Hey all new to sight my first technical post. I have and 87 that is still speed density. My modifictions are gt-40 upper and lower 65mm throttle body cold air some cheap msd ignition coil and cap ford racing wires long tube headers bbk high flow cats flowmasters, 24lb injectors i belive a 155 fuel pump not sure was on car when i bought it umm smog and a/c delete and the timing set about 14/15. i just ordered a bbk fuel pressure regulator and was wondering what the ideal fuel pressure would be?
Speed density fuel pressure
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Kdubslugga
Active Member
Every car will be different, the only benefit an AFPR will have is if you have it tuned on the dyno. I wouldnt want to go below 42 psi until you have it dynoed
Might want to take the 24's off a speed density car and put the 19's back on. Having those on there without any sort of tune or chip can cause headaches. With your mod level, you don't need them anyway.
You are correct though. 24's, adjustable FPR and larger flowing fuel pump could potentially cause tuning issues with speed density. The car can compensate slightly by the O2's, but over 3500RPM you'll more than likely run a little rich.
Convert to MA, otherwise, take the 24's off. As for what FP to use...base is 39 psi with the vac line off. Use that for a baseline but without a dyno, you have no idea if raising or lowering it is giving you a better Aif/fuel ratio.
You are correct though. 24's, adjustable FPR and larger flowing fuel pump could potentially cause tuning issues with speed density. The car can compensate slightly by the O2's, but over 3500RPM you'll more than likely run a little rich.
Convert to MA, otherwise, take the 24's off. As for what FP to use...base is 39 psi with the vac line off. Use that for a baseline but without a dyno, you have no idea if raising or lowering it is giving you a better Aif/fuel ratio.
i had 19's on it but they went bad and i had the 24s laying around with a mass air meter and a9l computer. unfortuntly my a9l got flooded out when my garage flooded one night so i am still speed density until i find a new computer. Is running the 24's going to cause that much of an issue?? what kind of issues?
potentiall running rich above 3500RPM. Do you notice black smoke behind you when you go WOT?
If the car is running fine, don't worry about it until you convert to MA.
But to answer your question, set the fuel pressure to 39 psi with the vac line off and capped.
If the car is running fine, don't worry about it until you convert to MA.
But to answer your question, set the fuel pressure to 39 psi with the vac line off and capped.
liljoe07
5 Year Member
It will cause it to run rich, as the ECM is now operating the 24's as it would the 19's. The O2 readings will pick this up and try to correct the pulse width, but it may be out of the ECMs capability to trim back the fuel that much.
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