ESE's works engine tuner

[Pagi]

Here's the proportions of Blair's "ideal bell" along with the effective length above the bell from Wobbly.

353645

Rather than having to remember or look it up each time, I start with this drawing and scale it as needed.


353650353650


I could soon, I hope, have the latest research done in F1 atmo

[SwePatrick]

Here's the proportions of Blair's "ideal bell" along with the effective length above the bell from Wobbly.

353645

Rather than having to remember or look it up each time, I start with this drawing and scale it as needed.

I have tried this design a couple of years ago on a small engine, didn´t work out well :(
I lost power everywhere.

I have actually had better luck with the left design at schetch below, the right is about the design i had that gave losses.
353651

This is why i´m asking, as it is far away from Blair´s ideal bell.
And if i´m allowed to guess is that a twostroke differs a lot from a foulstroke engine, much less amplitude in the pulses, but more often.
I also guess that a reed engine might differ from a disc engine.

And blow again a small test i did a couple of years ago with constant flow, with or without velocity stack.


https://www.youtube.com/shorts/OIjbA9g4tx8?feature=share

The straight pipe got sucked down as it had a lot of turbulens(created noise)
The velocitystack didn´t want to go inside the hose, needed to force it.
And when placed into the hose it wanted to jump out, probably because it created a 'high' pressuredifference from outside to inside.

[OopsClunkThud]

As sketched I would think the biggest difference impacting performance would be in the length.

[pete376403]

This came up of FB feed today - looks nice -apologies if it's been posted before https://www.facebook.com/rimarmotors

[TZ350]

This came up of FB feed today - looks nice -apologies if it's been posted before https://www.facebook.com/rimarmotors

I had a look. Very impressive bit of work.

[TZ350]

353653

Rode F5 at Tokoroa last Sunday. Great hopes of glory. Reality put paid to that ...... :killingme

[pete376403]

I had a look. Very impressive bit of work.

Still using carbs, though - show him you EFI setup

[SwePatrick]

As sketched I would think the biggest difference impacting performance would be in the length.

Yes.
And going with Blairs variant makes my intake very long, i want to keep it very short as i had great luck with short intakes before.

[TZ350]

https://www.facebook.com/rimarmotors


I had a look. Very impressive bit of work. Still using carbs, though - show him you EFI setup

Two Stroke EFI. https://www.kiwibiker.co.nz/forums/showthread.php/185773-Speeduino-2T-EFI-Project

[pete376403]

Two Stroke EFI. https://www.kiwibiker.co.nz/forums/showthread.php/185773-Speeduino-2T-EFI-Project

yabbut - i meant show that to the developer of the rimac

[Wos]

Rotax 124 rotary valve inlet

The crank web is camfered sharp.
Think bad for the inlet flow...

Better rounden that ?
If yes...

One complet radius?
2 small radiuses to keep volume of crankcase nearly untouched?

Bottom of inlet duct ending is sharp too...what to do there? What uses cranks rotation influences on flow in the best way...?

Thanks..Dankeschön :yes:

Grüße Wolfgang

[Frits Overmars]

Rotax 124 rotary valve inlet. The crank web is camfered sharp. Think bad for the inlet flow... Better round that ? If yes, one complet radius? 2 small radiuses to keep volume of crankcase nearly untouched?
Bottom of inlet duct ending is sharp too...what to do there? What uses cranks rotation influences on flow in the best way...?
I don't remember chamfers on the 124's crankwebs. But then it's literally half a lifetime ago.
I'd give the chamfers a radius, but not one complete radius, as that might remove too much material from around the big end pin bore. You do need stiffness there.
I'd leave the sharp bottom of the inlet duct alone. But you might radius the side walls of the duct.
Don't worry about increasing the crankcase volume. In fact increasing it may be a good thing.

[Wos]

I don't remember chamfers on the 124's crankwebs. But then it's literally half a lifetime ago.
I'd give the chamfers a radius, but not one complete radius, as that might remove too much material from around the big end pin bore. You do need stiffness there.
I'd leave the sharp bottom of the inlet duct alone. But you might radius the side walls of the duct.
Don't worry about increasing the crankcase volume. In fact increasing it may be a good thing.

Frits!

Many many thanks for yor answer and tips!

Crank is cleaer, that we dont should weaken it!...as there is not much Material round ;)

But i am so so confused about my conclusion to your text now...and before text expertices...do not find clear conclusion for me...

Maybe read back would help...maybe your next help!
Or ask without shame ;)

What to do with conrod length? Aiming to longer one to increase volume by length conrod?

Or better increasing case volume by taking off Material on crank webs or case inside?

Still confosed by the fact that there might be my missunderstandings...no clear view...read back...once more...eyeyey...

SOS Frits ! :brick::doctor: ��

Thanks wolfgang

PS...not only for frits ;) Did Saturday testings for liedolsheim...gained "some" reves by ....... catch us! :yes::yes::D

[Wos]

Hello together ✋

My personal view now to the long intake duct of the Rotax 124.

Thinking about a subwoofer as my model to undersand

Verry simplyfied piston is the speaker...box vomume is case volume...reflex tube is long intake duct.

If i have a very long reflex tube, that i cant change, have to increase volume of box, to come closer to frequency of reflex tube

If case volume would be zero you can restore zero mixture.
In a big elastic volume you can store a lot more mixture and energy, the process of filling this is long...

Yes there is a next thing the pipe resonance...partly coonnected with case...this i left beside
The closing of the door too...

This is my personal simple picture in the moment now frits

Critics welcome✋ ��


Open to learn and understand better ��

Thanks

Wolfgang

[Wos]

Hello together

Rotax 124

Using crank spin better with halfside radiused bottom of inlet ducts end?

My idea

Inlet is in axe above of crank center
One half of webs intersetion is spinning towards duct, the other half downwards case.

Idea is only radius the downward side of duct end...to ease the downstream finding better down the case, by lower turbulence

Second effect could be, that inlet flow in inlet direction would be less disturbed ...lower turbulence too

Good idea?

Thank you

Wolfgang

[JanBros]

my opinion : don't (as Frits already said). you are rounding the crank web so it can flow better over the web. by rounding the bottom of the duct, Coanda-wise part of the mixture will follow it and as a result hit the web and cause turbulence, exactly the thing you were trying to avoid with rounding the web.

[Wos]

my opinion : don't (as Frits already said). you are rounding the crank web so it can flow better over the web. by rounding the bottom of the duct, Coanda-wise part of the mixture will follow it and as a result hit the web and cause turbulence, exactly the thing you were trying to avoid with rounding the web.

Hey jan,

What a pleasure! Yesterday used your fantastic Excel sheet in case of pipe! Thanks for this:yes: top!
And for your answer

My picture was that boundary layer will be scrapt from crank web surface by a sharp edge of duct...and this could be turbulent... clearance there is 1,2 mm there....

But on the other side if sharp as you and frits told... maybe the turbulence there could help the main part of duct flow surfing over the radius on web

Even when my picture is completely wrong...like just to understand what is happening in this scenario ...hungry for this :cool:

Grüße Wolfgang

[190mech]

Wos,
I am not a super tuner like a lot of this group, just a 2stroke nut so this might not be the best idea..
What about adding epoxy to the bottom of the intake duct to smooth out that stepped area allowing the mixture to flow smoothly into the crankcase??

[TZ350]

.
353668

Happy to report that petrol in the carb bowl for the pilot jet and a separate methanol feed for the main jet idea works, or at least it appears so with an initial runup on the dyno.

Initial impressions. Idles and throttles Ok. Drank a surprising amount of petrol through the pilot jet. No stumbling when the throttle was quickly opened at any speed. Methanol fuel level stayed constant on heavy pulls. Power jet was suspiciously sluggish.

No dyno results yet, for some reason the PC has stopped talking to the Dyno electronics.

[Frits Overmars]

Power jet was suspiciously sluggish.With 3/4 of the power jet supply line, including the control needle, above fuel level in the float bowl, the sluggishness cannot come as a surprise.
That Mikuni fitted their first power jet on top of the inlet tract 45 years ago does not mean we still have to do it that way.
Having said that, I love the way you use separate float bowls for separate fuels.
353670 353671

[wobbly]

In the tests I did years ago having the powerjet discharge end mounted down from the top of the carb bore and later , shortened , gave a smoother and more
gradual flow rate transition much higher up the fuel curve. The Keihin carbs with the discharge nozzle mounted below 1/2 throttle , start to flow almost immediately the slide passes the tube.
Of course later , using a solenoid with PWM drive as Dellorto did , gave electronically the same gradual flow ramp up that didnt suddenly richen the fuel curve in the midrange as soon as the slide was high enough.

[speedpro]

Looking at the photo there is a restriction, the adjustment bit, close to the source of fuel. Once the fuel makes it up to the restriction then the flow rate will be restricted. If the restriction was closer to the carb throat like a normal power jet then air will flow through the restriction much more freely and once the fuel makes it that far THEN there will be a restriction to flow. Do like Frits said as well, of course.

[TZ350]

353672

Blue line was 100% Methanol, 75 pilot + 180 main. Red line is 50 pilot jet on petrol and 190 main on Methanol. Sounded rich, I guess that is due to the petrol component.

353673

Sucks an amazing amount of petrol compared to the Methanol. Maybe 20% petrol. Dyno's are notoriously thirsty so I expect on the track the ratio of petrol to Methanol will go up, maybe 50% petrol to Methanol. The under the plug cylinder head temperature reached the high 90's C. Exhaust about 360 C. I was expecting a cooler head and hotter exhaust, detonation?. :scratch:more things to think about.

[husaberg]

Having said that, I love the way you use separate float bowls for separate fuels.
353670 353671
Herbert Skinner would be so proud of Rob.

353672

Blue line was 100% Methanol, 75 pilot + 180 main. Red line is 50 pilot jet on petrol and 190 main on Methanol. Sounded rich, I guess that is due to the petrol component.

353673

Sucks an amazing amount of petrol compared to the Methanol. Maybe 20% petrol. Dyno's are notoriously thirsty so I expect on the track the ratio of petrol to Methanol will go up, maybe 50% petrol to Methanol. The under the plug cylinder head temperature reached the high 90's C. Exhaust about 360 C. I was expecting a cooler head and hotter exhaust, detonation?. :scratch:more things to think about.

Flanged front rim
TX650/750?

[TZ350]

Flanged front rim TX650/750?

The bike is a real mix and match of bits and bobs. 72 XS650 front end or at least bits of one. https://youtu.be/1QeSHLSwSXc?si=Df3eRCnkcoFWxfeE

Ducati caliper and 300mm Harley Flat Tracker disk rotor mounted on the XS650 disk carrier. I still have the front wheel for one of these Flat Trackers at home. Not that I ever had one, I just scored choice bits occasionally.

353674

[SwePatrick]

soon,, just some cables to do.

353675

And to add to methanol discussion, a lot of the info applies on twostrokes also:


https://youtu.be/8VQPYefeTXU?si=WfcmI2Lwfr-0-Qe0

[lodgernz]

Sorry Husa, I've forgotten how to search this forum using the Site: option in Google.
Can you remind me please?
Thank you

[husaberg]

Sorry Husa, I've forgotten how to search this forum using the Site: option in Google.
Can you remind me please?
Thank you
i never use google for search kb but others do they put kiwibiker in quotes "kiwibiker.co.nz" then search terms or images options

this took about 20 seconds

.
Use the Google "site:" search term to find all the posts about "balance factor" and how to check it posted on the ESE thread.
Copy and paste this line into your Google search bar:-
balance factor site:https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner



345305
https://www.kiwibiker.co.nz/forums/showthread.php/188167-Tf-125-motor-bucket-thingy?p=1131158831&highlight=google+search+kiwibiker#post1131158831


.
There is a lot of gold to be found in this thread.

To search for it use the good old Google "SITE:" search option which turned up this on Det Buttons: ......

det button site:https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner (https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?)

337313

Choose a likely looking option and check it out and you will probably find a quality post like the one below.


.........
.
There are over 12,000 images attached to this thread and there is a lot of gold to be found there too.

337312

To look through them use the "Thread Tools" option at the top of the page and then the "View Images" option.

Then they can be sorted by:-

"Posted Within" ........... I use from the "Beginning".
"Images Per Page" ....... and I prefer 70 images per page.
"Order Results" ............ and they can be in Descending or Ascending date order.

When you see a picture that interests, you can click on it to view it or click on the "N/A" symbol below it to go through to the original Post.

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


Page 1000 has a lot of directory information pointing to the good stuff. Click on the Blue chevron in link above to go there.



Also page 500 about mid way down BucketRacer has a links list on:-
How to build a 1978 30hp aircooled Suzuki GP125 https://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner/page500


I just search thread on this page above wobs post then advanced search search single content and add a person if you know who it was or search terms in the keywords at the bottom click search by post not thread.
or search via person and image or just thread images.

if you want i will post a picturegram

[Frits Overmars]

if you want i will post a picturegramPlease do, Husa.

[lodgernz]

i never use google for search kb but others do they put kiwibiker in quotes "kiwibiker.co.nz" then search terms or images options

this took about 20 seconds

https://www.kiwibiker.co.nz/forums/showthread.php/188167-Tf-125-motor-bucket-thingy?p=1131158831&highlight=google+search+kiwibiker#post1131158831




I just search thread on this page above wobs post then advanced search search single content and add a person if you know who it was or search terms in the keywords at the bottom click search by post not thread.
or search via person and image or just thread images.

if you want i will post a picturegram

Thanks Husa. The Google site: search doesn't seem to work for me anymore. Don't know why. I don't need any naked pictures thanks.

[TZ350]

The Google site: search doesn't seem to work for me anymore. Don't know why.

No, it does not work for me either. I have been using the KiwiBiker "Search Thread" tool at the top right hand side of this page.

[Flettner]

https://youtu.be/a4AoXxYKy64?si=HeIVzy8rbr9GEO09

Turns out it runs a whole lot better when you wire the Ignitech up properly.

[wobbly]

So now Mr Hintz tell us what not to do - the important part.

[Flettner]

Too embarrassing, can't say.

[Frits Overmars]

Too embarrassing, can't say.Apparently your embarrassment has scared us all, Neil; no one dares to post anything here anymore. Except for me, I'm too old to worry about losing face anyway :p.

[Storbeck]

I have transfer ports on my mind.

Much thanks to Frits for the leaning tower of Piza article.

I could have sworn that at some point I saw a document about transfer ports from Wobbly, but for the life of me I can't find it among these 2500 some pages.

Am I crazy and imagining things or does such a document exist and if so can anybody point me to it?

[wobbly]

I havnt done a paper as such , like the Exhaust duct one I did , but I have mentioned several times about the effect of stagger on the scavenging regime.
Reverse stagger ie RSA type favors top end and overev as it uses the larger width of the B ports being also higher to generate a big STA , also the A port being low reduces the vertical short circuiting
up to the Aux ports.
Normal stagger favors a wider power spread by suppressing the peak but pumps up mid and overev as well.
Both systems work by using the excess Blowdown pressure at TPO to determine what port flows when , and gives rise to the notion that the port to open first , flows last.

[lohring]

Below is some wisdom I collected mostly from Wayne.

Lohring Miller

353692

[Storbeck]

Below is some wisdom I collected mostly from Wayne.

Lohring Miller

353692

Thank you Wobbly and Lohring!

Lohring I assume what you have there is tidbits that were copied from the forum and saved? I'll go search around and see if I can find all of that in context, was it about a drawing you were working on (a clue for my search, I'll search through your posts).

[Wos]

We'll try to avoid that ;) see you tomorrow!

cheers #29

Congratulations to you Daniel and to your team könig motorsport!

You managed to avoid it in liedolsheim! Hut ab! :scratch: capeau! 😉 top!:niceone::niceone:

[Wos]

Hello together!

This is what we found in rotax 124 rotary housing
Expectet a more square inlet shape... dammed oval?
Slow opening and closing bit by bit.

Better give it a square shape?
For quicker harder pulse upstream the long duct to carb???

Thank you experts in rotary valve!:niceone:

Grüße Wolfgang

[Flettner]

Apparently your embarrassment has scared us all, Neil; no one dares to post anything here anymore. Except for me, I'm too old to worry about losing face anyway :p.

We need another Ryger riddle, that put some life into this forum.

[Flettner]

Below is some wisdom I collected mostly from Wayne.

Lohring Miller

What became of your OP uniflow engine?

