Fuel pump question
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Fuel pump question
Hello I am new at this forum thing , I have a 1978 ford f250 4wd 351M and I am trying to find out what the flow rate should be on the fuel pump . Thank you for the help
Last edited by Fishin Mike; Feb 12, 2022 at 07:26 PM.
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From: S/W Missouri, Polk county
This one is 80 GPH https://www.topstreetperformance.com...fuel-pump.html
Carter is 80 GPH https://www.jegs.com/i/Carter/180/M6882/10002/-1
Food for thought: Can a mechanical fuel pump put out too much pressure?
The fuel delivery system uses a mechanical fuel pump that provides the lower level of pressure that a carburetor operates on. Using the wrong fuel pump that delivers excess pressure can cause problems ranging from poor performance and lower gas mileage to flooding and carburetor damage.
"Ford 351M and 400 fuel pumps put out about 7 psi if "spot on". Holley and Motorcraft Carbs can take in excess of 7 psi due to longer float arms with large floats. Carter AFB & AVS & Edelbrock carbs have shorter float arms which is in part why they are more compact, and smaller floats and they are less tolerant of higher fuel pressures, 6 psi is the max that Edelbrock recommends for their carbs which are copies of the Carter carbs. They recommend that a max pressure used at 5.5 psi. High fuel pressure does not mean more power as many cars we considered as muscle cars used 4-6 psi."
Carter is 80 GPH https://www.jegs.com/i/Carter/180/M6882/10002/-1
Food for thought: Can a mechanical fuel pump put out too much pressure?
The fuel delivery system uses a mechanical fuel pump that provides the lower level of pressure that a carburetor operates on. Using the wrong fuel pump that delivers excess pressure can cause problems ranging from poor performance and lower gas mileage to flooding and carburetor damage.
"Ford 351M and 400 fuel pumps put out about 7 psi if "spot on". Holley and Motorcraft Carbs can take in excess of 7 psi due to longer float arms with large floats. Carter AFB & AVS & Edelbrock carbs have shorter float arms which is in part why they are more compact, and smaller floats and they are less tolerant of higher fuel pressures, 6 psi is the max that Edelbrock recommends for their carbs which are copies of the Carter carbs. They recommend that a max pressure used at 5.5 psi. High fuel pressure does not mean more power as many cars we considered as muscle cars used 4-6 psi."
Hotshot
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From: The Shenandoah Valley
Yep, using a Edelbrock carb or similar on a 351M or 400, the 7psi will overpower the inlet or float needle and if fuel isn't used fast enough, will flood the float bowl. Hollys can take it with those big floats and long arms.
Mechanical fuel pumps have a limit to pressure in the strength of the spring on the push / pull rod that moves the diaphragm through its stroke. When the pressure in the outlet side reaches a certain point, the spring on the push rod can no longer compress the diaphragm and the rod just moves but the diaphragm does not move until the exit side pressure is dropped enough to let the spring move it.
There may or may not be a seal on the push rod behind that diaphragm spring that if it leaks, fuel can find a path into the crank case ... but first the fuel has to leak through the diaphragm itself as the diaphragm is the primary seal relied upon.
Mechanical fuel pumps have a limit to pressure in the strength of the spring on the push / pull rod that moves the diaphragm through its stroke. When the pressure in the outlet side reaches a certain point, the spring on the push rod can no longer compress the diaphragm and the rod just moves but the diaphragm does not move until the exit side pressure is dropped enough to let the spring move it.
There may or may not be a seal on the push rod behind that diaphragm spring that if it leaks, fuel can find a path into the crank case ... but first the fuel has to leak through the diaphragm itself as the diaphragm is the primary seal relied upon.
Laughing Gas
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From: S.E. Louisiana;so far USA
The 1978 Ford Truck Shop Manual says for the 351M engine, the static pressure should be 6.0 - 8.0 P.S.I. and the minimum volume flow should be 1 pint in 20 seconds. The engine temperature should be normalized, at normal curb idle speed, in neutral.
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