What fuel pressure.....and why?
- Thread starter grego37
- Start date
-
Sponsors (?)
iskwezm
10 Year Member
67Dylan
New Member
SoCalCruising
Founding Member
We're assuming a standard carb setup. Some of the more exotic setups (e.g., Webers) require less fuel pressure, 3-4 psi.
Isn't atmospheric pressure at sea level about 14PSI? Or 1 Bar?
I've always been told 5-6PSI is ideal.
??
From Wikipedia:
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.
iskwezm
10 Year Member
jcode68
Active Member
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.
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.
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.
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.
thehueypilot
Active Member
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.
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.
Similar threads
