at about 3k rpm your AF goes rich because it kicks the pump up to full power.. The NA has two stages... The TT has three. Na kicks the fuel pump all the way up instead of the TT FPC having a middle setting to better meter AF.... Tested via Dyno pulls on both with the FPC being the only difference. No difference in peak power. TT fpc had a little more power from 2500-3500rpm... Nothing real big though.