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.