Well, when my cat-back was installed it eliminated the resonator and I have had it in for emmisions and they didnt say anything. To be honest with you most emmisions testing they don't even raise the car and look underneath. It will make your exhaust a little louder without it, because it's made to quiet things down just like the intake resonator in the fender. I don't think there will be a HP increase without it either.
1990 Ford Probe LX 3.0L V6 :s6:
SEE IT HERE:
1989 Mazda RX-7 Turbo II 13B-T "FC3S"
Turbo RWD Rotary Powa!