The factory exhaust manifolds ( actually headers) aren't that bad. In my case, Im running factory headers, stock cats, 3" Hearthrobe mid pipes and Corsa Extreme mufflers. My car made 550 rwhp on the dyno in over 85 % humidity. My tuner told me on a cooler day, the car would make upwards of 560 rwhp.
Granted, my car is supercharged, which you would think would require a much
"larger" exhaust system. but think about it. 550 rwhp, through stock manifolds. Larger longtube headers would unarguably produce more power. But my point is, if a supercharged motor can produce these kind of power level through stock manifolds, do you really need a "big" exhaust, on a relatively stock car. Just my .02, as usual.
2011 GT. Grabber Blue. Procharged. 3:73 manual.Billit LCA's. Corsa Extremes. GT 500 wheels. Racemaster DR's. T-56 Tremec. Dynotech DS . Centerforce DF. American Racing headers/high flow cats 560 rwhp.Donny Walsh tuned
2012 Pony Package. Race Red.3:31 automatic.BBK longtubes and catted X.FRPP Sport axlebacks. BBK throttle body. Dynotech DS. Brembo wheels and tires. Strut tower brace. Airraid CAI. Bama tuned.