Mine had a 70 series (dual in, dual out) when I bought it and I left it on. Without a cat its very quiet at low RPM, and not over loud while driving. Its got a weird sound to it at about 3500, kind of a tinny sound, like a piped V10 dodge. I really dont like that part of it. Luckily the boggers make more than enough noise to cover the sound up most of the time.
