 with such a low bmep and thus low dynamic compression.

[quallman1234]

TST100 Update - two stroke twin 100cc - 2x Derbi 50 cylinders...

https://www.youtube.com/watch?v=ZxXQ8rW24YM&ab_channel=GlenSkachill

[F5 Dave]

Nice one guys. Be on the track in no time.

[wobbly]

Next couple of pages for the TF125_WOB.
The transfers - this engine has no PV thus using the Aprilia reverse scavenging with the B - C highest will naturally kill front side.
Better to use normal stagger with the A highest as this regime naturally favors the generation of front side power, at the expense of course of overev.
But as we have a 50 stroke peaking at 11,000 I didnt consider overev was a driving necessity.
So without changing any axial or radial dimensions I have simply set the port heights to give close to the needed Transfer STA with normal stagger.

Then the Inlet/Reed page.
I changed the petal material to Carbon, then adjusted the 1st Mode thickness to give the correct rpm.
Then lifted the port roof and widened it a little to get the Inlet STA to match the Blowdown/ Transfer STA capability.

In the Exhaust page the duct exit is 36 , in the Pipe page it is 34, what is correct.

EDIT - at this point you dont need to choose between a duct mod or a head mod, as the head has no squish velocity and needs WAY more compression for AvGas.
Only issue is that if you do the insert trick later, then basically most of the pipe has to be changed to suit.

EDIT 2 - You dont need a knock gauge at all, the instant you get deto starting the EGT will flatline or drop if you are lean anywhere in the jetting with the advance you have.
Its good to have on the dyno to see how hard you can push the envelope without damage.

[koba]

Next couple of pages for the TF125_WOB.
The transfers - this engine has no PV thus using the Aprilia reverse scavenging with the B - C highest will naturally kill front side.
Better to use normal stagger with the A highest as this regime naturally favors the generation of front side power, at the expense of course of overev.
But as we have a 50 stroke peaking at 11,000 I didnt consider overev was a driving necessity.
So without changing any axial or radial dimensions I have simply set the port heights to give close to the needed Transfer STA with normal stagger.

Then the Inlet/Reed page.
I changed the petal material to Carbon, then adjusted the 1st Mode thickness to give the correct rpm.
Then lifted the port roof and widened it a little to get the Inlet STA to match the Blowdown/ Transfer STA capability.

In the Exhaust page the duct exit is 36 , in the Pipe page it is 34, what is correct.

EDIT - at this point you dont need to choose between a duct mod or a head mod, as the head has no squish velocity and needs WAY more compression for AvGas.
Only issue is that if you do the insert trick later, then basically most of the pipe has to be changed to suit.

EDIT 2 - You dont need a knock gauge at all, the instant you get deto starting the EGT will flatline or drop if you are lean anywhere in the jetting with the advance you have.
Its good to have on the dyno to see how hard you can push the envelope without damage.

Awesome.

36 is the correct figure for the exhaust duct exit. (and pipe entry).

[diesel pig]

.
356395 356394 I recall someone talking about dyno testing a rotary valve two stroke. Where the valve seized in the fully open position at WOT and max RPM. With the sympathetic inlet resonance it apparently still made the same power but it did not pick up again once the throttle was closed. Probably explains how maximum powerwise I got away with crazy ass timing. Looks like more subdued timing is required if I want to ride the thing.

It was this story that made me think that Frits 24/7 inlet would be worth looking into and after our Norwegian friend made a crude 24/7 inlet on his 50cc and run it on his dyno and worked it by just pulling a lever and it just worked intrigued me. but I will have to finish my case reed before mucking with a 24/7 inlet.

[diesel pig]

Just a follow up on my Ignitech questions I can get the coil pick up wires 250mm away from the ign coils all the way to the unit. Will I still need to run them into shielded cable? Because of the frame layout I will need to run the wires of the ignitech tachometer output and clutch control launch wires within a 100mm of the the ign coils will I need to shield them?

[pete376403]

Just a follow up on my Ignitech questions I can get the coil pick up wires 250mm away from the ign coils all the way to the unit. Will I still need to run them into shielded cable? Because of the frame layout I will need to run the wires of the ignitech tachometer output and clutch control launch wires within a 100mm of the the ign coils will I need to shield them?

You have a length of twisted pair shielded cable - why not try it?

[diesel pig]

You have a length of twisted pair shielded cable - why not try it?

I am one of those people that can do Auto wiring but loathe doing. If I can avoid even some of it I will but if the ones that know more than me say it must be done I will.

[wobbly]

Not needed as long as you have resistor plugs and caps.

[diesel pig]

Not needed as long as you have resistor plugs and caps.

Thanks, I will get resistor plugs for it and I think the caps are resistor but I will check.

[wobbly]

You should be running race plugs in a race engine - fine wire Iridium/Platinum R7262, stronger spark, more power + 1.5 Hp in a SKUSA CR125 over a BR10EGV.
And use the blue NGK Jetski caps - way more reliable than anything else.

[F5 Dave]

Always used those as the silicone absorbs damaging vibration and water resistant by design. Electric Blue colour? Sign me up.

[diesel pig]

I all ready use the blue NGK caps - the best I have ever come across. I will look into getting some R7262's. Thanks

[Vannik]

Next installment, EngMod2T first time users:

https://www.youtube.com/watch?v=1VE4KoKDP-s

[quallman1234]

TST100 update https://youtu.be/BEu84dZHPSY?si=ODmbpar46FCy_5Mc

[koenich]

Hope they switch away from those Airsal cylinders...two Bidalot 50cc incl. their pipe and you are looking at close to 40 rear wheel HP out of the box.

[Gradella23]

TST100 update https://youtu.be/BEu84dZHPSY?si=ODmbpar46FCy_5Mc

do someone know these guys? i can probably provide a far better 50cc cylinder for them

[husaberg]

do someone know these guys? i can probably provide a far better 50cc cylinder for them
I am picking one looks like this...

Nice work, I'm curious to hear the improvements from the intercooler. I suspect if you were at 100deg IAT it will be significant.
Speaking of gearing, what size rear sprocket do you run?
and the other this...

TST100 update https://youtu.be/BEu84dZHPSY?si=ODmbpar46FCy_5Mc

[TZ350]

.

I have ordered some of these open tip EGT K type probes, I will let you know how they go:- https://www.aliexpress.com/item/1005005541111391.html?spm=a2g0o.productlist.main.1 .435570beVW07Lc&algo_pvid=65eab04f-8ad7-468a-8d5e-3e41bf6b771f&algo_exp_id=65eab04f-8ad7-468a-8d5e-3e41bf6b771f-0&pdp_ext_f=%7B%22order%22%3A%22225%22%2C%22eval%22% 3A%221%22%7D&pdp_npi=4%40dis%21NZD%2113.08%219.55%21%21%2155.02 %2140.16%21%402101ead817526243478137202eef94%21120 00033469477452%21sea%21NZ%21131128996%21X&curPageLogUid=fRtKTTCCB8tk&utparam-url=scene%3Asearch%7Cquery_from%3A

356438

[F5 Dave]

Nice work Kyle. Recognise that section of road presumably by Glen's.
Hope it is smooth enough else those engine brackets may need some more support.

Racing this weekend, be finished by then?


do someone know these guys? i can probably provide a far better 50cc cylinder for them
Be down to budget. Mostly. Get it running first.
Rules (don't start us on the rules) imply should be based on road type engine or at least not use competition engine or parts. Cylinders mimicking road spec are closer to intension. Use of fzr parts etc help case.
You could argue all day.

[TZ350]

.
356443

Rotary valve conversion and AM6 50cc cylinder on a Suzuki RG50 bottom end.

It will have a long rod and I am going to retain the cavity left by the case reed. I want as much crankcase volume as I can get.

If I can find a Benelli 250 bottom end I might be tempted to build a 100cc twin too. Those clever engineers (I am very impressed, even a little jealous) can't be allowed to have it all their own way.

AM6 cylinders have 56mm stud centers, the same as the 70's Benelli 250 twin. The 250 is just an overbored Benelli 125 twin. So the gearbox is light and ratios close, perfect.

Currently we have a Suzuki RG50 Fitted with a RV and 70cc bored out AM6 cylinder making 24rwhp. So 100cc twin using two AM6 50cc cylinders might be pretty interesting to play with.

I need a two stroke 1970's Benelli 250 twin bottom end or complete engine. Condition, not that important. If anyone locally in New Zealand has something they would sell, please PM me.

[Storbeck]

I all ready use the blue NGK caps - the best I have ever come across. I will look into getting some R7262's. Thanks

I'm searching around trying to find these blue caps, only thing I can find that night be it is discontinued. Any chance you have a link or a part number?

[koenich]

.
356443
AM6 cylinders have 56mm stud centers, the same as the 70's Benelli 250 twin.
AM6 and Derbi d50 have 52 mm space pattern, 56 mm is Derbi EBS.

[diesel pig]

I'm searching around trying to find these blue caps, only thing I can find that night be it is discontinued. Any chance you have a link or a part number?

I am Sorry. I do not have a part number , I just get them form the local Yamaha Shop.

[husaberg]

I'm searching around trying to find these blue caps, only thing I can find that night be it is discontinued. Any chance you have a link or a part number?


I am Sorry. I do not have a part number , I just get them form the local Yamaha Shop.

i am picking its these.

ngk spark plug cap R7282
https://tygaeurope.com/wp-content/uploads/2016/09/product_a_l_alg-10227b-rotated-510x383.jpg

[F5 Dave]

My blue pills look like the red pills

[wobbly]

The R7376 plug has an identical nose configuration to the stupid expensive shorty plug and cap for less than 1/4 the price.
Its only difference is the insulator length , thus it uses a " normal " resistor plug cap.

[Wos]

My blue pills look like the red pills

Red or blue...Specifications of material are the same on ngk page

[husaberg]

Red or blue...Specifications of material are the same on ngk page

But try putting the red one on a shorter plug. :)
Works either way with the shorter one.

[SwePatrick]

So, i finally made a calculated pipe for my violated SGM Kartengine.(bored out to 144cc)
Running on E85 i made the other day 48.2hp to the wheel at 12700rpm
Depending on what is correct when calculating losses it is between 51,9 or 56,7hp to the crank(my dyno reports ~10% but some says it should be 15%.

However, I ran an BR10ECS.
The diskussion above about that expensive NGK plug, is it known to make any more power than 'normal plugs'?

