[sohc_vtec 2NR]

with your current mods i'm sure the new throttle body will have a pretty big impact on ur HP gain..ur intake will most likely function better too (pretend that the intake, throttle body, header, exhaust is a big straw...now the throttle body would be like a "pinch" in that straw and if you can get rid of that "pinch" then the ur mods work much better..the same analogy goes for the cat-converter in your exhaust system). i'm sure this mod will improve ur 1320 time.

as far as size go, bigger always isn't better...i'm assuming that 68mm would be your best bet