The more stuff the exhaust gas has to travel through, the longer it's gonna take to get out of the pipe. If you remove the cat and centre silencer you will reduce the 'back-pressure', which normally is better for performance, tho only marginally. I have heard of you needing a certain amount of back-pressure tho. There's nothing wrong with removing silencers, but if you remove the cat you will fail yer MOT if it's after K-reg, or something like that.

noise and slight power increase!

ok so whats so good about not having a cat converter or silencers?

The term 'Back Box' speaks for itself really!! Coz it's the back box of the system :-d

de-cat is a pipe which replaces the catalitic converter, or the term to describe an exhaust system with no catalitic converter.
straight through is and exhaust system which runs from manifold to back box, no silencers or catalytic converter.
back box is what u said, or known as the tail pipe.
hope that helps:thumbs:

dont know a right lot about zorst' so can someone explain what a de-cat is, straight through and back box? please cheers.

i think back box is just the bit that sticks on the end but im not 100% on that