Jeff, (jdmhatchracer94) did a ls with 8.0:1 compression pistons, delta 272/260 cams stock head I believe with a holset h1c, 12cm housing, and made 337whp and like 290tq. If I were you I would defiantly run the hy35. If you want a quick spool. It will carry your power to 7k easy. Once you get up in the power level(+350whp) it will start to level off on power. Assuming the motor is stock. What car is this in? I will then tell u if you can keep ps, and ac. Full size rad or half sized? What size injectors? and what ems system?