ESE's works engine tuner

[wobbly]

Yea sorry Frits - Kocinski did it in 1990 and Harada won in 1993 on a 56 by 50.7 , then they were nowhere against the square Honda and Aprilia's till 2000 was my point really.

[Frits Overmars]

Yea sorry Frits - Kocinski did it in 1990 and Harada won in 1993 on a 56 by 50.7 , then they were nowhere against the square Honda and Aprilia's till 2000 was my point really.

Point taken and agreed upon. My point was only that the short Yamaha stroke was a whole 0,1 mm longer than what you accused them of

[F5 Dave]

Point taken and agreed upon. My point was only that the short Yamaha stroke was a whole 0,1 mm longer than what you accused them of

Looser main bearings

[husaberg]

Yea sorry Frits - Kocinski did it in 1990 and Harada won in 1993 on a 56 by 50.7 , then they were nowhere against the square Honda and Aprilia's till 2000 was my point really.

Point taken and agreed upon. My point was only that the short Yamaha stroke was a whole 0,1 mm longer than what you accused them of

Not that it matters i am Pretty sure the XR79 Kevin won the 93 500 championship was 56mm x 50.7mm.
I am also pretty sure the YZ500 0Wf2 Rainey rode that year before he was injured was also 56mm x 50.7mm.

[JanBros]

JanBros - yes a shorter header pulls down the port negative pressure ratio earlier in the depression cycle , favouring power around peak.
And the shorter total diffuser length gives steeper diffuser angles that favor power around peak. Front side , after the clutch has locked is set by the length and steepness of the
final diffuser , then the rear cone angle(s) will set the amount of useable power directly after peak.

tnx for all your advice.

while trying to design a pipe, my brain short-cutted.
I'm struggling with why the diffuser needs to begin earlier (shorter header). why not just keep the +/- 66-34% , keep the header angle small and make the first diffuser steeper, and maybe make the belly a bit bigger to get steeper angles? isn't it so that the first parts of each sector are for the higher rev's (end powerband) and the last parts for the lower rev's (where the powerband begin's, what you call front side) ? and having the diffuser earlier makes it a bit "out of sync" with the rear cones ?

so what is the advantage off having the diffuser begin earlier ?

[Condyn]

Thank you Wobbly and Frits for clearly painting the picture of why square is better!

JanBros, take what I say with a grain of salt as I am only a hobbiest chump, but a head pipe typically has an angle of between 2-4 degrees and the first diffuser section will be much steeper than that resulting in a more pronounced suction.

Everything I am about to say is talking about my elevator shaft 70s air cooled piston port

On a cvt engine that TRADITIONALLY is tailored for a small amount of front side and mostly peak operating rpm, using a header longer than about 31 percent In my experience ends dismally. With a long header 32-34 there is usually a torque hole in the dyno graph or a double peak before falling off. Not good for a CVT, because if you fall in the hole, there is no getting through it. The header seems to be the most sensitive part of the pipe that sets up everything else. As of late I have been trending towards more shallow headers closer to 3 degrees with good elapsed time field testing results, but still keeping them around 30 percent. I have not dyno tested the more shallow (than my average) headers yet, but if they are working better in the field that is all that matters to me. Maybe the shallow header is helping spread the power out, and maybe that is exactly what is needed in my short duration drag runs where the pipe temp never stabilizes. All of this is just my thoughts and any of it could be dead wrong. I am open to any constructive criticism.

[wobbly]

Its all to do with the distribution of the depressions amplitude before and after BDC.
A shorter header pulls down the depression deeper and earlier between EPO and BDC , gaining peak and overev - but steeper headers seem to work better when longer is needed.
Usual story , this gain is always at the expense of the capability somewhere else.
Then a steeper and shorter first diffuser enhances peak and overev as well.
A steeper and longer last diffuser holds a deeper depression after BDC and just prior to the rear cone removing it all together - enhancing frontside ( power leading up to the peak ).

As the rpm rises the greatest negative pressure ratio amplitude moves rightward , culminating in the deepest portion happening just prior to it suddenly going positive.
At this point there is hardly any amplitude between EPO and BDC
Watching this happen , cycle after cycle on the screen is the only way to actually get a handle on the effects.
The total energy available is finite - so no free lunch.
The Wave viewer that shows the waves amplitude, travelling down the pipe elements in turn is a supremely enlightening use of trickshit science at work , Neels genius code in action.
Learn how to use its powerful visuals.

