Andrew reckons his 350HP GT25 was too small. You need to go the GT28. But seriously, the S15 GT25 is seriously good turbo, and certainly nice for street driving. You'll need to balance your engine to very fine tolerances if you want to run a big turbo and 9000rpm to make it worthwhile.

For my CA18, I've got the biggest GT28, with the .7 compressor and T25 flanged .86 exhaust turbine. I probably wont have it started before November, so I can't tell you if it's a good size. But a good condition S15 turbo would give you 180-190kW at the wheels, which is like 25% more than an HSV V8 Commodore, in a car 1/2 the weight. My brothers S15 turbo/SR20DET in his 1600 is seriously undrivable above 3000rpm..it's all sideways in all but 4th and 5th gear. Remember the days when it was cool to be able to chirp between gears.. seriously a different ballgame these days.

Chris

Any turbo bigger than the smaller GT25s will mean you'll need a custom manifold, which means new (modified) front pipe, new intake piping maybe, new oil lines and water lines. New boost signal pipe maybe etc. Only a couple of the smaller ones can be considered "bolt on". Yes they have the same exhaust flanges..but there's more to a turbo than just the exhaust flanges.