[husaberg]

We need another Ryger riddle, that put some life into this forum.

I believe ryger and his 2x banned minion were more fiddle than riddle:tugger:

[yatasaki]

Anyone riding on GP50 revival next week?

[lohring]

You're correct. Unfortunately I didn't note where that information came from. It was either twostroketech.com or here. Wayne has posted a lot of very similar advice several places. Frits has also posted his porting layouts. A lot depends on what you want in an engine.

Lohring Miller

Thank you Wobbly and Lohring!

Lohring I assume what you have there is tidbits that were copied from the forum and saved? I'll go search around and see if I can find all of that in context, was it about a drawing you were working on (a clue for my search, I'll search through your posts).

[Wos]

Dear Frits ;)

Have a look what i found:eek5:

Is this from you?

Grüße Wolfgang

[lohring]

What became of your OP uniflow engine?

The design lives on my computer. Maybe advances in 3D printing will let me revive it. However, after I turned 80 I decided I needed to limit my projects to less exotic things. I also transferred my big mill, lathe, and cutter grinder to a younger friend who will use them a lot more. I also donated my engines, tooling for cylinder modifications, and inertial dyno to another friend. He has already built some nationals winning engines for himself and some friends. With the above and my newsletter articles I hope I can pass on what it takes to keep the hobby and two stroke knowledge alive a little longer. I have been encouraging them to read twostroketech.com and this forum, but without much luck. I'm off to what may be close to my last national championship race in a few weeks.

Lohring Miller

[Peljhan]

Anyone riding on GP50 revival next week?

I will be there and make some photos. Bump me up we'll have a chat, can't miss me, guy in a wheelchair with camera. I will be with my friend Cerar, he is driving freetech.
20+ riders will participate. I think it is a record. And it's 10th aniversary this year.
Will you race?

[koenich]

Congratulations to you Daniel and to your team könig motorsport!

You managed to avoid it in liedolsheim! Hut ab! :scratch: capeau! 😉 top!:niceone::niceone:

Thank you :) nice to meet you!

[Gradella23]

hello everyone,
just received this beauty: 3d printed exhaust flange with transition from 75% area cylinder duct exit to 100% round area, with aux ducts gradually merging, thanks to @wobbly knowledge

it's 20mm long (40mm bore so 60mm duct+20 flange). I hope to ramp up cnc machining operations on the cylinder and crankshaft soon (not my machines unfortunately) and see if we can get this wobblyduct to go!

[wobbly]

What is the manifold being used on , im interested in the project ?

[Gradella23]

What is the manifold being used on , im interested in the project ?

hello wob, will be used on my 50cc self designed cylinder on an old Cagiva 50 engine.
still work in progress cause we lack time on the cnc machining end of the project... my partner in crime is spending all his f.cking days building his new house. I hope he's finally done with laying the damn parquet later this month

[diesel pig]

hello wob, will be used on my 50cc self designed cylinder on an old Cagiva 50 engine.
still work in progress cause we lack time on the cnc machining end of the project... my partner in crime is spending all his f.cking days building his new house. I hope he's finally done with laying the damn parquet later this month

Very Nice. I like three exhaust ports over bridged exhaust ports and just not because Aprilia did on there High HP RSA125 but because big exhaust bridges have all ways given me problems.

[lohring]

Is that a 3D printed cylinder?

Lohring Miller

[Gradella23]

hello guys, little update, almost ready to melt some aluminium....


Is that a 3D printed cylinder?

Lohring Miller

hello lohring, no it's a casted cylinder, i quote here my previous post where you can see the sand cores: the inner core is 3d printed directly in sand, while the outer core box was self built by me using 3d printed plastic models.

[wobbly]

Gradella , when you said 40mm bore I thought you were referring to the spigot - not the cylinder bore as it obviously is.
I have done a TZ50 where the spigot exit was 26mm = 100% of the port effective , and that was the same as the venturi size of the 30mm HV Lectron carb
it was fitted with.

[husaberg]

hello lohring, no it's a casted cylinder, i quote here my previous post where you can see the sand cores: the inner core is 3d printed directly in sand, while the outer core box was self built by me using 3d printed plastic models.

Sewing machine?

[yatasaki]

I will be there and make some photos. Bump me up we'll have a chat, can't miss me, guy in a wheelchair with camera. I will be with my friend Cerar, he is driving freetech.
20+ riders will participate. I think it is a record. And it's 10th aniversary this year.
Will you race?
I did,😎
We met😉

[Gradella23]

Gradella , when you said 40mm bore I thought you were referring to the spigot - not the cylinder bore as it obviously is.
I have done a TZ50 where the spigot exit was 26mm = 100% of the port effective , and that was the same as the venturi size of the 30mm HV Lectron carb
it was fitted with.

sorry, maybe I wasn't clear. Anyway i got a 29mm spigot exit = 660mm2 of exhaust port total area.

[Gradella23]

Sewing machine?

if you mean FDM print, yes, the external core box models are 3 printed in ABS, coated with a filling primer and sanded to the desired roughness.

[Rudex]

hello,

Wobbly, Why the kz R1 take little channel for water and kz10 take bigger channel?. Im no seeing any hole under the channel?.
Regards

https://i.postimg.cc/Z5dtzXdz/kz10c-VSkz-R1.png

[Vortex]

Hi Rudex,
This small milled groove is only for the air to escape that cooling chamber.

[wobbly]

The factory deleted the water entry up under the Exhaust duct completely with the R1 , as this means the duct heats all the cold water before it runs over the transfer tops.
The 10B and 10C they added a side water hose to push cold water over the duct top only.
The best solution is to use an extended spigot over the top of the duct with holes pointing back over the transfers , and have 2 x3mm holes up from the case to keep some flow
travelling up to the head.
Thr R2 has my spigot extension within the casting , it just needs the 3mm holes to move water around the duct from the case.
This can also be done to a Vortex , as it has a threaded hole in the cylinder - the CIK have confirmed to me in writing this is legal.

[jato]

Re auxillary exhaust ports; i am assisting a small amount with building a set of kawasaki triple cylinders - modern port layout with reedvalves fitted but still non powervalve. at this stage the aux exhaust ducts need to do a gentle loop around the outside of the forward cylinder studs - would this be a no go? the alternative is to relocate the studs but this is not the most preferred solution. any thoughts?

[Rudex]

Thanks Wobbly and Vortex,

Yes, You are right. I checked in R1 case and cylincer is closed. I read the whole thread and see your spigot sometime ago, great idea.
But , my question if the spigot input and the output are connected with ineer conduit, I cant see in picture. Do you have better pictures of case?.

Best Regards.



The factory deleted the water entry up under the Exhaust duct completely with the R1 , as this means the duct heats all the cold water before it runs over the transfer tops.
The 10B and 10C they added a side water hose to push cold water over the duct top only.
The best solution is to use an extended spigot over the top of the duct with holes pointing back over the transfers , and have 2 x3mm holes up from the case to keep some flow
travelling up to the head.
Thr R2 has my spigot extension within the casting , it just needs the 3mm holes to move water around the duct from the case.
This can also be done to a Vortex , as it has a threaded hole in the cylinder - the CIK have confirmed to me in writing this is legal.

[wobbly]

Yes , there has to be a slot in the casting between the crankcase and the gearbox as water enters at the bottom , travels up to keep gearbox heat away from the crank , then exits out the side
up into the cylinder via the external hose.
I tried to get the factory to change the water flow in the R2 by having the cold water entering as normal at the bottom , then up between the crankcase and gearbox , but then to flow forward
in passages over the main bearings . This cold water would then enter the cylinder up each side of the boost port.
Thus cold water cools the transfers immediately . I proved this worked by boring a hole above the boost port , behind the carb , and putting the water hose around into that.
It looked ugly as fuck , and is of course illegal to race , but added 1 Hp instantly.
This was a step to far for TM to do this homologation as I was still struggling with the R2 update to the ports and pipe designs.
I have not split open an R2 case , as no one has done enough Km for a rebuild yet.

[diesel pig]

Yes , there has to be a slot in the casting between the crankcase and the gearbox as water enters at the bottom , travels up to keep gearbox heat away from the crank , then exits out the side
up into the cylinder via the external hose.
I tried to get the factory to change the water flow in the R2 by having the cold water entering as normal at the bottom , then up between the crankcase and gearbox , but then to flow forward
in passages over the main bearings . This cold water would then enter the cylinder up each side of the boost port.
Thus cold water cools the transfers immediately . I proved this worked by boring a hole above the boost port , behind the carb , and putting the water hose around into that.
It looked ugly as fuck , and is of course illegal to race , but added 1 Hp instantly.
This was a step to far for TM to do this homologation as I was still struggling with the R2 update to the ports and pipe designs.
I have not split open an R2 case , as no one has done enough Km for a rebuild yet.

very interesting, I have a picture with flow lines ( the blue lines ) where I think the water flows based on my understanding of your description the other (brown)lines are where I think based on your other descriptions where barriers to flow would have to be place for the water to follow what I think you had said. If I have not done this right please let me know.

[Rudex]

Yes, I remembered when you tested the idea to put the hose in the front of transfers and You got more power.

Yes, the little slot is there, my question is If under this slot will be another bigger conduit for more flow travelling from bottom to the upper part before to exit in the hose to cylinder.
Checking the homologation files, It seems Modena KK3 and Vortex VTZ are similar.
Modena seems a copy of TM case, very similar. And Vortex with water cooled too is near to TM.
Vortex doesn't has the slot but the conduit is under for sure, and the water flow from the upper space to cylinder with the holes only. Modena has the holes under cylinder and use the hose output to lateral flow to cylinder.

BTW, Rexon motors applies similar concept you exposed, only lack the holes between boost port.

Regards




Yes , there has to be a slot in the casting between the crankcase and the gearbox as water enters at the bottom , travels up to keep gearbox heat away from the crank , then exits out the side
up into the cylinder via the external hose.
I tried to get the factory to change the water flow in the R2 by having the cold water entering as normal at the bottom , then up between the crankcase and gearbox , but then to flow forward
in passages over the main bearings . This cold water would then enter the cylinder up each side of the boost port.
Thus cold water cools the transfers immediately . I proved this worked by boring a hole above the boost port , behind the carb , and putting the water hose around into that.
It looked ugly as fuck , and is of course illegal to race , but added 1 Hp instantly.
This was a step to far for TM to do this homologation as I was still struggling with the R2 update to the ports and pipe designs.
I have not split open an R2 case , as no one has done enough Km for a rebuild yet.

[wobbly]

The best scenario would be to have the cold water going over the main bearings , then up each side of the boost port - but the small trick is to have small 3mm holes under the main Exhaust duct
This works with the extra spigot tube in an R1 as well as the R2 that has the tube cast in .
It is important to keep the Ex duct cool , but not use that heated water on the transfer tops - see the small red arrow I added to the R1 flow diagram..
Even better is having cold water between the bore and the inside transfer radius , that is worth 1 Hp in the RSA , and was done on the BSL500 and the KR3.
The Rexon looks good , but the water cannot " flow " anywhere ",so will simply heat up , not cool the alloy .
Unless they are very clever and have the water entry from the case , each side of the boost port.

[Rudex]

Check the pdf, interesting. Look at spigot entry water cooled and the gasked cylinder base and the exhaust port output.

https://www.rexon-motors.com/wp-content/uploads/2019/03/Preisliste-Rexon-2019-V1.pdf

https://www.facebook.com/rexonmotors/photos?locale=es_LA

https://scontent-mad1-1.xx.fbcdn.net/v/t1.6435-9/36763534_823719387824149_958484894848122880_n.jpg? _nc_cat=106&ccb=1-7&_nc_sid=8bfeb9&_nc_ohc=XMKIh_YYWZAAX9NK3z_&_nc_ht=scontent-mad1-1.xx&oh=00_AfB98SrOZlQvltfLLA10-gAurtc0wVFPfl9GhmZ0nFZUmg&oe=65475050


The best scenario would be to have the cold water going over the main bearings , then up each side of the boost port - but the small trick is to have small 3mm holes under the main Exhaust duct
This works with the extra spigot tube in an R1 as well as the R2 that has the tube cast in .
It is important to keep the Ex duct cool , but not use that heated water on the transfer tops - see the small red arrow I added to the R1 flow diagram..
Even better is having cold water between the bore and the inside transfer radius , that is worth 1 Hp in the RSA , and was done on the BSL500 and the KR3.
The Rexon looks good , but the water cannot " flow " anywhere ",so will simply heat up , not cool the alloy .
Unless they are very clever and have the water entry from the case , each side of the boost port.

[katinas]

Kawasaki used a similar cooling circulation scheme for KR 500, that envelopes the boost port first . Same with Suzuki RG/XR 500.

[Flettner]

Just feed it E85 and cool everything from the inside.

[Flettner]

Not this one because its air cooled.
By having two smaller exhaust ports, with extensive water cooling atound the ports and a heavily cooled bridge area, has to be better at keeping 'exhaust charge' cooler?

How much work has been done on twin port exhaust with water cooling, modern transfer layout and up to date exhaust design?

If we are in fact after maximim blowdown time / area.

[SwePatrick]

So,,,
Sorry to disturb your discussion, but i had a big success today and want to share it =)


https://www.youtube.com/watch?v=d1yTN5Y4Ees

Ok,, back to your discussion =)

[Pursang]

So,,,
Sorry to disturb your discussion, but i had a big success today and want to share it =)

No need to be sorry..thanks for sharing! :2thumbsup

[Flettner]

So, the limiting factor for the twostroke ( loop scavenge) is blowdown time / area, ultimately? Run out of time / area to let the gas pressure out.
So if we could magic up some more area, would it give us more time, i.e. hold max BMEP to a higher rpm?
Would we leave ports at 195 and 130 respectively?

[Frits Overmars]

So, the limiting factor for the twostroke ( loop scavenge) is blowdown time / area, ultimately? Run out of time / area to let the gas pressure out. So if we could magic up some more area, would it give us more time, i.e. hold max BMEP to a higher rpm?
Would we leave ports at 195 and 130 respectively?I came to the same conclusion some time (40 years) ago which resulted in my FOS symmetric scavenging system.
Here is a picture that you may have seen in another forum a while ago Neil.
353851

[Javier Ruda]

Hi wobbly, can I have your advice about EGT?

I added an EGT probe but now I realise that it is not that easy to understand what to do with that information, even after reading all your good writings on the subject.

The engine is a Rotax 122 (Aprilia RS125 motorbike) and EGT topped 600 ºC (1112 ºF) and remained constant after >1km pull.

Would it be correct to downjet 1 size and check if the EGT goes ~55 ºF (~30 ºC) higher?

Technical data:
• Unleaded fuel pump 98 octane
• Compression ratio 13.5:1
• Squish gap 0.9 mm on toroidal head
• Ignition timing 15º at 11000 rpm, 6º at 12000 rpm then flat line

[wobbly]

Your method is on the money , but the devil is in the details.
Temp rise from a jet change depends on the area delta , and history tells us you simply cannot rely on factory quality control for mass produced jet sizes.
If you are prepared to bet your motors health on a stamped number - you have to pin size all the orifices.
There are several flow/time based checking systems on the net , but I have only checked Dellorto sizes against pins and a Diesel injector rig , and confirmed the same results.
In that case a normal Dellorto change , say 142 down to 140 would give around 20*C , but I have all the measured intermediate odd sizes as well and 142 down to 141 is close to 10*C.

Next pitfall to be aware of is the timing curve.
15* at 11,000 is perfect if peak power is at that rpm , but if you are holding close to 12,000 with 6* of timing the egt will continue to rise faster and faster.
This is a self sustaining loop , in that the extra pipe heat makes more power , that creates more heat , that creates more power Ad Infinium.
You then have to add more fuel , not to make power , but simply to prevent egt runaway in the overev region.
This then negatively affects the fueling at 11,000 and you may never see the egt drop - that's why its good practice to flat line the ignition with as much timing as you can,
as soon after peak as you can , commensurate with how much overev you actually use for every gearchange point.

Most racebikes I have tuned will drop to 10* about 1000 rpm past peak then flatline , trying to balance the fine line between overev bandwidth and egt at peak.
Of course a solenoid powerjet changes all that , and can run a longer pipe - then using the switched lean off to extend the rpm.

[Javier Ruda]

Thank you wobbly for the all the good information :)

I was not aware of the jet production dispersion being so important, so I will try a method for the measurement.

