RRFPR or not?

[jacob80]

Hey guys, we have a megan racing RFPR and have decided to disconnect the vacuum line to disable the rising rate part of it. For megasquirt, you don't need a rising rate regulator, correct? From my understanding, the rising rate regulators are for stock ecu wiring with turbocharged application?

[RS Speed]

rrfpr are a good way to blow your motor, if you have megasquirt ditch the rrfpr and just run a regular FPR with a 1:1 ratio.

[WizardBlack]

You still need a vac reference; you cannot just unhook it from a RRFPR. You need to buy a STANDARD rate FPR and hook it up to vac.

[jacob80]

So we have to buy a new regulator? What purpose does the vacuum line serve other than increasing pressure? I thought that was the sole purpose of it. Hmm....

[WizardBlack]

So we have to buy a new regulator? What purpose does the vacuum line serve other than increasing pressure? I thought that was the sole purpose of it. Hmm....

Yes, the standard reg does indeed raise pressure. The rising rate regulator raises pressure at a different ratio. A standard item raises the pressure of the fuel to equal the pressure increase of the intake plenum in which the fuel is injected. Otherwise, the raised plenum pressure would push against the fuel trying to come out of the injector and reduce the effectiveness of the injector. Therefore, a standard regulator increases fuel pressure by the same amount that plenum pressure increases. ie., 1:1 ratio.

A rising rate regulator raises fuel pressure faster than plenum pressure goes up. RRFPR's are generally used only when you want to put a cheap turbo kit together to sell. The RRFPR will raise how much fuel you can inject before the injectors are maxed out. It must be higher than a 1:1 ratio because that is what practically all standard regulators are. It isn't necessarily easy on your fuel pump, however. (This depends on how much boost you are using and what your fuel pump is like)

The thing to remember is an RRFPR is a rising rate; not a rising pressure regulator. Even standard regulators are rising pressure.

[jacob80]

Well we have the megan racing RRFPR, what would happen if we disable vacuum on it? Would it still work or not

[boardkid280z]

Your fuel flow will drop considerably, maybe by more than 50%. If your injectors are big enough, you might be able to make up for it by increasing your injector pulsewidth at higher RPMS. But this is not the right way to do it. If you have too much fuel up top, just reduce your pulsewidth in Megasquirt. If you want to even things out across the RPM range, replace your RRFPR with a standard FPR.

As long as you have a wideband sensor on the car, you should be able to monitor and tune as necessary. But if you remove the vacuum line from our RRFPR and eveything is somewhat tuned now, you will find everything will go LEAN, LEAN, LEAN without the necessary fuel pressure. As you know that is very dangerous, and not a good idea.

 

In short, it's not a good idea, and what are you trying to accomplish?

[boardkid280z]

Well we have the megan racing RRFPR, what would happen if we disable vacuum on it? Would it still work or not

 

 

Also, to answer your specific question, "No it would not still work."

[WizardBlack]

Your fuel flow will drop considerably, maybe by more than 50%. If your injectors are big enough, you might be able to make up for it by increasing your injector pulsewidth at higher RPMS. But this is not the right way to do it. If you have too much fuel up top, just reduce your pulsewidth in Megasquirt. If you want to even things out across the RPM range, replace your RRFPR with a standard FPR.

As long as you have a wideband sensor on the car, you should be able to monitor and tune as necessary. But if you remove the vacuum line from our RRFPR and eveything is somewhat tuned now, you will find everything will go LEAN, LEAN, LEAN without the necessary fuel pressure. As you know that is very dangerous, and not a good idea.

 

In short, it's not a good idea, and what are you trying to accomplish?

 

The specific answer is; your fuel will get richer below 0 psi relative and leaner above 0 psi relative. All pressure regulators with vac reference are that way. The only difference between a RRFPR and LRFPR is by how much.

[mobythevan]

You can tune the car with the RRFPR or with a standard FPR. As long as you don't make any adjustments to the RRFPR after tuning(assuming its an adjustable RRFPR, if not then no worries about you cahnging it after tuning), all that matters is that the fuel delivery is the same every time. However, if you do something like this your fuel tables would be useless to a person with a standard FPR. Other than that it will work, just connect the vacuum line to the RRFPR and tune it. It doesn't make any sense to use the RRFPR with a standalone as they are usually a bandaid to help with a non-tuneable ECU or too small of injector, but it will work if you don't want to spend the money to get a standard FPR with a 1:1 ratio.