if you went std. then the clearance could be more than his, causing a miniscle amount of difference. there is nothing wrong with it, good topend job, and 2psi varience is nothing to rack your brain over. you could have more than that much differenc between right and left, and be perfectly fine. also gaskett thickness can effect it too. the new pistons cold have slightly higher wristpins, carbon buildup, etcetera. good manufacturers usually match the pistons in sets, but as a whole, they vary a bit. this us one factor in blueprinting an engine, so you can acurately calculate a build, and bolt on parts, knowing they'll match perfectly.