3 port engines are mainly used for acceleration and speed out of corners you wont get your car much higher top end because of the no. of ports ....... 5 port engines can get rid of gasses quicker thus making the RPM's higher but these engines tend to not have as much acceleration as the 3 port. if you really want to mod your engine there are plenty of pics on the net on how to D.I.Y mod...... havent seen any mods been done on the SX-12 RE persifically, but to be honest i would try! if you do not know what you are doing you can wreck your engine!!
hope ive helped ....... Dean