Fuel Pressure Regulator Location?

[LIME TWIST DART]

What's better, pre or post carb location for fuel pressure regulator? Particularly for a return style. I know closer to the carb is better and staying away from high heat sources is recommended. I have seen differing opinions about running it pre or post carb. In my case, with a dual feed, there is also the option to install between each feed. Of course between is still before. Tech from Mallory says ALWAYS before the carb. It seems that regulating pressure has to come before the intended target, right? However, I have read arguments that a regulator after the carb pressurizes the entire line. Not sure I buy this, but maybe so and does a return make a difference? If it does, what advantages can there be anyway? I plan on locating my Mallory 4307 m, return style, on a bracket between the feeds like the one pictured below. It seems logical to install it before the feed. I wanted to get opinions and settle this before I buy the bracket, feed and fittings. In case it matters: 413 stroker, 4781 850cfm Holley, 1" tapered spacer, Victor 340, 4000 stall, 3.91, Holley electric Black pump and Mallory 4307M return style regulator. Street driven, but no where close to daily. 3rd pic is my carb.
If there is already another good thread on this, please let me know.
Thanks!

 

[Mopar to ya]

Must be coming into the carb. If you run a Holley that maxes out at say 9 psi and you run a 12 psi pump, regulating it in the return does no good. If you run a mechanical, it probably needs no regulator unless you like the looks ... like me.

 

[LIME TWIST DART]

Must be coming into the carb. If you run a Holley that maxes out at say 9 psi and you run a 12 psi pump, regulating it in the return does no good. If you run a mechanical, it probably needs no regulator unless you like the looks ... like me.

Thanks for the input.

 

[goldduster318]

When you're doing a return style, the regulator is like a controlled leak back to the tank...just enough of a leak to bleed off pressure.

Now, I would imagine that having the regulator on the lines connecting to the car, and not necessarily before it would work as well...its just more likely that the carb would see any pulsations in the fuel pressure, where having the regulator before the carb would smooth those out somewhat. A Fuel injected car with a return system has the regulator on the return side of the rail, so clearly its possible.

I run a Carter mechanical fuel pump that puts out 9.5 PSI and I want 6. I have a holley dead-head regulator on the fender near the fuel pump with a -6 line running to it, and then a -6 line running back under the alternator and up to the carb. It keeps the fuel relatively cool, and there's basically no pressure changes at the carb (its about 2' of line before it).

If you put the line away from the carb, just make sure to put your gauge very near the carb to make your adjustment.

Having the bypass regulator with a return line should increase the life of your electric pump by decreasing the load on it when there isn't much fuel being used.

 

[Oldmanmopar]

It should be as the diagram of grumpy's above. After the carb. This keeps the fuel flowing and prevent boiling fuel. It is no good to dead end your fuel at the carb. You want to keep it moving at all times with a return.

Just ran into this helping someone with a 358 sprint. He had his regulator before the carb. Caused the metanol to get hot on the yellow laps and was dead on the restarts. After telling him he insisted it was correct. Until he walked around and saw how others were set up. Floats do not work properly when the fuel is boiling at a dead end . My car is wrong and I have a had hot restart problem. It will be corrected when its pro-charged.

 

[1972DusterPaul]

I just put a regulator in a couple days ago, there happened to be some filled up holes in the position I used on the inner fender...maybe there was one there before.

I have a pressure gauge closer to the carb. I will probably shorten up the hoses a little bit...but it was good to get my motor running.

Paul

 

[LIME TWIST DART]

When you're doing a return style, the regulator is like a controlled leak back to the tank...just enough of a leak to bleed off pressure.

Now, I would imagine that having the regulator on the lines connecting to the car, and not necessarily before it would work as well...its just more likely that the carb would see any pulsations in the fuel pressure, where having the regulator before the carb would smooth those out somewhat. A Fuel injected car with a return system has the regulator on the return side of the rail, so clearly its possible.

I run a Carter mechanical fuel pump that puts out 9.5 PSI and I want 6. I have a holley dead-head regulator on the fender near the fuel pump with a -6 line running to it, and then a -6 line running back under the alternator and up to the carb. It keeps the fuel relatively cool, and there's basically no pressure changes at the carb (its about 2' of line before it).

If you put the line away from the carb, just make sure to put your gauge very near the carb to make your adjustment.

Having the bypass regulator with a return line should increase the life of your electric pump by decreasing the load on it when there isn't much fuel being used.

It should be as the diagram of grumpy's above. After the carb. This keeps the fuel flowing and prevent boiling fuel. It is no good to dead end your fuel at the carb. You want to keep it moving at all times with a return.

Just ran into this helping someone with a 358 sprint. He had his regulator before the carb. Caused the metanol to get hot on the yellow laps and was dead on the restarts. After telling him he insisted it was correct. Until he walked around and saw how others were set up. Floats do not work properly when the fuel is boiling at a dead end . My car is wrong and I have a had hot restart problem. It will be corrected when its pro-charged.

