Full Flow

Our 2008 Shelby GT500 gained more fuel flow with VMP Tuning’s plug ’n play fuel pump voltage boosters

By Steve Turner

Modding your Mustang is like tipping over a domino in one of those intricate displays. Once you push the first one over, the rest of them all start to fall into place. Once you make that first mod the only guarantee is it won’t be the last modification. Case in point is our 2008 Shelby GT500—Project Vapor Trail.

Regular readers will know that we recently upgraded its supercharger with the new hotness from VMP Tuning. It stepped up from a VMP Gen1-spec TVS supercharger to one of the company’s Gen2 superchargers, which features a vastly improved inlet and many detail improvements that maximize the efficiency of the 2.3-liter Eaton rotors.

However, adding more boost and efficiency also meant asking more of the car’s fuel system. We had long gotten by with the stock dual fuel pumps augmented by a set of Ford Racing 80 lb/hr fuel injectors. This combo served PVT well, supporting high-600-rwhp on pump gas and over 700 rwhp on 100-octane unleaded. Adding the Gen2 pushed PVT beyond 700 rwhp on pump gas, which stretched this fuel system arrangement to the end of its rope.

“With the newfound power and boost of the Gen2 the stock twin pumps were now maxing out. Fuel pumps often max out when an alternator gets weak or fails altogether,” Justin Starkey of VMP Tuning explained. “In this case though, the alternator was putting out over 14 volts. The engine was simply consuming too much fuel with the new mods.”

Fortunately VMP offers a simple solution to increase the fuel system’s capacity and provide a safeguard against any drop in alternator output. That solution is the company’s Dual Plug ’N Play Fuel Pump Voltage Booster for 2007-2010 Shelby GT500s (PN VMPAMPPNP2-0710: $549). These boxes plug into the factory Fuel Pump Driver Modules and increase the voltage fed to the pumps, which increases the output of the pumps.

“We installed two VMP fuel pump boosters, this resulted in a 20-percent drop in fuel pump duty cycle and plenty of head room,” Justin said. “The VMP boosters supply a steady 17.5 volts to the FPDM versus the 14.5 volts the alternator supplies.”

To make the boosters fit our combo, Justin only needed to tweak our existing calibration to account for the increased fuel pump voltage.

“Using the FPDM, the computer supplies a pulse-width-modulated voltage signal to the pumps to maintain the desired pressure, the pumps are only using as much voltage as they need to maintain 40 psi of pressure, but they now have up to 17.5 volts available to them if needed,” Justin added. “Minor tuning adjustments to the feed-forward fuel pump voltage table are recommended to take into account the newfound capacity.”

The VMP boosters also provide a safety net in the event something goes awry. For example, if you were at wide-open throttle and the alternator failed, your engine would go lean. Big boost and lean is a bad combo.

If you missed see PVT run in our last story, you can see it rock the rollers right here…

“It’s worth noting that if the alternator fails, the battery only puts out 11.5 volts to the FPDM and the pumps.” Justin added. “In high-boost/high-power situations this results in an instant lean condition. The VMP boosters protect against this though since they are a voltage amplifier and regulator.”

As you can see from PVT’s datalogs, it now safely makes huge power on pump gas thanks to the VMP fuel pump boosters.

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