[stigler4profit]

Perhaps, but I did expand the size from a factory size of 1.something on the Mazda MX-3 to 2.5, now that I think of it probably 2" ( I have too many cars) cat back, into a quite muffler (universal) and it averages as good or better mpg than stock, and it runs better as well. And my wife drive it like a grandmaw. I view the engine as a pump and if I can aid it in it's internal parts moving with more ease.. so be it, every little bit helps.