ESE's works engine tuner

[SS90]

The last section of the expansion chamber, called the 'stinger', is in reality a bleed
pipe. Its function is to restrict gas flow out of the exhaust and create back pressure by
slowly bleeding off exhaust gas. This serves to assist the positive pulse wave in pushing
any spilled fuel/air charge back into the motor.


the stinger dimensions which I have found to be most
successful. You may find that a minor reduction in pipe diameter will raise the power
output, but do be careful. A stinger pipe smaller in diameter or longer than specified
could easily result in engine overheating and seizure. Therefore, I would suggest you
make only small changes and then thoroughly test the pipe before going any smaller.
Engine overheating, in its early stages, is indicated by the presence of oil burnt dark
brown under the piston crown. On the next stage the burnt oil turns black, until finally
'death ash' appears. After this, the piston can be holed at any time.

thank you Graham Bell

I think that Shellracing was questioning the Muffler system, and it's effect on power, opposed to the "stinger" section of the chamber...while the two are related, Have you found anything in Bells book on Mufflers, and their effect on power?

[Buckets4Me]

I think that Shellracing was questioning the Muffler system, and it's effect on power, opposed to the "stinger" section of the chamber...while the two are related, Have you found anything in Bells book on Mufflers, and their effect on power?

did Bell have a problem with noise ?????
or buraRats and neibours ?????
them where the days Ay Tz no 98db limit for the TZ350 back then

[Pudding]

Abstract from:- http://www.sae.org/technical/papers/941911

"The combustion chamber surface was coated with a 0.5-mm thickness of ceramic. Test results show it affects the performance at higher speeds and at higher loads to the extent of knock and loss of brake power by about 18%. "

So now we know for sure, ceramic coating does not work for high performance 2-stroke race engines.

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You guys are pretty smart, figuring out ceramic won't work and then later finding an SAE paper that proves you were right. Good on you clever bastards, tell Thomas I think he is good looking . I just love brains.

[F5 Dave]

Well he did say 'tailpipe (muffler)' so was combining the issue.

You can use the muffler as the stinger is space is restricted, but important to repack muffler, which should do regularly anyway as will create turbulence.

Often neglected is the baffle section if very steep will increase piston temp as well.
As always the interrelationship is a compromise & nothing should considered in isolation.

[SHELRACING]

Thanks SS90 / F5. I was referring to the Muffler rather than the stinger but all information is usefull, will repack my muffler anyway.

Another question then (probably obvious to some). What's the difference between 2 stroke and 4 stroke packing, as you may have guessed I have four stroke packing that worked well on a Pit bike type muffler, can I use it on the 2 stroke ??

Cheers Steve

Hey Sorry I may have dragged you a bit off topic TZ

[TZ350]

Hey Sorry I may have dragged you a bit off topic TZ

Its all good. Its interesting what others are working on, we all learn from it, and the suggestions others make.

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[craisin]

Thanks SS90 / F5. I was referring to the Muffler rather than the stinger but all information is usefull, will repack my muffler anyway.

Another question then (probably obvious to some). What's the difference between 2 stroke and 4 stroke packing, as you may have guessed I have four stroke packing that worked well on a Pit bike type muffler, can I use it on the 2 stroke ??

Cheers Steve

Hey Sorry I may have dragged you a bit off topic TZ

hey Ive still got the muffler that was on the RM when I first got it Steve it came off that chamber that had been altered at the front to suit the TS250 motor that was on it when I was given it.
I was going to put it on the four stroke.
you can have it if you want

[craisin]

sorry a mate came round i will PM you say hello to nana for me

[bucketracer]

Inspired by TZ350 I have been looking over SAE papers,

...............and Whats This!!!!

"The drop in delivery ratio caused by increasing the crankcase volume can be fairly well compensated for by tuning the exhaust and inlet systems. "

from SAE Paper:- http://www.sae.org/technical/papers/670030

didn't Speedpro say this earlier?
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[SS90]

No, I did, in one of my first posts.

I also went on to explain that there was advantages in having a ratio of 1.5:1, but no real gains over that.

It all goes back to the days when, due to production costs, (and piddly little cranks) most machines where about 1.3:1, and increasing that brought gains...... it seems the concept just got stuck in peoples minds, and they always took that approach.

That's when Teezee measured his, and found it was something like 1.33:1

So it looks like he could get some tangeable gains with increasing to something closer to 1.5:1, but of course,he (and most people are now aware) that it's not just a matter of "increasing and decreasing", you have to know what you have, and, what you should end up with.

Think of this....Lower/raise your primary compression...SURE! to what value?

We always measure our cylinder compression (don't we?), no-one in their right mind would alter cylinder compression with-out measuring 1) what they have now, and 2) working out what they want it to be!

The same is true of primary compression.

Although, mistakes with crankcase volumes are far less catastrophic than cylinder compression ratios!


I think it was the Yamaha race engineer Fujio Nagaio that did all the work for us in regards to maximum values.

He probably wrote the paper you read....the quote you used are his exact words!

