Good info, and I agree on the "myth" of backpressure. Erroneous as it may be to refer to "backpressure" when talking exhaust diameter and performance, that is how most people understand it, and it makes little difference to the average, practical person. I don't like the analogy in section V though because it implies that exhaust gas pulses pull the following gases along. They don't. How could they? They're just gas--it's the piston that pushes the exhaust out. I'm not disputing the benefits of velocity and scavenging, but if we're going to be pedantic about this, a pulse of gas can't "pull" anything along when it's not actually the source of the energy moving it.
For additional pedantry, we could discuss how an exhaust system should shrink in size from the engine to the tailpipe to account for the exhaust gases' cooling and increasing density.
Build Thread -- http://www.jeepforum.com/forum/f177/whats-chrokeese-build-thread-2525690/