What’s said to be unique vacuum-actuated wastegates, one per turbocharger, and electronic vacuum-actuated recirculation valves are used with the Twin Turbo for improved management of the engine’s boost pressure and subsequent torque response.
Cadillac announced today a new 420 horsepower, turbocharged V6 engine and eight-speed transmission that will be used on the all-new 2014 CTS mid-size sedan that debuts next week at the New York Auto Show. Cadillac said the force-fed V6 engine is the most power-dense six-cylinder engine in the mid-size luxury segment – displacing 3.6-liters at 118 horsepower per liter (88 kW/liter). Coupled to an eight-speed automatic transmission the new powertrain has better fuel economy – estimated at 17 mpg city, 25 highway, premium fuel required -and acceleration compared the current six-speed automatic. The extra gears are said to be worth a 1.5% gain in fuel economy alone. (Read Jim Dunne on Caught Testing – the Revised 2014 Cadillac CTS)
When the 2014 CTS sedan goes on sales this fall, it will also offer a naturally aspirated 3.6-liter V6 rated at 321 horsepower, as well as a 2-liter, four-cylinder, turbocharged engine rated at an estimated 272 horsepower. The Twin Turbo engine will also will be offered in the 2014 XTS large luxury sedan this fall. (Read AutoInformed on Cadillac XTS Sedan Unveiled With a V6 and All Wheel Drive)
David Leone, executive chief engineer of Cadillac, said the new V6 has 15% greater power density than BMW 535i’s turbocharged 3-liter six rated at 300 horsepower (223 kW), for a ratio of 100 horsepower per liter (74 kW/liter). The Cadillac V6 is also better than BMW 550i’s TwinPower 4.4 liter V8, rated at 400 horsepower (298 kW), or 91 horsepower per liter (68 kW/liter). Power density, of course, is one measure of efficiency for an engine’s size.
A pair of smaller turbochargers on what Cadillac is calling its Twin-Turbo V6 and an efficient charge air cooler are said to provide immediate power delivery. About 90% of the 3.6-liter Twin-Turbo’s peak torque is available from 2,500 rpm to 5,500 rpm, giving the engine a broad torque curve.
Using a pair of smaller turbochargers rather than a single, larger turbo helps ensure immediate throttle response, because smaller turbochargers spool up quicker, thereby supplying boost quicker to generate horsepower-building air pressure that is fed into the engine. The Cadillac Twin-Turbo’s integrated charge air cooling system also contributes to its immediate response, because the compressors blow through very short pipes up to the intercooler.
The charge-cooling heat exchangers lower the air charge temperature by more than 130 degrees F (74 C), packing the combustion chambers with cooler, denser air for greater power. The twin-“brick” configuration of the heat exchangers is similar in design and function to the 6.2-liter supercharged “LSA” engine used on the current CTS-V Series. (Read AutoInformed on Driving the Cadillac CTS-V Coupe)
The new engine is an upgrade of the 60-degree, 3.6-liter DOHC V6 used in today’s SRX, XTS and ATS Cadillac models. New aspects include:
- All-new cylinder block casting
- All-new cylinder head castings
- Strengthened connecting rods
- Machined, domed aluminum pistons with top steel ring carrier for greater strength
- 10.2:1 compression ratio
- Patented, integrated charge air cooler system with low-volume air ducts
- Two turbochargers produce more than 12 pounds of boost (80 kPa)
- Vacuum-actuated wastegates with electronic control valves
- All-new direct injection fuel system
- Tuned air inlet and outlet resonators
- aluminum cam covers
Launch feel is yet unknown until AutoInformed test drives, but Cadillac says the CTS sedan will reach 60 mph from a standstill in an estimated 4.6 seconds and achieve an estimated top speed of 170 mph (274 kph).