It's not just a matter of "lowering (or raising) the primary compression" if you want to make a fast two stroke, you have to apply values to each modification you make. Remember that the power stroke on a two stroke engine as bloody feeble (at best), and the difference between a fast two stroke and a slow two stroke is the STRENGTH of it's power stroke. (this is why two stroke engines make such big gains with cylinder compression) In my opinion, Tuning a two stroke well is when you pay attention to this concept.
Don't forget that, because of the limitations placed on 2 stroke 125cc bikes in Bucket racing, Teezee will never have "a properly tuned intake"...... the carb is too small, and as such, his engine will see quite big gains from getting the primary compression ratio to as close to 1.5:1 as possable!

I can't help but think that we are all waiting for Teezee's first dyno runs on the current set up, then compared to his planned mods he posted a week back.... I know I am!

[TZ350]

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Increasing the primary compression ratio to 1.5:1 or as close as, along with improvements to the transfer window (improvement hopefully) is very near the top of my to do list.

Picture-1 is what the piston looks like in the transfer window at BDC. Picture-2 is the underside of the piston. Picture-3 is the topside of the piston. Not very coloured on the underside, and I wonder if I can lean it out a bit more? but it sure looks like its hot on top, I don't understand it? maybe the oil?.

Hopefully get the bike onto a dyno tomorow. Its a home made one and used by a lot of Bucketers. The Guy who runs it sure knows what he is up to but I understand printing graphs is an issue and I will have to take a photo of the computer screen. heres hoping I can get a base line graph to start work from.

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[TZ350]

Abstract:from http://www.sae.org/technical/papers/690136

"In order to increase the air charge of crankcase-scavenged 2-stroke-cycle engines, the relations between delivery ratio and engine speed were investigated on a rotary disc-valve inlet port engine and on a conventional piston-valve inlet port engine by varying through wide limits the angle area and timing of the inlet port.

For the inlet port configuration tested on the first engine, it was found that there was an optimum cut angle of the rotary disc valve, which produced a certain angle area. To improve the delivery ratio characteristics at a given speed, it was not necessary to change this angle area; it was effective to change only the timing of the inlet port by shifting the disc valve around the crankshaft.

For the piston-valve inlet port engine, the results showed that a wide, low port, which was also found to have a higher flow coefficient, produced a higher delivery ratio over the entire engine speed range than a narrow, high port. For the configuration tested (with no inlet or exhaust pipes), the maximum delivery ratio of the wide, low port was nearly in proportion to the effective crankcase stroke"...................................


(1) Interesting, that there was an optimum cut angle of the rotary disc valve, which produced a certain angle area. To improve the delivery ratio characteristics at a given speed, it was not necessary to change this angle area; it was effective to change only the timing of the inlet port by shifting the disc valve around the crankshaft.


(2) And for piston valve inlets, that a wide, low port, which was also found to have a higher flow coefficient, produced a higher delivery ratio over the entire engine speed range than a narrow, high port.

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[speedpro]

(2) And for piston valve inlets, that a wide, low port, which was also found to have a higher flow coefficient, produced a higher delivery ratio over the entire engine speed range than a narrow, high port.

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The only trouble with achieving this is that on the motors we use such as TS100/125ERs for instance, if we move the port floor so that we get the timing we need then we get to a narrow part of the barrel which limits how wide the port can be made. In fact the lower part of the port has to be narrowed so you end up with a "T" shaped inlet port with a bridge down the middle. Because it's narrow at the bottom by necessity you need to keep a bit of height to get the area. I see why it would work though - you end up with the port timing required for good resonance and a reasonable port cross-section for velocity. Having said that you can with a bit of careful work end up with a pretty good piston port on a TS100 motor.

[SS90]

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Increasing the primary compression ratio to 1.5:1 or as close as, along with improvements to the transfer window (improvement hopefully) is very near the top of my to do list.

Picture-1 is what the piston looks like in the transfer window at BDC. Picture-2 is the underside of the piston. Picture-3 is the topside of the piston. Not very coloured on the underside, and I wonder if I can lean it out a bit more? but it sure looks like its hot on top, I don't understand it? maybe the oil?.

Hopefully get the bike onto a dyno tomorow. Its a home made one and used by a lot of Bucketers. The Guy who runs it sure knows what he is up to but I understand printing graphs is an issue and I will have to take a photo of the computer screen. heres hoping I can get a base line graph to start work from.

.

Hmmm,
Damn! I see the problem with the piston "shouding" the available transfer area, and I suspected as much, it's something I had to deal with before.

Somewhere at work I have a piston that I modified (with success) for just such a problem, I'll go there after lunch and see if I can find it.

It is (of course) dangerous to modify this part of the piston too much, as it weakens the skirt area, but obviously a little helps alot!

I know a few aftermarket manufacturers who make special pistons for just such an occasion, with webs cast inside the skirt to strengthen it. I'll have a look for those too.

[TZ350]

Thanks...Any ideas and pictures on unmasking the transfers would be helpfull.

I have run into problems before by cutting the skirt to unmask the transfer.

The problem with the GP is that its transfers are arranged on an angle, unlike most bikes that have the transfer windows square across the motor. Which means that pistons from other motors have to have their transfer windows cut back a long way.

On the pistons I have cutting the skirt, cuts away some bracing cast into the piston and the pistons are prone to cracking.

Wiesco pistons have a thicker forged skirt that might be more usefull and I am trying to get one the right size, 56mm with 16mm pin (1988-1990 KX125).

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