Don, IIRC several years ago Ryan Johnson told me that 1 7/8" Hedmans were worth 15-20hp over 1 7/8" TTI's on a engine similar to my 408. I'd think they'd worth close to 2X as much over a 1 5/8" header.
I run the 1 7/8" Hedmans with a 3 1/2" collector and have considered finding a pair of 2" with the W2 flanges to try. Honestly I don't think it would be worth the $$ but it would be a interesting test.
