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ermm... actually I think the FPR is a must have item for any EFI system, without it, the fuel-rail will not be able to build pressure, as it will just flow straight through, back to the tank....
Blocking it off, completely will see your fuelpump trying to force way too much fuel through the injectors, that is almost 90% of their lives at sub 30% Duty,
problem one, EFI fuelpumps don't like being blocked off that much on the high pressure side, they tend to brake when you do that.
Problem two, most OEM fuel injectors can not handle fuel pressures that high (5~6 bar). They have a hard time opening, as the solenoids are usually not strong enough to overcome the extra pressure it pulls against.
if on the other hand you where thinking of when a variable FPR is nice to have....
for one, when you are playing with boost, and you do not have funds for bigger injectors, you can increase your OEM injectors fuel flow rate, by adjusting the pressure the rail runs at(within limits). This mod would require an re-tune to be effective.
Usually the stock fpr regulator can't handle a walbro's higher fuel pressure, so thats where a fpr comes in. You set it to 3bar if your running a 3bar set-up and if your running a 4bar set-up you set it up to 4bar, etc.......
I really only think its necessary when you get a walbro. And its really not used to much in tuning, maybe just a little to lean or richen up your a/f mixture, but its more for adjusting your fp to the proper setting with the extra pressure form the walbro.
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Old set-up: 91 se-r sr20de+T 13.04@110mph w/ a t25 and s3's
New set-up: 91 se-r gti-r sr20det w/ a gt28r(Something MUCH bigger coming in FEB...),gti-r exhaust manifold w/ heat shield, MSD 72lb inj., N62 maf, Turbo XS RBV-25 bov, Calum ecu(TUNED BY STEVE), Hallman pro rx mbc, Greddy tt, B&M ss, Greddy FMIC, AEM wideband, Autometer gauges, AGX's on Road magnets, etc.....And it Does run
There are two versions on the 255 lph pump. High and low pressure. You need an AFPR for a high pressure pump or you will run pig rich and foul plugs quickly.
Otherwise an AFPR is not needed assuming the pump runs at stock fuel pressure.
