If you are building a motor for any kind of boost the compression must be lowered to withhold the extra pressure (for higher boost applications.....lesser amts can be run on a stock engine). if it is true that the part #'s for the block are the same and the pistons/rods/etc. are different that should sound completely correct. And 9:1 compression sounds just fine for boost. I built my honda......STOCK BLOCK with SRP pistons, eagle Hbeam rods. comp dropped to 9:1 and running 21 psi of boost (can run more w/ different MAP sensor), putting 300whp on a SINGLE cam. Weight w/ me in it. 2150lbs....VERY FUN!