It's a decat (removing the catalytic converter) using a proper decat. Some people use a straight bit of pipe which will be even louder as it will be even more free flowing. In terms of noise it's certainly louder but not unbearably so. Not much difference when in the car. The note is low in lower rpm and raspier up past 3000 with a standard back box.Originally Posted by Peter-E36
As it's more free flowing there is a trade off as there is a certain loss of back pressure which will loose low end torque as a result. But I'm happy with it and still have a non standard back box to add to the set up.