well greddy has it tuned to a GSR but not all engines perform the same. you could have two of the same car, same exact mods, and they would both need to be tuned differently. also, i would assume greddy tuned their cars in california which has a different atmosphere pressure/ different weather conditions (i'm in ohio).

boost spike is where it "spikes" up to a higher psi then what you want it to.

and uberdata > vafc