Richard Holdener
May 1, 2007

Much has been written about the Shelby GT500, and for good reason. The new super Stang is quite possibly the quickest and fastest production Mustang ever offered by Ford. We understand that the word production leaves a little room for interpretation, but in this context, it means a Mustang readily available from your local dealership.

While some of the specialty Stangs (Saleen, Roush, and Steeda) are also available via the dealership, this Shelby puts them all to rest thanks to an honest-to-goodness 500hp super-charged 5.4L Four-Valve cammer motor. The retro fastback styling of the '05 Mustang had us smiling, but we were less than amused about the loss of the supercharged Four-Valve Cobra motor at the close of 2004.

Let's face it-the supercharged 4.6L Cobra motor was the most impressive performance piece to be offered under the hood of a Mustang since the demise of the Boss 429. What made the '03-'04 Cobras so special was not so much the impressive (and obviously underrated) power output of the supercharged 4.6L, but the way the Four-Valve motor took to modifications. Adding a solid 100 hp to the '03-'04 Cobra motor was as easy as swapping pulleys and adding the proper tune. If our luck held, the supercharged 5.4L mod motor in the GT500 used for testing would follow suit.

This is a supercharged 5.4L, so adding serious power to the new GT500 modular motor requires only a few minor bolt-ons.

Given the impressive power output of the 5.4L in stock trim, many enthusiasts may be satisfied to simply leave well enough alone. For those looking to purchase a GT500 and park it in their hermetically sealed storage cocoon next to that never-enjoyed '00 Cobra R, you may want to skip the next few pages. This story-in fact, this entire series-is for true performance enthusiasts looking to take one badass "Shelby-ized" factory Mustang and make it even meaner.

Despite the ability to pump out an honest 500 hp, we think the 5.4L motor feels a bit underpowered. Ah, who are we kidding? Every motor (regardless of the power output) can use more power. After all, we have to make up for the extra heft that everyone is complaining about. For those old enough to remember them or interested enough to do the research, the original GT500s were a tad on the portly side as well. Though they lacked the response and ultimate handling (and overall track performance) of the original '65 (and '66) GT350, the 7.0-liter GT500 offered equal or better straight-line acceleration, to say nothing of the mystique of the big-block. Just check out the price difference between a fully restored GT350 and GT500 and you will begin to appreciate the appeal of having the big motor.

In our opinion, every motor should sport some sort of factory forced induction. The Shelby GT500 came equipped with an Eaton Roots-style blower, pumping out 8.5 psi to the 5.4L Four-Valve motor through an air-to-water intercooler. We upped power with these pulleys from Metco.

Speaking of big motors, the GT500 is blessed with a serious chunk of performance metal. By combining the displacement of the 5.4L Lightning with the four-valve heads of the Cobra, Ford has produced an affordable but still powerful version of the all-aluminum Ford GT motor. True, the GT500 makes do with an iron block (the GT is lightweight aluminum), wet-sump oiling (dry-sump for the GT), and a smaller and less efficient Roots-style blower (twin-screw for the GT). On the plus side, the GT500 short-block is topped off with a set of free-flowing four-valve heads pirated from the GT motor program. The combination of the longer stroke, the GT heads, and the Eaton supercharger allow the GT500 motor to thump out an honest 500 hp.

Unlike the big-block Shelbys of yesteryear, that 500hp rating is a real number-not some jacked-up reading achieved on the engine dyno with the motor ice cold, devoid of the accessories, and tuned to precision. By comparison, the 500hp rating applied to the GT500 motor comes at operating temperature with full induction and exhaust systems while running the factory ECU tune. If this GT500 motor is anything like the previous supercharged Cobra motors, look for the 500hp rating to be a tad conservative. Even if the rating is accurate, 500 hp is some serious power from a stock Mustang.

Our first modification was the removal of the factory air filter. At the stock power level, this resulted in a dramatic change to the air/fuel curve. Power will definitely be gained from the induction system after cranking up the boost.

While definitely excited about getting our hands on a stock Shelby for dyno testing, we were every bit as anxious to perform a few modifications. Given the recent introduction and the fact that few of the cars were actually in the hands of customers, the list of available performance parts for the GT500 was rather short. As a teaser, know that we have a complete Kenne Bell twin-screw supercharger upgrade kit slated for this GT500. For now, we will start the "Mods for GT500 Mods" series with more boost from the factory blower.

Not content to just crank it up and be done with it, we also took a look at the air-filter assembly, the exhaust system, and even some programming. Since we did not have access to an aftermarket exhaust or intake system for the GT500, we simply pulled off the stock after-cat to determine if the system represented any restriction to exhaust flow. On the induction side, we removed the factory air filter to see if there was any power to be had on the inlet side. Of course, this doesn't rule out power gains from after-cat exhaust or cold-air (or MAF) systems. We just wanted to get as much testing accomplished before replacing the Eaton supercharger. Look for more testing on the bolt-on components as soon as they become available.