5.0 Mustang & Super FordsCar Reviews
Shelby Cobra GT 500 Prototype Drive - Sneak Bite
Join Us Behind The Wheel Of The '07 Shelby Cobra GT 500 Prototype A Year Before It's Released
Horse Sense: When we asked if there might be other Shelbys, we were told we might see efforts along the same lines-probably other variations of the Mustang-but probably nothing like the recent show cars or other ultra-high-performance cars. So don't look for anything like a Cobra roadster from Ford; it sounds as if that'll remain a Shelby American exclusive.
We know you're anxious-but before we verbally spin the '07 Shelby Cobra GT 500's tires around a road-racing course, there are hardware and marketing details to steer straight. Foremost is this car could just as easily-and a lot less confusingly-be named the '07 Mustang Cobra because that's what it is, the next Mustang Cobra.
The Shelby prefix and GT 500 suffix are a happy confluence of heritage styling combined with Ford Motor Company and Carroll Shelby playing nice with each other again. Shelby was brought in to review the Special Vehicle Team's work and lend some input to the car's styling and dynamics, but otherwise the machine is the creation of SVT.
Which begs the question, what about SVT? Gone mainstream, we're told. SVT has gained marketing muscle and an engineering staff-an amazing 75 engineers were said to be working at SVT when we drove the GT 500, and the thinking was that up to 125 might be assigned there depending on the workload. If anything, SVT is tougher to erase from the Blue Oval flowchart than ever before, so that bodes well for the group's survival.
On the other hand, SVT has become a larger target on the corporate radar screen, so budgets are more closely watched and product development could suffer from focus groups and corporate hand wringing. Countering that threat is a tremendous depth of enthusiast talent throughout all levels of SVT, which certainly shows in the upcoming GT 500.
There's no danger of small thinking in the GT 500. The car delivers superb power in a near-perfect street chassis, but let's talk engine first, as it is the GT 500's defining characteristic.
Wanting Ford GT-like thrust in the GT 500, SVT replicated the GT's 5.4L supercharged Four-Valve engine using the iron 5.4 Triton truck block instead of the GT's exotic dry-sumped aluminum casting. Ford really didn't want a $20,000 engine in its newest Cobra, nor did any of us.
This means the GT 500 engine is wet-sumped, but because it's a slightly lower-rpm engine than the GT's-redline is marked at 6,000 rpm and the fuel cutoff is 6,250 rpm-it's said the dry-sumping would not be much of a power improvement over the GT 500's carefully designed oil-scraper design. While the Ford GT benefits from a lower center of gravity by dry sumping, the GT 500 wouldn't as the steering rack limits downward engine placement.
A reverse-rotation water pump was also fitted to the truck block in order to work with the blower drive.
Past the block, most of the engine is pure Ford GT excellence. That means the crank is a strong forging, while the connecting rods are Mahle forgings. The engineers said these were on par with the Manleys used in the '03-'04 Mustang Cobra, but more affordable. No one on hand could recall the piston source, but could say they were supercharger-friendly 8.4:1 forgings.
Best of all, the four-cam, Four-Valve cylinder heads are straight off the Ford GT, right down to the part number. That means the best cams, valves, springs, and ports. In fact, SVT said these heads surpass the vaunted '00 Mustang Cobra R castings for power production, and they are credited with the majority of the power gain over the previous supercharged Mustang Cobra engine, and not so much the displacement increase.
Originally, the GT 500 was to be boosted using a twin-screw supercharger from Lysholm, but the Swedish company couldn't come close to meeting Ford's 40-a-day production demands. Therefore, SVT reverted to the M1.22 Eaton Roots blower, which is supposed to be slightly more responsive in the midrange but lacking in top end. (We don't know about the midrange response, but we've definitely shown top-end limitations with the Eaton in '03 Cobra tests compared to twin-screws.) Water-to-air charge cooling is a given, as previously seen on the '03 Mustang Cobra and Ford GT. Manifolding is from the Ford GT or is close in function, and the exhaust is the expected 2 1/2-inch system.
SVT has yet to assign a definite power rating to this potent powerplant, referring to it as "450-plus horsepower" in preliminary literature. The engineers were fairly optimistic in conversation, as if they'd blown by 450 hp half-stepping it in the slow lane-so we'll estimate 465 hp and hope we're right.
No matter the ultimate power rating, it's high enough to warrant a double-disc clutch. Built by volume manufacturer Valeo, the clutch spans just 215 mm (8.44 inches) for low inertia, but with two discs it easily handles the big power. It isn't the Ford GT clutch, in case you're wondering; although a twin-disc as well, that one measures 240 mm and is built by AP.
As expected, Tremec got the transmission contract with its ubiquitous T56 six-speed manual. It's an improved version, boasting triple synchronizers in First and Second gears, as well as new design gears with wider teeth and reduced shift effort. First gear has been lowered from the '03 Cobra's 2.66:1 to 2.97:1, but the change in final drive gearing-which is 3.31-is supposed to even this out.
We were hoping for a super-tall Sixth-gear ratio for quiet, fuel-efficient freeway cruising, but at our drive time it turned out we were on the losing side of an internal argument over the issue. John Coletti, who oversaw the GT 500 program before his recent retirement (and $3/gallon gasoline), favored relatively low-ratio top gears to preserve responsiveness, while SVT Chief Engineer Jay O'Connell and Hau Tai-Tang, who directs SVT, favor tall cogs for increased mileage and reduced engine wear in exchange for the occasional downshift on the freeway. We prefer the latter, but so far the GT 500 prototype approximates the traditional Ford gear spread as illustrated by the '03-'04 Mustang Cobras.