My plug and dynosheet, and below link to a livefeed when i was dynoing it.
Dynosheet shows before and after testing with a no calculated pipe and a calculated in Mota.

356449
356450


https://youtube.com/live/1gIgPdXmPpY?feature=share
https://youtube.com/live/1gIgPdXmPpY?feature=share

[husaberg]

Hadn't seen this before, but why stop at 4?
https://amcn.com.au/editorial/passion-project-yamaha-yzr500/

[Wos]

So, i finally made a calculated pipe for my violated SGM Kartengine.(bored out to 144cc)
Running on E85 i made the other day 48.2hp to the wheel at 12700rpm
Depending on what is correct when calculating losses it is between 51,9 or 56,7hp to the crank(my dyno reports ~10% but some says it should be 15%.

However, I ran an BR10ECS.
The diskussion above about that expensive NGK plug, is it known to make any more power than 'normal plugs'?

My plug and dynosheet, and below link to a livefeed when i was dynoing it.
Dynosheet shows before and after testing with a no calculated pipe and a calculated in Mota.

356449
356450


https://youtube.com/live/1gIgPdXmPpY?feature=share
https://youtube.com/live/1gIgPdXmPpY?feature=share

Very hidden spark Position i think

Why not trying a cheap BR10EIx?

And for a new pipe you need new ignition map to gain max out of configuration ;)

[SwePatrick]

So, i finally made a calculated pipe for my violated SGM Kartengine.(bored out to 144cc)
Running on E85 i made the other day 48.2hp to the wheel at 12700rpm
Depending on what is correct when calculating losses it is between 51,9 or 56,7hp to the crank(my dyno reports ~10% but some says it should be 15%.

However, I ran an BR10ECS.
The diskussion above about that expensive NGK plug, is it known to make any more power than 'normal plugs'?

My plug and dynosheet, and below link to a livefeed when i was dynoing it.
Dynosheet shows before and after testing with a no calculated pipe and a calculated in Mota.

356449
356450


https://youtube.com/live/1gIgPdXmPpY?feature=share
https://youtube.com/live/1gIgPdXmPpY?feature=share

I can answer myself. :)
1.5-2rwhp

356453

[SwePatrick]

Very hidden spark Position i think

Why not trying a cheap BR10EIx?

And for a new pipe you need new ignition map to gain max out of configuration ;)

So there might be more lurking you say? ;)
Timing is as enginemanufacturer says it should be, now with 58mm bore it can make use of some more i guess.
But i´ve got a lot higher compression also, to make use of the alcohol.

[Wos]

So there might be more lurking you say? ;)
Timing is as enginemanufacturer says it should be, now with 58mm bore it can make use of some more i guess.
But i´ve got a lot higher compression also, to make use of the alcohol.

My experience is

If you use another pipe, ignition timing never fits to manufakturers advice... if you do only one change in complete engine system setup...you need another ignition curve that fits to new circumstances...

2 strokes are bitches 😉

Have good times with 😀

[SwePatrick]

My experience is

If you use another pipe, ignition timing never fits to manufakturers advice... if you do only one change in complete engine system setup...you need another ignition curve that fits to new circumstances...

2 strokes are bitches 😉

Have good times with 😀

Forgot to mention that from what i can see on the old sparkplugs timingmark, there isn´t much to gain, looks dam near perfect to me =)

[Wos]

Forgot to mention that from what i can see on the old sparkplugs timingmark, there isn´t much to gain, looks dam near perfect to me =)

As i can see

Your peak power rpm changed...👍 so you should change 15 degree ignition point to this....best using programmable and set ignition correct at new resonance beginning too...this is gaining much wider powerband ;)

[wobbly]

I would not use an EIX plug if they were free.
When run even close to deto, the ceramic shell around the center electrode would immediately crack, then fall of.
Saw many, many engines killed by those bloody things - they are cheap for a reason.

The dyno / track work has been done hundreds of times before, in many race engines.
NGK R7376 Iridium - Platinum or the expensive shorty equivalent, simply makes more power and is way more reliable than any other plug ( including the ND Honda part number ) - end of story.

The short body plug was originally configured for Honda racebikes with the front cylinder too close to the radiator, but in karting everybody uses them for extra elbow room
plus of course the proven power advantage.

[Flettner]

https://youtube.com/shorts/YVAGrbG3MfI?si=96VUzrVRnbH3sraE

Powervalve operation, twin ports.
How far round should the transfers come?

[Frits Overmars]

https://youtube.com/shorts/YVAGrbG3MfI?si=96VUzrVRnbH3sraE
Powervalve operation, twin ports.
How far round should the transfers come?They look fine to me, assuming they are aimed backward strongly enough.

[Flettner]

They look fine to me, assuming they are aimed backward strongly enough.

Seen here .........

[Frits Overmars]

...........:niceone:

[Frits Overmars]

Aren't you guys getting tired of having to look at my thumb for over a week now? I know I am :p

[Wos]

Frits, your personal thump is such a beauty:2thumbsup:)

Does your thump like to write? ��

So i tell you...rotax 124 had its rollout...had two eduro classic races...think its the strongest 124 rotax under the competitors ��

Inlet timing we achived a little to opening 145 closing to 85 and found litte improofment in rpm to 10300.

Pipes max is 8500/ 550 ms...

Think we have bonce back anyway, as we kept the 200 mm inlet tunnel...no way to adapt carb directly in enduro use.

Carb is very moody as you promised a year ago ;)... two jet sices between everything fine...and stuttering in higher revs / wont reve with 2 numbers richer main.

There is a tendency to enrich i think, cause of bonce back...

Nex we want to try closing 90 after tdc.

What do you think Frits?...step in right direction?
Step to small...to big?

Tell it all your fingers... special thanks to your thumps:killingme ��

Viele Grüße! ��

Wolfgang...nearby liedolsheim ;)

[ApolloMotoMoto]

Aren't you guys getting tired of having to look at my thumb for over a week now? I know I am :p

Ah ha! We've caught you now...

Openly admitting he enjoys answering endless questions about our favorite little pandoras box?

Or at the very least open amaussment, maybe even some kind of schadenfreude as we all discover our own ignorances.

It's as if Frits has -as many before him had, and as I imagine he hopes continues into the future- bushwhacked a fairly clear path through some fairly dark forest, and is now waiting paitiently for others to discover this neatly cleared path, walk it's course, and choose to pick up the tools for themselves to continue even deeper within the mystery.

Let's not disappoint him!

[ApolloMotoMoto]

So... Next on my list of things to do for 9x identical race engines I am preparing for Octobers race event is preparing some cranks.

We have Italkit rod kits that we sourced directly from Italkit.

I'll be pressing apart the stock cranks and pressing them back together with all the Italkit parts, crankpin, rod and bearing.

The main reason being the stock bearing radial clearance is way too big.

Stock big end bearing radial clearance is in the range of 0.050mm - 0.070mm total radial clearance.

Cranakpin is 16mm, rod big end is 22mm.

After everything I have researched, I have come up with values for an "ideal" range at these diameters being more like 0.035 - 0.045mm allowable total radial clearance for brand new parts, with an absolute service limit of 0.06-0.08mm depending on the engine manufacturer (reviewing 80cc 2 stroke service manuals because the diameters are similar).


What are your thoughts for the ideal bearing radial clearance for the big end bearing, given my diameters?

Also, how "true" would you be trying to get your race cranks after pressing?

If anyone has any techniques, tips, or considerations to share on the general process of pressing 2 stroke single cranks, I would appreciate it.

Attached are some images of the crank press tool I just acquired, I have a fairly standard 20 ton hydraulic shop press to do the pressing.

Given the tools, does it look like I am setup for success or are there any pitfalls I am not accounting for that need to be addressed with this tooling setup?

What is your preferred method of checking runout?

Should I recut the "center" featueres on the shaft ends of each half when I have them apart so I can check runout between centers?

[Frits Overmars]

rotax 124 had its rollout....think its the strongest 124 rotax under the competitors.
Inlet timing we achieved a little to opening 145 closing to 85 and found little improvement in rpm to 10300.
Think we have bounce-back anyway, as we kept the 200 mm inlet tunnel...no way to adapt carb directly in enduro use.
Carb is very moody as you promised a year ago....There is a tendency to enrich i think, cause of bounce-back.
Next we want to try closing 90 after tdc. What do you think Frits?...step in right direction? Step too small, too big?
356482
With that long inlet tract there is a very real chance of bounce-back. Closing the inlet disk 90° after TDC or even later could help. Alas, the fact that the inlet disk is hidden behind the clutch makes experimenting rather cumbersome.

For those who'd like to read a bit more about bounce-back here is a text that I wrote some time ago (and that you can also find at https://onedrive.live.com/?authkey=%21ABfdzwPhevl4qMs&id=8DD58EFB966FB3DC%216309&cid=8DD58EFB966FB3DC )
=====================================
In all inlet systems the inlet flow accelerates as long as the pressure upstream of the inlet tract is higher than the downstream pressure.
When both pressures are equal the flow has reached its maximum velocity and because mixture keeps entering the crankcase, the crankcase pressure rises above the upstream pressure and this rising pressure gently slows the flow down to a standstill (or suddenly instead of gently if the inlet port closes too soon, which can happen in both piston port and rotary induction systems).
In any case, the pressure at the crankcase side of the inlet tract will then be higher than the pressure at the bell mouth, and mixture will start flowing back towards the free world. The extent of this back-flow may be so small that it is not noticeable at the bell mouth, but it is happening nevertheless. Reed valve systems do it just as much as other inlet control systems.

If the inlet timing does not suit the rpm, we can either experience blow-back if the inlet port closes too late, or bounce-back if the inlet port closes too early.

Blown-back mixture is mixture that initially entered the crankcase but then reversed its flow direction because of the rising crankcase pressure while the inlet was still open.
This rising crankcase pressure resulting in flow reversal has rather little to do with the piston moving down after TDC. It can even happen before TDC if the Helmholtz frequency of the inlet system is too high for the engine revs (low revs, big carb diameter, short inlet tract, small case volume).

Bounce-back occurs if the inlet is slammed shut while the mixture is still on its way to the crankcase. The mixture flow then collides with the inlet disk or the piston, causing a large local pressure rise at the free world side of the disk or piston. Bounce-back may be hardly noticeable, but on the other hand it can be much more vicious than blow-back.

