ESE's works engine tuner

[Haufen]

Did you make sure it's really detonating? Maybe something else on the frame is causing the deto sensor to ring the alarm. As far as I understand it, that deto problem you are describing was there from the beginning when you first installed the deto gauge. Are there any other signs of detonation? On an aircooled engine you might be able to hear the detonation, too. Does it occur when the deto sensor is monted in a different place, too? Does it stop flashing the lights immediately when you hit the kill switch on the dyno?

I was once dealing with something similar, sounded just like an engine screaming for help. After a long search, I found out that something else made that sound which sounded exactly the same, and occured in the corresponding speed and load range, too.

[Frits Overmars]

...This over rev deto thing is another problem. Next time on the dyno I will try to...see whats going on and if lowering the pipes internal pressure at high rpm helps.
Thanks Frits and Wob for your help, you have given me a bunch of ideas to work on.

My pleasure, Teezee. Note: the initial blowdown flow is sonic; lowering the pipe pressure will not have any influence on the flow during this phase.
What helps is more blowdown angle.area (wider and/or higher exhaust ports) and improving the flow coefficient by radiusing the upper port edges.

[wobbly]

I wasnt making any inference that you or Frits were silly with that remark, its just that I am sure there will be a solution to the overev deto issue
without adding complexity that no one else has deemed as necessary.
Maybe when into the overev with a high Hp air cooled , the ignition retard that was needed initially to heat the pipe up, isnt needed, and in fact is over heating the plug of gas
in the header, that gets stuffed into the cylinder.
This overheated plug of gas then appears as deto in the squish later in the cycle.
I know from my dyno work that flat lining the timing after power peak prevents the egt from keeping on rising with rpm, past peak power.
In your case try reversing the curve, with a rising timing curve past peak power,of say 3*to 5* between peak power and peak rpm.
This will cool the gas temp in the header, and just maybe kill the deto issue.

[Frits Overmars]

Wobbly has a point here. limiting the ignition retard yields cooler exhaust gas which may even result in your whole engine running cooler.
And in case you fear a loss of overrev, consider lowering the compression ratio. Helps against deto too...
(and in case you fear a loss of power, you could be pleasantly surprised)

[TZ350]

Did you make sure it's really detonating? Maybe something else on the frame is causing the deto sensor to ring the alarm.

Very possible, and is one of the things I am looking for.

[TZ350]

I know from my dyno work that flat lining the timing after power peak prevents the egt from keeping on rising with rpm, past peak power.

In your case try reversing the curve, with a rising timing curve past peak power,of say 3*to 5* between peak power and peak rpm.
This will cool the gas temp in the header, and just maybe kill the deto issue.

I will try that, thanks.

What helps is more blowdown angle.area (wider and/or higher ports) and improving the flow coefficient by radiusing the upper port edges.

I will look at the radius next.

[2T Institute]

If you ride from full throttle to no throttle and nothing in between then you're simply not going as fast as you could/should be.

A fellow who I'll call a 'multiple 125cc GP winner' told me that is exactly how you have to ride a 125, off and 100%.

Adding some advance after peak would limit rpm a bit to.

[F5 Dave]

Not wanting to be a wanka (but it comes naturally so there you go), a kart track & a full size track do require some different techniques.

Being a fellow I'll call a multiple 50ccGP winner (because this is the internet I'll omit that I mean just nationally) I still find on some kart tracks there are occasions that I am not full throttle on a tiddler.

Being realistic either way most of us are nowhere near world level so don't ride like that - so its a mute point.

[teriks]

Wobbly has a point here. limiting the ignition retard yields cooler exhaust gas which may even result in your whole engine running cooler.
And in case you fear a loss of overrev, consider lowering the compression ratio. Helps against deto too...
(and in case you fear a loss of power, you could be pleasantly surprised)

One can get one of those pleasant surprises from running ridiculously low compression in the MB40 too.
Now that's a completely different beast with compression influencing ignition timing, but anyway.

[Buckets4Me]

A fellow who I'll call a 'multiple 125cc GP winner' told me that is exactly how you have to ride a 125, off and 100%.

so compairing a rs125 at pukekohe to a bucket at MtWellington is probably much like compairing a gsxr100 superbike to an rs125 at Pukekohe. And I know you dont ride them full throttle all the time. You would be highsiding the bike EVERY corner on the exit if you did that, or you would be waiting so long after the exit to get full power on that you may as well push the bike.

cracking the power on to hard or early on the exit of the corners will throw you off just ask Nigel about that.

