What should my fuel pressure be with afpr

[Corman12345]

I just bought a Afpr and was wondering what psi to set it for. I'm looking to run 15psi boost dailys

My mods are:
walbro 255
S-afc 2
EVO III 16g
denso 680cc

 

[DSMPowerTSi]

Stock base fuel pressure is 43PSI

 

[nine5raptor]

and without the vac line attached when you set it.

 

[markgholland]

I actually had a question regarding fuel delivery/pressure as well... I understand that the stock pressure rate is 43psi, but how do you compensate for more boost? I read on NABR at one point an equation to estimate the perfect fuel pressure for a certain boost level. Anyone know it?

 

[hoffman]

Don't worry about it. Set it to 43.5psi, at idle. Aslong as it rises 1:1 with boost pressure your ok.

 

[nine5raptor]

Originally posted by markgholland
I read on NABR at one point an equation to estimate the perfect fuel pressure for a certain boost level. Anyone know it?

If you want to make your life easy, you just use a 1:1 rising rate regulator and set your base to the factory rating.

The point of the 1:1 rise is to keep the pressure differential the same across the injector at all times. This allows for easy tuning as your fuel pressure is not changing all the time.

Likewise, quite a few aftermarket turbo (and supercharger) systems use FMU's that raise fuel pressure 8:1, 10:1 or more. Admittedly, these keep guys from blowing the motor, but if you run any amount of boost, you can get fuel pressures over 85-100 psi which can be too much for the injectors to close.

Along that line, if you need to make your injectors act larger, you can set your base fuel pressure higher, 60 psi for example, but then again be wary of getting pressures too high under boost (remember fp = base + boost).