Mark---Just making sure to not step on anyones toes...and yea, I agree, some variable is unknown for there to be that 9% change. My Z has lC's and injectors with an ECU and a boost controller. I still have stock turbos though...and to be honest, with the controller on with about 65% on the dial---the cars 18" tires will break loose @30mph! It's fast enough for me ( so my wife says). If the HKS controller can increase boost and reduce lag, why didn't Nissan do that and what benefit would I see from larger turbos given I am not going to start ripping the engine open so I am limited with how much boost I can apply anyway. Right now I keep it under 12psi to around 10psi.