Intakes generally change the acceleration at different revs. I've never dynoed my car, but my buddies Sunfire with a SRI pulls more whilst switching into second and third. And with a CAI pulls more off initial acceleration into second.
He straight piped with 2.75", new header, hi-flo cat, exhaust with cut muffler, etc, and he lost a fair amount of acceleration. He put a muffler on with 2" piping and got most of his pull back, and it still sounds cool.