No exhaust can = more power?

I was wondering if anyone out there has more info regarding race exhaust.
What makes for a better exhaust system? How does size, shape or length of pipe effect the power curve? If you can point me to some technical reading on the subject I'd be happy. I notice the motoGP bikes have very short stubby exhaust cans (Rossi's Yam) or none at all, is that the best system then?

Originally Posted by zunkus

I was wondering if anyone out there has more info regarding race exhaust.
What makes for a better exhaust system? How does size, shape or length of pipe effect the power curve? If you can point me to some technical reading on the subject I'd be happy. I notice the motoGP bikes have very short stubby exhaust cans (Rossi's Yam) or none at all, is that the best system then?

Exhaust size/shape is the basis of 2-stroke tuning ... having a certain pipe can double (or half) the power, it can make it have heaps of midrange, or all at the top ... on a 4 stoke it is less critical as it has a much lesser effect (on a 2-stroke you are using the pipe shape to assist the engine in retaining and exhausting combustion charges, a 4-stroke has valves that predominately determine this).

As for general rule of thumb ... long/thinner pipe = midrange, short/wider pipe = top end.

As for further reading, just google for 'motorcycle exhaust tuning', should be pretty fruitful

[admin]

Isn't that why Yamaha have the exup exhaust valve to limit or alter the cross section of the exhaust.

Two stroke exhausts are often called expansion chambers and their shape alters the pressure of the exhaust pulse and then reflects the pulse to act as a barrier to stop unburnt mixture leaving the exhaust port. Very technical stuff. This tends to work best at a certain rpm, which is why 2 strokes often have very narrow power bands.

I think the same holds true for 4 strokes but the gains are less impressive.

When removing the Sv's end can I've noticed the engine respose is more sensitive to my throttle hand. The engine seems be more willing to do what I'm asking of it. What would you call that and does it equate to more power? The feeling is nice that's for sure. The noise is a bit too much though. My neighbours are all going to heaven, none of them complained from the racket going on in my garage

[admin]

I guess the increased response is due the lack of back pressure?

Funny, just fitted my Fuel exhaust yesterday, and I could swear there is a little less grunt at the bottom end. Anyone else have any similar experience?

[northwind]

Here's a nice way of thinking about it- it's factually absolute rubbish but it does work reasonably well

Imagine you're pushing a door... When can you push it hardest? When it's easy to move, hard to move, or impossible to move? Well, you can move it fastest when it's easy to move, but you can't push as hard. Bikes with wide-bore headers and open end cans or no can at all tend to make good peak power (pushing the door fast) but relatively little torque (pushing the door hard)

The actual physics of it re wavefronts, volumes, scavenging etc just boggles the mind though, I couldn't even start to understand it.