In a new episode of Behind the Tune With Matt, Matt Peckham at Middleton Motorsports dives into a car that’s very familiar to the shop: a 2012 Shelby GT500 owned by a fellow technician. The owner slowly modified the car for a couple of years, but after a recent major fuel system upgrade, it was tuned on the dyno to see what the new combination could do on E85.

The GT500 is built around a VMP Performance Gen 3 2650 supercharger with a 2.6-inch pulley. “We’re just touching over 20, 21 pounds,” Matt said, describing the boost levels. The car also features long-tube headers and a JLT Cold Air Intake.This powerful setup created a new problem. “We were running out of fuel. Fuel pressure was dropping,” Peckham explained. To solve this, the team installed twin DeutschWerks 340 fuel pumps, a larger fuel line, and 1,000cc Fuel Injector Clinic fuel injectors.

With the fuel system now able to keep up, Peckham began dialing in the E85 tune on the dyno. After about 10 pulls and experimenting with the ignition timing, he found the engine’s sweet spot. The results were impressive for a car with a completely stock 5.4-liter engine. “It’s been making 765 to 769, I think it was our highest pull,” Matt reported, with torque checking in at a solid 718 lb-ft at the wheels.

While the power numbers are strong, Matt explained why the power curve begins to flatten out at higher rpm. He noted that these 5.4-liter engines have small camshafts, which ultimately limit the engine’s airflow. He also provided important context on the platform’s strength. “These engines aren’t like the 2020-and-up GT500s that can just go 1,000 wheel, no problem,” he explained. “They have a little bit of a limit on the rods, and rod bolts.”

The dyno session was a complete success. The new fuel system solved the dangerous pressure drop, allowing the VMP supercharger to be fully utilized on an E85 tune. The final result is a reliable 768-rear-wheel horsepower, a massive figure for a fun street car with a stock bottom end. The tune provides the owner with a powerful and well-sorted Shelby that he can enjoy without pushing the factory components past their known limits.