Mark Gearhart
December 7, 2018

It’s easy to get beyond the limits of a stock fuel pump on a Coyote-powered Mustang. When it came to installing a fuel system on my personal 2013 Boss 302, we wanted the simplest fuel system that could support around 850 rear-wheel horsepower on E85. The solution? A GT350 fuel pump converted to a return style fuel system.

The GT350 made enough horsepower from the factory that Ford engineers didn’t feel comfortable carrying over the GT’s single pump system. Instead the GT350 came with a twin-pump setup that’s capable of a little less horsepower than a GT500 pump, but for nearly half the cost. Even better? The GT350 pump fits into an S197 fuel tank.

As with all late-model Mustangs, the GT350 utilizes a returnless fuel system and the pumps are pulse modulated to maintain operating pressure. Single pump vehicles don’t have the capability to handle pulsing a twin pump setup, so a new wiring harness for the pumps are required. While it’s not difficult to build a twin relay harness, there’s several plug and play harnesses available on the market. If your mind is set on picking up a pre-made harness, find out if it’s designed for a GT500 pump as the pump’s polarity will need to be reversed in the harness. This is a simple pin swap.

S197 cars use a 5/16-inch fuel line and should be updated to a full 3/8-inch to coincide with the diameter of the factory fuel line. This simple conversion can be handled with a -AN-6 push lock hose end (Russell, PN 634083), 8-inches of hose, clamp, and a 3/8 to AN-6 fuel line adaptor (Russell, PN 640853).

Summit Racing’s Premium Braided Nylon Hose is used to add the return line to our fuel system. This affordable hose is E85 compatible and can handle pressures up to 500 psi. A AN-6 fuel cell bulkhead fitting (Russell, PN 670850) will be installed into the pump module hat to easily return the unused fuel.

Regulating our fuel pressure is Aeromotive’s EFI Bypass Regulator kit. It includes three AN-6 fittings as well as a pressure gauge. This new regulator is smaller and lighter to better fit in tight spaces. Capable of supporting applications up to 1,000hp, this regulator was the perfect part for the job while supplying a 1:1 rise rate via a vacuum source from our supercharger.

There’s a variety of ways to adapt your factory fuel feed line to accept a return. Some kits on the market use an inline gauge port adaptor, which is only 1/8 NPT and adapt up to a AN-6 fitting. We do not recommend this because the proper return size should be at least 3/8 NPT, or AN-6. In our case, the Edelbrock E-force supercharger on our Boss 302 came with fuel rails. A simple AN-6 tee and a AN-6 fuel line adaptor ensured a proper return line feed.

But does it work? Absolutely. Our Boss 302 was able to make 834.8 horsepower and 711.7 lb-ft of torque to the rear wheels with zero pressure drop on E85! We feel that 850-875hp would be a safe ceiling for this fuel system.

Parts List
$341.26 - FR3Z-9H307-E – GT350 Fuel Pump Assembly
$205.97 - 13130 – Aeromotive Bypass Regulator Kit
$106.99 - SUM-240615BP - Summit Racing Premium Braided Nylon Hose
$75-$159.99 – Twin pump wiring system (premade or make your own)
$18.99 – 670850 – Russell Fuel Cell Bulkhead
$13.99 – 610165 – Russell AN-6 90 hose end
(2) $7.99 – 610025 – Russell AN-6 straight hose end
$19.99 – 610095 – Russell AN-6 45 hose end
$10.99 - 640940 – Russell AN-6 Fuel rail adaptor
$6.99 - 660273 – Russell AN-6 ORB plug
$26.99 - 614405 – Russell AN-6 tee (two male, one female)
$12.99 - 640853 – Russell 3/8 to AN-6 fuel line adaptor
Total: $941.12

A very simple setup with the reliability and quietness of a stock fuel pump.
Tape the area below the hat up well so plastic shavings don’t fall into the pump as you drill for the return line bulkhead. Drilling our pilot hole through the bulkhead kept us from damaging the wiring below the fitting.
Make sure to use red thread locker on the bottom nut so it doesn’t back out. We also added a little bit of fuel resistant RTV between the plastic and bulkhead o-rings.
We installed a 2015-2017 pump and adapted the fuel line to 3/8-inch already, but it couldn’t hang with our newfound power.
It’s easiest to install the fuel line from the bottom; be sure to tape up the top of the line so dirt doesn’t get inside.
The correct tool (OEM Tools, PN 24398) to remove and install the fuel pump locking ring only costs $38 and is worth every penny.
With two wrenches the 90-degree AN-6 fitting can be assembled onto the fuel line right in the trunk.
Remove the covers for the factory fuel and brake lines in order to install the return line; a few zip ties come in handy here.
An adjustable AN wrench and a set of soft jaws makes quick work of assembling our hose ends.
There’s a variety of ways to adapt your factory fuel feed line to accept a return. Some kits on the market use an inline gauge port adaptor, which is only 1/8 NPT and adapt up to a AN-6 fitting. We do not recommend this because the proper return size should be at least 3/8 NPT, or AN-6. In our case, the Edelbrock E-force supercharger on our Boss 302 came with fuel rails. A simple AN-6 tee and a AN-6 fuel line adaptor ensured a proper return line feed.
Our Aeromotive regulator fits perfectly right behind the cold air intake box and away from the header’s heat
The Edelbrock E-Force supercharger has a 1/8 NPT vacuum reference port on the backside of the blower. We added a tee fitting as we plan to add a boost pressure sensor later. This reference will allow our regulator to add 1 psi of fuel pressure per 1 psi of boost. Static fuel pressure will need to be set with the vacuum reference line disconnected.
If using a GT500 style fuel pump wiring kit, the two guide tabs on the top of the fuel pump’s connector will need to be sanded flat. Also remember to flip the orientation on all four outside pins if using a GT500 wiring harness.
At this point, everything is complete and ready for wiring. The stock harness should be taped off and can be removed from the rubber hat to make way for the new harness.
Two fresh power wires need to be placed directly from the battery over to the new relays; tapping into the fuel pump module will trigger the pumps with key on.
But does it work? Absolutely. Our Boss 302 was able to make 834.8 horsepower and 711.7 lb-ft of torque to the rear wheels with zero pressure drop on E85! We feel that 850-875hp would be a safe ceiling for this fuel system.