Here is my setup:

Engine: 97 JDM GSR
AC compressor: 2000 JDM ITR
Tensioner: 2000 JDM GSR

I tried a aftermarket GSR belt and it seems too short and i have called Acura and it seems that ITR, GSR, and the civic SI all lists different part numbers but they can't tell me which one is longer or shorter. Does anyone know what belt i should be using?

 

You can purchase belts that are a little longer than what you need, just make sure they have the correct grooves on the belt to line up with your pulleys, there is plenty of room on the tensioner to tighten the belt so dont worry if its too long. Just go to a local parts store and tell them you need a slightly longer belt with the same groove count.

*edit-This might not help too much...but this is what i did, i just showed him the belt that was too small, and told the parts guy to get me a belt that was about 3-5" longer but looked exactly the same as the one i brought in.