As an experiment I once put a 200 mm elongation tube between the carb and the rotary inlet cover of a 125 cc Rotax.
It lowered the Helmholtz frequency of the inlet system so much that inlet flow velocity was still near its maximum when the inlet disk closed. Bounce-back was so severe that within seconds the dyno room was completely fogged up with mixture. It frightened me to death; a spark would have been enough to blow the roof off.

https://www.kiwibiker.co.nz/forums/text/plain;base64,SW4gYWxsIGlubGV0IHN5c3RlbXMgdGhlIGlub GV0IGZsb3cgYWNjZWxlcmF0ZXMgYXMgbG9uZyBhcyB0aGUgcHJ lc3N1cmUgdXBzdHJlYW0gb2YgdGhlIGlubGV0IHRyYWN0IGlzI GhpZ2hlciB0aGFuIHRoZSBkb3duc3RyZWFtIHByZXNzdXJlLg0 KV2hlbiBib3RoIHByZXNzdXJlcyBhcmUgZXF1YWwgdGhlIGZsb 3cgaGFzIHJlYWNoZWQgaXRzIG1heGltdW0gdmVsb2NpdHkgYW5 kIGJlY2F1c2UgbWl4dHVyZSBrZWVwcyBlbnRlcmluZyB0aGUgY 3JhbmtjYXNlLCB0aGUgY3JhbmtjYXNlIHByZXNzdXJlIHJpc2V zIGFib3ZlIHRoZSB1cHN0cmVhbSBwcmVzc3VyZSBhbmQgdGhpc yByaXNpbmcgcHJlc3N1cmUgZ2VudGx5IHNsb3dzIHRoZSBmbG9 3IGRvd24gdG8gYSBzdGFuZHN0aWxsIChvciBzdWRkZW5seSBpb nN0ZWFkIG9mIGdlbnRseSBpZiB0aGUgaW5sZXQgcG9ydCBjbG9 zZXMgdG9vIHNvb24sIHdoaWNoIGNhbiBoYXBwZW4gaW4gYm90a CBwaXN0b24gcG9ydCBhbmQgcm90YXJ5IGluZHVjdGlvbiBzeXN 0ZW1zKS4NCkluIGFueSBjYXNlLCB0aGUgcHJlc3N1cmUgYXQgd GhlIGNyYW5rY2FzZSBzaWRlIG9mIHRoZSBpbmxldCB0cmFjdCB 3aWxsIHRoZW4gYmUgaGlnaGVyIHRoYW4gdGhlIHByZXNzdXJlI GF0IHRoZSBiZWxsIG1vdXRoLCBhbmQgbWl4dHVyZSB3aWxsIHN 0YXJ0IGZsb3dpbmcgYmFjayB0b3dhcmRzIHRoZSBmcmVlIHdvc mxkLiBUaGUgZXh0ZW50IG9mIHRoaXMgYmFjay1mbG93IG1heSB iZSBzbyBzbWFsbCB0aGF0IGl0IGlzIG5vdCBub3RpY2VhYmxlI GF0IHRoZSBiZWxsIG1vdXRoLCBidXQgaXQgaXMgaGFwcGVuaW5 nIG5ldmVydGhlbGVzcy4gUmVlZCB2YWx2ZSBzeXN0ZW1zIGRvI Gl0IGp1c3QgYXMgbXVjaCBhcyBvdGhlciBpbmxldCBjb250cm9 sIHN5c3RlbXMuDQoNCklmIHRoZSBlbmdpbmUgcnBtIGRvZXMgb m90IHN1aXQgdGhlIGlubGV0IHRpbWluZywgd2UgY2FuIGVpdGh lciBleHBlcmllbmNlIGJsb3ctYmFjayBpZiB0aGUgaW5sZXQgc G9ydCBjbG9zZXMgdG9vIGxhdGUsIG9yIGJvdW5jZS1iYWNrIGl mIHRoZSBpbmxldCBwb3J0IGNsb3NlcyB0b28gZWFybHkuDQoNC kJsb3duLWJhY2sgbWl4dHVyZSBpcyBtaXh0dXJlIHRoYXQgaW5 pdGlhbGx5IGVudGVyZWQgdGhlIGNyYW5rY2FzZSBidXQgdGhlb iByZXZlcnNlZCBpdHMgZmxvdyBkaXJlY3Rpb24gYmVjYXVzZSB vZiB0aGUgcmlzaW5nIGNyYW5rY2FzZSBwcmVzc3VyZSB3aGlsZ SB0aGUgaW5sZXQgd2FzIHN0aWxsIG9wZW4uDQpUaGlzIHJpc2l uZyBjcmFua2Nhc2UgcHJlc3N1cmUgcmVzdWx0aW5nIGluIGZsb 3cgcmV2ZXJzYWwgaGFzIHJhdGhlciBsaXR0bGUgdG8gZG8gd2l 0aCB0aGUgcGlzdG9uIG1vdmluZyBkb3duIGFmdGVyIFREQy4gS XQgY2FuIGV2ZW4gaGFwcGVuIGJlZm9yZSBUREMgaWYgdGhlIEh lbG1ob2x0eiBmcmVxdWVuY3kgb2YgdGhlIGlubGV0IHN5c3Rlb SBpcyB0b28gaGlnaCBmb3IgdGhlIGVuZ2luZSByZXZzIChsb3c gcmV2cywgYmlnIGNhcmIgZGlhbWV0ZXIsIHNob3J0IGlubGV0I HRyYWN0LCBzbWFsbCBjYXNlIHZvbHVtZSkuDQoNCkJvdW5jZS1 iYWNrIG9jY3VycyBpZiB0aGUgaW5sZXQgaXMgc2xhbW1lZCBza HV0IHdoaWxlIHRoZSBtaXh0dXJlIGlzIHN0aWxsIG9uIGl0cyB 3YXkgdG8gdGhlIGNyYW5rY2FzZS4gVGhlIG1peHR1cmUgZmxvd yB0aGVuIGNvbGxpZGVzIHdpdGggdGhlIGlubGV0IGRpc2sgb3I gdGhlIHBpc3RvbiwgY2F1c2luZyBhIGxhcmdlIGxvY2FsIHByZ XNzdXJlIHJpc2UgYXQgdGhlIGZyZWUgd29ybGQgc2lkZSBvZiB 0aGUgZGlzayBvciBwaXN0b24uIEJvdW5jZS1iYWNrIG1heSBiZ SBoYXJkbHkgbm90aWNlYWJsZSwgYnV0IG9uIHRoZSBvdGhlciB oYW5kIGl0IGNhbiBiZSBtdWNoIG1vcmUgdmljaW91cyB0aGFuI GJsb3ctYmFjay4NCg0KQXMgYW4gZXhwZXJpbWVudCBJIG9uY2U gcHV0IGEgMjAwIG1tIGVsb25nYXRpb24gdHViZSBiZXR3ZWVuI HRoZSBjYXJiIGFuZCB0aGUgcm90YXJ5IGlubGV0IGNvdmVyIG9 mIGEgMTI1IGNjIFJvdGF4Lg0KSXQgbG93ZXJlZCB0aGUgSGVsb WhvbHR6IGZyZXF1ZW5jeSBvZiB0aGUgaW5sZXQgc3lzdGVtIHN vIG11Y2ggdGhhdCBpbmxldCBmbG93IHZlbG9jaXR5IHdhcyBzd GlsbCBuZWFyIGl0cyBtYXhpbXVtIHdoZW4gdGhlIGlubGV0IGR pc2sgY2xvc2VkLiBCb3VuY2UtYmFjayB3YXMgc28gc2V2ZXJlI HRoYXQgd2l0aGluIHNlY29uZHMgdGhlIGR5bm8gcm9vbSB3YXM gY29tcGxldGVseSBmb2dnZWQgdXAgd2l0aCBtaXh0dXJlLiBJd CBmcmlnaHRlbmVkIG1lIHRvIGRlYXRoOyBhIHNwYXJrIHdvdWx kIGhhdmUgYmVlbiBlbm91Z2ggdG8gYmxvdyB0aGUgcm9vZiBvZ mYu

[Wos]

Thanks a lot Frits!!

Yes Frits...little nightmare to change disc...most work is to remove old dry silikon sealing of cover and case 😉

Now i am looking forward to do this work 😉 as we can expect some more progress.

Think 5 degree steps to recognice a diffrence will be practical steps in our konfig Frits !?

Thanks! ;)

Grüße Wolfgang

[wobbly]

When the Rotax 256 was introduced it had 135/85. Going to 88* was a huge jump in peak and overev power.
Then going to 138 was an improvement, but any more and the mid range tuning became very difficult, with no more power to be had.
Going to 90* only gained about 0.75 Hp in the overev, but lost nearly 2 Hp at 10,000.
I believe going in 2* steps is plenty.

[husaberg]

As an experiment I once put a 200 mm elongation tube between the carb and the rotary inlet cover of a 125 cc Rotax.
It lowered the Helmholtz frequency of the inlet system so much that inlet flow velocity was still near its maximum when the inlet disk closed. Bounce-back was so severe that within seconds the dyno room was completely fogged up with mixture. It frightened me to death; a spark would have been enough to blow the roof off.
I can't remember the circumstances but Pops Yoshimura wore some pretty bad scars from dyno fire.

https://www.youtube.com/watch?v=JxqX5tp2JZw
video reminds me of the last time Brock qualified a car on Pole at Bathurst it was with a CO2 extinguisher, which was part of the on-board fire suppression, It was only after the quick lap time was set that it was figured out that Peters was squirting directly on the outside of the intercooler of the Cosworth Seirra he was running at the time. Clever but deemed against the spirit of the rules by teams assosication (not the stewards. )He got a 5k fine but it was a full second quicker than the nearest rival.

https://www.youtube.com/watch?v=RH-KXvyjkdk

[F5 Dave]

I used to put the fire extinguisher by the door. My health and safety talk to participants went something along the lines of. Don't stand anywhere that a wayward bike that breaks loose will go and for godsake don't stand behind the spinning wheel or where you can touch the drum.
If there's a fire, don't stand between me and the exit. I will use you for traction.

[Wos]

When the Rotax 256 was introduced it had 135/85. Going to 88* was a huge jump in peak and overev power.
Then going to 138 was an improvement, but any more and the mid range tuning became very difficult, with no more power to be had.
Going to 90* only gained about 0.75 Hp in the overev, but lost nearly 2 Hp at 10,000.
I believe going in 2* steps is plenty.

Thanks Wobbly!! ;)

If i am right...256 had carbs direct on inlet of rotary cover???

