THE DIFFERENCE IS 3INCH HIGH FLOW CATS, 3INCH DOWN PIPE, PORTED EXHAUST MANIFOLD... THE BOOST SETTINGS ARE ABOUT THE SAME ... DETONATION WAS AN ISSUE ..BUT I RAN THE SAME SETTING THAT I RAN IN NOVEMBER 2002 ON THE SAME DYNO WITH NO DETONATION SO I SUSPECT IT IS THE WINTER CHEAP WAWA GAS ..TIME TO HOOK UP MY AQUAMIST .. WHEN I RAN 22LBS --MY HP WAS 431HP W/THAT "MARBLE" SOUND GOING ON.. SO I WILL NEED A FUEL ADDITIVE OR AT THE MINIMUM 94 OCTANE SUNOCO..UNTIL THE GASS CHANGES OVER OR I GET MY WATER INJECTION HOOKED UP