Raffman

how much fuel pressure should there be?

I just installed a gauge.

billcarson

i run 5 psi off a regulated electric fuel pump.(to a carb of course).mechanical guys will chime in.

damoroso

I run between 6 and 7 PSI. Mechanical to a Qjet.

Mike Ward

Pressure is meaningless except on EFI. Flow is important on a carb.

I will never understand why carb guys endlessly farque around with pumps, regulators and gauges. Close the hood an drive it.

damoroso

Mike I agree with you for the most part, though fuel pressure can be an issue for a carburated system particularly if you run too high a pressure. For instance, Qjets don't typically like over about 7psi. Over that can cause all sorts of BS. Depending on the pump you run, you may need a regulator to hold down the pressure. If that's the case, then obviously you'd want a guage so you know where your at. For stock (or mostly stock) systems, I agree pressure shouldn't be an issue...

1969RAY

"Carb guys", like me, just like to farque around-its what we do.
Just let us be. And my "flow" is fine-its linoleum.

Mike Ward

That's exactly my point- guys reading too many Hot Rod magazines and falling for the glossy 'racing pumps' that give the impression that somehow a higher pressure pump will deliver more HP. As you correctly pointed out, too much pressure will just overwhelm the needle and float.

L-82kid

I run a pro-systems 750cfm (custom built holley hp) and the carb builder said to make sure fuel pressure stays around 7-7.5psi throughout whole rpm range.

last year I had a 750cfm mighty demon carb with a 80gph mech pump and it made 7.5psi of fuel pressue at idle/cruise but would drop to 3-4psi at WOT. It made 327rwhp 380rwtq on chasis dyno. I swapped to a 110gph mech pump at the dyno shop and power went up to 365rwhp 410rwtq and fuel curve looked alot better. I still get a drop from 7.5psi down to 5psi... The dyno guy and carb guy told me i would make more power with bigger pump and holding 7.5psi. I'm swapping to an aeromotive electric pump and bigger feed lines soon and will be going back to dyno. I have a reg set for 7.5psi...i plan on adding 125hp shot of nitrous to my set up so I have upgrade fuel system anyway.

RickyBerg

What carb do you run?

For my Holley the recomendation is between 5 and 7 psi.

At ALL times (from idle to WOT).

If you have a higher pressure there is a risk of the fuelpressure pushing down the needlevalves/floats and the carb is flooding.

//Ricky.

Mike Ward

And there you have an example of what I was saying- it's flow that counts, not pressure.

L-82kid

but isn't a drop in pressure at WOT an indication that the flow is not great enough to feed motor?

Mike Ward

As an indirect measurement, yes. This is why flow capacity of a pump is relevant- 'high performance high pressure ' pumps are not.

If two pumps have the same flow capacity but the 'performance ' version simply does it at higher pressure, nothing is gained.