what gear ratio does the 99 civic si come with? if i was going to turbo it what tranny would be best? ITR? if so what would that gear ratio be?

 

99-00 Si and USDM Type R have the same gear ratios in gears 1-5, R and also have the same 4.400 FD.

Depending on your target whp figures the Si/ITR gearing might be too short and thus you'll be spinning gears 1-3 and on street tires it would suck.