EDIT - look at the R1 pipe I have published , a very short header with steep first diffuser - pumping up peak and overev , along with a long very steep last diffuser - pumping up late front side.
This gives an engine with no PV , no PJ and a straight line ignition the max achievable from 10,000 to 14,800 with a peak at 13,800.

[Frank S.]

EDIT - look at the R1 pipe I have published , a very short header with steep first diffuser - pumping up peak and overev , along with a long very steep last diffuser - pumping up late front side.
This gives an engine with no PV , no PJ and a straight line ignition the max achievable from 10,000 to 14,800 with a peak at 13,800.

Hi Wobbly,
while looking at the R1 pipe I wonder what it would look like with a programmable ignition. What would you change? Would you make a complete new pipe or only adjust 1 or 2 parts of it?

[wobbly]

The main factor would be that retard past peak would dump heat into the pipe , thus the TL is way too short and it would rev past the mechanical limit we
have now of 15000.
Changing the TL to at least +25mm would mean every dimension would need to be adjusted to suit the fact that a ton of advance would pump up the mid
and even the rear cones now dont need to worry about limiting overev.
In short - start again.
You got a spare 3 months to sim ,CAD,laser.roll,weld,hammer,dyno,repeat.
Hardest decision is when do you stop.
Here we are 4 years later and it only took three weeks to do the R2 with around + 2 HP - easy.

[Frank S.]

This excessive overreving is exactly what I noticed after using the digital ignition.
But if you extend the TL, doesn't the resonance drop to lower rpms and you lose hp?

[wobbly]

Thats easy - change the Exhaust timing to get superposition ( that is an endless combination set of TL and EPO ) where you want it , to get back the Hp.
Just one of many options available - look at the RSA with a TL of 800 and an effective EPO of 81*, that gave max power at 13000 but it also had a PWM - PJ in play
so the KZ pipe would have to jigged around that issue.
But if you have a programmable ECU then a PWM - PJ is easy if the regs allow it.
Then you may as well add a 42mm carb , a PV and a Rotary Valve - see where this is going.
Jan spent a couple of days on my simulation of the RSA and got 60 Hp , having never used a sim before - see where that is going.

[crbbt]

speaking of 250's and pipes.

Wob, you wouldn't happen to have jig for making pipes for a NX5?

Or any interesting information about?

I am guessing the production racers would have been below your realm

[ken seeber]

Gedday. It's been a while.
This discussion on exhaust shape and length is very timely, particularly to myself. For some time (and with many distractions) I have been trying to get the DCI system to show a hint of life. A previous version, which went into the A ports showed it operating, but this was masked by the fact that, around TDC, the port communicated with the crankcase because of the transfer cutout in the piston.

This time it is into the B port, with no such communication.

So, with a normal old style kart exhaust, it does not respond in terms of even a small speed change, irrespective of the nominal rpm set point, ranging from 8 to 14k rpm. I will admit to a totally out of control testing regime in terms of temps and mixture etc.

So, the question is would I be better off with a different exhaust, one that provides a stronger depression around TPO?

I’m convinced it’s gotta work.

[diesel pig]

Jan spent a couple of days on my simulation of the RSA and got 60 Hp , having never used a sim before - see where that is going.

I wonder if a lot that power increase was Jan changing the "great leader's" exhaust pipe? I know Jan and Frits were not impressed with his exhaust pipe design.

[wobbly]

I did a NX5 pipe design for a LSR winning project but all that with laser dxf etc info was lost when my dyno laptop was stolen from my workshop.
But I may have a backup on an old hardrive - will have a look over the weekend.

Diesel - part of it was my smaller duct exit and yes , the Leaders pipe was a flawed design that Jan was forced to make work.
His radiused Exhaust timing edge was pure genius at the time , real outside the box thinking.
Its now proven in that an STA analysis of the measured numbers shows the Blowdown lags the Transfers by about 10% - but the added radius would dramatically improve the Cd of the port and
bring it into line without needing port timing increases that would compromise the really effective superposition factor.