Hard to say. When the car sounds meaner, butt dyno is interfered with by the ear dyno.
I did 2 1/2 exhaust with headers no cat and a sebring muffler. Added to that an aggesive bullfrog cam, electric fan and cold air intake. Just that alone was extreamly impressive for driving!!! N/A of course. The car "felt" 2x more powerfull even though it was not, just to give you an idea. Man that car was fun!! 82ZX Hardest part of the build was the headers, 6 into 1, have to remove intake and exhuast because of gasket, had the rest of it done by a shop.(for the exhaust)