13-02-2012, 02:38 PM
Ideal for a turbo engine is 18" of straight pipe............. don't need back pressure, you has a snail 
it will free the exit of gasses from the engine which should mean that you get on boost a little bit sooner (though it probably won't even be noticeable)
As far as legalities go, as said already, as long as it has 1 box in then its all legal as far as the police are concerned, as for the MOT, they can fail them on excessive noise but that is down to the testers opinion and nothing else!
Edit:- Ruan has answered everything pretty clearly there I would say
it will free the exit of gasses from the engine which should mean that you get on boost a little bit sooner (though it probably won't even be noticeable)
As far as legalities go, as said already, as long as it has 1 box in then its all legal as far as the police are concerned, as for the MOT, they can fail them on excessive noise but that is down to the testers opinion and nothing else!
Edit:- Ruan has answered everything pretty clearly there I would say