I personally ran a Garrett T25 with the larger A/R rating on my GA16DET with no problems, other than blowing out exhaust manifold gaskets (another issue entirely). With a very modest setup, and using only 259cc injectors, I was able to achieve a safe 10lbs of boost with an excellent track record of reliability (no difficult cold starts, no leaning out, etc.). I've seen people run as small as T20 turbos without any problems, so I'd stick with one or the other. The T28 setup Wes used was great, but also required a great deal of support parts to gain the best the turbocharger had to offer. If you're looking for a daily driver with that extra "umphf", I'd go T20 or T25. If you want a drag car, go T28.
P.S. the larger the turbo, the larger the boost, i.e. volume. 10psi on a T25 is not the same as 10psi on a T28! Just keep that in mind before you crank your boost controller up, detonate some cylinders, and blow your engine sky high.
P.S.S. also remember clearance issues when you decide what turbo to go with. If you are running a bottom-mount turbo manifold, keep in mind your exhaust housing of the turbo and downflow pipe have to clear the alternator and A/C (if you have A/C and want to keep it). I ended up having to cut my A/C bracket off, and shave down the bolts on the alternator to make my turbo elbow fit. Being the T28 is a larger turbo than the T25, I can forsee problems there. In some cases, the right turbo isn't the biggest one, but the one that will fit!
Last edited by BeyondBiscuits2; Dec 26th, 2012 at 07:20 AM.