MAC's suck compared to SLP's. I switched from MAC's to SLP's and went from 104 to 106 mph in the 1/4, plus the MAC's never fit right on my car at the y-pipe and at the slip-fit. As far as SLP's not making power, I ran what's in the sig with SLP shorties, offroad pipe, an SLP CAI and a cat-back with cutout. They work as long as you don't have leaks or a ****load of false knock.