In Reply to: i think the diff of those isnot size of turbo(more posted by tampaturbom3 on February 13, 2000 at 22:13:45:
i have lots of friends with import turbo cars, mainly rx7's and supras, so i know a good deal about turbos. the size of the turbo does have a good deal to do with the performance of the engine, but as tommy said, it also has to do with other components. basically, smaller turbos can spool faster due to their use of smaller impeller, which will give less lag and faster acceleration. the only drawback to small turbos is the fact that they also have smaller housings, which can't move as much air as larger turbos. the larger turbos, which can handle higher overall boost can't spool up as fast because they have larger/heavier impellers to get moving. a real world comparison to this would be a very powerful engine in a heavy car (example: ferrari 550) and a not as powerful engine in a lighter car (ex: ferrari 360). the 360 can accelerate faster than the 550, but when the 550 gets moving, all that extra power will let it take the lead. active autowerke uses a fairly large turbo in their setup, but due to the torquey nature of the m3's engine, the car can still get moving fairly quickly while the turbo is spooling thus making a smooth transition from na power to tc power.
other things to consider the efficiency of the turbos. some turbos can push same psi's as other turbos but make much better hp/torque numbers on the dynos. mixing and matching different impellers and housings can provide results like this sometimes. i've seen my friend's supra push out a ~50hp difference on a dyno with two different turbos running the same boost.
also, those other components that tommy mentioned. things like the intercooler and blow off valve are very important. as well as a food air/fuel computer and a boost guage. oil coolers help too when running high boost because the oil can heat up a lot when those turbos get going. exhaust systems really come into play here with more flow equaling more hp. a supra with a upgraded downpipe, exhaust, headers, cats will make ~60hp; even more with other parts upgraded.
all in all, the science of turbo charging is a delicate one. you need to keep everything balanced and you will be fine. otherwise you could be paying a lot for a replacement engine. the guys at aa really know what they are doing, so i would probably recommend sticking with a kit they have put together. as for the stage 2 or 2+, get the 2+, you could always dial the boost down when driving regularly and kick it high when someone is really asking for it.