[mike1967]

trouble with exhausts is the emissions design of the cat at the beginning thats where all the free flow is restricted and yes a bigger bore on the arse end of it does cause a low pressure that in theory will help very slightly to suck the gas out of the cat its tiny amount, but if you remove the cat and weld a internal bypass pipe in to the factory metal case and car is mapped correctly to delete it while still running with the legal limits of gasses at tail pipe they will never no and thats how most people do it correctly,, once thats done it can be mapped for pops and bangs etc on the over runs and well over 200bhp is common, we have been doing this for years no one has ever said hmmm dont like it or car dont feel right etc after job done..