can any1 shed some light on why you would use a 3" downpipe that reduces to 2.5 to meet the center pipe. wouldnt that not create some sort of pressure build up wer it reduces, wouldnt you be better off using 2.5 all the way.

 

turbo has a 3" opening where the downpipe connects. i'd much rather risk pressure build up in the downpipe than in the turbo. if you uprate your turbo or increase the pressure from your current turbo you usually have to swap the stock exhaust for a 3" turbo back system which includes a 3" centre pipe and backbox.

i'm just looking at havng a 3" system fitted at the moment because i want a bigger turbo. someone has told me that i can run 400bhp with a 2.5" system but i don't want to risk it.

 

that makes sense. im planning on goin to 300/300 and leaving it ther, i cant be arsed with changing downpipe at MOT time so am after a sport cat to go with my 2.5" system and find they are 3" reducing down. if thats the reason why then so be it, 3" sport cat it is!

 

my japspeed system is the same the center section(2nd decat) goes to 2.5" to join at the decat downpipe then 3" straight thro to the back box....

 

Simple solution, go 3" right through.