So, regulator before the carb to prevent pulsating pressure or regulator after carb to prevent boiling fuel. I would like to know if it can be plumbed to achieve both?

Preventing pulsating pressure and a guarantee of set fuel pressure are the most common stated reasons for running the regulator pre carb. Almost every time an argument is made for post, there is a mention of that being done on FI systems.
So, why on FI systems and not on carbs?

 

[LIME TWIST DART]

I just put a regulator in a couple days ago, there happened to be some filled up holes in the position I used on the inner fender...maybe there was one there before.

I have a pressure gauge closer to the carb. I will probably shorten up the hoses a little bit...but it was good to get my motor running.

Paul

Must be a good feeling. To hear it run.
I am trying to decide this issue so I can get my motor on the dyno and hear her run for the first time.
I have to say the way your regulator is plumbed has to be the most common way. I think it's the return line that changes everything up for me.

 

[qkcuda]

I put mine lower down, and ran the fuel line close to where the stock fuel pump ran it.

 

[famous bob]

I put mine lower down, and ran the fuel line close to where the stock fuel pump ran it.

I`ve ran 3, this will be the 4th hotrod w/ the reg. right befor e the carb. (DEADHEAD)
one was a superstock hemi, and 2 600 h.p. 406 sbc. dual feed to each end of the carb. never had a boiling problem or any starvation, or any fuel related problems , other than jetting. two were, and the third will be a street car. the hemi was a race car w/ 2 4`s still no problem. the 406`s both had 7 #. pumps , befrore going w/ the 14# pumps, didn`t make a bit of diff.- a whole bunch depends on how your p/u are designed, and line size, bends(fittings) etc.--just my 2 cents, bob

 

[Oldmanmopar]

I didn't listen back when building my car . It was nothing but problems. Three carbs later and I finally figured it out. It is dead ending the fuel at the carb. that is my problem. My Duster will be changed as I said. Keeping as much of the fuel moving as possible is really the best That I have experienced . Since , I have helped others with theirs. I just never have time for my own stuff.

In the pics below my car is also done wrong. So I am not telling you its what I have . It is what works.

 

[RustyRatRod]

It should be as the diagram of grumpy's above. After the carb. This keeps the fuel flowing and prevent boiling fuel. It is no good to dead end your fuel at the carb. You want to keep it moving at all times with a return.

Just ran into this helping someone with a 358 sprint. He had his regulator before the carb. Caused the metanol to get hot on the yellow laps and was dead on the restarts. After telling him he insisted it was correct. Until he walked around and saw how others were set up. Floats do not work properly when the fuel is boiling at a dead end . My car is wrong and I have a had hot restart problem. It will be corrected when its pro-charged.

BAM! This^^^^^^ They don't call him old man fer nuthin. I don't understand why some of yall argue that a regulator in the return, after the carb doesn't regulate fuel pressure the carburetor sees. It most certainly does. It regulates the entire system. That's how it's designed.

I've built so many fuel systems through the years I've lost count. Done it like that almost every time. It works.

 

[KitCarlson]

+1 on all that! Some truly understand hydraulics, others not.

Any minute leakage in a dead head regulator and it is broke.

 

[RustyRatRod]

Exactly. You could put the regulator all the way at the TANK in the return side and it will still regulate pressure for the entire system. Course it would be a beeotch to adjust. lol

 

[LIME TWIST DART]

Ok. It sounds like we have established that the system can be regulated with it installed post carb.
Does anyone want to speak on the the claim that post carb location leaves the carb vulnerable to fluctuation? Or, are we saying that the system is regulated with post carb and there are no greater concerns for fluctuations then there is with pre carb regulator?

 

[KitCarlson]

It seems there would be less fluctuation with regulator after carb. Also the fuel bowl serves as storage. After carb is better for vapor purge too, because it flows.

 

[LIME TWIST DART]

It seems there would be less fluctuation with regulator after carb. Also the fuel bowl serves as storage. After carb is better for vapor purge too, because it flows.

I have given this some more thought. Originally I was thinking that the only way to guarantee consistent pressure to the carb would be to release the fuel at the selected pressure right before the carb. However, does this mean the regulator no longer has control of the pressure, once it releases the fuel, as the carb consumes fuel at differing rates in response to throttle position,(fuel demand)? Can the pressure fluctuate between the regulator and jets depending on the rate the carb is consuming the fuel?
I am wondering if this is why EFI set ups use the regulator post fuel release.
Is it because somehow the regulator maintains consistent pressure behind it, regardless of how much fuel is being consumed?
I am not too familiar with EFI. Do these systems electronically maintain fuel pressure with sensors that constantly adjust the fuel pressure AT the regulator in response to fuel consumption/demand.

Does any of this make sense? LOL

 

[LIME TWIST DART]

Thanks for the input everyone. I think I'm gonna use a fuel log with the regulator mounted on the end, post carb. This will keep the reg close to the carb and up front, away from the headers. My goal was to keep it close to the carb, away from heat, off the fender and in a place thats easy to make adjustments.

Something like this: