RE: How much power can I expect...
Well, this is real ballpark. I had my car dyno'd in Houston at about 218 HP IIRC. 2 years later, got the cat back system, and with my mufflers open I dyno in Chicago area at 229.8 HP. With mufflers closed it was 222 or something like that. I expected more of a gain, but then again, this was 2 years later, and the Houston dyno I had fresh plugs, boots, yada yada. I really wish now I would have gotten a better baseline up here right before the mod.
And I don't remember my baseline torque.