Rising Rate Fuel Pressure Regulators

[Two80z4me]

In an N/A Application, what difference do they really make? Ive heard negative things about them being applied to a Turbo motor, but I've also heard good things about them in a N/A motor. Please, Experienced people, chime in.

[hoov100]

none, unless you have a need for more fuel, or your current fuel system doesnt have a FPR.

[Two80z4me]

none, unless you have a need for more fuel, or your current fuel system doesnt have a FPR.

 

thats all I needed to know.

[Tony D]

Define RRFPR, many people mistakenly refer to manifold referenced FPR's as 'rising rate' and say 1:1 RRFPR which is like "Freeze Plug" and "irregardless"---incorrect and outright misuse of the English Language.

 

A manifold referenced FPR is normally used in all EFI applications because it keeps the pressure drop across the injector pintile the same regardless of load.

 

Additionally, when under high manifold vacuum, it effectively 'decreases' the size of the injector by running less pressure through it, making for a longer pulsewidth at idle---easier to control larger injectors cleanly.

 

Rising Rate FPR's have ratios of manifold pressure to fuel pressure, like 1:2 or 1:3, whatever. This means that under boost, as you increase boost pressure 1psi, fuel pressure will increase 2 or 3 psi depending on the ratio chosen. At 20psi of boost, with a regular FPR, you will have static pressure of say 45psi and then the boost referenced correction, meaning you have 65psi in the rail.

With a 2:1 RRFPR, under the same situation, 45psi static, and 20psi of boost, you will have 45+ (20X2), or 45+40=85psi.

With a 3:1 RRFPR, under the same situation, 45psi static, and 20psi of boost, you will have 45+ (20X3), or 45+60=105psi.

 

As you can see, under boost, you will get considerably more fueling for the same pulsewidth at 105, or even 85psi, than you will from a standard FPR running 65psi. The percentages are easy enough to figure out. This allows you to run the N/A fueling map with it's set Millisecond pulsewidths, and get more fuel to the engine.

 

On an N/A engine, the RRFPR would be a total waste of money outside the ability to adjust the fuel pressure.

 

Now, that being said, there IS about a 7psi differential between idle and WOT. Meaning fuel pressure could be technically arranged to be slightly higher than idle pressure, or normal static/WOT pressure using a RRFPR, but it would take specific calibration steps to have it come into play. In this case you would use the RRFPR with the manifold vacuum attached and the engine running at idle to set what normally would be 'static' fuel pressure around 45psi (instead of the normal 26)

This would result in you gaining 14psi over base (-7 to -11 psia manifold pressure at idle, closer to 15psia at WOT so 4 to 8psia differential, using the same multiplication ratios giving you an 8/12 to 16/24psi rise in fuel pressure at WOT)

 

It's not normally used on N/A's it's easier to play with the thermal sensors on the car and get more fuel.