You're not gaining anything noticeable by removing emissions equipment. I don't get the logic of polluting way more just to get maybe 2-3hp, that is if your emissions equipment works. If you want peppier acceleration, install a 5-speed and at least 3.9 rear diff. A lightweight flywheel also helps and could be installed in conjunction with the transmission. No extra power is needed, torque multiplication and reduction of reciprocating weight does a better job of increasing acceleration than trying to squeeze out enough power to do the same. FWIW, USA-bound 240Zs got rather sluggish transmission and rear diff ratios. The 3.36 rear with a wide-ratio 4-speed is not a great complement to the engine. Europe and Japan were better off with standard lower-geared diffs and 5-speeds.