It was explained to me once that the crossover produced a scavenging effect - flow through one side of the system caused a draw that helped extract from the other side and so forth. Makes sense. Even with big pipes, it seems to help, so I'm inclined to believe the scavenging explanation above just reducing backpressure. In a way, it's like the equal-length tubing used on headers - it helps tune the system.

I've added the crossover to a car that didn't have one, and it wound up quicker and seemed to breathe easier.

I like the paint idea. I assume you use regular (non-hi-temp) paint. My guess would be to run the RPMs where you want the power, or just drive it the way you plan to and see where the paint burns off.

Thanks for the good tips.