at 13 pounds springs shouldnt even be close to an issue unless we're talking .650lift radical lift rates or something.
im using stock springs at 14. of course .420lift is why.
it could be exhaust related, but im only running 2.5" up pipe and no problem boosting to the moon. i know its not a 331 but ported 4v uses a tiny bit of airflow.
really more info is needed. i think if the a/f was too fat he'd notice the diesel like smoke, or if too lean to blowout hed burn a piston pretty quickly. dyno operators are pretty good about shutting it down.
plug blow-out, fat a/f, too much timing(counter-torquing), or actual boost at rpm is not really there. just dunno.
96 mustang GT-93 teksid 4v forged: ported heads, kellogg crank, billet i-beams, CP forged pistons, 9.4:1, BIG turbo, 4x28x12 fmic, big boost.
2011 GT 300A, 3.73, M6, spoiler delete, brembos