I have very much enjoyed the turbocharged LF4 V6 in my new ATS-V. There were some who were disappointed Cadillac didn’t simply put the LT1 V8 in the ATS-V. I like the Turbo V6 in this application — it is lighter, makes the same or more power, and is more efficient. It is a smooth, strong revving engine that matches the ATS-V well.
“The Cadillac Twin Turbo brings a new dimension of technologically advanced performance to the V-Series,” said Richard Bartlett, assistant chief engineer. “Delivering great power with world-class sophistication, it marks another large step forward in the product-driven expansion of Cadillac in the compact luxury segment.”
Unique to the ATS-V’s Twin Turbo are turbochargers with lightweight, low-inertia titanium-aluminide turbines, lightweight titanium connecting rods and an efficient, patented low-volume charge-air cooler, which contribute to optimal boost production and more immediate power delivery. With approximately 90 percent of the Twin Turbo’s peak torque available from 2,400 rpm to 6,000 rpm, the engine has broad torque curve that is conveyed in a feeling of responsive, sustained power at all rpm levels.
Additionally, a high-performance lubrication system is designed to maintain optimal oil pressure and ventilation during high-lateral driving maneuvers typically encountered on a track. Even the turbochargers are designed for track performance, with the compressors matched for peak efficiency at the engine’s peak power levels, which means they demand less heat rejection (intercooling) for higher sustained power during track driving.
“Track capability was one of the primary objectives for the Cadillac Twin Turbo in the ATS-V,” said Bartlett. “It expands the performance envelope of the ATS range, while advancing Cadillac’s legacy of delivering purposeful technology that inspires passion.”
Low-inertia turbochargers and vacuum-actuated wastegates
The twin, low-inertia turbochargers’ featherweight titanium-aluminide turbines are used with vacuum-actuated wastegate control for precise, responsive torque production. In fact, the titanium-aluminide turbines reduce rotating inertial load by 51 percent, compared to conventional Inconel turbine wheels. That means less exhaust energy – which spins the turbines – is wasted in stored inertial loads.
In practical terms, that means the relatively small size of the turbochargers and their lightweight turbines foster more immediate “spooling,” which virtually eliminates lag, for an immediate feeling of power delivery. They produce up to 18 pounds of boost (125 kPa).
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 efficient design also contributes to more immediate torque response, while reducing complexity by eliminating the need for a pair of throttle bodies.
Unique vacuum-actuated wastegates – one per turbocharger – are used with the Twin Turbo for better management of the engine’s boost pressure and subsequent torque response for smoother, more consistent performance. They 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 vacuum-actuated 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.
Patented low-volume charge-air cooling
The Cadillac Twin Turbo’s patented, manifold-integrated water-to-air charge cooling system also contributes to more immediate torque response, because the compressors blow through very short pipes up to the intercooler.
With no circuitous heat-exchanger tubing, there is essentially no lag with the response of the turbochargers. In fact, airflow routing volume is reduced by 60 percent when compared with a conventional design that features a remotely mounted heat exchanger.
“It is a very short path from the turbos to the throttle body,” said Bartlett. “The compressors draw their air directly from the inlet box and send their pressurized air through the intercooler basically immediately, for a tremendous feeling of power on demand.”
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. Also, the air cooler system achieves more than 80 percent cooling efficiency with only about 1 psi (7 kPa) flow restriction at peak power, which contributes to fast torque production.
Because the Cadillac Twin Turbo is based on the same architecture as the existing naturally aspirated 3.6L V-6, it benefits from many proven technologies including dual-overhead camshafts, variable valve timing and direct injection.
It also has unique features that strengthen the foundation to support the greater cylinder pressure that comes with turbocharging:
- Cylinder block and cylinder head castings that are specific to Cadillac Twin Turbo variants
- Lightweight, low-inertia titanium connecting rods are unique to the ATS-V’s engine and contribute to faster engine speed acceleration to match the quick spool time of the turbochargers, along with lowering the reciprocating loads on the rod and main bearings
- Machined, domed aluminum pistons with top steel ring carrier for greater strength
- An oil pan optimized for track performance
- 10.2:1 compression ratio
- Optimized direct injection fuel system for improved combustion efficiency and lower emissions
- Tuned air inlet and outlet resonators, aluminum cam covers and other features that contribute to exceptional quietness and smoothness.
The cylinder block casting has 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. It also features re-targeted piston oil squirters for improved temperature control.
The unique 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.
“The high-tumble heads were developed with advanced modeling programs that helped us determine the optimal design in less time and with less trial and error,” said Bartlett. “Literally hundreds of simulations were performed to optimize the port flow, injector spray angle and pattern, and piston topology to produce a highly efficient yet powerful combustion chamber.”
Large, 38.3-mm intake valves and 30.6-mm sodium-filled exhaust valves enable the engine to process tremendous airflow. In some conditions, the continuously variable valve timing system enables overlap conditions – when the intake and exhaust valves in a combustion chamber are briefly open at the same time – to promote airflow scavenging that helps spool the turbochargers quicker for faster boost production.
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.
The heads also feature integral exhaust manifolds with upper and lower water jackets that provide uniform temperature distribution and optimal heat rejection.
Six-speed manual transmission with Active Rev Match
The standard TREMEC TR6060 six-speed manual transmission has a strong track record proven in the supercharged CTS-V series. It is updated for ATS-V with selectable technologies that enhance driver control to help produce optimized shifts that can lead to faster lap times:
- Active Rev Match – anticipates the next gear selection and electronically ‘blips’ the throttle to match engine speed for a seamless gear change
- No-lift shifting – Part of the Performance Traction Management system, it allows gear changes without the need for the driver to take his or her foot off the gas pedal, keeping the engine at full boost and maximum power
- Launch control – Also part of the Performance Traction Management system, it enables maximum off-the-line acceleration.
The TR6060 transmission is used with a dual-mass flywheel and dual-disc clutch, which deliver greater shift quality and feel through lower inertia.
Paddle-shift eight-speed automatic transmission
The new Hydra-Matic 8L90 eight-speed paddle-shift automatic transmission is available in the ATS-V. Designed and built by GM, it delivers world-class shift times that rival the best dual-clutch designs.
For performance driving, the transmission offers full manual control via steering wheel paddles. A new transmission-control system and unique algorithms deliver shift performance that rivals the dual-clutch/semi-automatic transmissions found in many supercars – but with the smoothness and refinement that comes with a conventional automatic fitted with a torque converter.
The transmission controller analyzes and executes commands 160 times per second. Wide-open throttle upshifts are executed up to eight-hundredths of a second quicker than those of the dual-clutch transmission offered in the Porsche 911.
Smaller steps between gears, compared to GM’s six-speed automatic, keep the engine within the sweet spot of the rpm band, making the most of ATS-V’s turbocharged horsepower and torque to optimize performance on and off the track.
Additional performance-enhancing features include Performance Algorithm Shift and launch control via the Performance Traction Management system.