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Automotive Industry

GM Unveils V-12 and "Global V-8"

Automotive Industries, Sept, 2001 by Lindsay Brooke

Innovative features give new engines power, economy and lower emissions.

GM has pulled the wraps off two new, highly sophisticated engines that will play key strategic roles for the automaker beginning in 2003.

The long-rumoured Northstar XV12 is a lightweight 7.5L dohc V-12, designed for future Cadillacs and possibly truck applications. Its purpose is to recapture the luxury-engine image crown GM'S flagship brand lost decades ago. And the so-called Global V-8, shown at this month's Frankfurt Auto Show, forms the basis of a high-volume engine family for applications in North America, Europe and Australia.

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"Both are uncompromised, clean-sheet designs that take advantage of the latest piston-engine technologies," says Dr. Fritz Indra, head of advanced engineering at GM Powertrain. "They produce high levels of power and refinement, with greater fuel efficiency than our existing V-8s."

Speaking with Automotive Industries at the Monterey Historic races in California, Indra provided early details of both engines. While the Global V-8 is approved for production, the XV12 is still officially a prototype --though GM executives privately indicate it'll be built.

The ohv Global V-8 displaces 4.31, with output in the 300-hp range. It was developed for both transverse and longitudinal installations -- "maybe even Alfa Romeo," quips Indra. The all-aluminum engine features twin camshafts located near the top of the valley in the 75-degree cylinder block. Stacked one above the other, the camshafts operate three valves per cylinder (two intakes) via short pushrods. The set-up is reminiscent of the pushrod Mercedes-Benz Indy car V-8 developed with Ilmor and campaigned by Team Penske in the 1990s. In the Global V-8, the layout enables variable valve timing on both the intake and exhaust sides, which cannot be done on conventional ohv V-8s with a single camshaft.

"Another big advantage is up to 30 percent lower internal friction than a typical dohc engine," explains Indra. "This means greater fuel efficiency, particularly during idling and part-throttle operation." The engine also debuts an air-assisted gasoline direct-injection system, developed with partner Orbital Engine.

In North America, the Global V-8 is initially destined for GM'S Sigma platform, which includes the 2003 Cadillac STX (GMT265) crossover SUV; the 2004 Cadillac STS (GMT295) and 2005 Cadillac DTS and Buick LaCrosse (GMX271).

On a larger note, the Northstar XV12 was developed with partner Cosworth Engineering in the U.K. in a rapid nine months from concept to first running prototype. GM targets 750 hp and 450 pounds-feet of torque from the 60-degree V-12, putting it in a class beyond the current German, Italian and British (Aston) 12s. And it's a compact package, sized between GM'S Northstar V-8 and Vortec big-block V-8, and shorter in height than the small-block V-8. That's due to a linerless cylinder block, a nearly "square" bore and stroke (93 x 92 mm, with 100 mm bore centers), and a narrow 37-degree included valve angle. Indra says the engine weighs about 550 pounds without its Sachs 325A starter-alternator unit.

Early testing indicates the XV12, with its direct fuel injection, and ability to switch to 6-cylinder operation, beats the Vortec 8.11 V-8 in fuel efficiency. It's calibrated to run stoichiometric air/fuel ratios at 100-bar pressure until low-sulfur fuel becomes widely available for lean-bum operation.

"If we're serious about Cadillac, we need a V-12," asserts GM Vice-Chairman for Product Development Bob Lutz. "And we're very serious about Cadillac."

Automotive Industry

GM Unveils V-12 and "Global V-8"

Automotive Industries, Sept, 2001 by Lindsay Brooke

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