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Fuel Pumps

New 02/27/2005

As long as our 96-99 SHOs are a return-based system (vs no return fuel
line). A *little* more pressure should probably not be an issue.
Obviously enough pressure over the OEM design can be bad in any number
of ways, up to and including potential fuel leaks.

But on another front, fuel in the tank acts as coolant for the pump.
The extra flow could either help keep the fuel nice and cold
increasing power and fuel pump life, or the reverse, depending on the
routing of the fuel lines in the engine compartment and whether they
pick up heat or dump it off in a full cycle.

Fuel as coolant is one reason to avoid running your car low on gas
regularly, especially on certain Fords. The only place the pump has to
dump the heat from operation is into the gasoline.

I'll BCC a buddy of mine who is a fuel pump engineer at Walbro and see
if he has anything to add. He got me the right pump to replace the
weak on in my '89 SHO.

Jim Heaton
The bigger fuel pumps have ABSOLUTELY NOTHING to do with pressure. They are higher volume pumps. They move more fuel thru the system at a given pump speed. The stock fuel pressure regulator is the device that sets the pressure in the system, not the pump.

The thread that Josh started was about the stock FPR not being flow the volume at idle that the big pumps move, thus artificially increasing the fuel pressure at idle and causing drivability issues.

A stock engine only needs so much fuel. There is a formula that outlines Brake Specific Fuel Consumption and factors in engine displacement, HP production, aspiration (natural or un-natural), RPM and a few other things. It says, "this engine, that makes this much HP, at this rpm and is naturally aspirated will require this much of this type of fuel. Then you divide this number by the number of injectors and you reach a Brake Specific Fuel Consumption per cylinder and install those injectors.

In stock trim, our 19lb/hr injectors are just right, so a 110lph pump will supply plenty of fuel to the engine for normal HP numbers.

The problem comes when us lunatics go and squeeze an extra 150hp out of our engines and push them WAY beyond their design limits. Like Carter stuffing 10psi of boost or me shooting 150hp of nitrous into the engine, the fuel requirements change dramatically. The more power the engine makes, the more fuel it's gonna need. When you force feed the engine, there is a correction factor of about 1.5x to the BSFC formula. So 300hp N/A has different fuel requirements than 300 turbocharged HP. Once you figure out BSFC, then you can size the fuel pumps accordingly.

It suffices to say that most of us here only need a 110lph pump in the tank. That should support 300 naturally aspirated HP. Those that are shooting 50-75hp of nitrous, should invest in a 155lph pump. To be safe and allow for expansion and upgrade, a 190lph would do the trick nicely. Those of us punishing out engines on a regular basis, need the additional volume of a 255lph pump as well as other upgrades to the system.

Doug Lewis
Ford Performance Specialists Inc.

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