Make sure you do a decent catback intake lid then maybe some headers and a good Y-pipe maybe a cutout. That will get you around 330-340 rwhp and high 12s. If you want more than that thats were the real choices begin. If you like Nos the LS1 responds well. A friend of mine went 11.8 at 121 with the above mods and NOS kit 5177. If its an auto tranny a high stall converter is the best bet. With the above mods(exceptNOS) you will run 12.5-12.1 all motor with a good converter.
Another good choice is a cam and valvespring upgrade. MTI has the T1 cam. T1 with headers and bolt ons make anywhere from 360-380 rwhp. Add an LS6 intake and that will be 370-390 rwhp. Add some stage II heads to that and youll see 400-420 rwhp and run in the 11s all motor.
If you have cash...and lots of it....go to ARE or MTI and get the superstroker package. 427 CID LS1 with a solid lifter setup. 520+ hp to the wheels and run 10s all motor.
But like I said...it depends on where you want to end up.


99SS LQ4
611.8 rwhp
679.8 rwtq