Think this config is not compareable to setup with fucking long inlet tunnel at 124 like we have.

The accelerated moving mass in very long inlet duct needs a very late closing time of disc, if you want to avoid the bounce back Frits told us very impressiv.

The bouncing wave runs back to carb and enriches second time the mixture i bet :)

5 degree steps we did in the past...changed only a little

But for sure, ther will be a point were changing 2 degree matters...

And yes...in low reve use you should not open to early, cause carb need a level of suction / flow to start its work i think

But in case of long inlet duct, you first have to move the big masses in duct !? So i think there should be diffrent opening timings between short and long inlet konfigs!?

Bike is rideable nearly from idle in trial Situations as I kept ignition advance low there

Begin of resonance is about 5000, good for accelerate out of sharp slow corners.
Power usable from 5000 to 9500 and overev to 10300... in the moment ;)



Thanks ...every support welcome !!!:2thumbsup

Grüße Wolfgang

[lohring]

Below are two peoples' thoughts on crank pin assembly. The jig I built is like the first one and works very well with little or no truing needed.

Lohring Miller

356484

[ApolloMotoMoto]

Below are two peoples' thoughts on crank pin assembly. The jig I built is like the first one and works very well with little or no truing needed.

Lohring Miller

356484

Thank you very much!

[Wos]

;) in Classic enduro Championship race at Nordhausen/ Germany... have a look on the brick

356485

[Flettner]

Aren't you guys getting tired of having to look at my thumb for over a week now? I know I am :p

Whenever I post, it kills this thread ... the kiss of thread death.
😁

[Frits Overmars]

Whenever I post, it kills this thread ... the kiss of thread death 😁If you really have that power, I can think of a few other forums you could visit :whistle:

[Condyn]

Hello fellow sufferers, I have been stumped by something for a bit now. I drag race an air cooled snowmobile which uses a CVT (not sure of relevance but just to be complete I included)
I always have excessive wash width of 10mm on a 69.5mm bore, and rich plugs along with a chalky white thread base ring.
My engine responds well to jet changes, however when I go down a size from my known sweet spot EGT, the EGT increases again in a normal increment. This narrows my wash pattern, but the engine has a lean feeling on the warm up stand and my Elapsed time always gets worse. I have 130 logged passes and have rider awareness with this machine. It is a front runner (but I want it perfect lol)

This almost suggests to me that there is a mismatch with the compression ratio and or ignition timing at peak operating rpm on the cvt. Maybe something else?

-Comp ratio 15.5:1
-fuel c12
-ignition straight line 15 degrees
-spark plug Br9es
-stinger diameter 23.6x300 (no nozzle currently because it has always performed better better with full length stingers, maybe a much smaller nozzle than I have used is in order)

Am I beating myself up for nothing, or does anyone have suggestions to make my setup more synergetic?

[lohring]

The part of the text down to where it says "Jim Allen" is from Jim. The rest of the text is from Bill Givens. I like Jim's fixture, but both people have great insights. Jim mostly rebuilt small engines (26 cc) while Bill rebuilt larger engines.

Lohring Miller

[Frits Overmars]

The part of the text down to where it says "Jim Allen" is from Jim. The rest of the text is from Bill Givens. I like Jim's fixture, but both people have great insights. Jim mostly rebuilt small engines (26 cc) while Bill rebuilt larger engines.
Lohring MillerThank you Lohring.

[wobbly]

Condyn, what is the actual cylinder displacement - ie what is the stroke.
15.5 com is nothing for C12.
This is 2025, why are you using a straight line ignition from the 1970's.
Also a spark plug from a lawn mower.
What is the " sweet " EGT at what rpm, is this derived from a dyno run and if so what power is it making.
Many more questions to get some analysis, but this is a start.

[Condyn]

Wobbly, it is 452cc. 69.5x59.6 I use the straightline ignition because at many venues that I race, the rules state that a stock ignition must be installed. It is a vintage class from the 70’s. The egt is right at 650c at 9500 rpm, 3x bore from the piston. No, I am familiar with your logical jet selection chart, however I did not have the chance to install the probes on the dyno during the last session.

The field tests tell me that when I jet down it goes slower. I looked again with my wash light last night and I might be wrong on the wash width. It looked more narrow (around 5-6mm) I am going to take the heads off tonight to get better eyes on it. The piece that keeps me up at night is the egt continues to rise with a down jet (650 up to 670) however it makes a pop on the warm up stand at full rev and makes my pass slower by a tenth every time. Admittedly I do not always have the cht hooked up so I am not aware what the cht is doing when I jet down.

Edit, HP 104 to the crank on a low reading dyno. How low? I do not know, but I would guess 3% based on others results.

[Storbeck]

Wobbly, it is 452cc. 69.5x59.6 I use the straightline ignition because at many venues that I race, the rules state that a stock ignition must be installed. It is a vintage class from the 70’s. The egt is right at 650c at 9500 rpm, 3x bore from the piston. No, I am familiar with your logical jet selection chart, however I did not have the chance to install the probes on the dyno during the last session.

The field tests tell me that when I jet down it goes slower. I looked again with my wash light last night and I might be wrong on the wash width. It looked more narrow (around 5-6mm) I am going to take the heads off tonight to get better eyes on it. The piece that keeps me up at night is the egt continues to rise with a down jet (650 up to 670) however it makes a pop on the warm up stand at full rev and makes my pass slower by a tenth every time. Admittedly I do not always have the cht hooked up so I am not aware what the cht is doing when I jet down.

Edit, HP 104 to the crank on a low reading dyno. How low? I do not know, but I would guess 3% based on others results.


Slower in ET or slower in MPH?

Im wondering if the jetting down is increasing eghaust gas temp and therefore increasing the rpm at which you make peak power to the point that it is no longer in harmony with your clutching (CVT tuning, they're not really clutches but snowmobile people call them "clutches") , or to the point that the pipe is trying to rev higher than your ports will let it (?)

[Viking]

Deleted due to dubbelpost

[wobbly]

Show us a hi res of the piston.
I was going to say exactly what Storbeck said - I believe that the " tuning " is OK, as the EGT goes up as per normal, but that then puts peak power into the rpm
where you would have had unused overev previously.
This would indicate that a shorter " gearing" could be used, and this would make you faster due to the torque multiplication.
To test if you are close to pushing the outer boundaries at all, I would be looking at adding some static timing with the lean EGT setting.
I believe 1* to 2* would pull back the EGT to the original " best power " rpm number.
You can find out how close you are by then leaning down again, and if the EGT flatlines, that is the deto limit.
If this is the case, then its a matter of making a decision to go back on the timing, and add some com - as I said your com seems very conservative for 110 octane.
But - the leaner/advanced setup may be faster, you wont know without the dyno data to clutch it correctly.
PS - cht tells you nothing about the tune - just the under plug temp, BUT most cht will go spastic when getting into deto - but you already knew that as the EGT had already flatlined or dropped.

[koba]

Incorporating the changes wobbly has suggested in the TF125 model and re-running the sim has been very interesting.
(See suggestions over the last few pages)

This is without anything too major, IE setting the transfer heights but not changing angles etc.

Here is how this compares to the model I was using before (With my over-stiff reed petal mistake removed).


356494

356495

[koba]

I forgot to change the pipe entry from 34mm to 36mm.

I have re-run it and included all 4 versions for comparison.

356497

[ApolloMotoMoto]

So, I have a pile of cylinders I just finished ported that I am about to send off to Millenium Technologies to strip out the stock chrome bores and re-plate with Nikasil. Happy days :)

I just got off the phone with the guys at Millenium and they tell me they can do "round" port edges or "45 degree" port edges, with a defined profile view drawing to establish the desired chamfer geometry for the work order.

I have always done this myself, and I try to go for a nicely "rounded" edge with a radius of ABOUT 0.6 - 0.8mm for all port edges.

Some recent light reading has skimmed across the notion that the transfer port edges should NOT be chamfered because the chamfered edge will cause the incomming transfer stream to spread/spray out like a fan-nozzle on a garden hoze instead of maintaining the intended tragectory from the transfer port axial/radial aiming angles.

Instead, the transfer port edges should "just" be de-burred with the edge "broken" but not chamfered.


Given this idea;

How would you go about defining that on a work order?

Should I just tell them NOT to touch the transfer port edges and do it myself?

Perhaps put "de-burr only/ no chamfer" on the work order?

I have the rexcut cotton mounted points that Wayne recommended for port edge chamfering of Nikasil cylinders without chipping, but I would rather let Millenium do the work.


How about the exhaust port edge chamfer?

What radius size chamfer should I be calling out for the exhaust port of a 52mm jug?
-70% width single exhaust port with FOS Concept port shape

[TZ350]

Incorporating the changes wobbly has suggested in the TF125 model and re-running the sim has been very interesting.

356494



Hi Koba. Rick Ford was running an air cooled TF/TS125 with 22rwhp and that proved really reliable with little heat fade. We could get much more hp out of our aircooled GP125's but the heat fade made the extra power self defeating. We tried all sorts of tricks, like ceramic coatings and extra copper fins. The copper went all the way in to form the squish band. But air cooling was just not up to handling the waste heat from the higher HP.

356498 356500

[Frits Overmars]

So, I have a pile of cylinders I just finished ported that I am about to send off to Millenium Technologies to strip out the stock chrome bores and re-plate with Nikasil. Happy days
I just got off the phone with the guys at Millenium and they tell me they can do "round" port edges or "45 degree" port edges, with a defined profile view drawing to establish the desired chamfer geometry for the work order.
I have always done this myself, and I try to go for a nicely "rounded" edge with a radius of ABOUT 0.6 - 0.8mm for all port edges.
Some recent light reading has skimmed across the notion that the transfer port edges should NOT be chamfered because the chamfered edge will cause the incomming transfer stream to spread/spray out like a fan-nozzle on a garden hoze instead of maintaining the intended tragectory from the transfer port axial/radial aiming angles.
Instead, the transfer port edges should "just" be de-burred with the edge "broken" but not chamfered.
Given this idea;
How would you go about defining that on a work order?
Should I just tell them NOT to touch the transfer port edges and do it myself?
Perhaps put "de-burr only/ no chamfer" on the work order?
I have the rexcut cotton mounted points that Wayne recommended for port edge chamfering of Nikasil cylinders without chipping, but I would rather let Millenium do the work.
How about the exhaust port edge chamfer?
What radius size chamfer should I be calling out for the exhaust port of a 52mm jug?
-70% width single exhaust port with FOS Concept port shapeTell them NOT to touch the transfer port edges no matter what.
Jan Thiel once got a set of race-winning cylinders back from replating, that had to go straight into the bin: all ports chamfered in spite of strict orders not to do, and all power irretrievably gone. Needless to say those were the last cylinders ever to go to that replating firm.