Now I understand that without the solenoid powerjet you cannot have both peak power and overev. If fuel is used for peak power then it is not enough for cooling egt in low ignition advance overev, and if fuel is used to keep down that egt then it is too much for the peak power.

In fact the Zeeltronic ignition came with a curve 15° at 11000 rpm and 10° at 12000 rpm. I will use that one.

Thanks again wobbly :niceone:

[Flettner]

I came to the same conclusion some time (40 years) ago which resulted in my FOS symmetric scavenging system.
Here is a picture that you may have seen in another forum a while ago Neil.
353851

Thankyou, Ive cleaned out the pattern shop ready for another cylinder construction, for a water cooled twin port 125, a little more serious attempt this time, 54 x 54.

[wobbly]

Neil , please explain what advantage you are hoping to attain with a twin duct setup connected to a T port.
To me all it does is add a shit ton of circumferential wall area , for the same effective diameter , then you have to contend with a 2:1 header , or run two chambers.
Why - Jawa did it a million years ago and how may titles did that POS win.

[husaberg]

Why - Jawa did it a million years ago and how may titles did that POS win.

Jawa won a few :whistle:
but then went to centre port and won some more

[Grumph]

Jawa won a few :whistle:
but then went to centre port and won some more

Ha - I've ridden both in competition. The twin ports were much nicer to ride.

But that's in relation to the levels of suspension and the tyres of the period.

[yatasaki]

Ha - I've ridden both in competition. The twin ports were much nicer to ride.

But that's in relation to the levels of suspension and the tyres of the period.
Bike was killer for corners, making lap times better than some morinis and RDs from higher classes..on shorter tracks
But as you can see, engine itself wants to get rid of second pipe.

[Flettner]

Neil , please explain what advantage you are hoping to attain with a twin duct setup connected to a T port.
To me all it does is add a shit ton of circumferential wall area , for the same effective diameter , then you have to contend with a 2:1 header , or run two chambers.
Why - Jawa did it a million years ago and how may titles did that POS win.

Your comment on Bridged port " the more the hook on the edges of the port the better they go " makes me think if you take that to its end game, the more direct the outlet from each port the better the gas flow.
Plus, way back then they had shitty pipes and terrible transfers and direct air cooling.
Time to re visit it? With a twist on the standard concept ..... should give a lot more blowdown area.

I know it means nothing but my my little AG seems to go alright.

Let the debate begin.

[Javier Ruda]

Today I have just noticed that after chopping the throttle at high engine speed, the egt sensor shows a spike of ~20 ºC for about 2 s, and it is not a fast probe.

Is it normal?

That let me thinking about the pilot jet, but I think it is OK at 1.5 air screw turns.

[wobbly]

I would guess that as you roll off the throttle , the needle/tube annulus area is too small , and this is of long enough time duration to be shown on the data log.

[katinas]

Some testing with silencer reed valve. At first it was interesting just to try, honesty without too much hope. But after back to back tests always return to them and continued testing other things just with them.
There is no feel any difference at mid range, but feels little stronger when engine is on the pipe.

https://youtu.be/YRVyc8Mja0o
https://youtu.be/g0WVwmgPLGs

[Javier Ruda]

I would guess that as you roll off the throttle , the needle/tube annulus area is too small , and this is of long enough time duration to be shown on the data log.

Thank you wobbly. I think you are right. For better progression I reduced the annulus 1 point (needle +2, diffuser +1). I didn’t know that it could affect the throttle closing. It is a bit scary so I will revert it and check again.

[F5 Dave]

Thank you wobbly. I think you are right. For better progression I reduced the annulus 1 point (needle +2, diffuser +1). I didn’t know that it could affect the throttle closing. It is a bit scary so I will revert it and check again.

An old mate used to say "2 Strokes only seize on a closed throttle "

Let's not ponder the accuracy of that, but it certainly is food for thought. Perhaps with a side of supplementary Injector in the cases to prevent that lean blip.

My Air-cooled Honda 100s were keen to nip up only on long tracks if I wanted a clean running pilot fitted. But thermal compromise.

[katinas]

Not this one because its air cooled.
By having two smaller exhaust ports, with extensive water cooling atound the ports and a heavily cooled bridge area, has to be better at keeping 'exhaust charge' cooler?

How much work has been done on twin port exhaust with water cooling, modern transfer layout and up to date exhaust design?

If we are in fact after maximim blowdown time / area.

Old cylinders from useless engines, but not because of two exhaust ports.

With this configuration exhaust orient directly in front of B transfers, maybe this needed some attention.

[husaberg]

Didnt Kensational buld a twin port it was posted on Pitlane?

Neils, this is me Ken Seeber, more commonly known as Kensational.

It .

[Javier Ruda]

An old mate used to say "2 Strokes only seize on a closed throttle "

Let's not ponder the accuracy of that, but it certainly is food for thought. Perhaps with a side of supplementary Injector in the cases to prevent that lean blip.

My Air-cooled Honda 100s were keen to nip up only on long tracks if I wanted a clean running pilot fitted. But thermal compromise.

Absolutely. I only have seized on coastdown or a gear change.

Maybe a leaner slide could help, because it can improve the progression without leaning the pilot or the air screw or the needle tube. I think that the slide should have no effect or little effect at closed throttle, but who knows. I will check if the egt spike continues to happen.

[a.montani]

The factory deleted the water entry up under the Exhaust duct completely with the R1 , as this means the duct heats all the cold water before it runs over the transfer tops.
The 10B and 10C they added a side water hose to push cold water over the duct top only.
The best solution is to use an extended spigot over the top of the duct with holes pointing back over the transfers , and have 2 x3mm holes up from the case to keep some flow
travelling up to the head.
Thr R2 has my spigot extension within the casting , it just needs the 3mm holes to move water around the duct from the case.
This can also be done to a Vortex , as it has a threaded hole in the cylinder - the CIK have confirmed to me in writing this is legal.

Hello to everybody.
My name is Andrea (53 yo) and I am a mechanical engineer living in Italy.
In the middle of july I started to investigate (helped by Neels) how cylinder and engine case cooling impact on 2 stroke engine performances.
Info by wobbly are clear, cold water goes to cool transfers by the 2 holes on the spigot, while duct roof is cooled by other holes. Isn't it?
Is it possible to get other pictures of the spigot and the duct cooling case showed?
In this cooling system how TM manage water flow around the duct (duct floor)? Water exit is always on the cyl head. How is the water flow around the duct?

What about cyl head cooling? Are there any concerns lowering temperature of the head dome? And squish area?

What happens if I let cold water in through the head (currently the outlet) and out through the current inlet?

This is the first time in this forum, if I did something “wrong” please help to avoid this in the next posts.

Grazie 1000 and Regards
Andrea

[lodgernz]

Jan Thiel's book is now available in English. Here are the ordering details:

Price is 25€ per book plus shipping.
Shipping costs are:
Netherlands 7€
European Union 11€
Rest of Europe 14€
Rest of the World 22€

To order more than one book, email to LegacyJanThiel@gmail.com with details and Dolph will calculate the price.
Indicative shipping costs to NZ: 22€ up to 2 books, 53€ up to 7 books.

You can pay either by transferring the total to the following bank account:
Stichting legacy Jan Thiel
IBAN: NL95 BUNQ 2085 4413 19

or by PayPal to
LegacyJanThiel@gmail.com

Please add 3% for the Paypal fee.

Whatever payment method you use, please add a telephone number for the customs declaration, your email for shipping tracing, and leave your full shipping details in the remarks or email to LegacyJanThiel@gmail.com!

[diesel pig]

Jan Thiel's book is now available in English. Here are the ordering details:

Price is 25€ per book plus shipping.
Shipping costs are:
Netherlands 7€
European Union 11€
Rest of Europe 14€
Rest of the World 22€

To order more than one book, email to LegacyJanThiel@gmail.com with details and Dolph will calculate the price.
Indicative shipping costs to NZ: 22€ up to 2 books, 53€ up to 7 books.

You can pay either by transferring the total to the following bank account:
Stichting legacy Jan Thiel
IBAN: NL95 BUNQ 2085 4413 19

or by PayPal to
LegacyJanThiel@gmail.com

Please add 3% for the Paypal fee.

Whatever payment method you use, please add a telephone number for the customs declaration, your email for shipping tracing, and leave your full shipping details in the remarks or email to LegacyJanThiel@gmail.com!

I have been waiting for this! Since my dutch " ist Boss "

[wobbly]

Cylinder Cooling. The problem faced is that we have conflicting requirements in different areas.
We want cold water over ( and preferably ) between the bore and the transfers as well as between the crankcase and the gearbox.
Plus we want to keep the squish surface area as cool as possible as well.
The real hard factor to achieve separately is we want the combustion chamber surface to be hotter , to reduce the temperature delta between it and the burning/expanding gases.
This also reduces the flow of heat energy into the water , directly from the head inner surface.

The TM factory used my idea of a directional control tube over the Exhaust duct that forced cold water directly back over the transfers
by including it in the casting cores.
But they still have the original holes in the case and cylinder , under the Exhaust duct - blocked off.
Thus now in the R2 we have cooler transfers , but only very indirect cooling of the Exhaust duct within the casting.
This is easily fixed by drilling two small holes down into the cold water in the case , with matching holes up under the duct.

Reversing the flow idea may have some advantages , but the worst downside is that no matter how you do it , you will always have hot water between the crankcase and the gearbox.

[F5 Dave]

So perhaps a 2 piece head with ceramic inset in chamber. Nah probably fall out. Hmm. ,

[a.montani]

Cylinder Cooling. The problem faced is that we have conflicting requirements in different areas.
We want cold water over ( and preferably ) between the bore and the transfers as well as between the crankcase and the gearbox.
Plus we want to keep the squish surface area as cool as possible as well.
The real hard factor to achieve separately is we want the combustion chamber surface to be hotter , to reduce the temperature delta between it and the burning/expanding gases.
This also reduces the flow of heat energy into the water , directly from the head inner surface.

The TM factory used my idea of a directional control tube over the Exhaust duct that forced cold water directly back over the transfers
by including it in the casting cores.
But they still have the original holes in the case and cylinder , under the Exhaust duct - blocked off.
Thus now in the R2 we have cooler transfers , but only very indirect cooling of the Exhaust duct within the casting.
This is easily fixed by drilling two small holes down into the cold water in the case , with matching holes up under the duct.

Reversing the flow idea may have some advantages , but the worst downside is that no matter how you do it , you will always have hot water between the crankcase and the gearbox.



Thanks Wobbly for the clarification on the water flow in the cylinder.
I wanted to reverse the water flow in an existing engine to see if there was a performance increase.
The engine is from a direct drive kart so the heat coming from the gearbox is not present and the water marginally cools the crankcase.
The biggest problem is the cooling of the combustion chamber dome which could reduce the benefit of the cooling of the transfers.

What risk do I run if I try to reverse the flow of water?

Thanks

AM

[F5 Dave]

Wish I'd had one of these https://bikestarters.com/product/2-5kw-high-performance-bike-starter/
20 years ago when I was looking to buy a mate's 256 Rotax GP bike. I've since used home made versions, but these are clean.

Main reason I didn't buy the bike was that I'd likely be traveling by myself to Bears events etc.
With Mikunis it started beautifully with helper pushing. Or 5/10 × by yourself. At a trackday I slightly flooded it and arrived at staging hot sweating and puffing.
Nightmare.

Of course I couldn't have afforded the bike and starter even home made back then. . .

[husaberg]

Wish I'd had one of these https://bikestarters.com/product/2-5kw-high-performance-bike-starter/
20 years ago when I was looking to buy a mate's 256 Rotax GP bike. I've since used home made versions, but these are clean.

Main reason I didn't buy the bike was that I'd likely be traveling by myself to Bears events etc.
With Mikunis it started beautifully with helper pushing. Or 5/10 × by yourself. At a trackday I slightly flooded it and arrived at staging hot sweating and puffing.
Nightmare.

Of course I couldn't have afforded the bike and starter even home made back then. . .

A few weeks ago I watched a guy on a modern 4 (honda 600 I think getting pushed up and down the pits with his mates falling in heaps as it refused to fire For about 10 minutes.
I was struck with the realisation that if only Honda had of thought to add a starter motor to its street bikes over 205cc back in the 1960's.:msn-wink:
one of the reasons that the first KR250's were 180 cranks was it was easier to start as all gp were push starts back then. As well as easier on the coupling gears

[flyonly]

Jan Thiel's book is now available in English. Here are the ordering details:

Price is 25€ per book plus shipping.
Shipping costs are:
Netherlands 7€
European Union 11€
Rest of Europe 14€
Rest of the World 22€

To order more than one book, email to LegacyJanThiel@gmail.com with details and Dolph will calculate the price.
Indicative shipping costs to NZ: 22€ up to 2 books, 53€ up to 7 books.

You can pay either by transferring the total to the following bank account:
Stichting legacy Jan Thiel
IBAN: NL95 BUNQ 2085 4413 19

or by PayPal to
LegacyJanThiel@gmail.com

Please add 3% for the Paypal fee.

Whatever payment method you use, please add a telephone number for the customs declaration, your email for shipping tracing, and leave your full shipping details in the remarks or email to LegacyJanThiel@gmail.com!

Anyone getting this book sent to NZ who what’s to share shipping?


Sent from my iPhone using Tapatalk

[F5 Dave]

Anyone getting this book sent to NZ who what’s to share shipping?


Sent from my iPhone using Tapatalk

I'm happy to contribute to a group buy but I can't walk to post office etc so can't be distributor.

Local postage might eat up savings?

[F5 Dave]

A few weeks ago I watched a guy on a modern 4 (honda 600 I think getting pushed up and down the pits with his mates falling in heaps as it refused to fire For about 10 minutes.
I was struck with the realisation that if only Honda had of thought to add a starter motor to its street bikes over 205cc back in the 1960's.:msn-wink:
one of the reasons that the first KR250's were 180 cranks was it was easier to start as all gp were push starts back then. As well as easier on the coupling gears

It's other 2 problems we're the ally square tube frame was built '83/84 so wrong side of pre '82 class. And converted to 17' from 16'. No room for wheels that could carry 250 slicks. Chain scrapped against an ancient 150 or the frame if spaced.

[husaberg]

It's other 2 problems we're the ally square tube frame was built '83/84 so wrong side of pre '82 class. And converted to 17' from 16'. No room for wheels that could carry 250 slicks. Chain scrapped against an ancient 150 or the frame if spaced.

1981 waddon
353871353872



Cameron on KR250

First was heavy vibration, caused by the engine’s one-up/one-down 180-degree firing order, which broke front exhaust pipes (until the team provided a spring-joint in that pipe at the failure point) and sometimes shook the check-valve in the front brake master cylinder such that the rider could pull the lever to the bar without effect. At the US Loudon national the vibration of Harry Klinzmann’s KR-250 broke four of the six tubes supporting its steering head, allowing the remaining two to bend as the front wheel raked itself out!

The vibration problem was solved by changing firing order to 360 degrees (both pistons moving up and down and firing together). When used with a 100-percent balance factor this made the engine quite smooth because:

At TDC and BDC the pistons were going one way and the balance weights the opposite.
At mid-stroke, the front balance weight was yanking forward and the rear crank's weight was yanking backward.
The contra-rotating cranks were geared together by two thin, roughly 4-inch diameter phasing gears, which dipped into gearbox oil. Spinning at 12,000-rpm these gears whipped such heat into the gear oil that paint was burned off the early engines. The first-order “fix” was to drop the original 1,100cc gearbox oil quantity (up to the shaft axes) to 600cc (mostly only first and second wheels actually now touched the oil)

A better fix was to separate the phasing gears from the gearbox oil with a “fence” save for a 1mm hole to let oil in. Gear action would then throw the used oil back “over the fence.” The low oil level required pre-lubing every gear during assembly, for otherwise a dry gearbox would squeal at first start-up.

[F5 Dave]

Yeah it (1980 engine) was in an Armstrong frame before I believe (which likely would have been 82 eligible I guess). Holden probably would have had people to push start him, - before my time though.

[jato]

Re auxillary exhaust ports; i am assisting a small amount with building a set of kawasaki triple cylinders - modern port layout with reedvalves fitted but still non powervalve. at this stage the aux exhaust ducts need to do a gentle loop around the outside of the forward cylinder studs - would this be a no go? the alternative is to relocate the studs but this is not the most preferred solution. any thoughts?

bump - just in case this was missed ...

[Grumph]

bump - just in case this was missed ...

