Dual fpr's....will it work?

[jking29]

Ok, I have an idea that I am not positive will work as I think it will. I am going to be adding a 50-75 shot of nitrous this year and know that I am going to need a bigger fuel pump than my current 190. I want to switch to a Supra or 255 pump, but don't want to spend the $200+ for an Aeromotive fpr and don't really trust the Megan. I have more fabrication skills than money, so my idea is this. I want to take a second stock 1g turbo fpr and make an adapter to use it on the fuel supply to the solenoid for the nitrous system. My understanding is that the reason the 255 over runs the stock fpr is that return orifice is too small to deal with the extra volume. If that is the case then 2 stock fpr's should give enough return capability to be able to deal with the extra flow and not have over run issues. I would Y the return lines together to go into the tank, and since the turbo fpr is boost referenced, it would raise fuel pressure to the nitrous side of the system also to keep correct flow. Is there any issues I might be overlooking? I am looking for concerns and feedback from experienced people, not "just buy an Aeromotive" answers. Thanks!

 

[GVR4592]

Just get the Megan regulator, my cousin has had it on his car for over a year and it works fine.

 

[FORMONTOYA]

Since we're just speculating theories, I'll throw in my 0.02 worth (although I've never tried it).

As you already know, the reason the OEM FPR doesn't work properly is that the orifice is too small to pass the extra volume of fuel under idle and cruise conditions. While at WOT, the injector will practically alleviate the issue because the injectors will "pass the gas".

My theory is that with the orifice being "fixed" and not adjustable in the 2 FPRs you will create the opposite problem compared to having just 1.

You have 1 "fixed" orifice that can bypass "X" amount of fuel. Now you introduce another orifice that can bypass the same amount of fuel thereby allowing too much fuel to bypass the system thus reducing the fuel pressure. With no way of adjusting it in either direction you will create a lean condition for the motor which is far worse than the initial problem you're faced with at the moment.

That's my take on the idea. If you try it, let us know how it turned out for you.

 

[jking29]

Since we're just speculating theories, I'll throw in my 0.02 worth (although I've never tried it).

As you already know, the reason the OEM FPR doesn't work properly is that the orifice is too small to pass the extra volume of fuel under idle and cruise conditions. While at WOT, the injector will practically alleviate the issue because the injectors will "pass the gas".

My theory is that with the orifice being "fixed" and not adjustable in the 2 FPRs you will create the opposite problem compared to having just 1.

You have 1 "fixed" orifice that can bypass "X" amount of fuel. Now you introduce another orifice that can bypass the same amount of fuel thereby allowing too much fuel to bypass the system thus reducing the fuel pressure. With no way of adjusting it in either direction you will create a lean condition for the motor which is far worse than the initial problem you're faced with at the moment.

That's my take on the idea. If you try it, let us know how it turned out for you.

This is exactly why I posted this question here. This is the same theory I was pondering and was hoping someone would be able to help me work through any concerns. However, I believe the Supra pump flows about 80% more than the stock pump, so with 2 stock fpr's I should only be flowing approximately 10% less fuel to each of them. Do you think that that difference in flow would create a low fuel pressure situation?

 

[FORMONTOYA]

If you're going to try this system make sure you do some tests before you actually fire up the motor.

Turn a stock setup (pump, FPR, etc.) and see what the fuel pressure is (with the vacuum hose removed). Write that number down. Then apply, lets say 10PSI, to the vacuum port to simulate boost and write that number down (should be 10PSI higher than the previous number).

Then test the setup as you propose and use the same no-boost/hose removed and 10PSI boost and compare the results, just make sure you use the same boost PSI reference to keep the comparisons on equal footing.

I personally would NOT want to see anymore than a 2-3% max difference between the 2, probably less considering you want to use nitrous, but that's just me.

The pressure is what you will be more concerned with, especially the 1:1 rising rate as you will definitely have enough volume.

 

[91vr4evolution]

I don't think you would have a problem. The regulators open at a particular pressure, not a particular flow. I would imagine that the fuel pressure will be whatever the "stronger" regulator holds, eg. If #1 reg can hold 36psi at idle, and #2 can hold 38 psi at idle, when installed on the fuelrail together, the fuel pressure will be 38psi not 36psi, because the #1 will open at 36 psi, but be overrun by the pump until the pressure reaches 38 psi, and then the #2 will open, bleeding off the extra pressure. I think under boost, it would probably "fall" to the lower PR's, as there would be less/no overrun to bleed off.

All that said, I think you should just want until you can afford a AFPR.

Or if you have fab skills, make your own?