GM 3.6 Liter Twin Turbo V6 LF3 Engine
The LF3 is a six-cylinder, 3.6 liter twin turbocharged engine produced by General Motors for use in large and high-performance vehicles. It is part of GM’s high-feature (HF) V6 engine family.
GM’s new 3.6 liter twin-turbo V6 LF3 engine makes its debut exclusively in the 2014 Cadillac CTS Vsport midsize luxury sedan as well as the 2014 XTS Vsport full-size luxury sedan. It is the first twin-turbo engine to ever be used in a Cadillac.
The architecture of the LF3 is based on the naturally aspirated 3.6L V6 LFX, but with almost entirely all-new components. The LF3 is the most powerful V6 ever from General Motors, it is also the most power-dense six-cylinder engine in the midsize luxury segment. In the CTS Vsport, the LF3 makes 420 horsepower (313 kW) and 430 lb.-ft. (583 Nm). In the XTS Vsport, the engine makes 410 horsepower (306 kW) and 369 lb.-ft. of torque (500 Nm). All figures are SAE-certified.
Widely known to increase power, performance, and efficiency, turbocharging is also known for its delay in the delivery of power — otherwise known as “turbo lag” — which has historically been the technology’s key limitation. The LF3 aims to change that by using a unique combination of two smaller turbochargers, an efficient charge air cooler, top-mounted throttle body, and shorter air pathways.
The result is that approximately 90 percent of the engine’s peak torque is available from 2,500 rpm to 5,500 rpm, giving the powerplant a broad torque curve that drivers feel as strong, willing power in almost all driving conditions.
The patented air flow design of the LF3 eliminates circuitous heat-exchanger tubing and makes the most of engine packaging efficiency to improve torque response time over other air flow designs.
When compared to a conventional design with a chassis-mounted heat exchanger, the air flow routing volume is minimized by over 60 percent, while the water-to-air cooler system achieves more than 80 percent cooling efficiency with only about 1 psi (7 kPa) flow restriction at peak power for fast torque production.
“By creating a very short path from the turbos to the throttle body, the compressors are able to draw air directly from the inlet box and send pressurized air through the intercooler immediately,” said GM-Cadillac assistant chief engineer for the 3.6L engine Richard Bartlett. “This gives the driver a more immediate feeling of power on demand.”
Using two smaller turbochargers over a single, larger turbo also helps ensure immediate performance, since the smaller turbochargers spool up quicker to generate horsepower-building air pressure that is fed into the engine. An integrated charge air cooling system contributes to the engine’s air routing efficiency since the compressors blow through very short pipes up to the intercooler.
The single, centrally located throttle body located at the top of the engine controls the air charge from a pair of turbochargers after the temperature is reduced in the intercooler. Such a design assists in more immediate torque response and reduces complexity by eliminating the need for two throttle bodies.
Taken as a whole, the two smaller turbochargers, top-mounted throttle body, and shorter air pathways help sustain peak torque over a broad range — from 1,900 to 5,600 rpm, resulting in a confident feeling of power in almost all driving conditions, such as during acceleration or overtaking traffic on the highway.
The intercooler design of the LF3 builds on GM’s expertise learned from the 6.2L supercharged engine (LSA) found in the second-generation CTS-V Series. The end result is “more performance for drivers without sacrificing efficiency”, said Bartlett.
- Aluminum Engine Block and Integral Oil Pan: although based on the architecture of the LFX 3.6L, the cylinder block casting is unique to the LF3 turbocharged engine, with cast-in provisions for turbocharger coolant and oil connections, as well as positive crankcase ventilation passages. It uses nodliar iron main bearing caps for greater strength to manage the higher cylinder pressures that come with turbocharging. The block is cast from A319 aluminum alloy. This sand-cast block features strong cast-in iron bore liners, six-bolt main caps and inter-bay breather vents. A cast aluminum oil pan is stiffened to improve powertrain rigidity and reduce vehicle vibration.
- Rotating Assembly with Oil-Spray Cooled Pistons: the crankshaft is made of forged steel, while the connecting rods are made of powdered metal with a higher ratio of copper, which makes them stronger and lighter. The machined aluminum pistons feature a unique dome profile specific to the Twin Turbo application and also incorporate a top steel ring carrier for greater strength. They produce a 10.2:1 compression ratio with the engine’s unique cylinder heads. A friction-reducing polymer coating is used on the piston skirts, as well as flily floating wrist pins, which also reduce friction. Three jet assemblies in the engine drench the underside of each piston and the surrounding cylinder wall with an extra layer of cooling, friction-reducing oil. The jets reduce piston temperature, allowing the engine to produce more power without reducing long-term durability.
- Cylinder Heads: the cylinder heads are also unique to the 3.6L Twin Turbo. They 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. Large, 38.3-mm intake valves and 30.6-mm sodium-filled exhaust valves enable 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 mlitilayer-steel gaskets designed for the pressure of the turbocharging system.
