Cadillac Debuts 420-hp, Twin-Turbo V-6

General Motors Co.'s Cadillac unit says its new intercooled, twin-turbo, 3.6-liter V-6 engine produces 118 hp per liter the highest power density of any engine in the midsize luxury car market and the company's most potent V-6 ever.

The 420-hp engine, which makes 430 lb-ft of torque, will make its public debut next week at the New York auto show. The engine will hit the American market this autumn aboard the 2014 Cadillac CTS midsize sedan and XTS large sedan.

The new V-6 delivers about 90% of peak torque over a range of 2,500 rpm to 5,500 rpm. GM says the engine will be able to propel the CTS from zero to 60 mph in about 4.6 seconds and to a top speed of 170 mph.

The engine will be paired with an eight-speed automatic transmission that upshifts in 0.3 seconds during wide-open-throttle operation. Top gear is a long 0.69:1, enabling the engine to turn at only 1,800 rpm at 70 mph.

The new mill is a heavily modified version of the naturally aspirated 3.6-liter V-6 that Cadillac currently uses in its ATS sport sedan, SRX small crossover and the XTS. That engine rated at 321 hp will continue as the standard engine in the 2014 CTS.

The modified V-6 gets new block and head castings, stronger pistons and connecting rods, a new direct-injection fuel system, aluminum cam covers, sodium-filled exhaust valves and a higher 10.2:1 compression ratio. GM says it opted for two small turbochargers rather than one larger unit to reduce turbo lag. Also contributing to quick response time is the engine's unusually short air intake path from turbo to intercooler to throttle body.

GM says the new engine's cylinder heads were designed with "high-tumble" intake ports. They combine with redesigned piston heads to promote better air-fuel mixing.