if you want more boost, you need to go to a smaller turbo, it is all about working with what you got. being really rich kills power, being really lean kills motors, your best bet is to increse your boost slowly until you fall right around 11.8-12.2 afr and leave until you can get more fuel. big boost is possible without mpi, i ran 31 psi on a stock fuel pump stock injectors, a paper felpro headgasket and throttle body, on a super 16g at 11.8afr, it is possible you just have to know your cars limit, that is a little above that turbos range but it can be done safely you just have to watch your afr, and it has been said many times before but dont try it with out a good wideband