SBC Fuel Pressure

[eric8]

Got a new SBC 383 build I just fired up and have 12 PSI indicated fuel pressure from a Delphi MF0001 mechanical pump that is factory spec'd at 5 psi. Suggestions please!

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[Crew Chief]

Install a fuel pressure regulator.

[lefty o]

you dont want 5psi either, agree with the above add a regulator.

[eric8]

Doesn’t anyone make a simple mechanical fuel pump that puts out 6 psi? Seems like since that's what all carb manufacturers call for it'd be a no brainer. No one needs a carbureted mechanical sbc pump putting out 12 psi!

[Tuner]

A Holley pressure regulator will work if you care to spend the money instead of keep trying to get a useful pump.

If the needle and seat(s) are the correct size a steady 5 PSI is plenty. As long as the fuel volume is sufficient that pressure never drops below 4 PSI at WOT that is acceptable.

With the engine off, if the fuel pump does not have a return line and the pump outlet check valve does not allow back flow and holds pressure, if it is hot enough under the hood so the fuel line is over 180 deg. F, E-10 fuel vapor pressure will rise as high as 15 PSI in the line between pump and carb.

A few years ago it seemed like you had to buy three fuel pumps to get one that didn't have 12-15 PSI. New or rebuilt (which sometimes had a new pump in the box) it was a flustercuck for several years. That seemed to settle down the last couple years, I suppose they got tired of the comebacks, but what are they going to do with all those too-strong springs, they ain't going to throw them away when they can save them to use for later. Ya think?

[eric8]

Thanks guys. I also have a Carter M6624 "Muscle Car" fuel pump sitting on the shelf at home. I'll swap it on and see what it puts out just for shits and giggs, but if that doesn't work out I guess I'll just have to go the regular route. Is there a specific deadhead style regulator that is known to work well with mechanical fuel pumps? I know Holley was mentioned.

[novadude]

A few years ago it seemed like you had to buy three fuel pumps to get one that didn't have 12-15 PSI. New or rebuilt (which sometimes had a new pump in the box) it was a flustercuck for several years. That seemed to settle down the last couple years, I suppose they got tired of the comebacks, but what are they going to do with all those too-strong springs, they ain't going to throw them away when they can save them to use for later. Ya think?

It's still a problem, My friend just went through this 2 weeks ago with an expensive Holley billet 170 GPH pump for a BBC that was advertised at 7 PSI, no regulator required. It put out 12 psi. He sent it back and went with a RobbMc pump, and pressure is right at 6.5 psi now.

[BillK]

Eric,
Before you go crazy "fixing" this, make sure that the gauge is correct. I have seen way too many of those little 1" gauges that read absolutely wrong. Take it out and hook up a known accurate large gauge and see what you have. Any gauge that reads to 30 lbs or so will work. Even an inexpensive vacuum / fuel pressure gauge is better than the one you have.
This is all you need:

https://www.napaonline.com/en/p/BK_7000114

[rebelrouser]

I agree make sure the gauge is correct. But I will say that I have had several stock type mechanical fuel pumps with excessive fuel pressure in the last couple years. So I am not sure who is building them, I assume overseas, and it is some kind of flaw, or pattern failure. Most of these were older muscle, and show cars that the guys were just doing maintenance on and just replaced the stock pumps. They give me a call and the carb is flooding over, I get the carb and overhaul it, some even had bent floats. install the carb and same problem. So I have been checking fuel pressures now with a good gauge before doing any carb overhauls.

[Lizardracing]

Also, the liquid filled gauges tend to be less accurate when the gauge heat up from engine heat.

[eric8]

Thanks guys. Swapped in the Carter M6684 pump and just the right pressure I was looking for. Assuming we all trust the gauge