well after having a straight pipe system with no cat at all i can honestly say i get some gains however in my case i had lots of lag (mainly due to my exhaust diameter) but in the mid power band u really noticed the gains. i failed emissions most places and passed others the sound was the best part loud but low deep tone no can of bees sound liek some cat backs give. when i opted to redo my exhaust system i went high cat with smaller daimeter piping and a good rear section