i am having a custom downpipe made for my 180Q. im having the guy do a straight pipe all the way down taking out the cat an then connect to the restonator, with a cut out valve built into the downpipe just before the bend to go to the underside. this way it will sound some what stock an then when i want it loud ill open the cut out valve an it can be loud as hell. now my real question is if he does the piping in 2.5 an not 3 so he wont have to reduce it to go to the resonator will there be a big difference between the 2.5 to the 3?

 

Yes why nit there is big diffrence between them, try both

 

Oh Thanks Bike, i will tell you result