From what I've read, all of the "engine masters" competitors from this year like the Magnaflow mufflers for best power. I think the top 10 guys there were all using maganflows. That should tell you something.
"EVERYONE a the Engine Master contest used Magnaflow mufflers. I did test several others, but NONE were better on a 750 HP engine. The H pipe ,or X pipe setup is just for WEAK SUCK small blocks ( 302 Fords )It helps low speed power ( 4000 and less )Most BB anything have too much low speed power allready ( hense, you do not need it )A few years ago, I did some dyno testing on a 454 street motor. He brought his entire mandrell bent 3 inch exhaust, with the famous X pipe. Compared to my dyno headers, it LOST power every where. Poor guy, he spent 900 dollars on the trick exhaust pipes. Since I found out how good the Magnaflow stuff is, I always run all my dyno testing with mufflers.
JOE SHERMAN RACING ENGINES"
http://speedtalk.com/forum/viewtopic.php?t=7074
Regards,
Justin