[TZ350]

Attachment 279495

I have been having trouble with detonation in over rev and I hope to cure it by bleeding some of the pipe pressure off when the engine is running in the detonation zone.

A million 2 strokes have run at seriously high Hp levels without bleed systems needed to stop deto at high rpm.

I confused the pipes internal working pressure as set by the stinger/nozzle with the return pressure wave that Frits talkes about.

Jan Thiel
The problem is that the burned gases do not exit the cylinder!
A variable tailpipe might help.

Frits Overmars
A variable tailpipe area, like Jan says, can be a more practical approach. I designed a simple solution, shown in the drawing below.

Attachment 269228

'Opening' the end of the reflector will cause a substantial weakening of the reflected pulse and thus less charging of the cylinder.

So my pipe bleed idea may not reduce over rev deto, but now that I have it I will still give it a try and see what happens.

Howard Gifford
Another way to lower HP without sacrificing piston cooling would be to richen the mixture when you want to lower the power. With a signal to a fuel enriching solenoid you could achieve a power range. It would then be instantaneous and programmable.

Fuel enriching sounds like an idea to try too.

[Flettner]

With EFI you can " artificially " enrich the mixture where ever you like! Why not try an EFI system?
I finally have all the parts here to put together a YZ250 with Link (Atom) EFI ( transfer port injection ). Apart from the disadvantage of cost and weight there are a lot of advantages to be had with engine control.

[bucketracer]

Well I have to admit the motors output is everything I hoped for, and in all honesty what I expected.
The motor design was based on time angle area calculations. Time angle area sets the foundation for how well the motor will breathe and enables matching of port timings. Jennings proposed time angle area back in the early seventies (possibly earlier) but missed blowdown area. The concept of blowdown area was introduced by Blair, at least it was Blairs book "design and simulation of 2 stroke engines" that brought this to my attention. The first dyno run with the KERS was done with a reserved inlet timing in the hope of adding some midrange punch that would benefit kart track racing, it didnt! So I went back to the maths and set the timing to match the other ports. The calculations used for this motor suggested 32 crank hp at 11k, I assumed 15% loses which would be 27.2 rear wheel hp and we have 27.3 at 11.5k.
Of course its not as simple as just time angle area. We are incredibly fortunate with the internet age to have access to fantastic 2 stroke minds such as Jan Thiel, Frits Overmars, Wobbly, etc, etc and of course all the learnings of the ESE boys made available through the epic ESE thread. With the input and advice of these fantastic people it becomes possible for almost anyone to modify something as basic as a farm bike into a (modestly) high power 2 stroke motor. A dyno and an experienced operator helps too .
Big thanks to everyone that has helped both directly and indirectly to deliver this motor, especially TZ350 : Now to get it on to the track

A real testament to the intelligent use of Google and the Internet.

[TZ350]

Can anyone explain what the part inside the pipe is.

When unleaded became mandatory in 98 most teams had a hell of a time keeping deto under control, having to run very rich and retarded.

The cylinders with the straighter pipes always gave alot more grief, untill a lowly dyno operator at Yamaha discovered that when he stuck a large pressure probe into the header, the deto went away.

They managed to keep this secret for a couple of years but when teams like WCM got hold of the bikes, and left pipes lying,word soon got around.

The "things " intruding into the header take varying forms,but all do the same thing - the usually bottom "bent "pipes dont have the same issue, so dont need the so called deto buttons.

I am not running unleaded, but I will keep the idea of a deto button in mind.

[TZ350]

Some of Blairs thoughts on the important features in an expansion chamber.

Attachment 272017

I have been wondering about the static working pressure inside an expansion chamber but I did not see the answer there that I am looking for.

Clearly in a well tuned engine the pipe is at the right internal working pressure around peak torque, but does it continue to build up as the revs climb? And if it builds up, is high internal pipe pressure one of the things that stifles the torque curve on over rev.

Certainly reducing the pipes internal pressure on low throttle openings is a good way to avoid detonation during overrun into a corner or just trickling around the track.

So now the big question is, can we also get more over rev by moderating the working pressure in the expansion chamber?

This was some of my early thoughts that led to making the pipe blead system that I hope to try out next week.