What kind of racing are you doing, and do you have a specific RPM range where you need to develop maximum torque? Most fancy exhaust systems on street-driven vehicles are simply eye candy to impress the mouth-breathers at car shows, with no measurable power advantage that justifies the effort or expense involved.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!