After market fuel pressure regulator vacuum line

[Dusted RX]

I just got my FD back from the engine re-builder (spun bearings), and found that he had installed the after market fuel pressure regulator (1600 injectors added) without the vacuum line attached. When I questioned him about this he said it was quite common not to use the variable pressure function of the regulator. The car does idle much better without the vacuum line hooked up, and the re-builder says I will have plenty of fuel without the higher fuel pressure (BNR sequential twins).

For those of you with after market fuel pressure regulators, do you run with the vacuum line?

Mark

[Whizbang]

i always have, i figured if OEM uses it perhaps i should. But im also running an NA car

[RETed]

That's just stupid.

I guess, in theory, you can run without the boost reference and tune everything okay if your fuel pump can handle the flow...

But, WHY?

The increase in boost will cause the pressure at the tip of the fuel injector to drop.
You get less atomization this way.

This is the first time I've heard of someone doing this.
The only reason you would do this is because your fuel pump cannot handle the flow needed at the higher pressures???


-Ted

[TitaniumTT]

Ted nailed it especially about the D @ the injector nozzle without the boost reference. Not to mention if you were tuned WITH the reference you'll need to completely retune it without otherwise you will run lean everywhere in the map.

Sounds like the guy is making excuses for not remembering to hook something up especially if it was when he got it.

FWIW I have a -3 briaded line running from intake to both the reg and to the MAP sensor becuase they're so effin important I don't want to chance them blowing off or expanding etc etc etc. If I could do this in my WG, I would there too.

[vex]

I don't have a reference line hooked up to my FPR; but I have an issue with the ECU not handling positive pressure (NA based ECU). As such when it sees positive pressure it takes a dump in the fuel department going all the way down to 10.1:1 if not more before I have to let up because it stops climbing the RPM band (I have been able to nurse it to redline without positive pressure, so it's definitely is the ECU at fault not the FPR that's not hooked up).

But if you're running into positive pressure (more than 5PSI) you are definitely going to need to hook up the line.

[scotty305]

I've heard someone claim that running without a vacuum line to the pressure regulator eliminates a possible point of failure on racecars... one less line that can pop off and cause a vacuum/boost leak. They said this is pretty common for non-turbo cars but also an option with low-boost turbo setups, in the case of the turbo car you would increase the static fuel pressure so you end up with a reasonable amount of fuel pressure at full boost.