I once had 2 inch pipe installed behind a Chevy 350.....I first started the car with open headers....had GREAT throttle response and good power. I installed a 2 inch exhaust and immediately noticed a lag in throttle response, ability to rev and a HUGE loss in power. Use NOTHING less than 2.5 inch pipe for even a mild engine.

My 455 now has 2.5 inch exhaust, but I will be changing to 3 inch when funds allow.

I'd recommend a set of Magnaflow mufflers for a good sound.....I use flowmasters dumped under the car in front of the rear axle....not bad inside the car, but definitely louder than some people prefer.