Well, on my 94 classic I have a HotShot header(best in the market) and a stock cat all the way back. The previous owner didn't care too much for a noisey exhausy, so he kept it that way. My main question is, what kind of pro's and con's will I have if I decide to throw on an aftermarket catback? I really like my torque, is it gonna drop much? And, am I reaping any benefits having a header with stock exhaust?

Oh, to make the subject easier to deal with, I also have a CAI and reprogrammed ECU by JWT, running 93 octane all the time(required).

My other question would be:

What's different between a
USDM SR20DE and a JDM SR20DE?

Or, is it just for bragging rights, "I've got JDM!!"