bro
if u wan to change ur engine then u ll advised 4 gsr,evo
if not then u may change the whole set of exhaust piping start from the extrator to the end
then go 4 an air filter
after that u can do engine balancing,high cam,crankshaft,port n polish, etc
that is many to mod
but it depend on ur budget
yes yes... agree... so wut's ur budget?? u wanna go 4 halfcut... o jux mod on standard engine?? if mod on standard engine... there's a limit there.. u can't expect too much!! hehehee :D :D :D