Somewhere back in this thread I remember seeing inserts in stud bores which were shaped to be part of the aux exhausts - but had studs screwed into them above and below.

Husa ? Ring a bell or can we use your search ninja skills please.

[wobbly]

Easy way is to use oversize 4140 studs ( 1/2" =12.7mm ) with the stock 8mm threaded ends.
This was done to the TZ350 LSR title wining engine for both a 3port Exhaust , and a bridged reed intake.
Made over 100 Hp at 12,000.
The FEA confirmed the stress was equal at the thread root diameter when 1/2 the stud was ground away for the duct width needed.

[jato]

Thanks for that - a good solution!

[diesel pig]

Easy way is to use oversize 4140 studs ( 1/2" =12.7mm ) with the stock 8mm threaded ends.
This was done to the TZ350 LSR title wining engine for both a 3port Exhaust , and a bridged reed intake.
Made over 100 Hp at 12,000.
The FEA confirmed the stress was equal at the thread root diameter when 1/2 the stud was ground away for the duct width needed.

Interesting, How did one stop the exhaust gases causing problems in the cylinder bottom and top where the studs meet the different castings

[wobbly]

The studs were a neat fit in the overbored casting thru holes and you can see the groove for a Viton O ring just above the Exhaust cutout level.
Never had any heat issues with the gasket surfaces .
Hours of sim , and hours of TIG.
Fastest Pre 82 Post Classic 350 non streamliner on the salt ( 172 mph stuck in 5th pulling 12,000 ) , the second cylinder is in the Frepin frame now.
Not sure who's more scared of it with 100 Hp , me or Charlett.
He does record 13s around Hampton now , with this thing in it and +50mm swingarm I recon 10s easy.

[Grumph]

I see the inlet side studs are cut away too. Got a pic of the inlet side of the barrels please Wob ?

[wobbly]

Yep , my version of Kenny's factory OW , but faster.
Cant decide what would be scarier a TZ750 with 200Hp or a TZ350 with 100Hp.

[Grumph]

Thanks for the pics Wob.

TZ750 with stock frame would not be pleasant. Where's the Nico Bakker been hidden ?
In some ways the Frepin isn't ideal either. From all i've heard Fred was building for light weight prioritised over stiffness.
And yeah, i know yours is stiffer than the originals.

[diesel pig]

The studs were a neat fit in the overbored casting thru holes and you can see the groove for a Viton O ring just above the Exhaust cutout level.
Never had any heat issues with the gasket surfaces .
Hours of sim , and hours of TIG.
Fastest Pre 82 Post Classic 350 non streamliner on the salt ( 172 mph stuck in 5th pulling 12,000 ) , the second cylinder is in the Frepin frame now.
Not sure who's more scared of it with 100 Hp , me or Charlett.
He does record 13s around Hampton now , with this thing in it and +50mm swingarm I recon 10s easy.

It took me a little time looking at the pics to realise the water jacket had bin cut away to allow the welding for the exhaust ports, I take it they were patched up afterwalds?
Am I reading the code stamped into the top of the piston right and it's a different bore size?

[diesel pig]

I see the inlet side studs are cut away too. Got a pic of the inlet side of the barrels please Wob ?

Good spotting! what size reeds are you using? If I can ask Wobbly.

[diesel pig]

I forgot to ask this in my first Question. I noticed welding on the bottom of the cylinder is it a different stroke?

[husaberg]

I forgot to ask this in my first Question. I noticed welding on the bottom of the cylinder is it a different stroke?

top and bottom from memory
Frepin Replica TZ400
Most if not all the links


http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130563280#post1130563280

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130559561#post1130559561

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130920986#post1130920986

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130639230#post1130639230

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130930712#post1130930712

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130540263#post1130540263

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130346957#post1130346957

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130708802#post1130708802

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130930046#post1130930046

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130410366#post1130410366

http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130411359#post1130411359

One I missed
http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130929996#post1130929996
Bypass
http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130410293#post1130410293
http://www.kiwibiker.co.nz/forums/showthread.php/86554-ESE-s-works-engine-tuner?p=1130410828#post1130410828

[Tim Ey]

Re auxillary exhaust ports; i am assisting a small amount with building a set of kawasaki triple cylinders - modern port layout with reedvalves fitted but still non powervalve. at this stage the aux exhaust ducts need to do a gentle loop around the outside of the forward cylinder studs - would this be a no go? the alternative is to relocate the studs but this is not the most preferred solution. any thoughts?

I would definitely lead the auxilary ports around the studs.
This was done by DEA in a Vespa Smallframe cylinder. Very good design!
https://www.facebook.com/DeaEngineering/photos/pb.100057077397107.-2207520000/1928465263952237/?type=3

[wobbly]

Bunch of questions and answers - the long stroke is from cranks I had made with Mallory added for balancing and is 58mm ( +4 Banshee based ) by Shunchi in Taiwan.
They do HotRods and a couple of others.
The bore is 61.5 using race H1 pistons.
Best combination of rpm and port power I could get for an odd 175cc cylinder size.

The cylinder is a 250G as it had the best ducts Yamaha could do in the RD based case stud layout.
A deck plate was added as the rods are special RD400 with Peek coated flat cages @ 115mm to get some case volume and 1.3 ratio , and another plate was added on the top to get the piston edge -0.8 down at TDC.
The crank has rollers on both ends with straight cut low ratio gears , so the clip slot is moved into the middle balls.
The reeds are RS125 Honda from VeeForce , same bolts as CR125 and are what I used offset in the TZ400 , replacing CR250 to get them back on bore center in the flawed CPI cylinder design.

Re the addition of Aux port ducts - sweeping around the studs may look efficient , but then you have an even bigger disparity between the main duct and the Aux duct length.
This smears out the wave front exiting at EPO even more in time and amplitude.
Wasted studs are the best solution - was done first on the inlet in Eckerolds last 350 privateer title TZ/Bimota by my hero Helmut Fath.

I believe the Baker went bare to OZ , Trev put the engine back in a Yamaha frame.

Question from me - when Dennis won the Shorai challenge at Hampton on the TZ400 there was a shitty condition YB3 from OZ with a young lady on board , I want it , the bike or the girl would do .
Who , where etc etc.

[Storbeck]

Bunch of questions and answers - the long stroke is from cranks I had made with Mallory added for balancing and is 58mm ( +4 Banshee based ) by Shunchi in Taiwan.
They do HotRods and a couple of others.
The bore is 61.5 using race H1 pistons.
Best combination of rpm and port power I could get for an odd 175cc cylinder size.

The cylinder is a 250G as it had the best ducts Yamaha could do in the RD based case stud layout.
A deck plate was added as the rods are special RD400 with Peek coated flat cages @ 115mm to get some case volume and 1.3 ratio , and another plate was added on the top to get the piston edge -0.8 down at TDC.
The crank has rollers on both ends with straight cut low ratio gears , so the clip slot is moved into the middle balls.
The reeds are RS125 Honda from VeeForce , same bolts as CR125 and are what I used offset in the TZ400 , replacing CR250 to get them back on bore center in the flawed CPI cylinder design.

Re the addition of Aux port ducts - sweeping around the studs may look efficient , but then you have an even bigger disparity between the main duct and the Aux duct length.
This smears out the wave front exiting at EPO even more in time and amplitude.
Wasted studs are the best solution - was done first on the inlet in Eckerolds last 350 privateer title TZ/Bimota by my hero Helmut Fath.

I believe the Baker went bare to OZ , Trev put the engine back in a Yamaha frame.

Question from me - when Dennis won the Shorai challenge at Hampton on the TZ400 there was a shitty condition YB3 from OZ with a young lady on board , I want it , the bike or the girl would do .
Who , where etc etc.

This brings up a thing that I've seen a few places but never understood.

Auxiliary exhaust ports lower than the main port seems to be something that is completely universal and I get the impression it has been tested to death and there is not much question that is what works best.

But...why? I don't think I've ever seen an explanation that makes sense (to my possibly dim mind). Usually something about smearing or distorting the wave front...but...since the auxiliary exhaust ducts are longer than the main duct, wouldn't that mean that if they were opening at the same height, the wave from the auxiliary ducts would be behind the wave from the main duct, and in order for them to arrive at the same time you would need the auxiliaries to be higher than the main duct and open first.

OR conversely, if there is some advantage to having the wave front from the auxiliaries behind the wave front from the main duct, couldn't you make the auxiliary ducts longer, and the port height the same, thus getting more time area and/or more space for transfer ports?

The best cylinders seem to not do that, so...I dunno.

[OopsClunkThud]

I would definitely lead the auxilary ports around the studs.
This was done by DEA in a Vespa Smallframe cylinder. Very good design!
https://www.facebook.com/DeaEngineering/photos/pb.100057077397107.-2207520000/1928465263952237/?type=3

On the DEA (and other) vespa smallframe cylinders the aux ports pass inside the studs, but include a bump on the outer edge to clear the stud. The wasted studs could easily be applied to these to remove that bump.

[wobbly]

I must have explained staggered Aux port theory 100 times , but here goes.
Its a twofold act.

Firstly - At EPO , we want the highest amplitude , and longest duration initial wave front ( yes its sonic ) entering the duct and subsequently the header.
This will generate the highest and longest negative pressure ratio at the Ex port around BDC if the pipe geometry is correctly timed.
To achieve this goal we want a single port with the most efficient Blowdown geometry ( ie area ) dumping into the smallest duct area possible.
This is helped immensely by lifting the duct floor ( Jan's genius ) and or necking down the duct exit area to achieve Mach 0.8 ( some tosser called Wobbly's innovation ).

Having the Aux ports lower achieves two goals , it restricts the EPO area , thus generating a high and wide initial wave front , and that wave front is coherent ie because
the Aux duct length is considerably longer than that of the main , this would smear out the high pressure ratio we are striving to achieve if it was active at EPO.
The area at the point the Aux side ducts enter the main is the greatest , and having a later timed high intensity "pulse" entering that area after the main one has passed would in effect create a double
camel hump pressure front that confuses the already complex pipe / wave interaction.
Thus the staggered Aux port is reduced effectively to the role of only dropping the Blowdown remnant pressure before TPO.

Lastly , having concurrent 3 port EPO generates huge Blowdown efficiency , and this kills the front side power , as the staggered transfers actually use remnant Blowdown pressure to
stall flow in the highest TPO , and having very low remnant Blowdown pressure severely reduces the transfer scavenging regimes ability at lower rpm's.

So there you have it SOTA is now staggered Ex and transfers that are subtilty interactive.

[Flettner]

What if the axillary ports and main ports are the same length?

[wobbly]

That would eliminate the time smearing issue but if you then reduced or eliminated stagger , the quickly increasing area presented to the Blowdown pressure at EPO would be much bigger ,
thus the initial sonic wave front amplitude and duration would be commensurately reduced.

Plus then you also have a huge drop in Blowdown pressure at TPO - affecting the staggered transfers scavenging efficiency , and thus front side power capability.

All this theoretical analysis , for me anyway , only applies to outer limit tuning - playing with low bmep shitboxes holds no interest whatever ,
for others its the very reason for staying alive , so no adverse judgment on my part.

[Flettner]

That would eliminate the time smearing issue but if you then reduced or eliminated stagger , the quickly increasing area presented to the Blowdown pressure at EPO would be much bigger ,
thus the initial sonic wave front amplitude and duration would be commensurately reduced.

Plus then you also have a huge drop in Blowdown pressure at TPO - affecting the staggered transfers scavenging efficiency , and thus front side power capability.

All this theoretical analysis , for me anyway , only applies to outer limit tuning - playing with low bmep shitboxes holds no interest whatever ,
for others its the very reason for staying alive , so no adverse judgment on my part.

Im not thinking of low BMEP shitboxes, what if you have considerable more blowdown area? What would you do with it? How would you arrange the porting, Being able to push Peak BMEP to higher revs?

[wobbly]

I really dont know what to think Neil.
As it stands there is no more real estate for extra transfer area to match a big increase in Blowdown STA , and we are already at the outer limit of reliability
reving a 125 to 14800 all day - so increasing the bmep at whatever higher level ,to a higher rpm simply isnt possible.
It would need a complete rethink - Frits 360* radial transfer option comes to mind , but that concept needs a huge amount of practical R & D to work into a viable
mechanical layout - and of course where is the cash going to come from, and who is going to use it in what commercial environment.

[Gradella23]

I really dont know what to think Neil.
As it stands there is no more real estate for extra transfer area to match a big increase in Blowdown STA , and we are already at the outer limit of reliability
reving a 125 to 14800 all day - so increasing the bmep at whatever higher level ,to a higher rpm simply isnt possible.
It would need a complete rethink - Frits 360* radial transfer option comes to mind , but that concept needs a huge amount of practical R & D to work into a viable
mechanical layout - and of course where is the cash going to come from, and who is going to use it in what commercial environment.

regarding this, any thoughts about these weird exhaust port shape? i don't know anything about that, only that they're some italian guys selling vespa kits.
I found them casually on Facebook. Never seen anything like that before tbh, at least it's different

https://www.zeusengine.it/ and ZEUS special components on FB for more pics

[Gradella23]

regarding this, any thoughts about these weird exhaust port shape? i don't know anything about that, only that they're some italian guys selling vespa kits.
I found them casually on Facebook. Never seen anything like that before tbh, at least it's different

https://www.zeusengine.it/ and ZEUS special components on FB for more pics
Ok now i got It: It's some sort of symmetric scavenging with a second boost transfer under the main exhaust. Mm i can't decide if It's dumb or interesting, for sure It's out of the ordinary

[Flettner]

I really dont know what to think Neil.
As it stands there is no more real estate for extra transfer area to match a big increase in Blowdown STA , and we are already at the outer limit of reliability
reving a 125 to 14800 all day - so increasing the bmep at whatever higher level ,to a higher rpm simply isnt possible.
It would need a complete rethink - Frits 360* radial transfer option comes to mind , but that concept needs a huge amount of practical R & D to work into a viable
mechanical layout - and of course where is the cash going to come from, and who is going to use it in what commercial environment.

I remember you once lamenting that if you could lift the head for extra exhaust blowdown, you would. Im not lifting the head (ie no unconventional valve in the head) but I do have the opportunity to build a new cylinder, water cooled, 125cc, with an unusual exhaust port layout that will increase exhaust area. Yes based around the twin port. I just dont want to make a mess of the rest of the cylinder by not taking advantage of an optimised transfer layout, ie timings.
At the moment Im basing all my information largely on using 2 x 65cc ...... because I dont know any better.

[TZ350]

.
Another low BMEP shitter.

353898 353899

Having got excited about the idea of radiusing the edge of the piston in the transfer port area. I thought I would try it on the new Suzuki GP110 (48mm stroke) with its 54mm cylinder from a NSR250 twin.

Max crankcase volume. Long 115mm rod. Crank machined and lightened to within an inch of its life. Balance factor 50%. Tungsten slugs pressed in with 3 tons.

Probably doing the piston edge radiusing wrong.

353900

What it looks like down the bore.

353901

Ok, so this may have been a mistake. The transfer radiuses open the sides of the exhaust port earlier than desirable. Could be an issue. Will see how it goes.

[Flettner]

Wobbly, if the eye ports are essentially 'one way valves' exhaust out but no reverse pulse back up them, what height would you place them?
Exhaust out but then about TPO they shut, to not open again until blow down on the next cycle.
Eye ports and main ports same length.

[Flettner]

.
Another low BMEP shitter.

353898 353899

Having got excited about the idea of radiusing the edge of the piston in the transfer port area. I thought I would try it on the new Suzuki GP110 (48mm stroke) with its 54mm cylinder from a NSR250 twin.

Max crankcase volume. Long 115mm rod. Crank machined and lightened to within an inch of its life. Balance factor 50%. Tungsten slugs pressed in with 3 tons.

Probably doing the piston edge radiusing wrong.

353900

What it looks like down the bore.

353901

Ok, so this may have been a mistake. The transfer radiuses open the sides of the exhaust port earlier than desirable. Could be an issue. Will see how it goes.

Its all most of us can afford to play with.

[F5 Dave]

.
Another low BMEP shitter.

353898 353899

Having got excited about the idea of radiusing the edge of the piston in the transfer port area. I thought I would try it on the new Suzuki GP110 (48mm stroke) with its 54mm cylinder from a NSR250 twin.

Max crankcase volume. Long 115mm rod. Crank machined and lightened to within an inch of its life. Balance factor 50%. Tungsten slugs pressed in with 3 tons.

