### Baseline fuel changes for manifold referenced FPR

Posted:

**Sun Jan 13, 2019 9:31 am**Hey all, I'm running an 07 Si with a Kraftwerks supercharger kit (1000 cc Grams injectors) which has been tuned. I'm adding an external fuel pressure regulator with a 1:1 manifold reference, tapping into the manifold obviously, and I understand that this changes differential fuel pressure across the injectors over stock in most situations.

Should I just use sqrt(P2/P1) to determine fuel percentage change where P1 is 54 PSI (stock, what FPR will be set to cold and open air reference) and P2 is P1 + manifold pressure? e.g., under 5 psi of boost should I multiply the 5 psi column by sqrt(59/54) = 1.045 (4.5% increase) and 5 psi vacuum by sqrt(49/54) = 0.953 (4.7% decrease)? If that's not the correct route to go, do you have any recommendations? I just don't want my fuel tables to be way out of whack right from the get go. Thanks!

Should I just use sqrt(P2/P1) to determine fuel percentage change where P1 is 54 PSI (stock, what FPR will be set to cold and open air reference) and P2 is P1 + manifold pressure? e.g., under 5 psi of boost should I multiply the 5 psi column by sqrt(59/54) = 1.045 (4.5% increase) and 5 psi vacuum by sqrt(49/54) = 0.953 (4.7% decrease)? If that's not the correct route to go, do you have any recommendations? I just don't want my fuel tables to be way out of whack right from the get go. Thanks!