You can buy a 62mm throttle body, port the intake(enlarges the area/volume inside the intake).
Also a larger exhaust + headers = more HP (but at a cost).
Go
here and you will find several sites with performance upgrades.
upgrades are not cheap, I've spent more on HP upgrades then what the car cost
PFYC.com and
RSM/Z-spec hav some good upgrades for the 3.1.
ANd
www.milzymotorsports.com Is getting into some stuff for the Grand ams !