Probably doing the piston edge radiusing wrong.

353900

What it looks like down the bore.

353901

Ok, so this may have been a mistake. The transfer radiuses open the sides of the exhaust port earlier than desirable. Could be an issue. Will see how it goes.
Tbh it just looks you have created two obvious hot spots on the piston front.
Reduced squish cooling about 50%.
And opened the exhaust port early, but only on the sides.

[diesel pig]

Wobbly, if the eye ports are essentially 'one way valves' exhaust out but no reverse pulse back up them, what height would you place them?
Exhaust out but then about TPO they shut, to not open again until blow down on the next cycle.
Eye ports and main ports same length.

I am just going to state this so if I am right I will look good for a week and if I am wrong I will only look bad a week.
I think Flettner is at least thinking about controlling the port's with a sliding sleeve like a Bistrol aero engine but using a 2 cycle operation instead of 4 cycle operation of the Bistrol.

[Flettner]

I am just going to state this so if I am right I will look good for a week and if I am wrong I will only look bad a week.
I think Flettner is at least thinking about controlling the port's with a sliding sleeve like a Bistrol aero engine but using a 2 cycle operation instead of 4 cycle operation of the Bistrol.

No, conventional bridge port except twin outlet but with more ports further round the cylinder where exhaust normally cant go. Extra eye ports but with a rotating valve that can open and shut as needed. Extra blowdown but thats all.

I still have the sleeve engine in a box waiting for a spare YZ250 gearbox to materialize.

[wobbly]

So this begs the question - does your engine need more Blowdown STA , and more specifically can that extra port time area be matched by a commensurate increase in Transfer STA.
Generating oodles of Blowdown has more downside than it does any perceived advantages , by way of seriously killing front side power capability.
And my previous comments about having excess initial area at EPO still apply , in that this will reduce the amplitude and bandwidth intensity of the wave front exiting into the diffuser.
Again I reiterate all this I take from the perspective of trying to push the boundaries of what can be achieved with current SOTA techniques.

[Flettner]

So this begs the question - does your engine need more Blowdown STA , and more specifically can that extra port time area be matched by a commensurate increase in Transfer STA.
.

Thats my question, can I add more duration to the TP's
Or is what we have now peck twostroke? Unsurpassable.

[diesel pig]

No, conventional bridge port except twin outlet but with more ports further round the cylinder where exhaust normally cant go. Extra eye ports but with a rotating valve that can open and shut as needed. Extra blowdown but thats all.

I still have the sleeve engine in a box waiting for a spare YZ250 gearbox to materialize.

That begs the question do you mean the exhaust eye ports open when the revs rise, like some Yamaha's and Kawasaki's or do you mean the ports that open and close each revolution? A system I remember reading about decade's ago. A lotus test engine using that system had a a mini crank like set up driving off the end of the main crank opening and closing the exhaust valve (the valve would completely close the port each time) each revolution? interesting none the less either one.

[wobbly]

So now we have a circular discussion, what Hp are the transfers capable of now , and if its easy to add a bunch of Blowdown , yes of course its easy to lift the
transfers. But when you do that , you loose Blowdown STA and thus the Hp capability.
We ( you ) need to generate hard numbers of where you are at - then extrapolate out to where you want to be using whatever new geometry has been concocted.
I am assuming , you are not looking to exceed the RSA ( crank ) bmep of 16.5 Bar @ 13000 , but even a much less powerful device needs to have the STA numbers in balance.

Edit - and I am struggling to understand why increasing Blowdown capability is " good " but the return stuffing action from the rear cone is " bad " so needs to be reduced.

[Flettner]

So now we have a circular discussion, what Hp are the transfers capable of now , and if its easy to add a bunch of Blowdown , yes of course its easy to lift the
transfers. But when you do that , you loose Blowdown STA and thus the Hp capability.
We ( you ) need to generate hard numbers of where you are at - then extrapolate out to where you want to be using whatever new geometry has been concocted.
I am assuming , you are not looking to exceed the RSA ( crank ) bmep of 16.5 Bar @ 13000 , but even a much less powerful device needs to have the STA numbers in balance.

Edit - and I am struggling to understand why increasing Blowdown capability is " good " but the return stuffing action from the rear cone is " bad " so needs to be reduced.

No, reverse pulse is not reduced, its redirected back up the main port like a normal engine. The extra eye ports are only there for blowdown after that they 'disappear', at TPO its back to normal twostroke until next cycle.

[TZ350]

353907 353906

Bit of dyno time with the 250 today. Main jet setup for Methanol only and the Pilot jet draws Petrol exclusively.

Started with 3L of Methanol and Petrol. Finished with 1L of Methanol and 2L of Petrol. Much heavier Petrol consumption than I would have thought.

[Grumph]

2 : 1 ratio is about right given the pilot jet is flowing continuously.

[Flettner]

So now we have a circular discussion, what Hp are the transfers capable of now , and if its easy to add a bunch of Blowdown , yes of course its easy to lift the
transfers. But when you do that , you loose Blowdown STA and thus the Hp capability.
We ( you ) need to generate hard numbers of where you are at - then extrapolate out to where you want to be using whatever new geometry has been concocted.
I am assuming , you are not looking to exceed the RSA ( crank ) bmep of 16.5 Bar @ 13000 , but even a much less powerful device needs to have the STA numbers in balance.

Edit - and I am struggling to understand why increasing Blowdown capability is " good " but the return stuffing action from the rear cone is " bad " so needs to be reduced.

So if you had extra blowdown area, you wouldnt use it?
It could be made to not come into play until you run out of normal blowdown (time) area.

[wobbly]

Yes of course but only if the transfer ports could keep up ie balanced transfer and blowdown STA

[Flettner]

Yes of course but only if the transfer ports could keep up ie balanced transfer and blowdown STA

So whats stopping the twostroke making more power, lack of ultimate blowdown or transfer ability?

Ulitimately

[wobbly]

Both are equally important , if you do an analysis of the RSA the power capability of the engines Transfer and Blowdown STA are perfectly matched , when the affect of
the Ex port timing edge radius on the Cd during Blowdown is taken into account.
There is no more room for transfer chordal width around the bore , and you cant lift them without reducing the Blowdown STA.
So that engine is maxed out , porting wise , and any further power increases have to come from using pipe and or Exhaust duct trickery.

[Flettner]

Both are equally important , if you do an analysis of the RSA the power capability of the engines Transfer and Blowdown STA are perfectly matched , when the affect of
the Ex port timing edge radius on the Cd during Blowdown is taken into account.
There is no more room for transfer chordal width around the bore , and you cant lift them without reducing the Blowdown STA.
So that engine is maxed out , porting wise , and any further power increases have to come from using pipe and or Exhaust duct trickery.

So you are saying, if you had more blowdown you could run the transfers higher, to get suitable STA numbers, keep everything in equilibrium.

Time / area / pressure. The next thing to work on is pressure, transfer pressure, I guess.

Im trying to workout whether I should go ahead with this new cylinder, with extra blowdown .... or am I wasting my time?

[Flettner]

That begs the question do you mean the exhaust eye ports open when the revs rise, like some Yamaha's and Kawasaki's or do you mean the ports that open and close each revolution? A system I remember reading about decade's ago. A lotus test engine using that system had a a mini crank like set up driving off the end of the main crank opening and closing the exhaust valve (the valve would completely close the port each time) each revolution? interesting none the less either one.

Opens and closes every cycle but only open for blowdown fase, shut the rest of the time. When shut it turns the main exhaust port into a normal bridged port setup. Although twin outlets at approx 30 degrees each from centre. Much like this but with straight ports not curved and the extra 'Valved' eye ports further round the cylinder. When transfer happens they are shut, ie no influence on the transfer regime.
Am I wasting my time? I was going to get stuck into the supercharged twin (fourstroke) but thats going to cost too much, at the moment. A new cylinder cast is much cheaper and probably less time to build. And fuck fourstrokes 😁

[Grumph]

Ideally you'd do it in a sim. But the speed you can do cylinders - and at what seems to be lowish cost - makes me think you'd have it running before the sim finished...

Play to your strengths.

[pete376403]

Opens and closes every cycle but only open for blowdown fase, shut the rest of the time. When shut it turns the main exhaust port into a normal bridged port setup. Although twin outlets at approx 30 degrees each from centre. Much like this but with straight ports not curved and the extra 'Valved' eye ports further round the cylinder. When transfer happens they are shut, ie no influence on the transfer regime.
Am I wasting my time? I was going to get stuck into the supercharged twin (fourstroke) but thats going to cost too much, at the moment. A new cylinder cast is much cheaper and probably less time to build. And fuck fourstrokes 😁

Build a uniflow - supercharger, ported cylinder for intakes and poppets in the head for exhaust. Best of all worlds

[Flettner]

Build a uniflow - supercharger, ported cylinder for intakes and poppets in the head for exhaust. Best of all worlds

We .... dont do popets. We do ports.

[Frits Overmars]

Build a uniflow - supercharger, ported cylinder for intakes and poppets in the head for exhaust. Best of all worldsUniflow: OK.
Supercharger: hmmm, not very efficient.
Ported cylinder for intakes: OK.
Poppets in the head for exhaust: no way.
A blowdown angle.area analysis will tell you why. Poppet valves rest on their seats. They do not move. When they must open, they start moving with an initial velocity of zero. The open area slowly increases and the cylinder pressure slowly drops, generating a mediocre exhaust pulse.
A piston port is opened by a piston that has reached its maximum velocity when it starts opening the port. The exhaust area opens with a bang and the exhaust pulse is far stronger than what a poppet valve could generate.
One more thing: poppet valves are heated from all sides by the passing exhaust gas. They dearly need the contact with the valve seats to get rid of that heat.
But in a two-stroke they are heated twice as often and their resting time between exhaust phases is halved.

[Pursang]

Other options for serious power increases: RPM & FUEL.

Nicely done analysis here (Well...certainly the best I've seen...)


https://www.youtube.com/watch?v=x7q0w75ZXlQ&t=28s

[Flettner]

Uniflow: OK.
Supercharger: hmmm, not very efficient.
Ported cylinder for intakes: OK.
Poppets in the head for exhaust: no way.
A blowdown angle.area analysis will tell you why. Poppet valves rest on their seats. They do not move. When they must open, they start moving with an initial velocity of zero. The open area slowly increases and the cylinder pressure slowly drops, generating a mediocre exhaust pulse.
A piston port is opened by a piston that has reached its maximum velocity when it starts opening the port. The exhaust area opens with a bang and the exhaust pulse is far stronger than what a poppet valve could generate.
One more thing: poppet valves are heated from all sides by the passing exhaust gas. They dearly need the contact with the valve seats to get rid of that heat.
But in a two-stroke they are heated twice as often and their resting time between exhaust phases is halved.

Yes, exhaust piston on a OP uniflow gets a thermal hiding, key to a successful design is addressing this ..... as you know Frits.

[Flettner]

Other options for serious power increases: RPM & FUEL.

Nicely done analysis here (Well...certainly the best I've seen...)


https://www.youtube.com/watch?v=x7q0w75ZXlQ&t=28s

So, key to more power is same BMEP but at higher revs. More blowdown is needed to achive this, yes?

[skako]

Frits,

I'm thinking, if we raise the transfers, behind that we can see how much the STA blowdown fell. With one additional poppet valve in the head, they could compensate for the lost blowdown STA and increase STA to match the increased transfer STA. To begin with, I would take the total open time of the poppet valve = 2 x blowdown time < 90 degrees of the crankshaft. Thus, the poppet valve would have more time to cool down and the cleaning (scawening) of the cylinder would mostly retain its characteristic.
What do you think about that?

[Frits Overmars]

So, key to more power is same BMEP but at higher revs. More blowdown is needed to achive this, yes?Yes, although... The blowdown time.area is needed to have the cylinder pressure drop to below the transfer pressure by the time the transfers open.
But instead of dropping the cylinder pressure you could increase the transfer pressure. So it's either blowdown or blowjob :msn-wink:

[wobbly]

Neil , you are fixating on Blowdown as you believe you have a method to increase this aspect , but as I keep repeating using Hp = Tx RPM/5252 then to maintain
the T at a higher rpm you need more STA for ALL the ports as the time period is reduced - where is the increase for the Transfers coming from if the chordal width is already maximized.

[diesel pig]

Flettner, The more down this rabbit hole you go the more I think Frits idea for a cylinder design has more merit and manipulating the exhaust pipe returning sonic wave would be better for making the power band wider.

[Flettner]

Sooo, consensus says no to added blowdown.
I wont waste my time on it then, haha, what was I thinking.

[jamathi]

Both are equally important , if you do an analysis of the RSA the power capability of the engines Transfer and Blowdown STA are perfectly matched , when the affect of
the Ex port timing edge radius on the Cd during Blowdown is taken into account.
There is no more room for transfer chordal width around the bore , and you cant lift them without reducing the Blowdown STA.
So that engine is maxed out , porting wise , and any further power increases have to come from using pipe and or Exhaust duct trickery.

The engine was completely maxed out, but after my retirement I improved on it using ENGMOD.....

[pete376403]

Uniflow: OK.
Supercharger: hmmm, not very efficient.
Ported cylinder for intakes: OK.
Poppets in the head for exhaust: no way.
A blowdown angle.area analysis will tell you why. Poppet valves rest on their seats. They do not move. When they must open, they start moving with an initial velocity of zero. The open area slowly increases and the cylinder pressure slowly drops, generating a mediocre exhaust pulse.
A piston port is opened by a piston that has reached its maximum velocity when it starts opening the port. The exhaust area opens with a bang and the exhaust pulse is far stronger than what a poppet valve could generate.
One more thing: poppet valves are heated from all sides by the passing exhaust gas. They dearly need the contact with the valve seats to get rid of that heat.
But in a two-stroke they are heated twice as often and their resting time between exhaust phases is halved.


(Not trying to wind you up) ok next best will be opposed piston two stroke (Junkers, Napier, Commer) with inlet and exhaust ports. Also use turbocharger(s) to recover exhaust energy feeding into supercharger. However it's all getting a bit heavy and complicated. Maybe just a good dose of Nitro :-)

[Pursang]

I believe Frits knows a useful bit about model aircraft engines.

Do they have any clever details/tricks that can be scaled up?

The 'peripheral' exhaust port on the OS engine is quite different to motorcycle practice...except perhaps old Villiers engines.
Does it produce a swirl during scavenging or charge reverse pulse?

[Frits Overmars]

if we raise the transfers.... with one additional poppet valve in the head, they could compensate for the lost blowdown STA..... I would take the total open time of the poppet valve ....The total open time of the poppet valve won't do much good because, as I said, that valve opens really slowly, so 10° after it has started opening the open area is still minuscule and after another 20° it will be hardly any better. You'd better look somewhere else if you want to increase blowdown time.area.
Next: a big advantage of piston ports over valves is that there are no red-hot valves waiting to initiate detonation. And as I pointed out, exhaust valves in a two-stroke get even hotter than their colleagues in a four-stroke.
Lastly: if smearing the exhaust pulse energy because of the length difference between the main exhaust duct and the auxiliary ducts is undesirable, then how are you going to connect an exhaust port in the lower part of the cylinder with an exhaust valve way up high?


Sooo, consensus says no to added blowdown. I wont waste my time on it then, haha, what was I thinking.The way I read it, consensus says no to higher transfers because they force you to increase the blowdown time.area one way or another. I see no objection to added blowdown per se, and I am very anxious to learn what you were thinking.
An aspect of higher transfers that has not been mentioned yet, is the torque dip at 2/3 the rpm of maximum torque, caused by the exhaust return pulse entering the cylinder while the transfers are still open. The higher the transfers, the worse this gets. It was one of the reasons for my symmetrical scavenging with transfers that are no higher than an accepted 130° and exhaust ports with a very mild (compared to most competition two-strokes) 190°.

[Gradella23]

Ok now i got It: It's some sort of symmetric scavenging with a second boost transfer under the main exhaust. Mm i can't decide if It's dumb or interesting, for sure It's out of the ordinary

upping this cause it may have been lost in the meantime, but is somehow related to the topic.. how is that "under-exhaust port" transfer acting in terms of added transfer time.area?
i think the main issue is still matching that (assuming there is any advantage) with enough blowdown area (which i can't see in this layout)

[Flettner]

The way I read it, consensus says no to higher transfers because they force you to increase the blowdown time.area one way or another. I see no objection to added blowdown per se, and I am very anxious to learn what you were thinking.
An aspect of higher transfers that has not been mentioned yet, is the torque dip at 2/3 the rpm of maximum torque, caused by the exhaust return pulse entering the cylinder while the transfers are still open. The higher the transfers, the worse this gets. It was one the reasons for my symmetrical scavenging with transfers that are no higher than an accepted 130° and exhaust ports with a very mild (compared to most competition two-strokes) 190°.


