Hi folks end hope everybody’s having a decent Saturday.
I need to button up another project car that was previously (long time ago and original engine long gone) a fuel injection car so it’s got the return line like they all do.
It looks like many of you like to use a pressure regulator in the return line, rather than simply capping it off, and I was wondering if there’s a specific regulator that you would recommend or if a Holley rotary dial to select pressure unit is fine to use.
Thanks!
Anything adjustable should work
I’ve used a rotary dial before. Works fine
I’ve used a rotary dial before. Works fine
QUOTE(Tdskip @ Apr 13 2024, 06:36 PM) 
Hi folks end hope everybody’s having a decent Saturday.
I need to button up another project car that was previously (long time ago and original engine long gone) a fuel injection car so it’s got the return line like they all do.
It looks like many of you like to use a pressure regulator in the return line, rather than simply capping it off, and I was wondering if there’s a specific regulator that you would recommend or if a Holley rotary dial to select pressure unit is fine to use.
Thanks!
How are you running the return? With a "T" fitting, or flowing into one carb and out the other carb then returning to fuel tank? With the right fuel pump you wont need to regulate.
Matt
Id suggest the Holly unit its inexpensive, uses standard fittings so you can adapt it to the area is being installed & rebuild kits are available
https://www.holley.com/products/fuel_system...rs/parts/12-804
https://www.holley.com/products/fuel_system...rs/parts/12-804
Thanks for all the feedback.
Not really sure yet on how to run it…
Not really sure yet on how to run it…
I have the Holly as well, combined with a low pressure fuel pump.
I’d think you’d want the fuel pressure reg before the carbs, though, not after.
I’d think you’d want the fuel pressure reg before the carbs, though, not after.
Be careful here!
What many have alluded to are simple single input/output no return line regulators.
A regulator that is designed to return fuel to the tank is a different creature.
Make sure which one you have.
Simple type are direct feed before the carbs and only feed the carbs. You might have a tee past it to feed a pair of carbs. There will be no return to the tank.
The return line style will be installed past the carbs.
The return line style are better IMO but have more leak points and more complexity.
Making 200+ HP and require significant flow the return line style is what I'd use.
Everything would be expensive.
A common streetcar with below 150hp I'd try the simple one first.
Everything would be on the cheaper side of things.
What many have alluded to are simple single input/output no return line regulators.
A regulator that is designed to return fuel to the tank is a different creature.
Make sure which one you have.
Simple type are direct feed before the carbs and only feed the carbs. You might have a tee past it to feed a pair of carbs. There will be no return to the tank.
The return line style will be installed past the carbs.
The return line style are better IMO but have more leak points and more complexity.
Making 200+ HP and require significant flow the return line style is what I'd use.
Everything would be expensive.
A common streetcar with below 150hp I'd try the simple one first.
Everything would be on the cheaper side of things.
There are a few different kinds of regulators out there, and different ways to plumb.
Some use the simple dial type pre-carb in a "deadhead" (no return line) arrangement to limit pressure. Or as suggested, use a low pressure carb compatible fuel pump in a deadhead arrangement. For a lower hp setup it'll work fine in most cases.
A setup with a return can have some advantages like steadier pressure, and a cooler supply of fuel to the carbs. A couple commons ways to do it:
1. Have a multi-port regulator pre-carb. One outlet to each carb, and a third going back the tank.
2. Have a Y or T connector dividing the supply line to the carbs. Have exit lines from the carbs go to a second T - this is your return line. Regulator in the return line, then back to the tank. This way keeps a cooler supply of fuel running through the carbs. It's a small advantage, but why not take it?
Related note - EFI always have a return line, and many manufacturers including Porsche have used approach #2. No reason it won't well on a carb setup. I have my carb'd 911 racecar and MFI 914 racecar set up this way.
I don't recall the brands of regulators I used, but they were whatever recogizable brand was reasonably priced at Summit Racing, probably. Note that the common Holley units regulate down to like 5-8 psi last I knew, which is too high for Webers which like 3-3.5 psi.
Some use the simple dial type pre-carb in a "deadhead" (no return line) arrangement to limit pressure. Or as suggested, use a low pressure carb compatible fuel pump in a deadhead arrangement. For a lower hp setup it'll work fine in most cases.
A setup with a return can have some advantages like steadier pressure, and a cooler supply of fuel to the carbs. A couple commons ways to do it:
1. Have a multi-port regulator pre-carb. One outlet to each carb, and a third going back the tank.
2. Have a Y or T connector dividing the supply line to the carbs. Have exit lines from the carbs go to a second T - this is your return line. Regulator in the return line, then back to the tank. This way keeps a cooler supply of fuel running through the carbs. It's a small advantage, but why not take it?
Related note - EFI always have a return line, and many manufacturers including Porsche have used approach #2. No reason it won't well on a carb setup. I have my carb'd 911 racecar and MFI 914 racecar set up this way.
I don't recall the brands of regulators I used, but they were whatever recogizable brand was reasonably priced at Summit Racing, probably. Note that the common Holley units regulate down to like 5-8 psi last I knew, which is too high for Webers which like 3-3.5 psi.
Modern EFI no longer has return lines.
Pretty much everyone has gone to "dead head" with a static pressure regulator in the tank.
Modern stuff is usually not vacuum referenced anymore either.
This was done for evaporative emissions reasons.
Hot return fuel makes for higher gas tank temperatures and more evaporative emissions.
This was SO bad on K-Jetronic that Mercedes had an AC based fuel cooler installed on most of the V8 cars. This only cooled return fuel.
I'd have put that on the feed side...
Pretty much everyone has gone to "dead head" with a static pressure regulator in the tank.
Modern stuff is usually not vacuum referenced anymore either.
This was done for evaporative emissions reasons.
Hot return fuel makes for higher gas tank temperatures and more evaporative emissions.
This was SO bad on K-Jetronic that Mercedes had an AC based fuel cooler installed on most of the V8 cars. This only cooled return fuel.
I'd have put that on the feed side...
I am using this regulator with the stock fuel pump on my 2056 75my 914
https://www.partsklassik.com/p-1951-fuel-pr...ulator-pmo.aspx
https://www.partsklassik.com/p-1951-fuel-pr...ulator-pmo.aspx
Don’t forget the FP gauge and 2 more shouldered clamps.
Thanks for the discussion and all the considerations gentleman, very much appreciated.
Interesting points about how it's done on modern cars. Apparently I don't work on those!
One point that may be obvious, but I don't see it mentioned ... if you go with a deadhead arrangement with a regulator pre-carb, make sure you use a low pressure fuel pump designed to work with that plumbing arrangement. EFI pumps are usually designed to work at much higher pressures, and don't work well in a deadhead arrangement when regulated down to 3 psi.
One point that may be obvious, but I don't see it mentioned ... if you go with a deadhead arrangement with a regulator pre-carb, make sure you use a low pressure fuel pump designed to work with that plumbing arrangement. EFI pumps are usually designed to work at much higher pressures, and don't work well in a deadhead arrangement when regulated down to 3 psi.
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