I guess Boll in his original post can explain things better than me So what might be wrong in using a 3" cat with a 2.5" exhaust, apart from maybe a little bit more work. Would this be the case of bigger (cat) = BETTER?
i was contemplating the exact same thing about an hr ago with all the emphasis on high flow cats, wouldn't a 3" cat on a 2.5" system run well?
I would say no point in 3" cat on 2.5" system Why? 3" just refers the the inlet/outlet size which won't make any difference because it's being mated to a 2.5" pipe. The body of most high-flow cats (of the calibre mentioned in the post) is the same size 4"
if the body is the same, then no point. if the body is bigger, than i think it'd be worthwhile. people often say to avoid changes of diameter in an exhaust system as it can introduce turbulence. however given that at this point the gas has to go through a matrix of sorts, this won't be an issue.