The exhaust port top and bottom edges should be radiused but the side edges should not be touched but only deburred, which you can do yourself after replating.

I give the exhaust top edge a radius of 5% of the stroke which is a fair bit more than you proposed. It does alter the exhaust timing so you must that take into account before shaping the port.
356499

The drawing below shows the safe port shape for the benefit of piston longevity.
356501

[wobbly]

My advise is to demand they dont touch the cylinder at all, and do the edge break radius with Rexcut on the transfers prior to plating, this then means you can remove the flashed chrome inside the port
and do the same edge break on the chromed corner.
The Exhaust port as Frits says only needs the edge breaking on the vertical sides, before and after plating.
The ring guiding top/bottom chamfers should also be done before chrome, and I do a 15* angle around 0.5mm high in the alloy that is redone to around 1/2 that height with a Rexcut radius on the bottom timing edge after plating.
Using the FOS port shape ameliorates many of the issues encountered with port edge chamfers, so its then nowhere near as critical as many believe.

[Condyn]

Storbeck, that was a good thought process, however it drops both et and mph when I go one leaner on jet from my happy egt zone. I had to study my notes and logs again because I thought for sure you had it. We also cannot forget the tell tale pop on the warm up stand when I go too lean.

Wobbly, thank you for the advice with minimal information on my tune. I will try the timing advice after my next race as I have to move the stator. This time I will mark it per degree so I can do it in the field on the fly. Here is a photo of my wash from the last test session two weeks ago where I set my personal best ET. At the end of the run I have to turn around and blip back to the staging area so take that into consideration. It is a 4 transfer, single exhaust, piston controlled inlet turd.

[bad'rule]

*But air cooling was just not up to handling the waste heat from the higher HP. *
Hiya
Tz, have you thought of adding JetCool on them.Later Suzukies Cubs bike they all having these feature on their engine. It's a fan being skru to the mags.The air stream to cools those cylinder and the end had two holes aim to lower case of the engine.
You may search for suzuki RC 80,100 or the last of those Cubs with upward cylinder is RU or RG 110 sport, RGV120 .
Here's how their Mags cover looks

https://uploads.tapatalk-cdn.com/20250806/a8e69b6d52725b8dc629cab30b5b8ab2.jpg

[wobbly]

Condyn, the pop scenario is what KZ Kart tuners have used for years to " tune " their engines as to most all, EGT is voodoo shit.
The engines normally run to about 14500 on track, and in the pit, when the throttle is nailed and held open, if the main is correct it will hold 15500 popping like mad.
This practice has now been banned by the CIK due to " noise ".
So I think you are seeing the same thing, if you are referring to " popping" at full throttle.
But as I have explained a thousand times, EGT tells you everything you need to dial in to the edge of deto.

[Viking]

As a new member to this forum I start with a short presentation.
I tuned racing engines and built expansion chambers for about 50 snowmobiles and MX-bikes some thirty years ago.
Then work-life get in the way...
Now I´m aiming for retirement, and a return to two stroke tuning.
Started to learn simulation with EngMod2T, and became addicted, so it´s very hard to stop.
But the snowmobile must out on the racing track, therefore the simulation has to end.

What do Wobbly say?
Can I stop the simulation and be satisfied,
or is there some improvements that can be done?
(See attached picture of the results.)
The engine is based on a fan cooled 2-cylinder 400cc unit I built.
Back in the days it had 83hp on the dyno.

[F5 Dave]

That shit used to piss me off. You're trying to think/relax/fix your bike and some kun is revving the tits off his cold kart engine whilst on a stand with the wheels going 100mph at face level to junior wandering around the pits (it's a family affair) ready to rip it off and spit it to Invercargill.

[ApolloMotoMoto]

Tell them NOT to touch the transfer port edges no matter what.



My advise is to demand they dont touch the cylinder at all


Somehow I kind of knew thats what you were going to say, but I do sincerely enjoy an extra bit of confidence when I get the chance to hear it from the horses mouth.

Thank you for the recommendations, I shall study and implement them!

The port-edge chamfering I got back from PowerSeal was... attrocious, in a word. PowerSeal also said they could not hone my cylinder as there was too large of a gap between the skirts on the sides where the transfer feeds are.... the stones were "jumping around" when the hone got down to the area where the side gaps in the skirt are.

Hence my move to Millenium, who, after explaining the honing issue to them seemed to understand that my cylinders would likely be a problem for a 4 stone mandrel, but they said they have an in-house built 8-stone mandrel that will work for my bore size, and they are confident they can successfully hone my cylinders.



The drawing below shows the safe port shape for the benefit of piston longevity.



Using the FOS port shape ameliorates many of the issues encountered with port edge chamfers, so its then nowhere near as critical as many believe.

It took me a little while to fully understand how to implement the geometry from the picture as a function of my 52mm bore size (which I am assuming is close enough to the bore size those values are "tuned" for that I should be pretty safe), but I have been using this shape in any cylinder I port for nearly 10 years now. Originally I literally just copy-pasted the image from the drawing and scaled it to fit my application, but I now know how to properly build the "multi-radius" shape for a given application.

I have been cutting the exhaust ports to 70% width using this shape for exactly as much time and have yet to have a single "ring snag" event in any engine I have ported. Which is a testament to the statements above, the shape itself largely ameliorates ring-snag worries at 70% port width.

Thanks again for all the sharing of information.


This place is a hidden gem among the near infinite layers of "the internet".

[ApolloMotoMoto]

I give the exhaust top edge a radius of 5% of the stroke which is a fair bit more than you proposed. It does alter the exhaust timing so you must that take into account before shaping the port.
356499

...in all cases?


I have bumped into this idea a few times, but it recently came up on the EngMod2T users group:



Has anyone tested/documented and created formulas associated with radiusing the top edge of the exhaust port? Power range and HP gains? I have found a lot of benefit on an engine I did recently.

Wayne replies...



Jonathan Raulo , you have to realize this workaround was developed by Jan to ameliorate the negative effects of a flawed pipe design ( mandated by his boss ) that lacked top end power.

If you look at the raw STA numbers of that Aprilia the transfers were around 10% ahead of the Exhaust Blowdown capability, and Jans method of increasing the main ports Cd was an elegant solution at the time. But the natural down side of that **gradual ramp up** of wave amplitude at EPO would be to reduce the depression efficiency at BDC, where it really matters.

I have discussed this with Jan, and tested the radius in a KZ, the result being that I now believe that if you found an advantage with the radius, you were seeing a swings and roundabout effect of one element partially counteracting the other. It actually indicated the engine was lacking Blowdown.

The much more effective fix is to do something definitive about that issue, not use Jans band aid, but genius approach.


The back and forth discussion continues, I will share some more of Wayne's points:


In the Aprilia, as I noted above, the engine was Blowdown limited by around 10%, and as soon as this was helped by the radius increasing the port Cd - power went up.

I tested the idea in a KZ cylinder ( 25* roof ) that had won the Euro and World Titles a couple of years ago. This engine was always Blowdown limited, and the radius added just over 1Hp from the upper front side into the overev. Grinding out the radius and lifting the port to where that radius started , added another 1.5Hp.This made the Blowdown and Transfer STA all but equal. It now lacked the same amount of power down at 10,000 rpm, but in the Aprilia with a PV on the main port this would not have happened.

What do I mean by **gradual ramp up** - this describes what occurs in the EPO phase when the timing edge is radiused - the area increase gradually.

The total energy in the wave of a radiused or sharp timing geometry is the same, but the radiused edge waves amplitude is reduced, and smeared out in time.

This exact same thing occurs when in the past tuners have tried lifting the Aux up incrementally. Peak power rises, at the expense of band width right up to the point where the are coincident, then power drops everywhere. This is due to the two effects of lower amplitude time smearing plus the huge difference in path length of the main and Aux wave fronts.

Again I reiterate, the radiused timing edge was a genius band aid by Jan, but actually correcting the fault ( lack of Blowdown ) makes more power in a fully optimized scenario. As Jan said he now regrets not knowing the STA numbers as his first reaction would have been to lower the transfers.



So;

Is the 5% of stroke radius that Frits just recommended exactly what was done in the Aprilia RSA engine?

Frits:

Do you use this radius after you have "balanced" the blowdown and transfer STA numbers, or do you have to "account" for the blowdown boosting effect of the radius in order to properly balance the blowdown and transfer STA when using a radius timing edge?

How do you calculate the Blowdown STA increase that will result from the radius?

Given the "story" of the radius as presented by Wayne above, why do you continue to use it?

Wayne:

What are your thoughts on implementing the radius timing edge in my case?

I have a single exhaust port cylinder that is pretty severly blowdown limited because of this.

I have the ability to create plenty of Transfer STA to balance with the blowdown STA I can get with a 70% single port using the FOS 'multi-radius' shape.

IF I were to use the radius, it would seem to me that I could "cheat" a little bit more Blowdown STA out of my single port without making it physically wider or taller.

If I were to then tweak the transfer side STA to balance with this "radius boosted" Blowdown STA number, I am now "ahead of the game" compared to a sharp timing edge port of the same height and width with less Blowdown STA, and thus less Transfer STA to balance with it.

Oops! -I almost forgot the impact of the "wave energy smearing" effect.

So, what do you think Wayne, does the "smeared" wave energy of the radius timing edge negate the net Blowdown/Transfer STA improvement from using the radius?
-assuming each one has a pipe designed to "complement" their respective regimes
-and assuming in both cases the ACTUAL blowdown FLOW STA is in balance with the Transfer STA

[Frits Overmars]

Is the 5% of stroke radius that Frits just recommended exactly what was done in the Aprilia RSA engine?Pretty much. The exhaust top edge radius in the RSA (and in the latest RSW version) was 3,5 mm but it did not blend tangentially into the bore, which would have been rather challenging for CNC programming due to the elliptical shape of the port and the curvature of the bore.
Instead, this top edge radius center was slightly offset towards the cylinder bore center, which had the same effect as a fully-tangential radius of 2.5 mm.


