Re: Fuel pressure before the regulator
[Re: mopar dave]
#2821533
09/16/20 01:25 PM
09/16/20 01:25 PM
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Joined: Jan 2003
Posts: 19,384 Las Vegas
Al_Alguire
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Thats going to depend on whos pump and which pump. But as a generalization I would say 25-28psi is adequate for most everyone. Both our cars are at 28 at the regulator, both are BIG pumps as well and fuel pressure does not vary going down track. You also do not need 6 PSI with dual carbs unless your pump cannot keep up. Mine is a 4.5
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: Fuel pressure before the regulator
[Re: mopar dave]
#2821541
09/16/20 01:40 PM
09/16/20 01:40 PM
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Joined: Jan 2003
Posts: 31,076 Oregon
AndyF
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What should the fuel pressure be between the pump and the regulator if running twin carbs at 6psi. It doesn't matter as long as your regulator can handle it. We use a high pressure EFI pump on the dyno for all engines. When we run a carb engine the 100+ psi pressure from the pump gets dropped to 6 psi. On an EFI engine the high pressure gets dropped to 60 psi. If I was building a carb car these days I'd use a high pressure EFI pump inside the tank and then use a EFI to carb regulator to drop it down. But if your car isn't set up that way then just do what you have to do.
Last edited by AndyF; 09/16/20 01:41 PM.
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Re: Fuel pressure before the regulator
[Re: mopar dave]
#2821593
09/16/20 03:17 PM
09/16/20 03:17 PM
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Joined: Jan 2003
Posts: 14,514 So. Burlington, Vt.
fast68plymouth
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I’d turn the pump pressure back up to the 12psi......... or more, if it can do it without affecting reliability.
12psi from the pump is pretty low these days. I think even the old Holley blue pump was set at 14 psi.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Fuel pressure before the regulator
[Re: mopar dave]
#2821598
09/16/20 03:25 PM
09/16/20 03:25 PM
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Joined: Jan 2003
Posts: 31,076 Oregon
AndyF
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Ok, here’s what I have. An old SX fuel systems 160 pump. I believe they were bought out by Edelbrock because their billet pumps look identical. I tested this pumps free flow at 2 gallon per minute. The pump out of the box was 12psi, but I turned it down years ago and now I read 6psi. While testing my combo on the freeway flat footing it for about 5 seconds in high gear I see it drops about 1.5 to 2 psi. Just thought I would bump it up a bit. Test free flow with an orifice that matches the area of your needle and seat. That will give you a better idea of how much flow it can actually produce at WOT. 2gph is enough fuel for over 1000 hp but if it drops to 1 gph when using a restriction you'll be in trouble. I agree, 12 psi seems low for line pressure. That doesn't seem like it provides much margin for error.
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Re: Fuel pressure before the regulator
[Re: AndyF]
#2821603
09/16/20 03:37 PM
09/16/20 03:37 PM
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Joined: Jan 2003
Posts: 14,514 So. Burlington, Vt.
fast68plymouth
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For the flow test, I use a ball valve on the end of the hose going into the jug. I adjust the ball valve so the system pressure is the lowest I’m comfortable with........ like 4.5psi.
Then, don’t touch the valve....... empty the jug, and do the flow test. You want to see how much the system flows while maintaining the required minimum pressure.
For 750hp....... the flow @ pressure should be slightly better than one gallon per minute.
The free flow test at zero pressure tells you nothing useful.
We tested a system in a car once where the free flow was great, but the flow at 6psi was barely a dribble.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Fuel pressure before the regulator
[Re: fast68plymouth]
#2821624
09/16/20 04:56 PM
09/16/20 04:56 PM
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Joined: Jan 2003
Posts: 5,992 Anoka County, MN
Leigh
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For the flow test, I use a ball valve on the end of the hose going into the jug. I adjust the ball valve so the system pressure is the lowest I’m comfortable with........ like 4.5psi.
Then, don’t touch the valve....... empty the jug, and do the flow test. You want to see how much the system flows while maintaining the required minimum pressure.
For 750hp....... the flow @ pressure should be slightly better than one gallon per minute.
The free flow test at zero pressure tells you nothing useful.
We tested a system in a car once where the free flow was great, but the flow at 6psi was barely a dribble. That’s a good test fixture idea. Thanks for the useful tip!
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Re: Fuel pressure before the regulator
[Re: AndyF]
#2821631
09/16/20 05:24 PM
09/16/20 05:24 PM
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Joined: Aug 2003
Posts: 43,303 Bend,OR USA
Cab_Burge
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Test free flow with an orifice that matches the area of your needle and seat. That will give you a better idea of how much flow it can actually produce at WOT. 2gph is enough fuel for over 1000 hp but if it drops to 1 gph when using a restriction you'll be in trouble. I agree, 12 psi seems low for line pressure. That doesn't seem like it provides much margin for error. [/quote] I had a fuel delivery problem on my old street Duster that was cause by having to fine of a fuel filter before the pump, it was a BG400 paper filter which are 10 microns, not 80+ microns that Magnafuel says to use with their pumps I had one of heir 275 pumps and replaced it with one of their 300 pumps, both pumps free flowed through the three #6 AN lines for the six pack flow right at 1 gallon in 10 seconds I called Magnafuel to complain about no difference in volume and was told by their tech to restrict the flow for both tests to get a accurate result, I hooked up one line to the rear carb and flow the other two lines into the 5 gallon jugs with the 300 pump and it almost double the volume during 5 tests that way Restricting the free flow by one line increase the fuel delivery dramatically
Last edited by Cab_Burge; 09/16/20 05:26 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Fuel pressure before the regulator
[Re: BSB67]
#2822034
09/17/20 07:52 PM
09/17/20 07:52 PM
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Joined: Jan 2003
Posts: 14,514 So. Burlington, Vt.
fast68plymouth
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Of course........“In theory”....... it should make more with the TR.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Fuel pressure before the regulator
[Re: AndyF]
#2822187
09/18/20 10:19 AM
09/18/20 10:19 AM
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Joined: Jan 2003
Posts: 19,384 Las Vegas
Al_Alguire
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Turn the PUMP up all the way as high as it will go. Then use a regulator as close to the carbs as you can get it and set it to your desired number. As I say you don't need as much pressure with a 2x4 as you do with a single. But use whatever you prefer. Then test and see what you get. If nothing changes then proceed to check the pumps flow rate etc But start by turning the pump back up to max.
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: Fuel pressure before the regulator
[Re: mopar dave]
#2822558
09/19/20 11:27 AM
09/19/20 11:27 AM
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Joined: Jan 2003
Posts: 14,514 So. Burlington, Vt.
fast68plymouth
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I have a fuel pressure gauge between pump and regulator( at carb) How do you have the gauge between the pump and regulator “at the carb”? The gauge to check the pump pressure should be mounted “before” the regulator. Pressure should be set with a small amount of fuel flowing through the regulator(a small ball valve works good here). If you’re running a bypass regulator, you may need to block the return to set the pump pressure. Personally, I wouldn’t be running a bypass regulator with a pump that can only generate 12psi.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: Fuel pressure before the regulator
[Re: fast68plymouth]
#2822636
09/19/20 02:58 PM
09/19/20 02:58 PM
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Joined: Jan 2003
Posts: 14,514 So. Burlington, Vt.
fast68plymouth
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The gauge in this pic should be reading “regulated” pressure...... not pump pressure. That’s why it changes when you change the setting on the regulator.
To read the pump pressure, you need to tap into the line before it gets into the regulator.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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