Fox Mustang Fuel System - Sumpthing To Talk About

Horse Sense: Our test Mustang for this first-look tech report is Aeromotive owner Steve Matusek's clean '86 GT convertible. It has been in Aeromotive's stable for what seems to be an eternity, as evidenced by its early version of ProCharger's D-1 supercharger system and a vintage Cartech 5.0 bread box-style upper plenum that brings back memories of Mustang days gone by. The ragtop 'Stang is the same lab rat used to develop the first sump-tank fuel system for Fox Mustangs in 2001-a concept that may not have ever seen the light of mass production had it not been for the suggestion of Editor Steve Turner.

How many of you have ever had to think twice about engaging in street warfare with a 'Stang because it was sporting a sumped fuel tank?

There's no doubt that the sight of a deep fuel tray, an enormous pump, and AN -10 braided line at the back of a street Mustang is intimidating, and it can cause great concern about the radical beast that may be underhood of the super-fueled 'Stang you've rolled up behind.

Let's go back in time for a moment. Before sumped fuel tanks became hip, 'Stangbangers' original solution for improving fuel systems to support more horsepower was to add bigger and louder external fuel pumps. As the suction of a fuel system is arguably its most critical element, adding a big pump proved to be only somewhat effective, mainly because of the limited capacity of OEM pickup tubes, which pull fuel from the small, baffled section of stock tanks.

Upgrading to oversized pickups also had limited success, as stock tanks' baffled areas are designed to feed fuel from the bottom. They're sized for the factory pump, not high-volume aftermarket pieces.

At fuel levels below half of a tank, external pumps can suck the baffled chambers dry before they're able to replenish, which is no good for engines with power adders. Other problems associated with using fabricated pickup assemblies in stock fuel tanks include pump cavitation, vaporlock, irregular fuel pressure, exaggerated pump wear, and lean conditions during low and high loads.

Aeromotive Fuel Systems has been the front runner in complete, bolt-in, return-style fuel systems (tank, pump, regulator, lines, and fittings) for '86-'97 Mustangs. More times than a few, it's the business end of Aeromotive's A1000 or Eliminator system you're looking at when you find yourself following a sump-equipped 'Stang. The company's original EFI Mustang system was developed as a method of satisfying increased fuel needs, while eliminating the problems inherent to the suction side of the fuel system, all based on the gaining popularity of power adders for street/strip 5.0 'Stangs and the higher performance levels enthusiasts were achieving with nitrous and superchargers.

Aeromotive's early stab at a solution was to install a drag-race-style sump in the factory tank. The sump featured extra baffling to prevent starving the pump during hard takeoffs and extreme cornering and braking on the street or track. It's also outfitted with a billet port in the factory location for return fuel. The idea behind a sump also was to ensure there would always be enough fuel available to feed the system when the fuel level is low and as its temperature increases.

Low-fuel-level efficiency was the primary focus for Aeromotive's second generation of sumped Mustang fuel tanks, which until now, have been the tanks that most street and race enthusiasts go to when it's time to step up their Ponies' fuel systems. The updated tanks feature a revised design in which the walls of the sump are raised almost to the top of the tank, and the fuel returns to a separate area at the back of the sump. Returning fuel into a dedicated reservoir minimizes aeration and cools the fuel before it enters the suction side of the sump.

This photo depicts a component-by-component breakdown of Aeromotive's new upgraded sump box. The box itself is the same as the second-generation piece, with redesigned baffling to facilitate internally mounting an A1000 fuel pump. A point of interest on the filter side is the filter-housing assembly, which is designed to rotate and seal off fuel passages any time the billet filter cover is removed. This feature is notable because it enables enthusiasts to remove and service the 100-micron filter without spilling fuel or losing any pressure in the system.

Although each new sump/pump/tank assembly is sold as a finished and complete unit, Joe walked us through the process of how the unit comes together. Once the pump, filter housing, filter, AN -12 hard line, and baffle are installed and the sump is welded into the fuel tank, gaskets are inserted between the fuel-pump canister and filter housing and the sump's front panel.

