What fuel pressure.....and why?

grego37 · Jan 17, 2007

on a street/strip car what is a good fuel pressure,
and what is too much?

iskwezm · Jan 17, 2007

4-6 psi should be enough as long as it doesnt drop at WOT.

chromedog · Jan 18, 2007

you dont want it above atmospheric pressure (about 7 psi)

67Dylan · Jan 18, 2007

iskwezm said:
4-6 psi should be enough as long as it doesnt drop at WOT.

That sounds about right to me as well.

SoCalCruising · Jan 18, 2007

We're assuming a standard carb setup. Some of the more exotic setups (e.g., Webers) require less fuel pressure, 3-4 psi.

ForceFed70 · Jan 18, 2007

chromedog said:
you dont want it above atmospheric pressure (about 7 psi)

Isn't atmospheric pressure at sea level about 14PSI? Or 1 Bar?

I've always been told 5-6PSI is ideal.

chromedog · Jan 18, 2007

ill have to look into that... i know you want less than 7 psi as a general rule, and atmospheric pressure is the reason why.

ForceFed70 · Jan 18, 2007

chromedog said:
ill have to look into that... i know you want less than 7 psi as a general rule, and atmospheric pressure is the reason why.

??

From Wikipedia:

The average atmospheric pressure, at sea level, is about 101.3 kilopascals (about 14.7 pounds per square inch).

The reason you can't run more that 7PSI is that it's too much pressure and will lift the seals and end up dumping too much fuel into the engine.

Increaseing atmospheric pressure would allow you to run a higher fuel pressure, but it's like this by design....not because of the pressure of the atmosphere. Carbs could easily be designed to run at 15psi... they just arn't.

10secgoal · Jan 18, 2007

You just don't want the fuel pressure to over power needle and seats. If you set the fuel pressure, and the carb is not leaking internally(you can see it if it does), it's not too high.

grego37 · Jan 18, 2007

the main reason I ask, is that Aeromotive makes an electric fuel pump that is fixed at 7lbs and no regulator is required.

Sounds like they didnt do their homework, the should offer it fixed at 6lbs

I ordered their other pump that is not fixed at 7lbs, and one of their regulators.

iskwezm · Jan 18, 2007

grego37 said:
the main reason I ask, is that Aeromotive makes an electric fuel pump that is fixed at 7lbs and no regulator is required.

Sounds like they didnt do their homework, the should offer it fixed at 6lbs

I ordered their other pump that is not fixed at 7lbs, and one of their regulators.

most pumps on the market are preset at 7 psi.

jcode68 · Jan 18, 2007

Good topic, don't mean to hi-jack but... I'm running a Holley mechanical pump #HLY-12-289-11 rated at 6.5 to 8 lbs. The fuel pressure guage which is connected to the fuel line at the carb is reading between 9-10 lbs. I don't notice any leaks, but when I step on it, I get a lot of smoke out the tailpipes and smells rich. Would the higher pressure cause it to run very rich on heavy acceleration?

ForceFed70 · Jan 18, 2007

jcode68 said:
Good topic, don't mean to hi-jack but... I'm running a Holley mechanical pump #HLY-12-289-11 rated at 6.5 to 8 lbs. The fuel pressure guage which is connected to the fuel line at the carb is reading between 9-10 lbs. I don't notice any leaks, but when I step on it, I get a lot of smoke out the tailpipes and smells rich. Would the higher pressure cause it to run very rich on heavy acceleration?

I guess it's possible, but not very likely. Under hard acceleration, you will be placing alot more demand on the fuel system and I would expect to see a drop in fuel pressure.

Where I suspect it would be most noticeable would be at idle.

grego37 · Jan 20, 2007

jcode68 said:
Good topic, don't mean to hi-jack but... I'm running a Holley mechanical pump #HLY-12-289-11 rated at 6.5 to 8 lbs. The fuel pressure guage which is connected to the fuel line at the carb is reading between 9-10 lbs. I don't notice any leaks, but when I step on it, I get a lot of smoke out the tailpipes and smells rich. Would the higher pressure cause it to run very rich on heavy acceleration?

you may want to get a regulator and tame that pressure down all the way to 6.5lbs

bnickel · Jan 21, 2007

i used to run one of those purolator deadhead style regulators and regularly set it around 3-4 psi, got decent mileage that way and for the basically stock engine it was on it was plenty of pressure, but then again the 600 carter i ran was only supposed to run about 5-6psi. i think some of the holley HP carbs and some demons are set for around 8-9psi.

D.Hearne · Jan 21, 2007

You've all got it wrong. In a carb setup, the fuel pressure cannot be greater than that needed to overcome the pressure exerted by the float in the fuel bowl this is needed to keep the needle/seat valve closed. The actual pressure needed depends on the carb. A bigger float would allow a higher line pressure to be run as it would exert more pressure on the needle valve. This is the reason you should always run a regulator with an electric fuel pump.

grego37 · Jan 21, 2007

thehueypilot · Jan 22, 2007

I have run 7.5 - 8psi w/o any issues. Holley say's not to exceed 8psi as it will over power the needle off it's seat.

FUEL PRESSURE REGULATORS
The needle and seat assemblies that are installed in Holley performance carburetors
can satisfactorily control fuel pressure up to about 8 PSI. If the fuel
pump is putting out more than 8 PSI, a regulator should be used to keep the
fuel pressure within safe limits and avoid the possibility of flooding.

What fuel pressure.....and why?

grego37

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iskwezm

chromedog

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67Dylan

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SoCalCruising

ForceFed70

That's why they call it "dope"

chromedog

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ForceFed70

That's why they call it "dope"

10secgoal

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grego37

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iskwezm

jcode68

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ForceFed70

That's why they call it "dope"

grego37

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bnickel

D.Hearne

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grego37

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thehueypilot

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