I found this little bit of info while I was researching for my turbo project. It gives a wide range, but it is useful:
You can get calculate a rough estimate on Engine horsepower using the following formulas:Lower value: 0.052 x CID x (psi boost + 14.7) = bhpHigher value: 0.077 x CID x (psi boost + 14.7) = bhp
In your case, 4 pounds would give you around 290 horsepower on the low estimate side. 8 pounds would be around 360. I didn't see if you said how much pressure you're planning to run.
I've also heard that the best injection fluid for your money is windshield washer fluid. You have to get the -30°F formula. They are something like 30-40% methanol.
In my personal taste, the methanol injection is a whole lot of stuff to mess with, for a 5% horsepower increase on something just built for fun. But then again, that may be your idea of fun, and that's cool.
As for the squeaking, I highly doubt it's the turbo. I would even almost say impossible. I run my oil pressure gauge right on the turbo, a couple inches upstream of the oil restrictor, and it does take a few seconds to get oil pressure when I start up. (maybe 4-6 seconds?) The whole engine system should be able to operate safely on the residual oil film for a few seconds, at low speeds. That's also why I've never understood the people that start their engines and slam them immediately to redline. It sounds like you have an ignition switch separate from your starter switch, as I do. I tend to start up more like an old radial airplane engine, where I crank for a few seconds to limber everything up and get the juices flowing, then flip the ignition on for a smooth start. My rule of thumb is to crank until I get 4 to 5 inHg manifold vacuum, then light it. It still takes a bit for oil pressure though.
If you do think the turbo needs new bearings, it doesn't cost much to have them replaced, and have the assembly balanced.