What should the fuel pressure be between the pump and the regulator if running twin carbs at 6psi.

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

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.

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.

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.

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.

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!

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

Well, I will have to retest. This same system worked great at 5.5 psi with my single 1100 Dominator. Not sure what system uses more fuel , the Dominator or the twin 750’s with 1.325 Venturi.

If it makes about the same hp between the two induction systems, then they use about the same amount of fuel

Of course........“In theory”....... it should make more with the TR.

Won’t know til it goes down the track.

When you make more power with more air you need more fuel also, correct
I've dyno tested one tunnel ram on my old 526 C.I. mule motor, it gained 35 HP on a DTS engine dyno going from a single 1050 CFM Dominator to two of them including using the one off of the single four barrel intake, it was a Indy tunnel ram with a dominator top, the single carb intake was a Indy 440early -3 dominator intake

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 will. Only reason I turned it down was because my regulator wouldn’t control it. Didn’t know pump was at 6psi and I ran it all those years that way.

I have a fuel pressure gauge between pump and regulator( at carb) and a gauge on the regulator at carb. When i turn the adjusting screw in on the pump, neither pressure gauge shows increased pressure, but when i adjust pressure at regulator both pressure gauges show the change in pressure. I dont get it. I thought the regulator at carb only controlled pressure between regulator and carb? Anyone here know how many turns on the pressure screw on the pump when these pumps left the factory pre set to 12psi? I currently have it at 1 full turn out, but not seeing any increase in pressures.

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.

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.

Ok, now i understand. Dah, yes it has a return. I turned the adjuster on pump til it bottomed, then out 1 turn. Drove it today a bunch, i didn't see any issues yet.