Do you use this radius after you have "balanced" the blowdown and transfer STA numbers, or do you have to "account" for the blowdown boosting effect of the radius in order to properly balance the blowdown and transfer STA when using a radius timing edge?If I were to balance the angle.area values before applying the radius, applying the radius afterwards would upset the balance, so....


How do you calculate the Blowdown STA increase that will result from the radius?Calculating the blowdown angle.area is both a geometric and a gasdynamical challenge. I apply not only a timing radius to the exhaust port top edge with its elliptical shape, but also a timing radius to the piston top edge. These radii affect the blowdown cross-flow area but also the flow coefficient, which cannot be taken into account in EngMod.
The initial supercritical blowdown flow between the port edge radius and the piston edge radius experiences a partial DeLaval effect and the resulting energy conservation, compared to flow through a sharp-edged orifice, more than compensates the “smearing effect” that Wobbly refers to.


Given the "story" of the radius as presented by Wayne above, why do you continue to use it?Your question suggests that I started using the exhaust top radius after Jan had applied it. But Jan started using that solution in the early 2000s if I remember correctly.
I applied a timing edge radius to the piston in 1963 when I was 15 years old because it was the easiest way to modify the transfer timing with the very limited tooling at my disposal, and when I was lucky enough to get my hands on the book below a few years later, I also started applying a top edge radius to the exhaust port.

[Condyn]

Condyn, the pop scenario is what KZ Kart tuners have used for years to " tune " their engines as to most all, EGT is voodoo shit.
The engines normally run to about 14500 on track, and in the pit, when the throttle is nailed and held open, if the main is correct it will hold 15500 popping like mad.
This practice has now been banned by the CIK due to " noise ".
So I think you are seeing the same thing, if you are referring to " popping" at full throttle.
But as I have explained a thousand times, EGT tells you everything you need to dial in to the edge of deto.

It is exactly as you described. Popping while over revving on the warm up stand with no load. I actually no longer do this anyway because it pisses everyone off, but I have stayed away from finding that EGT since my last experiences with it. I do not see EGT as voo doo, but I understand you perfectly.

[jonny quest]

Condyn, pipe wall temperature is a big tuning issue on snowmobiles.

They don't get hot quick enough in a drag race compared to dyno tuning.

We usually clutched 200rpm lower on the track compared to dyno.

[wobbly]

Apollo, as stated in one of my replies the STA numbers of the RSA, as calculated off the raw timing numbers in EngMod showed that the Blowdown was down near 10%
in direct comparison to the transfers.
Jan adding the radius gave a good increase in power, so one could assume the increase in Cd due to the sort or radius the RSA actually had, would be close to that 10% number.
Jan's reaction when this was discovered, was to lament the fact that he never tested the engine with lower transfers.
Again , in the sim, if the main Exhaust port is lifted to what is effectively the beginning of the radius timing, close to 200* duration, the numbers are very close to alignment.
Frits is also right about the synergistic effect of a port radius and a piston timing edge radius - this is another level of sophistication that obviously works, in theory and in practice
as he has tested and proven this.
Then you have the logistical nightmare of shaping the head squish band to suit this.

But it is something that you must do your own due diligence on.
Having the piston radius right around the piston causes an issue with the exit flow adhering to this shape over the boost port, and creating short circuiting when the pipe efficiency is high.
In my testing the timing edge radius gave a good increase all the way up to peak, but lost in the overev.
You can fix this by deleting the radius over the boost, ie CNC cutting it with a reflex radius tool, or using a vertically set dividing head, and then adjusting the boost timing to suit, and or lifting
the boost port floor height to prevent flow adherence at and around BDC.

EngMod is a single dimensional code so this is an area that cannot be simulated effectively.

[Flettner]

What conclusion did 'we' come to about the exhaust dam? How far can one go?

[wobbly]

Viking , may I suggest you join the EngMod 2T Users Group on FB, I am an Admin so can approve you instantly.
Looking at your sim screenshot, I see a few things.
It has very good superposition, but to me it could maybe be improved by increasing the diffuser depression early in the cycle below zero pressure ratio.
This can be achieved with a shorter/steeper header, and a steeper first diffuser section - these adjustments are seen as improved peak and overev power.
The rear cone plugging amplitude is impressively high, but a little narrow in width.
Maybe a slightly longer tailcone, with increasing multiple angles would help.
Is that rpm at peak power ?

[Frits Overmars]

....Frits is also right about the synergistic effect of a port radius and a piston timing edge radius - this is another level of sophistication that obviously works, in theory and in practice as he has tested and proven this.
Then you have the logistical nightmare of shaping the head squish band to suit this.Not a nightmare at all Wob. If you let the squish band follow the dome of a piston with a timing edge radius and you center the head insert in the cylinder bore, as would be good practice with a non-radiused piston, you will end up with a thin, sharp, vulnerable edge on the insert that is susceptible to overheating and detonation.
But the solution could not be simpler: do not center the head insert in the cylinder bore, but around a collar on the cylinder.
356505


You could also center the head insert in a larger-diameter part of the cylinder, like this:
356506

[ApolloMotoMoto]

So, part of the issue with PowerSeal ...failing... to accomplish the Nikasil plating I had originally planned for (redirected to Millenium now);

I ended up behind the race teams testing schedule, and we have riders flying across the country for the "official test" of these engines for our next race... Good times.

To make up some lost ground, we are going to do the test with the chrome bores, and then send those cylinder in for Nikasil replating immediately after the test.

I still have some leftover pistons from the last batch that I had configured for Caber F-Cast rings (Chrome bore compatible).

And now I am measuring these chrome bores to see just how lucky I am... (if I was planning to do this, I would have specifically asked for cylinders in the right size range for my pistons, in this case I told my partner they were all getting re-bored and re-plated so the bore size didnt matter.... heh)


I had initially spec'd a piston to wall clearance of 0.060mm / 0.0023" (52mm air cooled cylinder, cast aluminum, forged piston).

Wiseco says they have tuned their process to the point where their forged pistons no longer "need" extra clearance relative to a cast equivalent, for what that is worth.

The best I can come up with are 3 pairs of pistons/cylinders with 0.054mm / 0.0021" clearance.


Would you run a 52mm jug that tight?

What factors go into deciding "how tight is too tight" for a given engine combo?

Is there a "generally accepted" rule of thumb (that actually works...) that is merely a function of bore size?

[Wos]

So, part of the issue with PowerSeal ...failing... to accomplish the Nikasil plating I had originally planned for (redirected to Millenium now);

I ended up behind the race teams testing schedule, and we have riders flying across the country for the "official test" of these engines for our next race... Good times.

To make up some lost ground, we are going to do the test with the chrome bores, and then send those cylinder in for Nikasil replating immediately after the test.

I still have some leftover pistons from the last batch that I had configured for Caber F-Cast rings (Chrome bore compatible).

And now I am measuring these chrome bores to see just how lucky I am... (if I was planning to do this, I would have specifically asked for cylinders in the right size range for my pistons, in this case I told my partner they were all getting re-bored and re-plated so the bore size didnt matter.... heh)


I had initially spec'd a piston to wall clearance of 0.060mm / 0.0023" (52mm air cooled cylinder, cast aluminum, forged piston).

Wiseco says they have tuned their process to the point where their forged pistons no longer "need" extra clearance relative to a cast equivalent, for what that is worth.

The best I can come up with are 3 pairs of pistons/cylinders with 0.054mm / 0.0021" clearance.


Would you run a 52mm jug that tight?

What factors go into deciding "how tight is too tight" for a given engine combo?

Is there a "generally accepted" rule of thumb (that actually works...) that is merely a function of bore size?

We run wössner forged pistons that are plated with ptfe with clearance 0,05 in aircooled nicasil plated aluminium cilinders bore 54.

Wössner states the ptfe is a break in surface...but even after 50 hours it isnt worn off completely...only down the skirt you see pure aluminium... ;)

Ring we changing half the time!

Grüße Wolfgang

[Sketchy_Racer]

Slightly off topic, but related to racing two strokes,

Those who used to work with the 250 and 500gp bikes, do you remember if they use oil pumps in the gearbox, and if so, do you think the main purpose was, lubrication or cooling?

Cheers,
Glen

[jato]

Testing my memory here but i recall when the TZ 250 first went to pumped gearbox oil there was a net weight saving as there only needed to be 5 or 600 mils of oil to keep the pump happy, and therefore the gearbox happy. the RGB 500 didn't have a pump but ran a heavy weight gear oil. other 500 gp bikes i believe all run pressure lube. if possible you should do so , heaps of benefits - slightly smaller/lighter gears that are well lubed take the place of heavier/bigger gears. the sliding gear slides easier during a shift as it slides on a "cushion" of +- 30 psi oil. if you have a wet clutch the oil (depending on design) can be getting flushed through taking heat with it so the clutch can be slightly smaller and still be durable. a trans oil cooler becomes a possibility too. it'll be a faster more reliable bike imo

[Viking]

Viking , may I suggest you join the EngMod 2T Users Group on FB, I am an Admin so can approve you instantly.
Looking at your sim screenshot, I see a few things.
It has very good superposition, but to me it could maybe be improved by increasing the diffuser depression early in the cycle below zero pressure ratio.
This can be achieved with a shorter/steeper header, and a steeper first diffuser section - these adjustments are seen as improved peak and overev power.
The rear cone plugging amplitude is impressively high, but a little narrow in width.
Maybe a slightly longer tailcone, with increasing multiple angles would help.
Is that rpm at peak power ?



Wobbly,
I´m allergic to facebook, but I can´t resist your invitation, so I will show up there some day.

Regarding superposition and shorter/steeper header and steeper first diffuser section:
Earlier depression seems to be a good improvement, so I buy that.
My engine is for a snowcross racing snowmobile equipped with a CVT-clutch,
so overrev power is not useful.
I might transform the gain made, to the front side of the peak in some way.

Regarding plugging amplitude:
Your suggestion will be tried in the future.
What width is prefered?

Regarding rpm:
Yes, the engine peaks at only 8000rpm.
Transfer and exhaust ports width are limited by the cylinder studs and crankcase interface surface.
Also experience made from earlier similar engines, that had the peak at 9600rpm was very
difficult to tune for various hard snow and muddy snow on the track.

[SwePatrick]

That by rule violated Kartengine i´m experimenting with.
I made some progress the other day.

New personal record for this engine.

But what make me most astonished is the overrev capabilites.
It pulls up agains't 15k

And before you judge me because of boring it to 144cc, i bought it for about 100bucks with some missing parts.
It will never see the Karttrack again.

