You don't build for maximum NA power and then boost.

Your goal of 250 NA on a b18 block and then throwing 10 PSI of boost to it is a recipe for a grenade, not a motor.

If you want to boost, build the motor for boost. If you want NA power, build for that.

You would be very limited in how much boost you could add to a high compression LS/VTEC or PMtype R. While no FI pro, I would think even 10 psi would be too much (if you are building an 11:1 or so motor) unless you were running a small turbo.

Perhaps one of the turbo gurus here could chime in?

 

all motor then turbo is bad. For you to get arround 200whp all motor your looking at like 12.1-1 cr and then if you turbo with that high of a cr you will have plenty of problems. You will probably have a block of aluminum to take to scrap yard.