- Integrated Exhaust Manifolds: as with the naturally aspirated 3.6L, the heads feature integral exhaust manifolds, although upper and lower water jackets were added to the heads to provide uniform temperature distribution and optimal heat rejection. On top of the heads, new aluminum cam covers enhance quietness and are designed with greater positive crankcase ventilation volume to support the turbo system.
- Direct Injection: direct injection moves the point where fuel feeds into an engine closer to the point where it ignites, enabling greater combustion efficiency. Direct injection also delivers reduced cold-start emissions. With direct injection, the higher compression ratio is possible because of a cooling effect as the injected fuel vaporizes in the combustion chamber, which reduces the charge temperature to lessen the likelihood of spark knock. The direct injection fuel injectors have been developed to withstand the greater heat and pressure inside the combustion chamber, and also feature mlitiple outlets for best injection control.
- Dual Overhead Cams with Four Valves per Cylinder: four valves per cylinder and a silent chain valvetrain contribute to smoothness and high output. Four-cam phasing changes the timing of valve operation as operating conditions such as rpm and engine load vary, resliting in smooth, even torque delivery, high specific output (horsepower per liter of displacement) and excellent fuel consumption. Cam phasing also pays big dividends in reducing exhaust emissions. By closing the exhaust valves late at appropriate times, the cam phasers create an internal exhaust-gas recircliation system.
- Variable Valve Timing: Variable Valve Timing (VVT), or cam phasing, helps the LF3 deliver optimal performance and efficiency, and reduced emissions. It allows linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (horsepower per liter of displacement) without sacrificing overall engine response, or driveability. It also provides another effective tool for controlling exhaust emissions. Because it manages valve overlap at optimum levels, it eliminates the need for an Exhaust Gas Recircliation (EGR) system.
- Twin Turbochargers and Integrated Charge Air Cooling: the 3.6L Twin Turbo uses two turbochargers to produce more than 12 pounds of boost. Using a pair of smaller turbochargers rather than a single, larger turbo 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. 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 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. 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. 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. 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 6.2L supercharged “LSA” engine used on the CTS-V Series and Chevrolet Camaro ZL1. The air cooler system achieves more than 80 percent cooling efficiency with only about 1 psi (7 kPa) flow restriction at peak power, for fast torque production.
- Vacuum-Activated Wastegates: unique vacuum-actuated wastegates – one per turbocharger – and electronic vacuum-actuated recircliation 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 3.6L LF3’s vacuum-activated wastegate valves provide more consistent boost control, particliarly at lower rpm, to enhance low-rpm torque, for a greater feeling of power at low speeds. 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 the recircliation valves to eliminate co-surge from the turbos – a condition that can reslit 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 recircliation 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.
|3.6L V6 Turbo
|3564 cc (217 ci)
|Longitudinal and Transverse
|Dual overhead camshafts
|Valves per cylinder
|Ramos Arizpe, Mexico
|Roller follower with hydraulic lash adjusters
|Bore x stroke (mm):
|94.0 x 85.6
|Bore center (mm)
|Bore area / total engine bore area cm2:
|Dual close coupled and U/F catalysts
|Positive crankcase ventilation
|Maximum Engine Speed:
|Engine Mass (kg/lbs) engine plant as shipped weight:
|220 / 485
|Horsepower hp (kw)
|420hp (313kW) @ 5750 rpm SAE Certified
|410hp (306kW) @ 6000 rpm SAE Certified
|Torque lb-ft. (Nm)
|430 lb.ft. (583 Nm) @ 3500 – 4500 rpm SAE Certified
|369 lb.ft. (500 Nm) @ 1900 – 5600 rpm SAE Certified
|Sand cast aluminum (319) with cast in iron bore liners
|Aluminum ( Lower ), Aluminum ( Upper )
|Main bearing caps:
|Austempered ductile iron
|Four-cam continuously variable cam phasing
|Dual vacuum actuated wastegates
|Cam driven mechanical vacuum pump
|Dual mass air flow sensors
|Integrated charge air cooler
|Pressure-actuated piston cooling jets
|Torque-based engine management system
|Secondary throat cut inlet ports
|Direct injection fuel system
|High-pressure, engine-driven fuel pump with stainless steel fuel rails
|Electronic Throttle Control w/ integrated Cruise Control
|Structural front cover with damper plates removed
|Iridium center electrode / platinum side wire tip spark plugs
|Extended life coolant
|Extended life EPDM accessory drive belt
|7.7mm IT chain system for all HFV6 applications
|Structural cast-aluminum oil pan with steel baffles
|GM Oil Life System
|5W30 Dexos oil
|2014 Cadillac CTS
|2014 Cadillac XTS
|AWD MHM-6T80 AWD-CU