356509

See more at https://www.youtube.com/@Patricks_Projects

[wobbly]

The 250/500 GP bikes mostly used a transmission oil pump. The very small amount of oil was stored in a low " sump " as the main benefit of this pump around system
was to keep a huge amount of oil from being " churned " by the primary drive, reducing heat and parasitic losses - as is the case normally.

Viking - if you want more upper front side then that is achieved by increasing the length and angle of the last part of the diffuser ,leading up to the parallel section.
What is the geometry of your current rear cone - maybe I can suggest an alternative.
As I said your design has good superposition, but even with that the pressure ratio rise after EPO is not spectacular - many " good " designs I have are " off the chart " past 3X.

You can open a locked FB account, and this would normally prevent you from gaining membership - but as I know who you are, and have a license from Neels, I can let you in.

[Sketchy_Racer]

Testing my memory here but i recall when the TZ 250 first went to pumped gearbox oil there was a net weight saving as there only needed to be 5 or 600 mils of oil to keep the pump happy, and therefore the gearbox happy. the RGB 500 didn't have a pump but ran a heavy weight gear oil. other 500 gp bikes i believe all run pressure lube. if possible you should do so , heaps of benefits - slightly smaller/lighter gears that are well lubed take the place of heavier/bigger gears. the sliding gear slides easier during a shift as it slides on a "cushion" of +- 30 psi oil. if you have a wet clutch the oil (depending on design) can be getting flushed through taking heat with it so the clutch can be slightly smaller and still be durable. a trans oil cooler becomes a possibility too. it'll be a faster more reliable bike imo


The 250/500 GP bikes mostly used a transmission oil pump. The very small amount of oil was stored in a low " sump " as the main benefit of this pump around system
was to keep a huge amount of oil from being " churned " by the primary drive, reducing heat and parasitic losses - as is the case normally.



Thanks for the input guys, oil pump to be incorporated in the new design.

Cheers,
Glen

[Maxdelta]

In a 3 port exhaust layout, what's a practical minimum thickness for the septum between the main exh port and the aux port? I imagine if this gets too thin that it could become overheated and cause problems

[wobbly]

Max - 2.5mm

[Frits Overmars]

Max - 2.5mmSo 2.6 mm is too thick?
Yes I know, I can be a bastard :devil2:

[wobbly]

Haha, a bloody Dutchman that swears perfectly in German and English, how could you not like that guy.

[Wos]

Haha, a bloody Dutchman that swears perfectly in German and English, how could you not like that guy.

:rolleyes:

As a german...swear it on the bible...if wanted on the coran!!!!

..truth is in between!!:bleh:

:msn-wink:

What we are taking about... 65 cordal main or 70?? Gp racer or daily user? 😉

A 50cc bidalot with 65 cordal main can run 8 hours with only 2 mm bridge at liedolsheim endurance competition on save side!?

Tell me the truth please! 😉:clap::clap:

Grüße Wolfgang

[Frits Overmars]

Haha, a bloody Dutchman that swears perfectly in German and English, how could you not like that guy.Wob, you're underestimating me. On the job you learn words from your colleagues that you won't find in a dictionary. I think back fondly on Miguel Sauca, the Spanish draughtsman who came with Jan Thiel from Bultaco to Garelli. So now I can also swear perfectly in Italian and Spanish. And in Dutch of course, and a little in French, and even in Finnish.
Come to think of it, I cannot swear in Japanese. I wonder if that's a flaw in my upbringing or a testimony of Japanese civilization.

OK, back to the harsh reality.

In a 3 port exhaust layout, what's a practical minimum thickness for the septum between the main exh port and the aux port? I imagine if this gets too thin that it could become overheated and cause problems I try to answer this type of questions with a universal answer that is independent of bore, stroke, etc.
In this case my answer would be that the width of a vertical bar between two ports must be at least 5° of center angle.
Example: a cylinder with a 54 mm bore has a circumference of Pi x 54 mm = 169,65 mm.
That circumference comprises a total center angle of 360°. One degree center angle has a cordal width of 1/360 x 169.65 mm = 0.47 mm. And a bar with a width of 5° center angle is therefore 5 x 0.47 = 2.36 mm wide.

Now would be the time to say that you can forget most of what I wrote above. I can simplify it to:
The minimum bar width must be 0.044 x the cylinder bore diameter.

[wobbly]

Very well done Frits, thinking rationally like that obviously comes naturally.
Sadly my immediate reaction only accounts for the obvious proven 54 bore at a 70% chordal, where 2.5mm is commonplace - so yes 2.6mm is too big.
Also in my opinion anyone saying a 65% chordal is happy with 2mm ( even if it is a 40mm bore ) simply means its closer to a lawnmower than a race engine.
Some might opine that Im so narrow minded it could fit between the blocks at Giza - and no a credit card wont go, been there , tried that.

[Wos]

Very well done Frits, thinking rationally like that obviously comes naturally
Sadly my immediate reaction only accounts for the obvious proven 54 bore at a 70% chordal, where 2.5mm is commonplace - so yes 2.6mm is too big.
Also in my opinion anyone saying a 65% chordal is happy with 2mm ( even if it is a 40mm bore ) simply means its closer to a lawnmower than a race engine.
Some might opine that Im so narrow minded it could fit between the blocks at Giza - and no a credit card wont go, been there , tried that.

Frits! Are the winner bikes in liedolsheim lawn mowers:angry: :wings:

Fact is...bidalot has only main cordal 65...max 66...and 2mm bridges to the boosts...
Not the optimum as nearly everybody knows ! ��

But these zylinders are strongest in this competition...untouched Ducts... 21 -22 hp/ crank
Very fast lawnmowers.

Frits! Once you were involved in liedolsheim...supported jan schäffer with a simson...and he did second place inthe 8h race!!
:Punk:

https://www.youtube.com/watch?v=1X4N3BJwoT0

Can you give us a idea, which power the engine made?



Think it was before bidalot sold its rf 50 wr and before its problems with their original pistons were solved...

Lap times are nowdays at low 1.54 ;)

Thanks

Grüße Wolfgang

[Wos]

Wob, you're underestimating me. On the job you learn words from your colleagues that you won't find in a dictionary. I think back fondly on Miguel Sauca, the Spanish draughtsman who came with Jan Thiel from Bultaco to Garelli. So now I can also swear perfectly in Italian and Spanish. And in Dutch of course, and a little in French, and even in Finnish.
Come to think of it, I cannot swear in Japanese. I wonder it that's a flaw in my upbringing or a testimony of Japanese civilization.

OK, back to the harsh reality.
I try to answer this type of questions with a universal answer that is independent of bore, stroke, etc.
In this case my answer would be that the width of a vertical bar between two ports must be at least 5° of center angle.
Example: a cylinder with a 54 mm bore has a circumference of Pi x 54 mm = 169,65 mm.
That circumference comprises a total center angle of 360°. One degree center ⁶angle has a cordal width of 1/360 x 169.65 mm = 0.47 mm. And a bar with a width of 5° center angle is therefore 5 x 0.47 = 2.36 mm wide.

Now would be the time to say that you can forget most of what I wrote above. I can simplify it to:
The minimum bar width must be 0.044 x the cylinder bore diameter.

Thanks Frits for the Formula! ;)

Is the Formula independent from width of main ex or made for the known sturdy and effektiv 70 percent cordal width?

Think the narrower the main...the higher is life span of every involved part there.

Conclusion could be that it is possible to use narrower bridge bars, if main is under 70 percent?? Right or wrong??

Thanks again Frits! 😉

Grüße Wolfgang

[Frits Overmars]

Are the winner bikes in liedolsheim lawn mowers?Engines for eight-hour races are prepared for reliability rather than power. They do not nearly reach the piston speeds that Wobbly is use to and in this respect I can understand Wobbly's remark.


Fact is...bidalot has only main cordal 65...max 66...and 2mm bridges to the boosts. Not the optimum as nearly everybody knows !A port width of 70% of the cylinder bore in combination with the optimum port shape will give the optimum blowdown angle.area. But making the main exhaust port narrower yields more place for auxiliary exhaust ports, in which case the 70% main port width is not sacred and keeping it narrower may give a better total blowdown angle.area.


Frits! Once you were involved in Liedolsheim...supported Jan Schäffer with a Simson...and he won the 8h race! Can you give us a idea, which power the engine made?Sorry Wolfgang, I don't even remember what year it was; I would have to look it up in the Langtuning dyno-computer but that computer is not online for security reasons and at the moment I am not even in the same country.

EDIT: I overlooked your link ( https://www.youtube.com/watch?v=1X4N3BJwoT0 ). Now I see that this particular race was 12 years ago.


Thanks Frits for the Formula! Is the Formula independent from width of main ex or made for the known sturdy and effective 70 percent cordal width?
Conclusion could be that it is possible to use narrower bridge bars, if main is under 70 percent?That formula is only dependent on the factors mentioned in it, as should be the case with any formula. Do you see any port width mentioned?
The bridges between the ports in a cylinder have more than one function. They must guide the flow but they must also keep the cylinder together. And they do not always succeed, as you can see below. So do not make them too narrow.

[Wos]

Thanks for answers and lot of input from you Frits! Top!

Yes for sure, the mecanical and thermal stress is a factor and it may depend from material and quality of cast methods...

Dont be afraid...in case of endurance reliability counts 😉 level a bit under freetech50...

Liedolsheim Engines peak at about little over 14 000...reso begin about 10 000...overrev to 17 000...

The year you were involved should be 2013 😉

Grüße Wolfgang

[SwePatrick]

The final pulls of my Kartengine (running E85 fuel).

I had a good week, let´s just say that.
52.5whp is in my book quite good from 144cc

52.5/0.85=61,76 possible crank hp(calculating with 15% losses)

I will park this engine for now, waiting for a good chassi for it.

Enjoy:


https://youtu.be/Ojh0SQDX6Ug?si=6b-5JIyCkWrjmzEO

[Viking]

Viking - if you want more upper front side then that is achieved by increasing the length and angle of the last part of the diffuser ,leading up to the parallel section.
What is the geometry of your current rear cone - maybe I can suggest an alternative.
As I said your design has good superposition, but even with that the pressure ratio rise after EPO is not spectacular - many " good " designs I have are " off the chart " past 3X.




Wobbly,
I´m in the middle of a over one year long moving project, so my calculation and simulation computer is lost in some of the 94 moving boxes i have. Most likely its in another place 450km from my current location.
I have not done any EngMod2T simulation for over two years now, so my abstinence is profound.

