i used to have a buick grand national that was extemely powerful but it relied alot on the turbo and exhaust. well after a short period of time the car became very under powered and the turbo never kicked in i also lost alot of mpg. because i was all over it to get it to move. the cat was so badly burned up inside and crumbled that it was literally chocking the motor. i had that changed along with a full "hooker exhaust" system put on and it ran like a hot-rod should. huge difference, like two different cars. sorry guys for bringing a gm into the discussion.