Cadillac ATS-V bulks up for track duty

  • 05-Jun-2015 01:35 EDT
2016-Cadillac-ATS-V-Coupe-020.jpg

The ATS-V possesses the on-track poise expected of contenders in the premium sport sedan category.

In developing the Cadillac ATS-V high-performance variant, General Motors’ engineers were faced with an unfamiliar problem; a base car that was a little too light.

Not exactly, but that was the gist of the issue. After years of developing cars in which mass reduction was a seeming afterthought, GM has with recently developed models such as the ATS, on its Alpha platform, so thoroughly optimized on mass for the base model that the car was left needing a stronger foundation when more power and traction were added for the ATS-V model.

In both its two-door coupe and four-door sedan variants, the ATS-V received a raft of needed chassis reinforcements that produce a 25% increase in torsional rigidity, reported Cadillac Chief Engineer Dave Leone. This improvement was achieved through the installation of a front shock tower-to-plenum brace along with underhood V-braces, reinforcement to the rocker bulkhead, stamped steel bolt-on braces between the rear suspension cradle mount and the floor of the unibody, and (the centerpiece of the upgrades) a large aluminum platform beneath the front suspension subframe that the company terms a “shear plate” that connects the front suspension and its cradle more securely to the car’s unibody.

The effect of that huge aluminum reinforcement plate is felt primarily on corner turn-in, where the ATS-V responds crisply rather than by twisting the car’s structure, according to Leone.

With the platform suitably braced, GM’s engineers beefed up the suspension components too. That includes replacement of bushings in the multi-link double-pivot MacPherson strut suspension with zero-compliance ball joints, stiffer front springs, and thicker front anti-roll bar that combine to produce a 50% increase in roll stiffness. The ZF Servotronic II steering rack is also stiffer than that on the regular ATS, which also contributes to improved steering feel.

At the rear, there are stiffer bushings, springs, and anti-roll bar along with stronger cradle mounts. Revised rear suspension geometry incorporates more anti-squat and has less migration of the rear roll center.

A standard electronic limited-slip differential helps put the power down on corner exits, while different-diameter halfshafts suppress axle hop under acceleration by not having the same frequency response to torque. The left side shaft, which is provided by GKN as an assembly with its constant velocity joints, is 55 mm (2.2 in) compared to 30 mm (1.2 in) for the standard-issue right shaft, for a 2.6:1 difference in rigidity between the two.

Brakes are the same Brembo six-piston one-piece front calipers with 14.5-in (368-mm) rotors at the front and four-piston rear calipers with 13.3-in (338-mm) rotors at the rear as were used on the heavier outgoing-generation CTS-V, which provided impressive stopping power without fade or increased pedal travel during track testing at the Circuit of the Americas in Austin, TX.

Damping is by the BWI Group’s Magnetic Ride Control that Cadillac brought to market. This latest iteration of the technology provides improved differentiation between its two modes, according to John Barrick, Program Engineering Manager for the ATS-V. “Now we have two true modes,” he said. “Before it was more like one and a half modes.” The increase in maximum damping is 40% greater than before.

The new system’s quicker response time means that the damper adjusts itself for every inch the ATS-V travels at 60 mph (97 km/h), while the previous system covered three inches between adjustments to settings, Barrick added.

The 18-inch forged aluminum wheels help reduce mass and mount Michelin Pilot Super Sport tires molded with three distinctly different zones of compound. The outer shoulder is hardened to withstand the cornering force of hammering around tracks without burning the rubber off the outside of the tires. The middle section is optimized for wet traction, and the inner portion is sticky race-ready rubber.

On the track, the tires contributed to an impressive 1.25 g lateral acceleration in the turns.

Just as engineers attended to every detail under the skin, so did the designers when working on the skin itself. “All of the design elements have a purpose,” said Andrew Smith, Executive Director of Cadillac Global Design. “They contribute to lift reduction, enhanced cooling, reduced mass, or all of the above.”

Most obvious is the carbon-fiber hood, with its bare carbon heat extractor vent. The hood saves weight compared to a steel hood, and the extractor not only helps hold down engine bay temperatures, but the air exiting it atop the hood reduces lift at speed.

The enlarged openings in the front fascia feed more air to the various heat exchangers behind it, and the splitter on the bottom scrapes directs air from the road surface, minimizing lift. The ATS-V’s fenders are widened to cover the wider wheels and tires, and the rocker panels and rear spoiler provide the final touches on overall balance of lift on the car. The optional carbon-fiber package provides enlarged splitter, hood air extractor, rear spoiler, rocker panels, and rear diffuser.

Those aren’t the only aerodynamic devices. Under the car, the lower control arms at the rear are sheathed in plastic covers that Barrick says reduce drag by two counts.

Naturally, as a high-performance variant, once the necessary supporting infrastructure was established, the ATS-V needed a suitably more powerful powertrain.

It is an SAE-certified 464-hp (346-kW), 444-lb·ft (601-N·m) twin-turbocharged, direct-injected 3.8-L V6 engine matched to a six-speed manual or eight-speed automatic transmission. The car accelerates to 60 mph in 3.8 s and reaches a top speed of 189 mph (304 km/h).

The engine features turbocharges with low-ineria titanium-aluminide turbine and vacuum-actuated wastegates for reduced lag and stronger low-rpm response. The turbos’ compressors are matched for peak efficiency at peak power levels, providing maximum on-track performance.

The engine’s response is augmented by a patent-pending low-volume charge-cooling system that improves packaging efficiency while permitting maximum boost pressure. The engine itself enjoys some reduced inertia courtesy of its titanium connecting rods.

The Hydra-Matic 8L90 eight-speed automatic is the faster and more efficient transmission choice. The car features steering-wheel-mounted paddles for manual shift actuation, but when the ATS-V is switched to attack mode, the transmission’s computer makes flawless shift decisions while the driver hammers the car around a circuit. In most respects, it is the better way.

However, for those drivers who think it is not the fun way, Cadillac offers the Tremec TR6060 six-speed manual transmission. We’ve seen automatic rev matching on downshifts elsewhere, including GM’s own Chevrolet Corvette, but the ATS-V adds to that no-lift upshifts. The driver depresses the clutch, makes the manual gearchange using the H-pattern shifter, and releases the clutch pedal all as usual. But the accelerator pedal stays on the floor throughout and the car automatically cuts power just long enough to compete the shift motion.

Though this defies the accumulated muscle memory in anyone able to operate a manual transmission, it makes upshifts shockingly quickly. So, maybe computer-matched downshifts and automatic power-cut upshifts leave the driver doing less of the manual shifting job, both ensure that the shifts are smoother and faster.

The EPA fuel economy estimates for the automatic transmission-equipped ATS-V are 16 mpg city and 24 mpg highway, while the manual gets 17 mpg city and 23 mpg highway.

An electronically controlled limited-slip differential helps the power get to the road effectively, with a 3.73:1 final drive ratio for the manual transmission and a 2.85:1 for the automatic, thanks to its abundance of gear ratios that permit a very low first gear.

Apparently, enthusiasts will have to accustom themselves to both the notion of sporty automatic transmissions and sporty compact Cadillacs.

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