Question: Correct fuel pressure for 75 vette with 670cfm Holley.

[Derrick]

I just installed an anodized aluminum fuel line from Jegs and it came with a fuel pressure gauge installed on it. The fuel pressure fluctuates rapidly from 1-3psi. Does anyone know the correct pressure it should be at or why it would fluctuate like that?

Thanks

 

[Hib Halverson]

The reason the pressure fluctuates is the gauge is not damped and it is reading actual pressure. With an engine driven fuel pump, the pump strokes once per every two revolutions, so at idle, pressure is going to flucuate rapidly. The faster engine revs, the smoother the pressure will be.

What is the pressure at 3000 rpm?

 

[Derrick]

thanks for the quick reply. I'm not sure how it works at 3000 rpm...but I'll check it out tomorrow.

Shouldn't the pressure be closer to 6k or 7k rpms?

 

[Vettehead Mikey]

The reliability/accuracy of the gauge you mention is horrendous- do a search here and on other sites and you'll see a string of complaints.

Since the ongoing measurement of fuel pressure is (almost) an irrelevant parameter on a carbureted engine, why not just ditch the gauge?

 

[Hib Halverson]

thanks for the quick reply. I'm not sure how it works at 3000 rpm...but I'll check it out tomorrow.

Shouldn't the pressure be closer to 6k or 7k rpms?

1) Based on the other comment about the gauge, I'd first make sure what you've got reads accurately.
2) Contact Holley's tech support and ask them the recommended fuel pressure for that carb.

 

[Derrick]

@ 3k rpms the gauge reads exactly 3 psi with no fluctuation. It'll fluctuate from 6k-7k (at idle) when the engine in cold and then 3k-4k (at idle) once the engine has warmed.

 

[JohnZ]

If you're not experiencing fuel starvation symptoms, just ignore it.