Now, I have been sitting here thinking (sometimes dangerous). Need you guys to tell me the better of both evils. This is from the view of a weber IDA.

I. Attached to carb hat before throttle
1. Boost in float bowl same as before throttle
a. No extra flow from main jets because still in the presurized area
2. possible your idle jets will get a surge of fuel
a. resticted surge (has to go through the idle jet then the tiny progression holes
b. This will be as the RPM's drop (+/- I dont know)

II. Attached to intake
1. FPR will drop pressure when throttle closes
a. boost will push the fuel back into the fuel line maybe only for a fraction of a second but thats what should happen. That the reason we have a RRFPR in the first place to stop that.

III. Idea of Ideal set up
1. RRFPR reference point off carb hat
2. Blow off valve referance off intake
a. BOV will release pressure as soon as the intake has a lower psi than the intercooler piping



What ya think?????

 

First, never ever ever use a rising rate fuel pressure regulator on a carb engine. Rising rate regulators are just a crutch (a bad one at that) for cars with speed-density fuel injection systems when adding forced induction without recalibrating the computer.

I don't think they are even available for carb applications (PSI in the 2-7 range) so the point is moot.

Second, with a carb, always boost reference the regulator to the air that the carb is seeing, IE the carb hat.

 

Please disregard the above statement. I believe he is under the impression this is for N/A applications.

You have to use a rrfpr on a blow though turbo application. Otherwise engine go boom. Because the boost from the turbo will push the fuel back to the fuel pump and cause a lean situation.

And this is a turbo application do to the referance of a carb hat and BOV

 

No.

Rising rate fuel pressure regulators raise fuel pressure out of proportion to reference pressure.

You don't want that. What you want is a regular old boost referenced regulator.

So say normally you have 4psi fuel pressure, that is 4psi over the atmospheric pressure in the float bowls, which is the same pressure as the air going into the carb. But now you're using the turbo to raise the atmospheric pressure (what we call boost pressure) by whatever PSI, let's say 6psi. So now you need to raise fuel pressure *also* by 6psi, so that the effective fuel pressure (compensated for boost) is still 4psi, 10psi actual minus the 6psi of boost working against it.

If you used a rising rate pressure regulator... let's say you use one that is 5:1. You're not under boost, fuel pressure is 4psi, everything is happy. You go get that 6psi to get your turbo jollies. Air pressure goes up 6psi, and your rising rate regulator adds 5:1 fuel pressure, so you're adding *30* psi of fuel pressure. Now you have 34psi of actual fuel pressure, minus 6psi of boost working against it = effective fuel pressure of 28psi! In other words you've got waaay too much fuel pressure and your engine is drowning in fuel because you're blowing the needle and seats wide open and spraying fuel out of the float bowl vents into the engine!

I repeat, you *never* want to use a rising rate fuel pressure regulator on a carb application. Straight rate only. Which conveniently enough is the only kind of boost-referenced fuel pressure regulator you can get for a carb.

 

heh, i have been dealing with this quite a bit lately. still havent figured out the right spot. LOL

 

OK, i eat crow for wrong terminology and only terminology. I mean FRP that will raise fuel pressure on a 1:1 basis with boost. Not RRFPR. BTW all that time to type and you still didnt vote?

 

peejay; dude, we are (atleast me and the few running turbo carb rx7's on here) running the mallory 4309 CARB SPECIFIC 1:1 ratio rising rate fuel pressure regulator. there is no 5:1 so i really dont know where this is gong with your debate. hahaha, not saying what you wrote isn't valid. it's completely true, but that is why they make rrfpr's for CARBS with a 1:1 ratio. WOOT.

 

Voting takes too much time. I have to move the mouse around and click on stuff.... so strenuous..

 

I'm running this one mallory 4307M

 

guess your much quicker with your fingers than your whole hand

 

I don't think you understand what peejay's saying. A 1:1 regulator is not a rising rate regulator. Think about what the term rising rate means. If it's a rising rate regulator the difference between fuel pressure and boost pressure increases with every pound of boost. With a 1:1 regulator the difference in pressure remains the same.

 

well there you go, now if he would have explained it like that i would have gotten the fact that he meant LITERALLY a RR fpr isnt suitable. everyone here uses RRFPR very loosely.

 

well, this is a really useless debate, isn't it? The guy wants to know where to have the boost sensing line connected to, and all you guys are talking about is wether or not this would be called a rising rate regulator or not.
So let's put things clear: he wants a regulator that will increase fuel pressure on a 1:1 basis according to boost. In other words: the difference between the fuel pressure and the pressure of the air blown in will stay stable all the time (let's say 4psi). That means the actual fuel pressure will rise won't it? Is this a RR-FPR? Hell, I don't know. Do we understand what he means? Yes! So why not answer his question then, instead of deating about terminology?

 

so where would you put it?

 

the only place to put the boost sensing line is .........IN THE INTAKE MANIFOLD AFTER THE THROTTLE BODY//CARBURATOR..
if you install it before the throttle body// carburator, the boost will spike causing your fuel pressure to spike flooding the carb especially, not good

 

Intake manifold is the only RIGHT place to put it. Sure, it'll work if it's refrenced to the carb hat, but it'll run like **** compared to connecting it to the manifold. I've already typed out a long explination why a few times, and I'm too lazy right now to do it again.

 

Not to cause an argument, the float bowl is in the boost spike area. Wouldn't the boost pressure and the fuel pressure equalize?

 

yes , they both equalize but the throttle shaft is closed so where does all the extra fuel go?

flooded motor

 

This is a fun debate.

Extra fuel this is my problem, I dont see where it comes from. When there is a boost spike the float bowl and the fuel line equalize in pressure do to the FPR. The only way there would be a gush of fuel is from a delay in the reaction time of the FPR. I believe a FPR that delayed would be detrimental on deceleration and acceleration.

 

Which is why you use a bypass type regulator, so fuell pressure change is instant.

All the other blow through turbo guys reference fuel pressure to the carb hat... Hmm what are they doing wrong?

 

From my somewhat limited experience, I'm gonna say yeah, they're doing it wrong.

 

it made a huge difference for me when i switched over to the intake manifold source. even tho my carb as of now cant handle the boost, it did accept it a little better when i was going thru the intake manifold!

 

I have mine set on for the Carb hat, BEFORE the Holley carburator.
My engine is broken in, and driving better than ever, pulling G's like a monster.

On a small carb setup (Nikki/Weber) with small bowls, the reference point should be the same as on a Fuel Injection car - the Intake manifold, AFTER the throttlebody.