Recommendation on fuel pressure regulator for return line on dual carb |
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Recommendation on fuel pressure regulator for return line on dual carb |
Tdskip |
Apr 13 2024, 04:36 PM
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#1
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Advanced Member Group: Members Posts: 3,686 Joined: 1-December 17 From: soCal Member No.: 21,666 Region Association: None |
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! |
brant |
Apr 14 2024, 08:11 AM
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#2
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914 Wizard Group: Members Posts: 11,617 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
Anything adjustable should work
I’ve used a rotary dial before. Works fine |
mate914 |
Apr 14 2024, 08:41 AM
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#3
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Matt Group: Members Posts: 739 Joined: 27-February 09 From: Eagles mere, PA Member No.: 10,102 Region Association: North East States |
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 |
914werke |
Apr 14 2024, 01:18 PM
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#4
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"I got blisters on me fingers" Group: Members Posts: 10,030 Joined: 22-March 03 From: USofA Member No.: 453 Region Association: Pacific Northwest |
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 |
Tdskip |
Apr 15 2024, 09:31 AM
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#5
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Advanced Member Group: Members Posts: 3,686 Joined: 1-December 17 From: soCal Member No.: 21,666 Region Association: None |
Thanks for all the feedback.
Not really sure yet on how to run it… |
theer |
Apr 16 2024, 01:56 PM
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#6
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Senior Member Group: Members Posts: 676 Joined: 31-July 15 From: Dover, MA Member No.: 19,014 Region Association: North East States |
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. |
technicalninja |
Apr 16 2024, 02:35 PM
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#7
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Senior Member Group: Members Posts: 1,171 Joined: 31-January 23 From: Granbury Texas Member No.: 27,135 Region Association: Southwest Region |
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. |
stownsen914 |
Apr 17 2024, 10:01 AM
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#8
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Senior Member Group: Members Posts: 913 Joined: 3-October 06 From: Ossining, NY Member No.: 6,985 Region Association: None |
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. |
technicalninja |
Apr 17 2024, 10:14 AM
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#9
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Senior Member Group: Members Posts: 1,171 Joined: 31-January 23 From: Granbury Texas Member No.: 27,135 Region Association: Southwest Region |
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... |
rfinegan |
Apr 17 2024, 10:23 AM
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#10
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Senior Member Group: Members Posts: 973 Joined: 8-February 13 From: NC Member No.: 15,499 Region Association: MidAtlantic Region |
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 |
rhodyguy |
Apr 17 2024, 11:38 AM
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#11
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Chimp Sanctuary NW. Check it out. Group: Members Posts: 22,071 Joined: 2-March 03 From: Orion's Bell. The BELL! Member No.: 378 Region Association: Galt's Gulch |
Don’t forget the FP gauge and 2 more shouldered clamps.
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Tdskip |
Apr 17 2024, 05:28 PM
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#12
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Advanced Member Group: Members Posts: 3,686 Joined: 1-December 17 From: soCal Member No.: 21,666 Region Association: None |
Thanks for the discussion and all the considerations gentleman, very much appreciated.
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stownsen914 |
Apr 18 2024, 06:36 AM
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#13
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Senior Member Group: Members Posts: 913 Joined: 3-October 06 From: Ossining, NY Member No.: 6,985 Region Association: None |
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. |
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