ESE's works engine tuner

[andreas]

Simply, was never acquainted to that method.

[SwePatrick]

Forget the 35 we go to 36 and lost lots of hp
Here you got new exh.

Wow!
That is the most odd pipe i´ve seen.
I wouldn´t bother building that

[wobbly]

The only YZ85 pack I have is for a non PV engine used for flat track racing.
Here is the sim power for its pipe Vs the one shown here I said was weird.
The flat track pipe is already 9mm longer.

I could easily make the flat track pipe longer again to gain back the approx 1 Hp loss up the front side , but that wasnt needed for the application.
With some extra length it would easily match the others power, but with a longer length its up 6Hp @ 12750 and 10 Hp up at 13500.

So clearly its the design that is at fault.
The pipe shown , working back from the tuned length , has a header at 34.7% and a diffuser at 68%, so now I see the power characteristics you can understand why I said " Stuffing "
was on the wrong track , as is the pipe shown here.

[andreas]

Wobbly, can I buy this drawing?

[wobbly]

Only if I get to do it properly with your actual engine info in EngMod.

[andreas]

It would be a treat, but the bike doesn't belong to me, and the pipe is not prioritized to that extent.
I'll proceed to tinker along the same outlines as before. Maybe with a highly speculative parallell first third of the header, and possibly a second wide range pipe for heavy sand.

[dutchpower]

It would be a treat, but the bike doesn't belong to me, and the pipe is not prioritized to that extent.

Non pv bike std.engine and Odd Pipe

[dutchpower]

Changing crank / head / cdi curve and little on the cil. over 30 hp

[Frits Overmars]

Non pv bike std.engine and Odd Pipe

Piet, seems like you could use some software updates.
They're free, you know. Call me.

[wobbly]

I still come back to the fact that no one anywhere ever , I have seen , has published a proven pipe design with a 1.8* header at 34,7%.
Maybe its a thing that everyone has missed for 30 years .
I have close to 150 customer files in EngMod , it needs proving one way or another - but I am fully aware it may be very end use specific to the small YZ .
Same with the 12/30* rear cone.

[husaberg]

I still come back to the fact that no one anywhere ever , I have seen , has published a proven pipe design with a 1.8* header at 34,7%.
Maybe its a thing that everyone has missed for 30 years .
I have close to 150 customer files in EngMod , it needs proving one way or another - but I am fully aware it may be very end use specific to the small YZ .
Same with the 12/30* rear cone.

Out of interest how much time does it take to add in another pipe in the sim Wayne?

[wobbly]

If I have a well working sim and you give me the dimensions it would take 3 sips of single malt.

[Condyn]

Even with the crap transfer geometry of the old piston port air cooled twins I spend my time on, What has proved to work well on the engine dyno is 32/66 with a 3.5-4 degree header angle. I have built and tested dozens of pipes. Anything over 33% with a shallow header has simply not revved. The next batch we will be testing is even less header at 30/31% and longer diffusers 68/69% with shorter and steeper baffles. (CVT utilized engine)

On the chassis dyno and field testing there was another issue. We found the power to fall off relatively dramatically on the top of the run. Something is not in sync, * EDIT * possibly when the pipe temp climbs to a certain range. Or maybe the compression ratio is too high… It must be heat related one way or another.

[wobbly]

The long ( over 32% ) header length scenario with its reduced overev is easily seen and understood when looking at the depression values around BDC .
As the rpm rises the max depression point moves to the right , leading eventually to virtually nil depression before BDC. A short header starts the depression earlier in the cycle , thus keeps the leftward biased wave shape for longer.

In a CVT especially my opinion would be you don't want a long ( 68%) diffuser either , as this will naturally dictate shallower angles than is possible with a short ( 64% ) length - as always , tempered by the law of
diminishing returns.
In this case where you are never low in the power band , I would be looking at 29/30% - 64/65%.
Having a short header with a long diffuser makes the angle issue even more evident - thus is a classic mismatch for the end use.

Yes , a sharp power drop after peak may be affected by heat - too much com or to much advance ( high MSV, same effect ) due to more heat being transferred into the piston/water , than is dumped into the pipe at EPO.
An overly steep rear cone will have the same effect after peak as well - but a 3 angle setup makes it a lot easier to fine tune the peak vs overev dichotomy.

[Condyn]

Very Interesting Wobbly. Am I incorrect in assuming that with Virtually non existent inner radii in the transfer ducts that having steeper diffuser angles would make for even less trapping efficiency? I will try anything suggested.

Here is a log of a test pass I made. 500 foot drag race. The engine rpm is held constant within a couple hundred (yellow). The red line represents the shift curve of the jackshaft connected to the secondary clutch.
The orange line is pipe bulk temp in Fahrenheit which is a K type thermocouple in the center section of the pipe on the centerline. The blue line is cylinder head temp in Fahrenheit. As you can see the pipe temp climbs the entire way through the track and drops off when the throttle is shut where the CHT continues to climb after shutdown. A flat ignition was unfortunately used at the time.