Thankyou Frits, I figured there would be some use in more blowdown, somewhere.

[beta]

The total open time of the poppet valve won't do much good because, as I said, that valve opens really slowly, so 10° after it has started opening the open area is still minuscule and after another 20° it will be hardly any better. You'd better look somewhere else if you want to increase blowdown time.area.
Next: a big advantage of piston ports over valves is that there are no red-hot valves waiting to initiate detonation. And as I pointed out, exhaust valves in a two-stroke get even hotter than their colleagues in a four-stroke.
Lastly: if smearing the exhaust pulse energy because of the length difference between the main exhaust duct and the auxiliary ducts is undesirable, then how are you going to connect an exhaust port in the lower part of the cylinder with an exhaust valve way up high?

The way I read it, consensus says no to higher transfers because they force you to increase the blowdown time.area one way or another. I see no objection to added blowdown per se, and I am very anxious to learn what you were thinking.
An aspect of higher transfers that has not been mentioned yet, is the torque dip at 2/3 the rpm of maximum torque, caused by the exhaust return pulse entering the cylinder while the transfers are still open. The higher the transfers, the worse this gets. It was one the reasons for my symmetrical scavenging with transfers that are no higher than an accepted 130° and exhaust ports with a very mild (compared to most competition two-strokes) 190°.

All good, and then when you know that most of the KZ european/world championship winners in the last years had 198° exhaust 194° aux and 138° A port transfers and they work great (Wold Champ winners) what you have to think? :innocent:
At the parc fermè you see all these cylnders with 1.5mm of gaskets underneath :sweatdrop

[41juergen]

All good, and then when you know that most of the KZ european/world championship winners in the last years had 198° exhaust 194° aux and 138° A port transfers and they work great (Wold Champ winners) what you have to think? :innocent:
At the parc fermè you see all these cylnders with 1.5mm of gaskets underneath :sweatdrop

Maybe because they need more compromise on the given straight line ignition curve whereas any road racer bike used a programmable ignition curve to get the best out of the whole setup and have no gears to shift through?

[beta]

Maybe because they need more compromise on the given straight line ignition curve whereas any road racer bike used a programmable ignition curve to get the best out of the whole setup and have no gears to shift through?
I don't know but it really surprise me the first time I did measure the port timing of the trasnfers.

[wobbly]

Beta , the reason behind the jacked port timings is that I have been instructed that the homologated ports/pipe have to suit " the majority " of the factories customers.
The Euro/Worlds engines are run to over 15,000 rpm all day , then rebuilt after every ( and often replaced during one ) meeting - completely not suited to 98% of the customer base.
In my perfect world the timings would be left down at 196/132 and I would be allowed to shorten the pipe to get the revs and top end power that is being hamstrung by the straight line ignition.
Its a very niche scenario with no useful crossover to " normal " tuning knowledge.

[Flettner]

So what of an extra transfer under the exhaust, an idea worth pursuing?

[wobbly]

Absolutely , but that involves proving having no Exhaust area below TPO actually works as a concept first.
Build a cylinder with both ideas and we will never know the effect each has on performance.

[F5 Dave]

Surely one cylinder, then jb weld transfer closed for 'after' test. Should last long enough. Then burn out. . . Or put on shelf.

[Flettner]

Absolutely , but that involves proving having no Exhaust area below TPO actually works as a concept first.
Build a cylinder with both ideas and we will never know the effect each has on performance.

Would we make it the same height as the rest of the TP's or should we reduce its timing a little?

[Grumph]

Would we make it the same height as the rest of the TP's or should we reduce its timing a little?

I'd be very tempted to open it first. You've already got the cylinder contents heading in that direction by that point.
If the transfer below the exhaust is used to give a pressure pulse to the area below the piston, something's gonna happen.
Any flow back up that port will of course be exhaust contaminated - but if aimed straight across the piston might not affect the scavenge regime.

Happy to be shot down in a puff of exhaust smoke....

[OopsClunkThud]

In CFD simulations the sharp edge of the exhaust port has very little impact during blowdown but as the pressure ratio drops a larger and larger radius is needed to keep the flow from creating eddies* (mixing the exhaust and fresh charge). From this it would seem that if the exhaust floor was raised then it would be helpful to add as large a radius as possible since it has no impact on timing.

But this would get in the way of an extra transfer below the port.

* The downward 25° angle of the exhaust prevents the eddies forming on the roof of the port.

[Pursang]

So what of an extra transfer under the exhaust, an idea worth pursuing?

Possibly some 'challenges' in keeping it well separated from the exhaust duct heat, with a good entry angle.
Maybe it is the transfer to hold up the 'tower' and the (former) A's need to aim elsewhere??
Wobbly is right about evaluating one change at a time but if it is to work well it will be the interaction of multiple elements.

Still... if anyone can, You can do it!

[Pursang]

Yes, exhaust piston on a OP uniflow gets a thermal hiding, key to a successful design is addressing this ..... as you know Frits.

Now we are talking about transfers under the exhaust port....how about secondary transfers under the exhaust piston exhaust ports? Cooling plus some extra transfer STA.
Might also block charge from the intake end escaping out the exhaust. (good for economy, maybe not for racing).

[Frits Overmars]

...How about secondary transfers under the exhaust piston exhaust ports? Cooling plus some extra transfer STA. Might also block charge from the intake end escaping out the exhaust.We're talking opposed piston uniflow scavenging, right? I'm sure the exhaust piston would love the extra cooling.
But preventing charge coming from the transfer side from escaping out the exhaust? I don't think mixture coming from the transfer side will be influenced by any charge originating from behind the exhaust ports.
I'd sooner see it happening the other way around: the main transfer charge pushing the charge coming from behind the exhaust ports, into the exhaust before it has had a change to do something useful, like scavenging the spent gases.
​Besides,with transfer streams coming from both sides we couldn't call it Uniflow any more :whistle:

[Flettner]

Possibly some 'challenges' in keeping it well separated from the exhaust duct heat, with a good entry angle.
Maybe it is the transfer to hold up the 'tower' and the (former) A's need to aim elsewhere??
Wobbly is right about evaluating one change at a time but if it is to work well it will be the interaction of multiple elements.

Having a twin exhaust port does change possibilities.
Water cooling is going to have to be applied very carefully.

[Flettner]

We're talking opposed piston uniflow scavenging, right? I'm sure the exhaust piston would love the extra cooling.
But preventing charge coming from the transfer side from escaping out the exhaust? I don't think mixture coming from the transfer side will be influenced by any charge originating from behind the exhaust ports.
I'd sooner see it happening the other way around: the main transfer charge pushing the charge coming from behind the exhaust ports, into the exhaust before it has had a change to do something useful, like scavenging the spent gases.
​Besides,with transfer streams coming from both sides we couldn't call it Uniflow any more :whistle:

If we are talking OP uniflow, there are many possibilitys, including differential piston sizes / strokes and certainly piston phasing offsets.
Three main issues though
Exhaust piston thermal control
Combustion chamber shape
Transfer flow....

Exhaust piston is a challenge but Im hanging my hat on a steel aluminium composite. To do this I need make an electrode for spark eroding the piston crown underside .... but my CNC is out of action, for some time, so thats put a stop to that, for now.

Combustion chamber shape for spark ignition does hold both advantages and disadvantages, plenty to sort through to get an acceptable outcome.

Transfer, an issue because all the charge wants to do is rush straight for the exhaust. Swirl will slow this but leaves an unscavenged plume in the middle. So far with my OP engines Ive used a combination of some ports swirl and some aiming at the centre of the piston directly opposite each other to help clear the central plume. Now I have a completely different system .... involving transfer 'tumble'. Best idea Ive come up with so far to solve OP uniflow charge transfer issues.

But this will all have to wait ..... CNC electronics are expensive to fix, unfortunately.

[TZ350]

353941

Why ......... with the best power main jet fitted. On straight Methanol this thing would run on after a full throttle 10,000 RPM dyno pull. With the petrol meth combination it still runs on after a big dyno pull.
I would expect that enriching it up would be the cure but interestingly the richer I made the methanol main jet the worse the running on became. Why?????....... :scratch:

Two thoughts, one the Methanol float chamber runs low during a pull (4,3 Delorto Methanol float seat) or there is so much combustion-able fuel being blown through into the pipe mixing with air drawn back through the stinger that its feeding the engine through the exhaust port. Could that be possible? I know that at closed throttle the average pressure in the crank case and exhaust chamber are near atmospheric. So atmospheric air does flow back into the system through the stinger.

When I can I will ask someone to observe the fuel level during a pull to see what happens. Any other suggestions of what to look for would be very welcome.

[F5 Dave]

Is ignition ignitech?
Or are you running a wasted spark ignition? Hmm, single engine, so not likely. . ,

No. No idea

[Grumph]

Very basic question. What plug are you running ?

[husaberg]

Questions i would ask.
Is the main jet really big enough?
is the needle jet too small and acting as a defacto main jet?
Is the fuel flow adequate..

[F5 Dave]

Questions i would ask.
Is the main jet really big enough?
is the needle jet too small and acting as a defacto main jet?
Is the fuel flow adequate..

Ooh. 3. Takes us back to probably my first post near page 1 I guess

[husaberg]

Ooh. 3. Takes us back to probably my first post near page 1 I guess
Yes i was thinking this also, although i thought it was rob talking about his imported tuner (Thomas)

okay you both said it.
First place i remember seeing it was in Bells book

.

This is Thomas a Vietnamese race mechanic, you know that place where they have all those hot 50's and 125's are big bikes.

Thomas, ESE's Race Team's Tuner is fettling number 9. adjusting the port timing for Taupo.

Its hard to see but he has taped a degree wheel to the magneto flywheel so he can mark out the exhaust port height he wants.

None of this raise the port 3.5mm for a gazillion HP nonsense. He knows what timing he needs and sets the crank position there before marking the port and then doing the hells death port job that we all dream of.

You should see him setting up a carb. Talk about pain staking, he starts with a main jet so big the bike floods at about half throttle (apparently this proves the oriface of the needle/needle jet combo is big enough) and then he slowly step by step works back until it runs clean.

Most people start at the bottom with a carb and work up, He starts at the top and works backwards.

Never seen him blow one up. But then he is intelligent with the throttle and does not ring its neck when the engine is in distress.

Boy o Boy am I Looking forward to Taupo.

.


Just add another nut to the end of flywheel, then you can add a bolt that secures the degree wheel. Pointer must be secure (I use a clamped on scriber) & degree wheel should be as big as possible. Barrel must be bolted down well or gives incorrect readings, this can be a problem if engine has thru bolts & a few gaskets used. Use feeler gauge to determine if port is closed by piston, doing it by eye is imprecise.

When starting with another carb just pull the mainjet out, no point putting a big one in. If the engine doesn’t bog past ½ way then the needle is too fat.

[speedpro]

It may seem irrelevant and in this case it may be, but a long time ago in Wellington I was trying to get a crankcase reed RGV/TS combo to run. I'd set the timing to more or less what I knew worked on previous engines. The problem was that it would not rev out properly. Looking down the wide open carb when it was having it's little hissy fit I could see flames dancing around down by the reed valves. In the end out of total frustration I advanced the timing way past where I'd ever had it previously and the damn thing ran sweet. If all else fails give it a go I reckon.

Some sort of valve on the end of the pipe to close it off might be a good idea until the issue is resolved.

[F5 Dave]

And your piston didn't close the bridged ex port if I remember.

[Flettner]

I dont know, but with ethanol you do need to up your fueling when the engine gets hot, or else this very thing happens. Clearly EFI is the go for this but in your class its not legal I guess. Are you running a surface fire plug? Mazda rotary have B11 heat range, surface fire, although a bit expensive.

[TZ350]

Is ignition ignitech? Or are you running a wasted spark ignition? Hmm, single engine, so not likely. . , No. No idea

Yes, good thought. It is a twin Ignitech but with both channels firing into a single coil. Wasted spark?, could be I suppose if the channels are firing 180 apart. I will have to take another look at the settings.

[TZ350]

Very basic question. What plug are you running ?

I have tried several different kinds. Surface gap, and very cold 10's and 11's NGK's and cold Champion competition plugs with fine wire electrodes. Maybe platinum acts as a catalyst for Methanol???? must check that.

[TZ350]

Questions i would ask. Is the main jet really big enough? is the needle jet too small and acting as a defacto main jet? Is the fuel flow adequate..

Good questions, I will have to check them carefully. Definitely big question mark over number three.

The Methanol float bowl has a 4,3 Methanol needle seat and the hoses are fairly large internal diameter. But best by test, so I will see if I can get someone to observe the fuel level during a run.

353943

[TZ350]

I dont know, but with ethanol you do need to up your fueling when the engine gets hot, or else this very thing happens. Clearly EFI is the go for this but in your class its not legal I guess. Are you running a surface fire plug? Mazda rotary have B11 heat range, surface fire, although a bit expensive.

Under plug head temperature hits 105 deg C when making best power but runs on. Bigger jet, and the head temp only hit 85 deg C but runs on much worse.

EFI is specifically banned for Pre 72. Otherwise EFI would have been my choice.

[Flettner]

Yes, good thought. It is a twin Ignitech but with both channels firing into a single coil. Wasted spark?, could be I suppose if the channels are firing 180 apart. I will have to take another look at the settings.

I had that issue, run it with just one channel firing, see whar happens. Although with me it didnt run on, it just ran crap. On petrol.

[TZ350]

.

Here we go:- "Fire and Flame" with Platinum and Methanol https://youtu.be/A2VpA_301rg?si=4JvV0KvNTtNQ8OMD not the total answer for me as not all the plugs I tried had Platinum electrodes.

[Grumph]

I have tried several different kinds. Surface gap, and very cold 10's and 11's NGK's and cold Champion competition plugs with fine wire electrodes. Maybe platinum acts as a catalyst for Methanol???? must check that.

Ran 12's in air/oil cooled GSXR's on Meth/Toluene as they were the only way to get an accurate plug chop. I'm sure you're getting higher head temps than we did.

Don't like surface gap plugs as I've said here before. The plating flaked and I had a runaway Mach 3.

[Pursang]

If we are talking OP uniflow, there are many possibilitys, including differential piston sizes / strokes and certainly piston phasing offsets.
Three main issues though
Exhaust piston thermal control
Combustion chamber shape
Transfer flow....

Exhaust piston is a challenge but Im hanging my hat on a steel aluminium composite. To do this I need make an electrode for spark eroding the piston crown underside .... but my CNC is out of action, for some time, so thats put a stop to that, for now.

Combustion chamber shape for spark ignition does hold both advantages and disadvantages, plenty to sort through to get an acceptable outcome.

Transfer, an issue because all the charge wants to do is rush straight for the exhaust. Swirl will slow this but leaves an unscavenged plume in the middle. So far with my OP engines Ive used a combination of some ports swirl and some aiming at the centre of the piston directly opposite each other to help clear the central plume. Now I have a completely different system .... involving transfer 'tumble'. Best idea Ive come up with so far to solve OP uniflow charge transfer issues.

But this will all have to wait ..... CNC electronics are expensive to fix, unfortunately.

In my OP 'vision' the exhaust porting is almost circumferential. Plenty of STA to allow for secondary transfers behind/below the exhaust ports.
This provides some cooling. Additional piston cooling could be achieved by feeding these transfers like old style boost ports, through the piston skirt.
In order to keep these transfers passages away from the exhaust heat their angle of entry is likely to be directed up the the cylinder axis toward the transfer piston crown.This could displace the stubborn centre plume.
My comment about blocking the main fresh charge from over scavenging was based on the idea of curtains of colder charge passing almost perpendicular to the exhaust ports, timing them late enough that the primary scavenging had been achieved. Pressure and volume of the secondary transfer might be controlled by finding the correct combination of piston diam, stepped piston and/or exhaust crankcase volume.

