ChevyAsylum, the crossover does act to remove some of the raspiness from the exhaust, and it also can add some power, due to cross scavenging that otherwise wouldn't occur.
Car Craft I think it was, did some testing with a V8 engine, and there were some very clear differences between no crossover, and X, and H crossovers.
The X-crossover was the best at cross scavenging and would build big torque from idle to about 3500 rpm. Then from 3500 to 5500 rpm, the H-crossover made better power and torque, they theorized it was because the X would seem to over-scavenge at certain engine speeds...(whatever that means). And then again at rpms above 5500, the X was clearly superior.
I don't really know the impact of "cross-scavenging" on a straight 6, but on a V8, it does help. It couldn't hurt to try it. Summit Racing had the best price going for an aluminized X-pipe crossover kit. I got one for my IROC-Z Camaro when I built my custom dual exhaust, and it's really nice. Worth every penny.
Up to 3500 rpm...isn't that the vast majority of a stovebolt's operating range?
I'm going to a big swap meet this weekend. I will be looking for a pair of Fentons...but they are quite rare. I once found one, but its twin was missing.
If I find a pair, I'll be buying another X-crossover from Summit this summer.
