Well, what version of the 3L do you have? If it's a straight 3L then you can throw some svt components at it and get some power. On top of that, full exhaust and a CAI or SR Intake and add a tune. All that stuff would work the best at getting you 50 more hp on top of a straight 3L. If you have most of that done, pretty much the only thing you can do for that much of a jump is nitrous, which you said you don't want to do.
