Optimum exhaust tube length?

[V8Pinto]

For maximum top end horsepower, is there a rule of thumb for the optimal exhaust tube length as measured from the head (or ex valve) to the end of the pipe?

I realize there are a hundred variables, I was just looking for a good place to start tuning.

This would be in a stock 08' motor with stock compression.

 

[Commuta_Busa]

as you stated there are alot of variables. a good stepped header also adds more spice to the sauce... I wouldn't venture down this path unless ou've got someone already who will do the fab work for you. He should be a well accomplished header fabricator.

To start look at rpm, header length, and diameter.

 

[Mr Bogus]

we have a system to establish the tail pipe length on our gas motors, not sure it will work on a bike.. but here goes

Take some plain old cheap enamel spray paint and shoot a line down the length of the collector, make a run, kill the motor and look where the paint is burned off to, that is optimum length for the collector.. we used a sliding collector so we could tune the thing

 

[V8Pinto]

Thanks!