I talked to a few people and they said it was possible to run up to 15psi on a stock bottom end. Is this at all possible?

I highly doubt it. With a lower compression head gasket, id say 12psi MAX and thats still pushing it. Id just sit tight at 10psi but thats me.

I just bought 310cc/m injectors from Hahn. Is it still too much even with those

It has nothing to do with the fuel really. Bigger injecters will allow you to boost more but the internals wont handle it. Your crack a piston easy.

I know that the motor can physically handle so much power before it breaks. But what matters more, psi or cfm?

according to hahn the 420A could handle 300 HP safely. That's a lot of power. Our internals are pretty strong but the rings are the weakest link I believe. 8 psi is the max I can recommend with a star kit from what I've heard from nameless. 8 psi should put you at around 220WHP maybe... he said 10 wasn't very safe.

But you are on to something if you lower compression you can run more boost, haha you'll just have to be the test rat to prove it hehe.... There's detonation that will kill your pistons and there's shear pressure that will kill em, hehe shear pressure is probably what your worried about cuz you can deal with detonation with timing, fuel mix, and AF ratio.

The rings are not a weak link. it's ALWAYS the pistons that fail. The detonation breaks off ring lands, the rings themselves are always fine..

So as long as I can control detonation I should be ok for a 12 psi blast every now and then?

Murix's friend ran 12 psi with thick head gasket, large injectors, and s-afc for a while with no problems. Then he rebuilt his engine for more boost.

I wouldn't recommend it though.. that was probably some really good turbo tuning.

I'm planning to get a thicker head gasket too.. but the reason i'm getting it is to provide lower compression until i can afford the rebuild... i'm going to run 9 psi intercooled at the most.