As far as a name goes...Opposed Piston Multi Flow works for me!:cool:

[Flettner]

In my OP 'vision' the exhaust porting is almost circumferential. Plenty of STA to allow for secondary transfers behind/below the exhaust ports.
This provides some cooling. Additional piston cooling could be achieved by feeding these transfers like old style boost ports, through the piston skirt.
In order to keep these transfers passages away from the exhaust heat their angle of entry is likely to be directed up the the cylinder axis toward the transfer piston crown.This could displace the stubborn centre plume.
My comment about blocking the main fresh charge from over scavenging was based on the idea of curtains of colder charge passing almost perpendicular to the exhaust ports, timing them late enough that the primary scavenging had been achieved. Pressure and volume of the secondary transfer might be controlled by finding the correct combination of piston diam, stepped piston and/or exhaust crankcase volume.

As far as a name goes...Opposed Piston Multi Flow works for me!:cool:
Lets get building then👍

[wobbly]

I always had to run 11 plugs in the Aircooleds on Meth , or got deto/ preignition burning up the middle of the piston or overheating the plug body.
10.5 in Watercooled running 18:1 , same issue.

[Pursang]

Lets get building then👍

Based on your previous work it shouldn't be too difficult to do some 'proof of concept' testing.
Should we take OP discussion to the 'Clean' thread?

[TZ350]

Ran 12's in air/oil cooled GSXR's on Meth/Toluene


I always had to run 11 plugs in the Aircooleds on Meth , or got deto/ preignition burning up the middle of the piston or overheating the plug body.
10.5 in Watercooled running 18:1 , same issue.

353946353947353948

Interesting that the "C" port side of the piston and head is getting the hottest.

Methanol/Petrol. NGK B10EG plug. Plug certainly getting hot. Petrol pilot jet is responsible for the colour I guess.

Will have to see if I can source some NGK B12's or equivalents.

[TZ350]

.
Ok, NGK B12's, couldn't find anything affordable and/or without Iridium (Platinum) electrodes. "Fire and Flame" with Platinum and Methanol https://youtu.be/A2VpA_301rg?si=4JvV0KvNTtNQ8OMD

So purchased some equivalent heat range old school Champion N52R's and C53VC's. They will take two or three weeks to get here.

[Grumph]

I've got D12's left but no B's. Asked around down here but no-one's got any tucked away sorry.

The Champions are really doing it old style.

[TZ350]

I've got D12's left but no B's. Asked around down here but no-one's got any tucked away sorry. The Champions are really doing it old style.

Thanks for asking around for me. Yes, the Champion plugs are old style but they wont have any Platinum in their electrodes. As best as I can make out, Iridium plugs have Platinum/Iridium alloy electrode's or a Platinum earth electrode button. I already have the special tools for adjusting the N-52R retracted gap plugs (NGK 11's). The others are cold surface gap's (NGK 10.5's). So these Champions are still not as cold as NGK 12's. I will keep looking.

[wobbly]

Gota be R plugs for Ignitech remember.
Back in the middle of last century R didnt mean Resistor.
And a Big Block McLaren didnt need an ECU.

[TZ350]

Back in the middle of last century R didnt mean Resistor.

Champion N52R Yes, the "R" did not mean resistor or even racing. It meant retracted gap. the earth strap is retracted back inside the plug body. Extra clearance for high dome pistons I guess.


Gota be R plugs for Ignitech remember.

I am hoping to get away with a higher resistance plug cap. Something like 25k. Currently it is 10k Ohm's. Any suggestions here would be helpful.

[wobbly]

A " normal " setup would be 5K in the plug and 5K in the cap , having extra secondary series resistance probably has more down side effect on turning ignition energy into heat , than it does
forming a more effective RC filter for EMI suppression.
I have used high quality spiral wound ( read expensive ) suppressor wire in one project using the twin fire CDI setup , as the expensive resistor caps for the also expensive shorty plugs were unreliable as they kept going
open circuit .
This seemed to be just as good at noise suppression , as the Ignitech gave no problems.

[TZ350]

.
Have had another thought on this running on problem. Maybe the Blow Down Time Area is insufficient at 10k RPM, leaving a lot of hot nasty stuff in the cylinder. The factory ran these engines to 8,500, with a similar size exhaust port (72%) and blow down I guess. I will have another look at this with EngMod2T.

[husaberg]

I've got D12's left but no B's. Asked around down here but no-one's got any tucked away sorry.

The Champions are really doing it old style.

I will see if i can dig up a few Lodges or a KLG
11.5 but 70$ nz
https://www.nzperformance.co.nz/ngk-r6725-115-racing-spark-plug-2

if you feeling rich you could pay over 2x the rate at Repco $157Nz
https://www.repco.co.nz/parts-service/ignition/spark-plugs/ngk-racing-spark-plug-r6725-115/p/A1054497

[Grumph]

In the late 80's running the GSXR mentioned before, we were offered by the then NGK agent a set of the plugs made for use in the IOM.
No idea of the heat range - but they were made for use from sea level to quite high altitude and widely varying temperatures.

$NZ65.00 each in the late 80's. Relatively speaking the rare competition plugs haven't gone up much at all.

No, we didn't buy them.

[TZ350]

.Have had another thought on this running on problem. Maybe the Blow Down Time Area is insufficient at 10k RPM, leaving a lot of hot nasty stuff in the cylinder. The factory ran these engines to 8,500, with a similar size exhaust port (80atdc & 72%) and blow down I guess. I will have another look at this with EngMod2T.

353949

Ok. EngineMod has the inlet, transfers and blow down peaking about 8,500 rpm and the exhaust port at 7,800 rpm. I had asked EngMod to design a pipe for peak HP at 9,500 rpm. Indeed the engine makes peak power at 9,500 rpm and will touch 10,000 but runs on. I wonder if the rpm mismatch with the exhaust is my problem? Residual hot exhaust gases making it run on. It may be I have to reconsider the expansion chamber and more closely match it's design to the ports potential.

Any thoughts on interpreting RPM figures in the right hand column of the EngMod screen shot would be greatly appreciated.

[TZ350]

353950

When I initially setup the EngMod 2T model for the F81M. I chose 9,500 rpm for peak power. Looking at the target STA's and the STA's achieved. It looks like I will have to lower my ambitions a bit and accept that I my not be able make as high a reeving engine as I would have liked.

[wobbly]

Peak power at 9500 is perfectly achievable , send me the .pack as analyzing the thing needs way more than just timing and STA numbers.
I mean when did any engine making good Hp , since the middle of last century , have all the transfers opening together - that alone leaves a heap on the table.
Normal stagger pumps up the front side by default , and allows many opportunities to then re engineer the peak and overev characteristics.

[jonny quest]

Are you too rich?

I had an MX bike that would run on after throttle was closed. It was pilot jet being too big. It was enough fuel to feed engine through pilot passage.

[TZ350]

Peak power at 9500 is perfectly achievable , send me the .pack

Thanks Wobbly. F81M-RS10,pack file emailed to wobbly1

Thanks Again.
TZ350.

[TZ350]

Are you too rich? I had an MX bike that would run on after throttle was closed. It was pilot jet being too big. It was enough fuel to feed engine through pilot passage.

Thanks for the pointer. It certainly got worse the richer it was. Food for thought, much appreciated.

[wobbly]

Beta , just to be on the same page , was the 198* Duration you actually measured done with the CIK dead stop blade ( 0.2mm @ 45* = 0.28mm actual height change ) and
CIK rotary digital encoder.
I use a 0.7mm blade @ 45* as this gives exactly 1mm of height change on a 50mm digital gauge - easy to then calculate the real timing.

[husaberg]

i came accross this today i have not read it all.'

Step 1: DETERMINE THE CORRECT NEEDLE AND OR NEEDLE JET.

Whether or not your carburetor is a MIKUNI or a KEIHIN, it does not matter. This is the most important step in jetting your carburetor--period!

1. Remove the main jet.

2. Place needle clip in mid-position.

3. Start motor and run it on the stand.


Condition: Motor running and main jet out. Needle or needle jet is correct: Carburetor should run clean to approximately 3/4 throttle. From 3/4 throttle to full throttle, the motor should start to break up as a result of too rich condition.

Correction: None needed.

Condition: Needle or needle jet is too rich. Carburetor runs clean to approximately 1/2 throttle but breaks up before 3/4 throttle as a result of too rich condition.

Correction: Mikuni replace needle jet with next leaner and test again. Keihin replace needle with next leaner diameter and test again.

Condition: Needle or needle jet is too lean: Carburetor runs clean beyond 3/4 throttle and has an erratic throttle response.

Correction: Mikuni replace needle jet with next richer and test again. Keihin replace needle with next richer diameter and test again.


The emphasis here is to find the correct needle or needle jet diameter, which will allow more fuel to pass than is needed but not so much that the needle itself has no control below 3/4 throttle.


Step 2: DETERMINE THE CORRECT PILOT JET.


1. Make sure the bike is warmed up if at all possible.

2. Main jet out.

3. Needle clip in mid position.

4. Turn air screw all the way in then 1/4 turn out.

5. Start motor and run it on the stand.

6. Adjust idle so the bike will just barely idle.

Condition: Motor running and main jet out.



PILOT JET CORRECT:

With one hand on the throttle maintaining RPM at approximately 1/8 throttle, turn air screw 1/4 turn at a time clock wise until you bottom it out. Motor should become slightly erratic and you should have to play with throttle to maintain RPM. Start turning air screw counter clock wise, 1/4 turn at a time until you have reached 2 3/4 turns out. Between 1 1/4 and 2 1/4 turns, your motor should have reached its highest RPM maintaining a steady throttle. Adjust air screw again between 1 1/4 and 2 1/4 until you have determined highest RPM. Quick throttle response should be clean without bog.



PILOT JET TO RICH:

RPM does not reach a peak between 1 1/4 and 2 1/4 turns, stays the same or keeps rising out to 2 3/4 turns.

Correction: Mikuni replace pilot jet with next leaner and test again. Keihin replace pilot jet with next leaner and test again.


PILOT JET TO LEAN:

RPM does not become erratic and motor maintains throttle when air screw is turned all the way clockwise.

Correction: Mikuni replace pilot jet with next richer and test again. Keihin replace pilot jet with next richer and test again. Remember, with a steady throttle approximately 1/8, there should be a distinct difference in RPM from 1 1/4 turns to 2 1/4 turns if the pilot jet is correct. The emphasis here is to find a pilot jet that will run crisp without bog and without the main jet.


Step 3: DETERMINE THE CORRECT MAIN JET.

The main jet selection process is easy once you have the correct needle diameter or needle jet. You now only have to correct a rich condition from 3/4 throttle on up and you know what a rich condition sounds like. Your pilot circuit is correct and without bog.

1. Replace main jet with one that is at least two sizes smaller.

2. Needle clip in mid position.

3. Start motor and run it on the stand.


By replacing the main jet with one that is too small, you are looking for a condition that is too lean. You adjust your main jet from a too small to lean condition.

Condition: Motor running and main jet in.


MAIN JET CORRECT:
Carburetor should run clean and crisp to full throttle.

Correction: None needed.


MAIN JET TOO RICH:
RPM reaches a peak slowly with a deep sound. Excess fuel and oil mixture at end of silencer. Spark plug fowls easily and is dark in color.

Correction: Mikuni replace main jet with next leaner and test again. Keihin replace main jet with next leaner and test again.


MAIN JET TOO LEAN:
RPM reaches a peak quickly but erratic. A quick full snap open of throttle causes the motor to hesitate BEWAH sound or a complete bog. Motor sounds like it has a ring to it. End of silencer white. Spark plug is white in color.

Correction: Mikuni replace main jet with next richer until the BEWAH bog just barely goes away, then replace the main jet with the next richer and run it. Keihin replace main jet with next richer until the BEWAH bog just barely goes away, then replace the main jet with the next richer and run it. The emphasis here is find a main jet that is just rich enough to allow you snap the throttle wide open without the motor bogging as a result of the main being too lean. Should be a quick crisp throttle with no hesitation.



Step 4: DETERMINE THE CORRECT NEEDLE TAPER AND CUT AWAY.
This step in the jetting process can be made very simple if you remain close to stock. However, your needle taper is adjusted for 1/2 throttle to 3/4 throttle. Start off with a rich taper (shallow taper angle) and keep going leaner (steeper taper angle) until it will not maintain constant RPM at 1/2 throttle (runs erratic). Go back to the leanest taper angle that ran the smoothest at 1/2 to 3/4 throttle and that should be the correct taper.

The needle taper final test should be under track conditions with the greatest effect entering and exiting corners. Do not change the needle diameter or needle jet size during this process because that has already been determined. Adjust taper and throttle cut away only.

Throttle cut away effects from idle to 1/4 throttle. The correct cut away will maintain steady 1/8 throttle with quick throttle response. Generally the stock cut away is very close. Experiment with different cut away until it maintains the best response to 1/4 throttle.



QUICK TIPS:
Keep it simple, buy the optional OEM needles or needle jets that are available, as this may speed up the taper selection process. Don't skip any steps or you're just guessing.

[190mech]

husa, Thanks for sharing!!!

[HSuomi]

353941

Why ......... with the best power main jet fitted. On straight Methanol this thing would run on after a full throttle 10,000 RPM dyno pull.

Does this mean that the engine RPM stays high after the dyno run when you pull the clutch?

I'm having similar issue on my 90cc methanol dragster and I'm wondering does it actually make any power in this situation? Im curious because I just built a DIY slider clutch and I wonder if the bike can be stopped with brakes after the 1/8 mile or does it just keep going? :D I have not tested if the engine stops with kill switch in this high reving situation...

[Grumph]

That's a good point. Clarification please Rob. Ignition on or off when running on after a dyno pull please.

My runaway Mach 3 was sitting on 9000rpm with all the plug leads off and only stopped when it ran out of fuel in the bowls.
Which was a giveaway it had another source of ignition.

[peewee]

hey guys let me ask a question. I had a 10mil billet crank made for my banshee engine. I sent four skf roller bearings (nj206ecp normal clearance) to the crank shop to have ring grooves machined then fitted on the crank. I received the crank and unboxed it to find the outboard clutch side bearing was a koyo of c3 clearance. ive not yet talked to the shop to hear their explanantion as theyre closed for the weekend but is this oddball c3 bearing going to cause me problems at some point down the road ? if so im going to demand they put a same type skf bearing on.
for some reason they sent the fourth skf bearing back to me (with groove already machined) and I don't see anything wrong other than the groove appears to be machined so the skf markings would be toward the webs and not visible but I don't see how that would affect anything ? so im stumped until I hear what they have to say

[F5 Dave]

They must have messed one up and got a local replacement.
Why weren't they all C3 as typical?

[peewee]

i didnt know they were supposed to be c3. figured normal clearance. and im not sure how much press fit the inner race has on the web pins. i asked them in a email what bearings i need to send and they said nothing about c3.

yes perhaps they screwed up the 4th bearing and got a local replacement. i hope to figure this out monday but i dont have a good feeling if all the bearings arent the same

[husaberg]

IME all are at least c3 not sure with horizontally split cases though...

[peewee]

looking back through my emails they said they use koyo c3 ball bearings typically but wasnt very clear what roller style they use. he just said nj206 so i assumed that to meen normal clearance. and if they needed to be c3 i dont know why they didnt call to say the normal clearance bearings i sent werent the best choice

[TZ350]

Does this mean that the engine RPM stays high after the dyno run when you pull the clutch? I'm having similar issue on my 90cc methanol dragster and I'm wondering does it actually make any power in this situation? Im curious because I just built a DIY slider clutch and I wonder if the bike can be stopped with brakes after the 1/8 mile or does it just keep going? :D I have not tested if the engine stops with kill switch in this high reving situation...


That's a good point. Clarification please Rob. Ignition on or off when running on after a dyno pull please.

My runaway Mach 3 was sitting on 9000rpm with all the plug leads off and only stopped when it ran out of fuel in the bowls.
Which was a giveaway it had another source of ignition.

My experience with this engine.
RPM stays high after the clutch is pulled in.
Power? hard to tell. But on another bike I ran on methanol it would still pull reasonably hard, nothing like full power. But still made slowing on the brakes challenging. A bit like still being on 1/4 throttle.
Kill switch does nothing. I found I could turn the ignition off and the engine would keep going no problems. The only way to slow the engine was to choke it with a hand over the carb.
Left to its own devices on 100% Methanol. At 9-10,000 rpm with the throttle closed and the clutch in it would run on to 11-12,000 rpm. Shut the throttle at say 8,000 rpm and there would be no issue.
At 9-10,000 rpm it must develop another source of ignition. Because the kill switch was no help at all.

