Smarty/EZ/TST can make it go above 50 psi. Smarty only boost fools to 45 psi. After that you will need a pressure box to fuel the turbine more and boost fool further. Fuel has a lot to do about boost. More fuel usually equals more boost. But too much boost isn't good. Turbo is efficient to a certain boost and then after that it is just boosting hot air.