What do you do with a spankin'-new...
What do you do with a spankin'-new Shelby GT 500 with only 50 miles on it? Well, strap it to the chassis dyno and find more power, of course. That's just what Jeff Reasons had in mind when he left his car in the capable hands of Rick Anderson at Anderson Ford Motorsport. Rick cooked up a combination that delivered 129 more horsepower to make sure Jeff's GT 500 made more power than his supercharged Fox convertible.
Horse Sense: Don't think you're out of the bolt-on game if you don't have a GT 500. Most companies that make parts for the GT 500 already have a robust lineup for 4.6 and 5.0 Mustangs as well.
Easily the most hyped, most lusted-after Mustang in recent memory, the '07 Shelby GT 500 is the most powerful factory Mustang yet. For most people, 500 hp at the flywheel and all that exclusivity of Shelby and SVT would be plenty. But those would probably be the same folks who lock the car in the garage, hoping for dollar signs in 20 years. Those people probably don't read this magazine. The horsepower-crazed members of the 5.0&SF army know this car was born for bolt-ons, much like its Terminator predecessor.
Sure, we can't all have a new one, but someday we can all hope to eventually own a Shelby GT 500. For those who joined the game early, the bolt-on world is their oyster. Just a few parts are all that's needed to see huge gains in performance. We've covered many of the pulley and cold-air combinations for these cars, and they work well, but we wanted to get deeper into the car and check out some more serious gear, particularly PMAS' new Velocity mass air meter and Bassani's long-tube headers and full 3-inch exhaust. Fortunately, Anderson Ford Motorsport was more than willing to experiment on our behalf.
Of course, to do so, we needed a willing participant to let us tear into a new GT 500. Great minds think alike, as new '07 Shelby GT 500 owner, Jeff Reasons, couldn't wait to tear into his car. Jeff also owns a Fox convertible with an AFM Stage II S-Trim supercharger kit. It lays down more than 518 hp at the wheels. All Jeff wanted was his GT 500 to make more power than his Fox. In a demonstration of how far base horsepower and easy bolt-ons have come, it took only the aforementioned mass air and exhaust, as well as a pulley and tune, to move Jeff's GT 500 to the king of the hill in his garage.
Here's Jeff's GT 500 after the full treatment. Visible are the AFM Power Pipe, PMAS Velocity mass air meter, Metco 2.6-inch blower pulley, and Metco idler pulley. Due to the wide engine, you can't see the Bassani long-tubes from this angle, and the Predator tune is hiding in the Silver Oak processor. All told, this simple combination of parts provided huge gains across the entire rpm range.
Here's the complete Bassani Xhaust system for the GT 500. This system is serious business, replacing the solid factory system with massive 1 3/4-inch to 1 7/8-inch stepped, long-tube headers (PN BA-S5407R; $1,460); a 3-inch X-shape-crossover with high-flow cats (PN BA-5407R-3; $399); and 3-inch Aft-Cat with mufflers (PN BA-5407R-5; $799). This system is a thing of beauty and should give plenty of exhaust to support even more power in the future.
Always wanting to learn what the limits are and how to work around them for more power, Rick had long suspected the stock airbox on the GT 500 would limit power.
One sure way to find out is strapping it to a flow bench. AFM has one in the form of a Super Flow SF-1200, which Rick uses to develop his Power Pipes, among other things. With the stock air filter in place, the stock box flows 826 cfm at 25 inches of water. Removing the filter bumped the flow slightly to 898 cfm, but we know the factory mass air meters don't like the wild air blasting through. The filter straightens and smoothes the airflow.
Obviously 826 or so cfm isn't enough air to make the kind of power even a bolt-on GT 500 is capable of producing. Moreover, Rick learned that the stock mass air calibration is set up to max out its voltage before the injectors max out their flow, causing the air/fuel ratio to richen considerably. While this keeps things nice and safe, it severely limits power production. Rather than simply tuning around this, Rick opted to use PMAS' new Velocity mass air meter in conjunction with a new AFM Power Pipe and a custom Predator tune (PK-GT500PVP; $785), which is calibrated not to prematurely max out the voltage. PMAS says the design of the meter reduces signal noise and improves airflow over the factory meter design, and it will support up to 1,500 hp. At the same 25 inches of water, the Velocity meter flowed 1,422 cfm on the AFM flow bench, nearly doubling the flow of the stock meter/airbox combination.