Yamaha TRX850 Enthusiasts Forum

Standard TRX 850

Max power @ 6500 rpm:
6500/60 = 108.33333333333 rps

1 revolution = 0.0092307692 sec
for 214 Degrees of 1 Revolution it is 0.005871795 sec (that is from when exh opens 44 before BDC and Inlet opens 10 before TDC (assume open and close rates are the same)
Speed of sound 382.2m/s @ 100 Deg Celsius (thumbsuck)

382.2 x 0.005871795 = 2.2442m Seeing the negative pulse must go all the way back through exhaust 2.2442 / 2 = 1.1221m (in order to suck inlet gas)
That is the length of the exhaust open pipe including internal port to valve seat. 1 Pipe per cylinder, no interconections (no powerbombs)

It seems short...did I miss anything? Cam info take as per Cobba info.

I wish it was that simple then all your cheaper aftermarket exhaust systems would give you further gains. Check out this link and it will explain in basic terms the nature of the beast.
2-1-2 exhaust if designed correctly will always give you further gains in midrange than a 2-1 due to the pulse nature of the 270* crank.
Smaller headers give you velocity and the conical nature of the Akra system spreads the peak of the pulse across a wider rpm range so it doesn't spike so much at a given tuned rpm.


http://www.epi-eng.com/piston_engine_te ... nology.htm

Yes...my statement only reflects the pulse issue. The dynamics of the gasses flowing is another beast.
I am however enjoying the learning curve .....something you have enjoyed for a long time....
thanks for the link