The V6 twin-turbo engine debuts in 2014 Cadillac CTS

Cadillac announced details of a new Twin-Turbo V6 engine and eight-speed transmission – firsts for the brand and signature features of the all-new 2014 Cadillac CTS midsize luxury sedan debuting next week at the New York Auto Show. Rated at an SAE-certified 420 horsepower (313 kW) and 430 lb.-ft. of torque (583 Nm), it is the most powerful V6 ever from General Motors.

The new engine is a comprehensive upgrade on the 60-degree, 3.6L DOHC V6 offered in today’s SRX, XTS and ATS. However, almost every component is unique. New features 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 and other features that contribute to exceptional quietness and smoothness.

Improved base engine parts

Because the Cadillac Twin-Turbo is based on the same architecture as the existing naturally aspirated 3.6L V6, it benefits from many proven technologies including dual-overhead camshafts, variable valve timing and direct injection. Key features also include:

• A durable forged steel crankshaft that contributes to greater high-rpm smoothness
• A friction-reducing polymer coating on the piston skirts, as well as fully floating wrist pins that help reduce friction
• Pressure-actuated oil squirters drench the underside of each piston and the surrounding cylinder wall with an extra layer of cooling, friction-reducing oil
• A cast aluminum oil pan is stiffer to improve powertrain rigidity and reduce vehicle vibration. It bolts to the transmission bell housing as well as the engine block, eliminating points of vibration.

The cylinder block casting is unique to the turbocharged engine with cast-in provisions for turbocharger coolant and oil connections, as well as positive crankcase ventilation passages. It uses nodular iron main bearing caps for greater strength to manage the higher cylinder pressures that come with turbocharging.

The cylinder heads feature a high-tumble intake port design that enhances the motion of the air charge for a more-efficient burn when it is mixed with the direct-injected fuel and ignited in the combustion chamber. The topology of the pistons, which feature centrally located dishes to direct the fuel spray from the injectors, is an integral design element of the chamber design, as the piston heads become part of the combustion chamber with direct injection.

Hardened AR20 valve seat material on the exhaust side is used for its temperature robustness, while the heads are sealed to the block with multilayer-steel gaskets designed for the pressure of the turbocharging system.

Integrated charge air cooling

Another feature of the Cadillac Twin-Turbo is its manner of processing the pressurized air charge through the cylinder heads and into the combustion chambers. A single, centrally located throttle body atop the engine controls the air charge from both turbochargers after the temperature is reduced in the intercooler. This design fosters more immediate torque response, for a greater feeling of power on demand, and reduces complexity by eliminating the need for a pair of throttle bodies.

Using a pair of smaller turbochargers rather than a single, larger turbo also helps ensure immediate performance, because smaller turbochargers spool up – achieve boost-producing turbine speed – 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.

Vacuum-activated wastegates

Unique vacuum-actuated wastegates – one per turbocharger – and electronic vacuum-actuated recirculation valves are used with the 3.6L Twin-Turbo for better management of the engine’s boost pressure and subsequent torque response for smoother, more consistent performance across the rpm band.

A wastegate is used to regulate the boost pressure of the engine. It provides a method to bypass the exhaust flow from the turbo’s turbine wheel, which can be reintroduced into the exhaust stream – via a bypass tube – to maintain optimal turbine speed across the rpm band. Conventional wastegates are pressure-activated, allowing control of the actuator. The Cadillac Twin-Turbo’s vacuum-activated wastegate valves are independently controlled on each engine bank to balance the compressors’ output to achieve more precise boost pressure response.

The wastegates also work in concert with the recirculation valves to eliminate co-surge from the turbos – a condition that can result in dynamic flow reversal, such as the moment immediately after the throttle closes. This overall system integration contributes to the engine’s smoother, more consistent feeling of performance.

In addition to the vacuum-actuated wastegates and recirculation valves, the engine employs dual mass air flow sensors and an integral inlet air temperature/humidity sensor, a dual-compressor inlet pressure sensor and dual manifold pressure sensors.

Engine technical data

Source: GM