im using 2.25 piping and spooling around 3000 rpm
seems like a few people have used 2" straight through
some use 2" on the compressor side to the intercooler inle and 2.25" or 2.5" from the intercooler to the throttle body
is this a mitsubishi or subaru tdo5?....sounds a little high to start spooling on the 5e