[TZ350]

.

YouTube clip discussing reading Methanol plugs. 4 stroke stuff but still interesting to me:- https://youtu.be/fn6TtIUnIcc?si=THXtk6IXDDUshoGi

The comment about colored plugs mean to much top end lube, suggests to me that with a 2 stroke, a colored plug might not be unusual. It might explain those gunky green ish plugs.
Cadmium heat/mixture burn on the base ring and ignition timing on the earth strap makes sense.

Some more:- https://youtu.be/uNz1na3lqLY?si=jDBnhkA9HTEVDSom and https://youtu.be/rxGP4HDgabw?si=8KV39HspitMtogfw

Ok, so its American drag racing, but practicable guys talking about their methods. They can adjust individual cylinder fueling and ignition timing. 20-25 psi of boost. NGK 9 and 10 plugs. Nickle, No fine wire or platinum electrodes.

[beta]

Beta , just to be on the same page , was the 198* Duration you actually measured done with the CIK dead stop blade ( 0.2mm @ 45* = 0.28mm actual height change ) and
CIK rotary digital encoder.
I use a 0.7mm blade @ 45* as this gives exactly 1mm of height change on a 50mm digital gauge - easy to then calculate the real timing.

Hi,
0.2 blade and digital degree reader yes.

[F5 Dave]

My experience with this engine.
RPM stays high after the clutch is pulled in.
Power? hard to tell. But on another bike I ran on methanol it would still pull reasonably hard, nothing like full power. But still made slowing on the brakes challenging. A bit like still being on 1/4 throttle.
Kill switch does nothing. I found I could turn the ignition off and the engine would keep going no problems. The only way to slow the engine was to choke it with a hand over the carb.
Left to its own devices on 100% Methanol. At 9-10,000 rpm with the throttle closed and the clutch in it would run on to 11-12,000 rpm. Shut the throttle at say 8,000 rpm and there would be no issue.
At 9-10,000 rpm it must develop another source of ignition. Because the kill switch was no help at all.
My last ride on a bucket involved a sticking throttle. Something fell into or apart in a crash damaged whirlpool throttle that I should have replaced but looked OK. I shut the throttle but the carb didn't believe me. It must have been stuck at maybe 1/3 throttle but peak power revs.
They make a surprising amount of power in that condition and can catch you quite unaware, as it did. Uphill sweeper Full Beans knee on deck then slam off throttle, brake and into a hairpin. Except that didn't happen.

My point being, you must fix this to your satisfaction. Running on can be inconvenient, or it can be seriously dangerous. Don't "she'll be right".

[diesel pig]

My last ride on a bucket involved a sticking throttle. Something fell into or apart in a crash damaged whirlpool throttle that I should have replaced but looked OK. I shut the throttle but the carb didn't believe me. It must have been stuck at maybe 1/3 throttle but peak power revs.
They make a surprising amount of power in that condition and can catch you quite unaware, as it did. Uphill sweeper Full Beans knee on deck then slam off throttle, brake and into a hairpin. Except that didn't happen.

My point being, you must fix this to your satisfaction. Running on can be inconvenient, or it can be seriously dangerous. Don't "she'll be right".

I completely agree with that statement. And it can take years to get over some injuries as I can shore you.

[Pursang]

Solved a problem with a 500 Maico that started running way too fast at idle. Scary during an enduro.
Bike had been fitted with new throttle, cable and rebuilt carby (40mm Bing).
Cable end ferrule was slightly smaller diameter than the adjuster screw recess.
Someone (or thing) had tweaked/tugged the cable and it was no longer seating inside the nut but up on the outer edge, lifting the slide, say 6mm. Rubber boot held it there.
It made an appropriate sounding clunk noise when shut quickly and because of the long soft spring the variation in free play was barely detectable.
Solution: Ferrule was bushed with teflon tape and secured with tie wire hooked under the adjuster lock nut.

[aljaxon]

to get a wider power band using FOS exhaust can i just reduce the belly diameter?



im new here, for the last week ive read the last 500 pages on this thread and dont feel qualified to ask my questions but here i am. i want to make yet another pipe. or 3 to see what works best.
ive made a dozen or more pipes using blair, 2t calc and FOS and had a bit of advice from frits on the pitlane forum. ive used janbros excell sheet to get my porting something like.

a new project 74cc kitted moped has only 4 gears - spaced out too far so i need a wider powerband.
porting 180 122, revs to 10500 in third but drops to 7500 when i change up into top.

i dont have engmod2t and being a only humble bricklayer some of it may be above my head.
i am incorporating wobblys duct recomendations 90% for a single ex port. i might try lower as well cos my headers first 2 sections form the "duct" because my cyl tract is only 29mm. ive welded the cylinder up a bit to get a better shape. it was diverging. its now converging slightly and its oval.
ex port effective diameter is 25.1mm blowdown area is 244 so effective diameter 17.6mm
the kits have poor port and tunnel layouts

i have a few other questions about pipe design, would i get a better pipe if i worked out the actual temps in the pipe and applied them to each separate wave ? obviously a wave is like a car doing 70mph. just cos it hits a cooler bit of pipe ie a 30mph zone it isnt going to slow down immediately.

using an average temp could be wrong. or is the temp difference too insignificant to have an effect on wave speed and cone function? to my laymans eye the suction wave travels at a faster speed than the stuffing wave which travels through cooler sections of the pipe.

i do appreciate questions have been asked a thousand times before and it like how long is a piece of string. i dont have engmod so i can run a sim. so its basically guesswork.
i have access to a pals dyno and so can make 3 or 4 pipes and compare them.
i have static ignition set at 16 degrees. its aircooled big fins runs cool reed valve (with stuffer) 21mm carb. i can post up a portmap but all i want is some general advice about wider powerband.

i hope to get a reply even if its dont give up your day job or leave it to the experts lol. but either way its been very interesting reading this thread and ive learned more in the last week reading this than in 12 years of tinkering in my shed.

[jbiplane]

Our new IGBT ignition

https://www.youtube.com/watch?v=CxAyxqQv7CQ

[Flettner]

Wobbly, how high can I make the exhaust dam and get away with it?
More than say 5mm? On a 48 stroke.

[aljaxon]

i tried a reply yesterday with questions, it said it was awaiting admin approval. but its not appeared? so ill try again now.


i want to make a pipe using FOS. ive done a few. if i want a wider powerband due to having wide spaced gears do i simply reduce the belly diameter? i need a 500rpm wider powerband.
blairs recomendations were for iirc 2.125 - 3.25. frits says 3.5 but his belly is shorter which lowers the cones angles back a bit. its a single ex port with 4 real transfers and 3 boost transfers from the reed valved inlet duct.
ive used a wobbly duct 90% on a pipe i recently made for this project and due to cylinder tract being 29mm bore 47mm so duct = 94mm. the 65mm shortfall in duct length ive made as my first 2 sections of the header giving the 90% constriction and then back to 100% of effective ex port. so im thinking instead of 3.5 x exd i go to just under 3? and keep header same so start of diffuser is same diameter to give a shallow angle to the reduced belly? i leave the belly length as it is 8% of tuned length?


also when designing a pipe im thinking that the suction wave travels slightly faster than the stuffing wave due to it passing through hotter parts of the pipe. so should i take the time to work this out? i could take readings of a similar pipes temps and act accordingly. i apreciate all this will do is adjust header and belly lengths a tiny bit.

i also appreciate waves when reaching a cooler section wont slow down to that speed instantly just like a car slowing down entering a 30 limit. cept the wave it will be speeding. :tugger:
most software or calcs just assume an average speed of sound in an average pipe temp. which in the real world doesnt happen?

i havent got engmod2t just a calculator and pencil. i have nicely balanced ports using janbros excel to get my areas angles sta's and blowdown amongst other things.

[wobbly]

Here is just a few ramblings in reply to pipe geometry.

The cooled part of the duct is ideally around 1.5 x bore so 47 bore = 70.5 duct length - as this contains the outer limit of overscavenged mixture available to be shoved back into
the closing port by the return wave.
So fins on an aircooled extension , or water access is helpful to stopping deto induced by over an heated returned mixture volume.

The slip joint out to 2x bore is the steep expansion back to 100% of effective chordal Ex area, and is not technically part of the duct.
In a full noise design the steeper the transition , the better the peak and overev power , but it quickly becomes diminishing returns.

The first general pipe geometry to establish is the piston to header end @ 28 to 32% of TL , longer for broader power delivery , and piston to diffuser end @ 64 to 68% , again
longer for broader power.

The mid section in my opinion isnt an input , its the result given by the chosen diffuser % and the tailcone included angle - again the longer the tailcone the broader the power delivery.
Going from a 28* to a 22* rear cone will hugely affect the power delivery , and those dimensions are absolutely proven empirical data , the mid section length does affect volume , but it
is a secondary function to the other two variables.

If you are not using a simulator but then worrying about the temp induced speed of those waves at varying length positions , is simply way over thinking the issue.
Real world experience gives you the simple diffuser length % data, not a wave speed analysis.

And what is an Ex dam Neil , if you mean the port floor being above BDC to reduce the duct area , then there is only one source of actual dyno tested information.
Jan ( and myself by extension ) have tested 3mm above in a 54.4 stroke , and this works well as long as the Blowdown geometry is optimized for the bmep.
No one to my knowledge has tested above this level and achieved an actual verified result , its part of a list I have had for years - but sure , going higher then grinding it down and testing in increments
is easy to say , but I shit my pants doing any testing of ground Exhaust ports in a chrome bore sitting at 72%.

[aljaxon]

thanks for that wobbly. ive sussed the duct and already made a pipe with a finned header section. i am guilty of calling the steep diverging 0.5 x bore length part of the "wobbly duct".

i was told by a pipe manufacturers "friend" some top secret percentages 12 years ago and realised they were only 1 or 2 percent different to blairs. and the FOS is the similar,

the longer header for wider power confuses me because it then creates a sharper angle on the diffuser which i thought sharper angles - more narrow powerband?
and does my diffuser angle want to be half that of the baffle/rear cone?

without angles i dont know what my diameter will be at mid point.


its because i cant run a sim that i wanted to try and narrow the sums down as much as i can. and once its built there wont be much altering/ testing going on.

today i worked out my diffusers tuned length wants to be 435mm i assume that is the midpoint of the cone? i will compare that to the percentages rule of thumb

i an learning lots. i only learnt today that from 90 degrees ATDC to BDC with my con rod length and stroke isnt 50% of the time of half a revolution but 44%. ive never known this. i then looked at piston speeds at every degree from tpc to epc and averaged them out to see if i could get the stuffing wave returning halfway through the blowdown degrees on the compression stroke, overdesigning?

if im designing and cutting my sections to within 0.5mm then who knows it might be worth considering every variable.
either way i have a big dustbin


im not convinced that pipes designed for modern multi port engines are applicable to my old single port machines with poorly designed transfer tunnels and ducts. but thinking about it a pulse is a pulse. maybe my pipe wont be reaching the same temps and with the motor being aircooled, small finned, running lower compression and general lower state of tune the pipe might need tailoring to this?

[F5 Dave]

I was going to say what is the engine? If you look into, say an RD350 , the transfers hug the vertical. But your port description confused me so maybe something real odd with rv and boosts added?

[wobbly]

One big misconception needs binning immediately - low power , air cooled ,low compression , crap transfers etc etc has nothing to do with the bulk pipe temp , or more specifically
for tuning , the EGT in the header.
You only need to look at the old KT100 Yamaha used in karts forever , they were seeing near 700*C EGT on 91 pump gas as the idea was to utilize as much of the fuels energy to heat the pipe
and make it rev to 16,000 - not heat the fins and loose power from thermal runaway.

Yes header length is a bit counter intuitive , but the vast majority of engines will like close to 32% , and only super tuned , on the edge things will like 29% as this starts the depression at the port face as soon
as possible . In a sim you see the peak depression value moving rightward past BDC as the revs rise , so starting the negative pressure ratio quickly helps maintain this high amplitude value
closer to BDC at peak power rpm.

There is no relationship to diffuser and rear cone angles to give any guidance in what to use - an 18* rear cone will naturally be combined with a small diameter mid , that also then dictates shallow diffuser angles.
A 28* tailcone can only be used with fat mids that also naturally require steep diffusers , and in a few odd cases where a steep rear is wanted to lift peak but kill overev potential.

The mean reflection point of a single rear cone is 1/2 its length if it was extended to a point , but how the hell do you calculate that for a diffuser or tailcone with 3 steepening angles.

What is important is that crap transfer angles and ducts are very easy to overscavenge ie short circuiting is the enemy - best example from many years ago was trying to drag more power out of
a TZ750 , a pipe only a little over 100mm Dia would loose power no matter how clever Erv Kanemoto was at designing the things.
Just as well as nothing bigger would fit anyway.

[aljaxon]

all sounds good wobbly. if i go for a single stage diffuser am i losing out too much? i tried getting my head around blairs multi stage diffusers but to the "power e" mashed my brain. ive searched for a rule of thumb to set multi cone angles percentages. the closest i found was using 2t calc software and borrowing the dims. sort of.

the bike has a gilardoni 74cc reed kit fitted. so not too ancient but nothing like the optimum.

[F5 Dave]

Google. . Oh, a Puch. We never got those.

[Frits Overmars]

i want to make a pipe using FOS...You are trying to mix the FOS concept with the Wobbly concept and you were told more than once that it won't work. I've been trying to answer your questions in the French Pit-Lane forum, but as several people pointed out, you keep repeating the same questions when the answers do not suit you. You even started a new Pit-Lane thread to do it, and now you come here to do it once again.


when designing a pipe im thinking that the suction wave travels slightly faster than the stuffing wave due to it passing through hotter parts of the pipe. so should i take the time to work this out?You'd be wasting valuable time doing that. A typical suction wave might travel at about 300 m/s while a typical stuffing wave might travel at about 600 m/s.
Suction waves always travel slower than stuffing waves. Some reading about gas dynamics might be useful.
Re your quest for a wider power band: forget about cone angles for a while. Concentrate on Helmholtz resonance and try a shallow header in combination with a large pipe volume.

[aljaxon]

frits it wasnt that the answers didnt suit me, it was the cylinders architecture that couldnt be changed. you were very helpful in telling me what i couldnt do in this regard but didnt tell me what i could do. i still dont know. there were only you and janbros offering me advice. janbros suggested tapering back towards the FOS dimensions. i would have loved to have heard something similar from you. or another solution. even if it was less than ideal.

that was on a mobylette with an 82cc parmakit. i tried doing a copy of that motor with the timings you suggested but (still havent a clue as to the pipes start dimensions ) now need some way of getting it past the lack of power at mid range. and with it being a single gear it means fitting a high bite clutch. so i shelved that project. the original project with the flawed durations revs to 12000 and produces peak power at 9k rpm and ive left it alone. . 65mph for a mobylette is fantastic


this is a new project. its a Puch M50 sports. 4 gears. 74cc cylinder. different stroke and porting. im trying to find a pipe to work with the wobbly duct.
you told me the FOS concept wont work with it. but you say the FOS concept is a good start point from which to test and develop, can i not do the same so as to get it working with the wobbly duct? i wont be developing anything i havent a clue. i will just be going for best case scenario.

with me being a humble thick bricklayer i think at times frits you lost your patience with me.

i still want to know what i CAN do in the way of designing a pipe to go with the wobbly duct.
can you or anyone please explain in simple terms why the FOS wont work with the duct? because the reasons might be the same ones that prevent blairs calcs from working. because thats my back up if im not using the FOS.

together of course with wobblys suggested percentages.

is the thinking that smaller belly diameter is for wider power motocross and larger belly diameter is for gp race bikes held by both jennings and blair not valid anymore? and those constants 2.125 - 3.5 x ex port diameter for the mid section are not applicable?

[aljaxon]

Google. . Oh, a Puch. We never got those.

No puchs at all in NZ?
in the uk 16 yr olds were limited to below 50cc and puch were one of the first to have gears. ( later called sports mopeds.) M50 sports were slow 40mph and heavy 85kg, yamaha fs1e's -fizzies and the later puch grand prix were 10 kg lighter. and 5 to 10 mph quicker. mine did as many miles being pushed. in fact thats how ive heard some people say puch as in push or poosh.
https://live.staticflickr.com/65535/53316371246_5a61cfb383_b.jpg