Thread: Fuel pressure

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What is the ideal fuel pressure for carb application

6 PSI at the carb for a street application.

Also, take a look at this link:

http://www.holley.com/HiOctn/TechSer.../FMFPTech.html

Originally posted by DennyW
It really depends on the carb and engine setup you have. From the small imports on up. Example: This is from the edelbrock site:
Fuel Pumps and Pressure
Avoid extremes in fuel pressure. At IDLE, there should not be any more than 6.0 psi; if the vehicle has an adjustable fuel-pressure regulator, set it to 5.5 psi. With most fuel pumps the minimum fuel pressure is encountered at high rpm and WOT. Fuel pressure should not drop below 2.0 psi. If it does, a fuel pump with more capacity may be required. Note that some later model vehicles (the 5.0L Ford is one example) have mechanical pumps that will give more than 6.0 psi at idle. The vehicle will perform well, but may be prone to stalls on quick turns and stops with the clutch disengaged. If this problem occurs, check the fuel pressure. If it is more than 6.0 psi at IDLE, it should be reduced through the use of a regulator, such as Edelbrock #8190, or by creating a restricted by-pass bleed to the fuel return line. Edelbrock Street Fuel Pumps are highly recommended for all Edelbrock Performer Series carburetor installations.
Myself, using a large volume mechanical pump, 3/8" lines, 780 Holley, I only need to run 3 lbs.
They say a gallon of fuel is 6 lbs. They figure by weight, and by engine size to determine pressure. But, if you think of it, your not pushing a gallon of fuel to the carb. Suction and volume is very important also. Using steel line, and little as possible on the rubber line. And you want to keep the bends to a minimum.

really need to know the kind of carb. greg. a Q- JET runs around 5 lbs. max. on the st.

The high output pump is putting out 7.5 psig Iam getting a fuel pressure reg. The carb is a edelbrock 750 --Trying to cure the richmixure that i can't seem to tune out.

Originally posted by Greg Peterburs
The high output pump is putting out 7.5 psig Iam getting a fuel pressure reg. The carb is a edelbrock 750 --Trying to cure the richmixure that i can't seem to tune out.

The reg. should help, when you buy a pump look for high volume, not high pressure, 7.5 is to much for that edelbrock. 5- 5 1/2 lbs. would be what i would use around town. Danny w only ran 3 lbs. of pressure on a big, high rpm motor. hes d-man on carbs. .

Greg, I ran my Edelbrock at 4#, they dont like as much pressure as a Holley.

i have a question about the fuel pressure in my 1976 gmc jimmy. i recently built a 383 stroker. its has about 450hp @6500 rpms. its also has a holly fuel {mech} pump 110gph. when the motor is cold the fuel pressure is about 9 psi. after it warms up and is driven a mile or so the fuel pressure drops to 2 1/2 - 3 psi. it runs good doesnt seem to be starving for fuel. is there something wrong. i thought the fuel pressure should be a constant 6 psi for a holley 750dp. any input would be helpful.

thanks,
chris

Originally posted by 76jimmy
i have a question about the fuel pressure in my 1976 gmc jimmy. i recently built a 383 stroker. its has about 450hp @6500 rpms. its also has a holly fuel {mech} pump 110gph. when the motor is cold the fuel pressure is about 9 psi. after it warms up and is driven a mile or so the fuel pressure drops to 2 1/2 - 3 psi. it runs good doesnt seem to be starving for fuel. is there something wrong. i thought the fuel pressure should be a constant 6 psi for a holley 750dp. any input would be helpful.

thanks,
chris

you don't say if you have a psi reg. or not but you need one to get the psi to around 6 psi normal driving and not below 2 1/2 at WOT. i don't know how much psi that pump carriers but it shouldn't change that much from cold to hot. the motor would run ok at 3 psi normal driving but at WOT its going to drop even more, then its not gonna run good. sounds like to me you have a bad pump . when the psi get down to 3 psi does it stay there until the motor gets cold again or until you cut it off and then start it right back up? where do you have the psi gauge mounted?

the pressure guage is located in the dual holly feed line @ the carb- 6an. i currently do not have a pressure regulator installed. after the motor warms up the fuel pressure drops and stays @ 2 1/2-3 psi @ idel. it will not rise again until the motor cools down for a few hours. also this is the second fuel pump i have tried and its doing the exact samething. i checked the fuel pump rod, restictions in the fuel line, i cant find anything wrong.

Originally posted by 76jimmy
the pressure guage is located in the dual holly feed line @ the carb- 6an. i currently do not have a pressure regulator installed. after the motor warms up the fuel pressure drops and stays @ 2 1/2-3 psi @ idel. it will not rise again until the motor cools down for a few hours. also this is the second fuel pump i have tried and its doing the exact samething. i checked the fuel pump rod, restictions in the fuel line, i cant find anything wrong.

Something is wrong, sounds like the hose might be sucking closed or the cap not vented or the sock in the tank is stopping up after it runs awhile. Try blowing the sock off of the line in the tank and check for soft spots in the rubber hoses. if you get it fixed you need to get that 9 psi down to 6 psi or it might be to much pressure. if its not to much trouble after the pressure drop take a line loose at the pump and run a line into a can of gas and then crank it up and see what happens. if it still does the same thing it will be the pump or lines going to the carb. and if it fixes it it will be the something behind the pump. be careful with that can of gas.

ps.. be sure the gauge is ok