This well-designed system contains all of the critical components without compromising functionality. A baffle plate normally covers the pump, but we took this shot to show you exactly how the heart of this trick setup looks. "A derivative of the age-old problem of vaporlock was the driving force behind the development of this variation of our sump system," says design engineer Joe Miller. "Whenever high-temperature gasoline and low pressures are combined, the gasoline flashes to vapor. The situation is most prominent on the suction side of the fuel pump, where the gas pressure is essentially a vacuum. On EFI Mustangs, it's vapor bubbles-not vaporlock-that take their toll on the fuel pump. By installing the pump inside the tank, we're trying to get liquid fuel as close to the inlet of the pump as possible and eliminate vapor bubbles getting into the pump, eventually breaking it down to a point of failure."

Hopefully you're sharp enough to have caught our "until now" reference about the popularity of the second-gen sump system, because Aeromotive's latest development in this area may become the new leader. In its latest version, the company places a derivative of an A1000 pump and a 100-micron, stainless steel, suction-side filter inside the sump box to further eliminate the potential for suction-side cavitation or vaporlock, and reduce audible pump noise to zero.

We caught a tip about this new setup at last year's NMRA World Finals and set a plan in motion to be the first to show it off to the 'Stang Nation. This report completes 5.0 Mustang & Super Fords' coverage of this system, as we're the magazine that gave 'Stangbangers a first look at Aeromotive's original Eliminator sumped-tank fuel system for Fox Mustangs in 2001.

Our introduction to the new system, unofficially dubbed the "In-the-Tank Pump Sump" (an official name wasn't established before our deadline for this story) by design engineer Joe Miller, took place during an early spring trip to Aeromotive's Lenexa, Kansas, headquarters, where Joe assembled an in-tank pump for us and gave us insight on the fuel setup's improved design. It's important to note that tanks are fully assembled when they're sold, requiring only simple wiring (pump and pump-speed controller, if applicable) and external plumbing when installed.

We also watched technical specialist Jared Cox perform the first-ever installation of the upgraded tank in the same Fox 'Stang that received Aeromotive's first Mustang sumped-tank fuel system in 2001. You may remember Jared as the whiz kid who installed Aeromotive's sumped tank and A1000-driven, return-style fuel system on our supercharged '02 Mustang GT ("On the Brink of Insanity," May '07, p. 166).

The system is still an easy bolt-on, and it looks clean with its billet filter plug and pump cover/AN-fitting bung. We noticed that once the engine starts, the buzz of the A1000 fuel pump is gone, which will make a big difference in the cruising experience for 'Stangs that receive this upgrade.

Before swapping tanks, Jared drains fuel out of the original sumped container. This piece has history, as it's Aeromotive's original sumped Fox tank. Our project 'Stang, an '86 convertible belonging to company owner Steve Matusek, has served as the lab rat for all of Aeromotive's sumped Mustang systems.

While we're used to doing fuel-tank swaps with the help of a transmission jack, Aeromotive's crew handles the job with brute strength. Trickery and custom work aren't necessary for installing the upgraded fuel tank. Just like the generations before it, the latest model bolts directly into the stock location without any hassle.

Until now, the front panel (behind the tank) of a Mustang's stock fuel-tank cover has been the preferred mounting location for Aeromotive's A1000 or Eliminator fuel pump. "We moved it all inside the tank to simplify things and take all the guesswork out of figuring out where to mount the pump," Joe says. This Eliminator is headed for retirement now, but the post-pump filter will be serviced and reattached to the tank cover.

The OEM fuel-tank cover requires trimming, but it fits over the sump without a problem. Steve was concerned about fingerprints on the sump and cover, but keep in mind that we're covering the first installation of this just-finished unit. While there aren't any fitment issues to speak of with our prototype, we're sure the fit and finish for production tanks will meet or exceed Aeromotive's usual high standards.