I replaced my stock exhaust, got a PCIII, and kept the stock air box. I plan on doing the desmog this week or next week. I also got custom maps for both cylinders for the PCIII from Johnnycheese. You would probably see some improvement (HP and Torque), I just chose to change the exhaust and put on the PC III at the same time. If you just add the PCIII alone and then change the exhaust, you would need a new map (either from Dynojet or a custom made one) because of the exhaust change.
