Check out the dynos forum. I think that's where I saw a post about the Borla providing most of it's gains at the lower rpms (where we need it most, IMHO), while not matching the high rpm peaks of some other brands.
Besides, there's more to it than just power. Well, for some of us anyway. Exhaust is one of those areas that sparks a lot of debate about who does what best, but that really wasn't the question, now, was it?
The tips go from 2" ID to 3" OD, to answer the original question. The pipes after the rear split go down to 2" each.
Yes, with my intake also opened up, I notice more oomph at the low end, but I don't have any numbers for you.
