To get an idea what its going to sound like, screw a 3 foot piece of pipe into your lawn mower where the muffler is now, then you will know.
The 180 degree headers for V8 engines sound like six cylinder cars due to firing order. On each bank, each cylinder fires one after another, no skips, the tubes look like a jungle gym under the car crossing everywhere. The idea is that as the first pulse hits the collector, it creates a vacuum pulling the next one out quicker, this then creates another pulse and vacuum and so on and on...... They work quite well on some cars, but sound just like six cylinder cars.
A well tuned header for the six cylinder with mild camshaft and low rpm would probably have about a 32" long x 1 1/4" diameter primary pipe, with a 2 1/4" diameter x 18" or so collector. Long pipes help low rpm torque, small diameter pipe keeps the gases moving quickly,. The collector size is determined by cubic inch and rpm. I have run a lot of computer simulations on dad's pro engine analyzer and each time come up with the long headers. The short cast headers do very little other then change noise levels.
Pipe diameter will change the noise levels some. Small pipe will RAP more, larger pipe will be deeper sounding.
Joe
