does any body know how much difference the exup valveon the r1 makesand would it be worth trying to fit it to an indy

i dont know for sure. But i believe it reduces top end power and is primarily present for mid end and emissions.

For an engine to run smoothly at low revs it needs a constricted exhaust, i.e. back pressure.
At high revs it needs an open, free flowing exhaust, that allows gasses to escape as quickly as posible.

This is what the exup valve does, a wonderfull invention.
So good in fact that when the ten year Yamaha patent ran out, Honda then copied it.

( sorry Joel )

Paul G

Ask any Yamaha race team and they will tell you that they junk the exup valve. YThe same for sidecar racers who use the R1

I conclude it does nothing for power whatsoever. Its just a means for a production bike with a cheap 4-1 exhaust system to improve its bottom end performance and emissions.

A well designed 4-2-1 exhaust will give you better mid - top end performance. If you want to pootle around at 3k revs and maximise your fuel consumption you shouldn't be building a BEC

Cheers

Paul

Agree with what Paul said

Great minds think alike.....

quote:

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Originally posted by ChrisGamlin
Agree with what Paul said

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The only difference it makes is for the drive-by noise tests. It makes no difference whatsoever to the bottom end/mid-range power....

The only use oin a BEC is for if you're using the standard clocks (as I am), as it stops them (along with various other items) from showing a fault code....