Searched for some information on my 3D CAD computer, but the only expansion chamber models to this engine, that I found, had a rear cone of 13°/22°.
Very kind of you to offer some help with my simulations of this engine, but I think we can spend our
time on a more interesting engine project.

Attached you see pictures of a 4-cylinder engine for another of my snowmobile project.
Vikings like brutal force, and so do I.
The engine is based on dual Rotax 670 rotary valve inlet snowmobile engines, with my own designed cylinder head and flexible crankshaft coupling device.
I have not yet decide if the cylinder volume will be 1340cc, 1480cc or 1000cc (to be able to participate in dragracing competitions).

Attached also a simulation in EngMod2T of one cylinder of a 2-cyl 740cc (or 4-cyl 1480cc).
Do you see any room for improvements?
Yes, Vannik need to extend the Y-axis pressure ratios to at least past 4X.

[wobbly]

Aha, so do I start calling you Ragnar, your Viking name from the TV series, I will keep an eye out for it on the EngMod Group.
As in the previous screenshot, the only real issue is not turning that huge EPO pressure ratio energy into a negative ,soon enough around BDC.
In the best sims I have the wave is negative before the 60 marker - this shows that the diffuser is not efficient enough, early in the cycle.
I assume this engine will be CVT, so you can also use a rear cone geometry I have been working with lately to seriously pump up power around peak.

For a CVT, a two angle 50/50 with the steepest first, for a roadrace engine the same but with 3 decreasing angles.
In the roadrace version the shallow last rear cone gives a huge boost in overev, not needed in your case.
But this geometry pumps up peak and or overev power, at the expense of front side power - no free lunch as usual.

So - I have only used it in cylinders with 3 ports that are all activated with a servo PV.
With those cheap arse Rotax diaphram things it is impossible to lift the valves slow enough over a wide enough span.
Using an Ignitech running this, you can lift the PV at any rate up to say only 800 rpm before peak, and have more power everywhere.

Are you using the so called " Wobbly Duct " - if not, PM me your email and I will send you the paper I wrote on this.

In this screenshot the return amplitude is restricted, enabling much more overev power.

[Vannik]

Hi Wayne,

Currently my way of thinking on this topic is summarized in this picture.

356519

[Frits Overmars]

Hi Wayne, Currently my way of thinking on this topic is summarized in this picture.
356519:niceone: ..........

[koba]

Hi Koba. Rick Ford was running an air cooled TF/TS125 with 22rwhp and that proved really reliable with little heat fade. We could get much more hp out of our aircooled GP125's but the heat fade made the extra power self defeating. We tried all sorts of tricks, like ceramic coatings and extra copper fins. The copper went all the way in to form the squish band. But air cooling was just not up to handling the waste heat from the higher HP.

356498 356500

I've found the same thing with my MB100 based stuff.
The old aircooled nail worked great at 13.5:1, for 3 laps.
I think it ended up at about 11.8:1, running on any old fuel.
This one was built to keep going, be easy to ride and still use standard road internals.

EDIT: Yay, saved Frits from looking at his thumb for too long. My comments may not be better! :lol:

[wobbly]

Neels, fully agree. I was pointing out how the sim wave front could be improved, but should have addressed as well the consequences lying in wait for sub optimal transfer duct geometry.
I am not familiar with that Rotax engine - does it have lift shafts ?

[Vannik]

I am not familiar with that Rotax engine - does it have lift shafts ?

Neither am I, Viking will have to inform us.

[wobbly]

Neels, whilst working late last night it occurred to me that assuming the Rotax depression wave acts along the same lines as the R3 I am testing, then we have a
situation where at 1000 rpm below peak power, the pipe - now too long for the tuned rpm, acts to create an even sooner, greater depression at the port.
Thus it makes me think that at BDC, there will be a large, unavoidable span of rpm where even with an inefficient diffuser, we will have excessive short circuiting, simply due to the pipe geometry and
the port acting in concert, to pull the suction early and low.
I dont have any " inefficient " diffuser designs to test in a big cylinder, to see the wave front shape created in that Rotax for example at lower rpm.
I would be really interested if Viking could post the screen shot, or send me the .pack to understand what happens in this scenario.
Here is the KZ at 1000 rpm below peak to show the effect in that engine.
I assume we would only see the down side of this effect on lift shafts, using your excessive short circuit, scavenging model.

[Vannik]

Wayne, that is huge suction, and it comes from the pipe still resonating (non zero positive pressure at export opening to allow buildup of pressure and suction pulses) although the plugging pulse is too early but still strong. My thinking is that it will cause short circuiting with lift shaft ports.

The effect of short circuiting on pipe bulk temperature is quite severe, the following is some guidelines I am working on (The names in brackets are the particular scavenging model names):

When using the different scavenging models in EngMod2T the following pipe wall temperatures are a rough guide:
• Normal Scavenging, almost no short circuiting - ~350°C
• Small amount of short circuiting (Yam12) - ~300°C
• Medium amount of short circuiting (Small) - ~250°C
• Severe short circuiting (Severe Short Circuiting) - ~200°C

I do wish there was an elegant way to get EngMod2T to predict the amount of short circuiting and to calculate its effect on the bulk pipe temperature!

[Frits Overmars]

... we have a situation where at 1000 rpm below peak power, the pipe - now too long ?? for the tuned rpm, acts to create an even sooner, greater depression at the port.
Thus it makes me think that at BDC, there will be a large, unavoidable span of rpm where even with an inefficient diffuser, we will have excessive short circuiting, simply due to the pipe geometry....Wob, I noticed that you tend to use a somewhat smaller header length percentage than what I am used to. The difference is maybe just 1 or 2 %, but it could have a noticeable effect.

Short-circuiting due to too short a pipe is somewhat self-regulating due to the much lower exhaust gas temperature resulting from the escaping cold mixture, as Neels points out.
I think this was a reason for provoking deliberate short-circuiting and/or high-speed loop-scavenging in yesterday's direct-drive kart engines.

[Storbeck]

I'm not a Viking but I am pretty sure he's using 670 Rotax cylinders that look a lot like this (pictures from ebay ads I found on the interweb).

The experts can opine if those are lift shafts, to me they are not the MOST squared off lift shaft transfers I've ever seen....but they don't look much like a teacup.

[wobbly]

The Eagle Eye of Mr FOS strikes again - of course the pipe is too short at the lower rpm - dumbarse.
And yes, I had not considered the effect of the short circuiting regime on the EGT - again an obvious error, thankyou.
The short header and short steep first diffuser section is aimed specifically to peak and overev generation, then using a steep longer last diffuser section to regain the front side.
Especially in engines with no PV, that ameliorates many evils.

[Viking]

Hi Wayne,

Currently my way of thinking on this topic is summarized in this picture.

356519



My thinking between my simulation iterations was focused on why I don´t achieve a faster pressure drop in 'Pexport'.
Even if the Rotax 670 cylinders tiny auxilary exhaust ports are modified to enough STA,
the small auxilary exhaust ducts are very restrective and might be the problem - not the diffuser.

[Viking]

Neels, whilst working late last night it occurred to me that assuming the Rotax depression wave acts along the same lines as the R3 I am testing, then we have a
situation where at 1000 rpm below peak power, the pipe - now too long for the tuned rpm, acts to create an even sooner, greater depression at the port.
Thus it makes me think that at BDC, there will be a large, unavoidable span of rpm where even with an inefficient diffuser, we will have excessive short circuiting, simply due to the pipe geometry and
the port acting in concert, to pull the suction early and low.
I dont have any " inefficient " diffuser designs to test in a big cylinder, to see the wave front shape created in that Rotax for example at lower rpm.
I would be really interested if Viking could post the screen shot, or send me the .pack to understand what happens in this scenario.
Here is the KZ at 1000 rpm below peak to show the effect in that engine.
I assume we would only see the down side of this effect on lift shafts, using your excessive short circuit, scavenging model.



I would happily send you .pack-files, but my moving schedule is to start opening the moving-boxes in October/November, and until then I am computer-lost.

[Viking]

I'm not a Viking but I am pretty sure he's using 670 Rotax cylinders that look a lot like this (pictures from ebay ads I found on the interweb).

The experts can opine if those are lift shafts, to me they are not the MOST squared off lift shaft transfers I've ever seen....but they don't look much like a teacup.



Thank you Storbeck,
this is the kind of cylinders I will use on the engine.

Bad designed main exhaust duct, auxilary exhaust duct and transfer ducts.
Even the inlet RV duct in the crankcase is bad.
But the engine is legendary,
and dominated on the racing tracks 1992-2000 in snowcross and dragracing.

[Storbeck]

Thank you Storbeck,
this is the kind of cylinders I will use on the engine.

Bad designed main exhaust duct, auxilary exhaust duct and transfer ducts.
Even the inlet RV duct in the crankcase is bad.
But the engine is legendary,
and dominated on the racing tracks 1992-2000 in snowcross and dragracing.

Viking indeed it was!

The watercraft version was very competitive also.

[SwePatrick]

Curiosity killed the,,, butt? :D:D:O

And well worth it.
New record again, 53.6whp 13000rpm (dyno reports 59.1 crankhp)
144cc
E85

I call this engine DONE! (for now)
I might build a strange sprintchassi to mount it in.


https://www.youtube.com/watch?v=qkgZ3tB9uJk

[Frits Overmars]

The Eagle Eye of Mr FOS strikes again ....Wob, to console you, here is proof that I also make mistakes. For example, yesterday, when I didn't get around to congratulating you on your birthday (I was rather busy in a Ferrari on a nice German racetrack, the Lausitzring). So here you go, to your health, Wob. And to mine, because traditionally my birthday is one day after yours.
356539

[Viking]

Wob, to console you, here is proof that I also make mistakes. For example, yesterday, when I didn't get around to congratulating you on your birthday (I was rather busy in a Ferrari on a nice German racetrack, the Lausitzring). So here you go, to your health, Wob. And to mine, because traditionally my birthday is one day after yours.
356539



Frits,
I must help you keeping away from the alcohol, so instead you maybe can help me figuring out an ignition order and balance solution for my next project. :-)

I started a pre-study some years ago,
to find out the possibilities for a 5-cylinder engine to my snowmobile.
Vikings like power, and 400+ hp in a snowmobile can´t be wrong.

My initial calculations shows that 1:st order forces is zero,
but some free moment will occur.

Is the firing order 1-5-2-3-4 the best solution?