12psi on c1 or c5 is alot, but can be done. as for 300hp i dont know. even with engine management, youll have to run it rich as hell to preven detonation, and running rich will lower your hp. the ls has lower compression and a tad more displacement. also since the cams arent performance oriented towards N/A power you get more boost kept in. i also disagree the ls is better then the gsr or other like tranny, to a certain degree. a car without long gears thats turbo are the 6-speeders(like skylines; they have crossed ratios). main reason why is first gear, for turbo you want a short(numerically high) first gear to help reduce lag and get you into the power band. but, highway racing, a ls geared turbo motor will have advantage over gsr.