The top-shelf Mustang, the Shelby GT500, has been substantially updated yet again. This is no stripe-and-trim job. There's a new engine block, steering system, and newly recalibrated handling. What's surprising is that the GT500 was already heavily massaged for last year (here's our review of the 2010 Mustang Shelby GT500). That's the one we named the Performance Car of the Year. Apparently Ford wants to keep the flies off its pony. Let's take a look.
Ford's entire stable is changing quickly. The standard Mustang, base and GT, will have new engines this year. The V8 GT will soon have over 400 hp, narrowing the gap between it and the GT500. That more than anything is probably why the GT500 needed some extra giddyup. While we won't drive the new car until this spring, here's mechanical walk-around.
The Specs
At first glance, the news in the engine bay isn't all that promising. It's still a 5.4-liter supercharged and intercooled V8 backed by a six-speed manual transmission. Peak power climbs just 10 hp from 540 to 550 thanks mostly to a increase in exhaust-pipe diameter from 2.5 inches to 2.75 (The larger pipes reduce back pressure). Torque remains at 510 lb-ft, but it occurs 250 rpm lower, at 4250. A larger intercooler has also been added, for more consistent performance.
The argument could be made that the GT500 didn't need more power. What it really needed was less weight, especially over the nose. And thanks to an aluminum block, the engineers trimmed 102 off the front, which should be a welcome change. More on that in a bit.
Like all Mustangs, the GT500 now has electric power steering, and SVT used this opportunity to retune the effort curve. The stock suspension has not been changed, but there's a new optional Performance Pack that should tighten this car down even more. With this optional model, the front spring rates are 20 percent stiffer, the rears go up eight percent and there's also a stiffer rear antiroll bar. Ride-height and rake changes (it's slightly lower in the front) attempt to increase corner-exit traction.
Perhaps most critical are what's in the fenders: New forged 20-inch wheels are lighter than the 19s and wear wider, Mustang-specific Goodyear performance tires. SVT engineers claim that the Performance Pack car is nearly 3 seconds a lap quicker around Gratten Raceway, a Michigan track that the local car companies use for testing. For those not accustomed to racing times, 3 seconds is an eternity. Acceleration figures should be better, but by only a tenth of a second or so. We expect it to hit 60 mph in the low 4-second range and cross the quarter-mile in less than 12.5 seconds.
Cosmetically, the changes are minor. Performance Pack cars will wear those massive wheels, and their stripes will be slightly thinner. Only fanatics will recognize the difference.
In other news, a glass roof becomes available on the GT500 for the first time. The convertible model returns, but it's been stiffened structurally by 30 percent and now sports standard 19-inch wheels.
The Engine Block
Aluminum engine blocks are hardly new. Aluminum is advantageous because it's lighter than iron, and is a better conductor, so the blocks are generally better at managing heat. But aluminum can't withstand the stress of a piston whizzing up and down the cylinder. It's too soft. The most common solution is to install iron liners in the cylinders. This fixes the durability problem but it adds weight and an insulation barrier between the piston and water jackets.
There are some aluminum coatings out there, like Nikasil, that can be substituted for iron liners. But Nikasil can be affected by the high sulphur content of many low-grade fuels. So most of the auto industry has switched back to using liners in aluminum blocks.
Ford, however, has a new, patented coating process that debuts on the 2011 GT500. It's called Plasma Transferred Wire Arc Spray Bore, which we'll shorten to PTWA. This process uses a consumable steel wire like a MIG welder and coats the aluminum cylinder with iron oxide.
Now hold on a second. Isn't iron oxide rust? Yes, but there are different iron oxides separated by crystalline structure. Get the right kind of FeO and you have a very hard, durable finish, according to Ford's manager of materials and manufacturing research Matt Zaluzec.
The coating operation starts with a machine that cuts small, spiral grooves in the cylinder. Next the tip goes down the bore. High-voltage electricity arcs from the steel wire to a ground and a blast of compressed air sprays the plasma on the cylinder walls where the material—when combined with atmospheric oxygen—turns to the right kind of iron oxide.
PTWA is not new—the aerospace industry uses it to toughen aluminum components like turbine blades—but Zaluzec said, "We applied the Henry Ford method," meaning that the company was able to make the technology affordable. Typically PTWA had been done in a vacuum with an expensive consumable wire.
Expect to see more of this coating in future cars. The iron-oxide layer is just 150 microns thick, a fraction of the iron liner's typical 2 to 3 millimeters. That saves about a pound per cylinder. What's more, Zaluzec reports that the coating offers a double-digit friction reduction, which is one reason the new GT500 has more power and better fuel economy (15 highway, 23 city).
The Bottom Line
We'll have to reserve final judgment for when we actually get our eager hands on the steering wheel. But on first inspection, the GT500 should be an even stronger performer than its predecessor. Plus, the increased fuel economy means it now won't be penalized with a gas-guzzler tax.
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