Rising Rate Fuel Pressue Regulators used for turbo setups (actual info only please!)

[Ondonti]

Okay there has been some good info posted but I think there is a serious lack of looking at this from an unbiased perspective.

If you are trying to say RRFPR's are great, thats not an appropriate comment for this thread as we are looking for information not opinions.

I dont feel like being preachy, so...
Would someone else mind explaining the issue of how fuel pressure effects fuel flow at the injector? (I know a there are a good number of us who understand this issue and the limitations it sets on usefulness of the device)

We can cover other questions etc or whatever people feel is important when it comes to understanding these devices and their limitations.

[m90daytona]

here is a awsome website for fuel pressure vs. injector flow. i have posted links to this website before.

http://www.rceng.com/technical.htm

basically, w/ an rrfpr you can make the same power w/ a much smaller injector.

[mwinkle353]

It's all about the pressure.

Take a garden hose and force water through it to get 15 psi at the pump's outlet. Run that setup for 60 seconds and measure the total volume that has passed through the setup. Now increase you pump's flow so that you get 50 psi at the pump's outlet. Measure the total volume passed through the new setup. I'll garantee that you'll surpass the first test's volume by a factor of 4.

Now reduce the scale of this test. Use an injector, pump, and pressure regulator. You'll get the same results as the garden hose tests.

If the ECU doesn't change the pulse width of the injector, but you increase the pressure; you get more fuel per pulse width.

This is the basic principle of the rising rate of gain regulators. This way, if a calibration cannot supply any more fuel above a certain pressure, the pulse width will stay consistant above that pressure. This is where the regulator starts to shine. By adding the required fuel to match the added air of the turbo/super output.

Since our PCM's allow a working range of 29" Hg of vacuum to about 1.26 psi of boost, we don't need any device to change the fuel delivery. In this case, the stock (or aftermarket adjustable) 1:1 ratio regulator must be used. But if you are to surpass the 1.26 psi of boost, then you'll need to add more fuel above the upper limit of the MAP sensor's max voltage. There's where we can use the function of a regulator of greater than 1:1 ratio.

The only necessary thing to worry about is "tuning" the rate of gain of such unit, so that you add the proportional amount of pressure to allow the required flow of fuel. Each motor/setup will be different. And that's where the "tuning" comes into play.

[Ondonti]

I would liek to point out that you need to exponentially increase fuel pressure ans you increase boost.

Fuel flow does not increase in linear fashion with fuel pressure increase.

Just try playing with that website that was posted.

going from 50 to 100 psi fuel pressur only equals a 33% fuel flow gain.
going from 100 to 150psi fuel pressure only equals a 12% fuel flow gain.
100 to 200 psi equals a 27% fuel flow gain (not even close to realistic either)

These numbers are not realistic either as actual fuel flow gain is MUCH smaller once you go above about 4.0 bar (80psi).
The math equation is really only accurate for much lower fuel pressures.

[m90daytona]

i think the equation works well when dealing w/ realistic numbers. nobody is going to run 200 psi. when dealing w/ less than 100 psi i would say that the equation is accurate.

[DustyR/T]

good info.

[Ondonti]

Quote:

Originally Posted by m90daytona i think the equation works well when dealing w/ realistic numbers. nobody is going to run 200 psi. when dealing w/ less than 100 psi i would say that the equation is accurate.

From my readings the numbers get inaccurate before 100psi.

[m90daytona]

i used that website to get the injector size for my car and so far so good. 38lb injectors are idling very well and should be good at least to 375whp but could possibly be good for 400-450whp. i dont think the equation is flawless but i think it will get you pretty close to where you should be. if you wind up going to high or too low that can be adjusted w/ an rrfpr and/or aftermarket ecu (like megasquirt) to compensate either way.

[Ondonti]

Does anyone know what the stock injector pulse width is at WOT & redline?

[mwinkle353]

the same pulse width as WOT at any other rpm.

[Ondonti]

eek sorry I meant injector duty cycle :P

[Shadow24V]

duty cycle shouldnt go above 80% IIRC, above that they never fully close and fluctuate between partially and fully open.

[Ondonti]

Quote:

Originally Posted by Shadow24V duty cycle shouldnt go above 80% IIRC, above that they never fully close and fluctuate between partially and fully open.

Thats what is said in books but in practice lots of cars run past 80% from the factory.
It also depends on injector brand, and injector style (disc,pintle,ball etc) those all have pressure issues as well that are brand and style specific. Dont remember them all at the moment.

[m90daytona]

the main reason you shouldnt run an injector over 80% is heat. if the injector is too small and you run a large duty cycle, say 90%, the injector gets hot, and heats up the fuel that could cause knock/detonation problems. at least thats how it has been explained to me though i agree it probably depends on the type/brand of injector.

[c2xejk]

I don't believe ours have any problems. If you are curious if they do. Hook them to a battery and let them sit there for a while with nothing flowing through them...

For reference, Neil Emiro did this with the T3 fuel injectors. He told me that after 24 hours they still were not hot...