It depends on how much boost you plan on running. Most turbo companies say that you can run 7-9 PSI on stock internals with the full turbo kit that they offer. Personally, I think that any engine is going to need at least some reinforcement if you plan on going Turbo.

First you are going to need some new valve springs, because the factory ones aren't going to be able to handle so much power... the last thing that you want is the springs wearing out, so you get valve float and end up having one of your valves smacking a piston head. The factory Honda crank is terrific, and most pro-drag Honda's still use factory, cranks so you should be fine with the one you have. You may want to consider some forged connecting rods, and some low compression piston heads.

If you have a 5th gen prelude (H22a4) then you are also going to want new sleeves, or sleeve gaurds because you have an open deck engine. The 4th gen Lude motor is closed deck, so you shouldn't need these parts if that's the case.

~Peace