Tom Wilson
February 7, 2006
Photos By: Ford Motor Company

In fact, like a good street suspension put to work on a road course, the GT 500 suspension felt a hair soft or plush, if anything. It does a wonderful job soaking up bumps and undulations, and our impression was the sharp-edge potholes in the real world would be absorbed nicely indeed, again better than in the '03 Mustang Cobra. But combined with the huge weight, the comfy suspension needs a calm hand in the 90-mph sweepers.

Steering feel-which the engineers were working on that day-was good but everyone on hand agreed it could use a little more personality. Our weak development-driving skills would not allow us to pinpoint a steering change we'd make and, truthfully, if the rack-and-pinion goes to market just the way we drove it, we'd be pleased.

Braking was a mixed bag. The basic package was powerful and modulated well with a firm, reasonably short-travel pedal. But fade was significant when trying hard, which the engineers immediately and disgustedly attributed to the experimental brake fluid. Our bet is we won't see that fluid in production, and the GT 500 will stop powerfully with its modest nosedive and complete composure every time.

Shifting was '05-Mustang rubbery, probably as good as it gets with some isolation in the shift mechanism and given the half-tranny, half-body mounting of the new Mustang shifter. Clutch action was unremarkable-a good thing as it felt perfectly normal despite its twin-disc composition.

In short, the GT 500 is a musclecar with sports car intentions. The huge power and comfortable ride give it the musclecar aura, while the unexpectedly well-balanced and rigid chassis allows remarkable finesse for something so heavy and powerful. Like everything about the new Mustang, the GT 500 is a big improvement, in this case upon the earlier Mustang Cobras. When it arrives next summer, the Shelby Cobra GT 500 will definitely be worth the wait.

Photographed at Eaton's 100,000-square-foot Athens, Georgia, supercharger plant, this is a prototype of the GT 500's M122H hybrid Roots blower.

Say "Eaton Roots blower" and fond memories of being g-forced back into the seats of Terminator Cobras will immediately spring to mind, followed shortly thereafter by similar reminiscence of force-fed Lightning and Harley pickups. Farther back in the memory banks are the blown V-6 T-birds and Cougars of the late '80s and early '90s.

Each one of these Ford factory applications of Eaton-manufactured intercooled, positive-displacement supercharging has been a hit with enthusiasts, and we can safely predict the M122H sitting proudly atop the GT 500's fearsome 5.4 will continue this torquey tradition. In our initial look at the new Cobra (July '05, p. 54) we mistakenly said the GT 500 would have a screw blower. Well, it won't; but it will have the M122H, or what Eaton refers to as a hybrid-thus explaining the "H" in its designation. It's a hybrid of the fifth-generation Roots design as used on the Terminator and a patented, all-new sixth-generation that won't debut until 2008. It's still a Roots-unlike a screw blower, all air compression will take place in the manifold and not within the blower itself.

Displacing 122 cubic inches of air per revolution, the hybrid's greater thermal and mechanical efficiency translate into more power available at the Cobra's wheels. Check out the cutaway for construction details.

So why all the excitement? Efficiency. Both mechanically and thermally, the hybrid is substantially more efficient than its Gen V predecessors-thanks to reengineered rotor and port designs-and the GT 500 is the first production application of this hybrid design. The full Gen VI Roots, when it eventually comes along, will be even more efficient as it will have an optimized center-to-center distance between rotors, also known as "pitch spacing." In the meantime, the hybrid essentially combines Gen VI rotor and port designs with existing Gen V pitch diameter, or rotor spacing. In even more basic terms, think of it as Gen VI rotors in a Gen V housing.

According to Eaton, thermal efficiency is up by about 15 percent over the Gen V, meaning substantially lower blower-discharge temps. Lower air-charge temps offer less chance of detonation, permitting more spark advance to be dialed in. More advance equates to more power. And because the hybrid is also more mechanically efficient with fewer parasitic losses than its older Gen V siblings, it consumes less horsepower to generate boost. Are you detecting a pattern here?

Eaton's engineering and product strategy manager for Air Induction and Cylinder Head Systems, Craig Sell, nicely sums up the hybrid in fewer words than it takes to describe his title: "Turbo efficiency from a Roots blower." Sounds good to us. - Dale Amy