GM Launches All-New 4-cyl. Engines in Cadillac ATS

DAWSONVILLE, GA – General Motors ushers into production a pair of all-new 4-cyl. engines with the launch of the ’13 Cadillac ATS, targeting reduced friction to gain efficiency and a revised combustion strategy to further tame the noise, vibration and harshness typically associated with potent little powerplants.

The naturally aspirated 2.5L 4-cyl. and turbocharged 2.0L 4-cyl. gasoline direct-injection engines effectively replace existing 2.4L 4-cyl. and turbocharged 2.0L 4-cyl. GDI mills in the auto maker’s portfolio. The ATS also will feature GM’s venerable 3.6L GDI V-6, a Ward’s 10 Best Engines winner in the Cadillac CTS in 2008 and 2009.

Both outgoing 4-cyl. engines also earned Ward’s 10 Best Engines nods – the 2.4L for its application in the Chevrolet Equinox cross/utility vehicle in 2010 and the 2.0L outfitted in the Buick Regal GS in 2012. Those direct-injection engines as a family date back to 1999.

With tough new federal fuel-economy regulations looming, as well as demands for Cadillac-worthy performance and NVH, GM saw the need for a clean-sheet design.

The new engines, built in Tonawanda, NY, also will see duty elsewhere, replacing their predecessors in a variety of GM applications over several model years. For example, both will find their way into the ’13 Chevy Malibu midsize sedan this fall.

Expect big volumes, too, given the 2.4L appeared in nearly 79% of all ’12 Equinoxes and 69% of all ’12 GMC Terrains, reflecting consumer demand for downsizing. The engine also powers the Chevy Captiva, a fleet CUV. The outgoing 2.0L turbo appeared only in the Buick Regal sport sedan in ’12.

But the similarities basically end there, says Ed Groff, assistant chief engineer at GM Powertrain.

“The bore centers of the 2.0L carry over, but that’s just because it is the optimum bore center and not to be common with the old engine,” he says. “The only thing common is me.”

An 86 x 86 mm bore and stroke actually makes for 1.988L of displacement, Groff says, allowing the 2.0L turbo to slip under displacement tariff thresholds in markets such as China.

“The design drove the bore centers, not manufacturing, because these engines are built on entirely new assembly lines,” he says.

GM increases the displacement of the second new 4-cyl. engine to 2.5L from 2.4L to gain the low-end torque so important for a brisk launch. Peak torque rises to 191 lb.-ft. (259 Nm) at 4,400 rpm from 172 lb.-ft. (233 Nm) at 4,900 rpm and horsepower increases to 202 at 6,300 rpm from 182 at 6,700.

GM expects the 2.5L will achieve benchmark status in its class when third-party evaluations are soon completed.

“It’s designed to be completely competitive,” says Ken Kelzer, global vehicle chief engineer-performance cars at GM. “Given the weight of the car, this isn’t a base engine someone must settle for.”

A base curb weight of 3,315 lbs. (1,504 kg) makes the ATS the lightest in its competitive set, which would include the sprightly BMW 3-Series and Audi A4.

Fuel economy in the ATS with the 2.5L bumps up to 22/33 mpg (10.7-7.1 L/100 km) city/highway, according to U.S. Environmental Protection Agency estimates, a few ticks better than the 2.4L in its primary applications.

The 2.0L turbo boasts 22/32 mpg (10.7-7.3 L/100 km) city/highway, according to GM estimates, and again better than its predecessor.

But Groff notes, “The fuel-economy play was to displace a 6-cyl. with a 4-cyl.”

To maximize torque, GM increased the stroke for the 2.5L to 101 mm from 98 mm with the previous 2.4L. The engine also operates more quietly at higher operating speeds.

Both the 2.0L and 2.5L feature aluminum blocks although with slightly different castings. They carry aluminum heads, and overall dimensions are nearly identical.

The new engines are 13 mm shorter than their predecessors after GM relocated the oil pump off the front of the engine to the oil pan, which also greatly improves NVH.

“One of the less-than-desirable characteristics in freezing cold weather was oil-pump whine, and we fixed that by putting it in the pan,” Groff says.

GM switches to a 2-stage pump so oil pressure can change depending on speed and load to reduce pumping loses. The 2.5L includes a 2-stage thermostat, which allows the auto maker to vary oil viscosity depending on conditions, and the switch was made to 5W20 oil from heavier 5W30.

The new 4-cyl. engines also were developed specifically with the ATS in mind, making architectural accommodations for the car’s optional all-wheel-drive system, its rack-mounted electric power-steering, targeted 50/50 weight distribution and short front-to-dash layout.

“We’re working with other applications at the same time, but we made several key architecture decisions to accommodate the ATS,” Groff says.

Reducing mass with lightweight components also was a major focus and included items such as hollow camshafts with pressed-on lobes instead of cast ones.

Additional NVH measures include an integrated noise cover for the intake manifold, which improves under-hood appearance, as well as a cast exhaust manifold instead of a fabricated one and isolated injectors and fuel rails to mitigate ticking.

Proprietary computational fluid dynamics analysis delivers an all-new combustion system that raises the compression ratio to 11.3:1 on the 2.5L, while reducing knock. Compression ratio on the 2.0L turbo rises to 9.5:1 from 9.2:1.

In total, GM reduces friction on the new 4-cyl. engines 16%. 

The twin-scroll turbocharger design of the 2.0L provides up to 20 psi (1.4-bar) of boost pressure, greatly reducing turbo lag and broadening the power brand. An electronically controlled wastegate and bypass further optimize performance and efficiency, GM says.

Higher-flowing intake and exhaust ports improve the engines’ efficiency and power, while increased cam-phasing authority for the continuously variable-valve timing helps achieve a greater balance between efficiency and performance.

Exhaust and intake manifolds on both engines switch sides, compared with their predecessors, completing GM’s aim for similar engine architectures globally.

“It’s part of our plan to reduce complexity, reduce architectures and keep things simple and interchangeable,” Kelzer says. “Let’s get the volume – make millions, not hundreds of thousands.”

GM mates both 4-cyl. engines, as well as the 3.6L V-6, to a 6-speed automatic transmission. A 6-speed manual is optional on the 2.0L.

GM expects 50% of ATS customers will select the 2.0L turbo, with the remainder split between the 2.5L and 3.6L V-6.

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