Dale Amy
February 1, 2005

Horse Sense:
Advantages of in-tank pumps are that they’re much quieter and heat fuel less than the inline pumps often used on high-horsepower return-style fuel systems.

Since Ford began switching the Mustang to returnless fuel systems, installers and tuners have been searching for means of supplying sufficient go-juice to support high-horsepower supercharged or turbocharged modulars, without going to the trouble and expense of swapping everything out in favor of a traditional return-style system. Though the full-zoot return-style route may still be the only choice in extreme cases, the folks at Pro-M Racing have come up with a returnless setup they say will support up to about 800 hp at the wheels, with the key, oddly enough, being Focus fuel pumps.

Before we get to it, a quick review of the differences between return-style and returnless fuel systems will lay some groundwork. In a traditional return-style system, the electric fuel pump operates at fixed voltage, supplying a basically fixed flow of fuel through the supply line. Fuel pressure at the injectors is limited by a mechanical regulator. The injectors use what they need of this supply, and any unused fuel simply heads back to the tank via a return line. In contrast, current returnless systems operate in an "on-demand" fashion, with the computer calling for only the amount of fuel the engine actually requires at any given time. A sensor in the fuel rail continually monitors fuel pressure and reports it to the EEC processor, which alters voltage applied to the fuel pump(s) in order to maintain the prescribed pressure.

The problem for tuners? We can't just slap on a "helper" inline pump the way we used to with the older return-style systems, for a couple reasons. First, the typical inline pump requires a fixed voltage for proper, long-life operation and, second, fuel pressure at the rail sensor must be maintained within a limited window of variation. If pressure goes too high (or low), the EEC V assumes there's a problem and goes into a failsafe or limp-home mode.

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A partial solution came with the introduction of the blown '03 Cobra, with its pair of in-tank pumps. Swapping to a stock Terminator tank/pump assembly is a great answer for a power-adder returnless GT (or naturally aspirated Cobra) at moderate power levels. But for cars with higher boost or heavier modifications, Pro-M Racing has taken that idea one step farther by substituting SVT Focus fuel pumps in place of the OEM Cobra pumps in the Cobra tank. The reasoning is simple. The OEM Cobra pumps, we're told, can flow 190 lph each, whereas the SVT Focus pumps are each good for 255 lph. That's a lot of fuel. As part of the upgrade, GT and pre-'03 Cobra owners will also have to install a Terminator-style fuel pump electronic driver module, because the combined draw of the twin 30-amp Focus pumps would overwhelm their single-pump factory driver.

Pro-M Racing can sell you whatever bits you need. If you have an '03 or '04 Cobra, all you'll need are the Focus pumps, while those with a factory naturally aspirated returnless 'Stang will need the pumps, the Terminator fuel tank, and the higher-capacity driver module. Our photos detail the steps necessary to retrofit the SVT Focus pumps into the Terminator tank. This one's headed for our fuel-starved 3g GT.

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