The experts will correct - but I think a point being slid over too
casually is that a race engine is really a different animal.  A clue is in
the word "harmonics"; that's related to engine speed.  Race engines are
designed to produce power over a much narrower range of RPM than is the
street engine.  So, "tuning" the exhaust to those speeds is relevant.  The
street engine is a huge compromise as it tries to deliver useable torque
over a much larger range of RPM.  "Tuning" the exhaust is no longer
particularly relevant.  So, again, it's apples & oranges.  That's not to
say the exhaust can't be poorly designed for any application!

//Jack

On 31 Aug 2002, at 20:57, Jim Arnott wrote:

> And Phillip K. Smith's "The Scientific Design of Exhaust and Intake
> Systems" will tell you exactly how to select the proper diameters and
> lengths. All you need to know it the displacement of the cylinder, the
> cam timing, where you want the power to occur and a few other easily
> calculatable data points from you engine and you can build something
> *much* better than anything you can buy.
>
> Jim
>
> Kim Brennan wrote:
> > In a message dated 8/31/02 6:28:18 AM, clive.harman-smith@NTLWORLD.COM
> > writes:
>
> > The wrong length pipe can cause a standing pressure wave in the exhaust
> > system, this means that is is harder for the engine to get the burnt fuel out
> > of the pistons, and causes a loss of power. Block your exhaust pipe and
> > you'll see what I mean. If the exhaust can't get out, the engine won't run
> > for very long. ON the other paw, if you have just the right length, the
> > exhaust system acts as a partial vacuum and actually aids in removing the
> > spent fuel from the pistons.
> >
> > Why? Harmonics. You have pulses being caused by the pistons. These occur
> > rhythmicly and as with any other rhytmic system, you can get reinforcement of
> > the waves in a positive or negative fashion. In this case the waves are
> > pressure points in exhaust gases. High pressure is a positive reinforcement,
> > low pressure is a negative reinforcement.