Inside the LFX

Cadillac SRX / Overview / Inside the LFX

The Cadillac SRX's new LFX 3.6L direct-injected V-6 delivers an SAE-certified 308 horsepower (230 kW) and 265 lb.-ft. of torque (359 Nm), with efficiency-enhancing features including direct injection and continuously variable valve timing. Peak torque is achieved at only 2,400 rpm and is maintained through 5,300 rpm. The LFX is also E85 ethanol-capable.

"The development team was challenged to achieve 300 horsepower in the SRX and exceeded the target," said Liz Pilibosian, chief engineer. "The horsepower and low-end torque of the 3.6L deliver greater power on demand at launch, on steep grades and when passing. The power band of the LFX engine also contributes to a better shift feel."

The LFX engine is a technically advanced 60-degree V-6 with dual-overhead camshafts, continuously variable valve timing and direct injection. Supporting elements that contribute to its performance, refinement and durability include:

The cylinder block and cylinder heads are cast in aluminum for low weight.
A composite intake manifold saves approximately 5.5 pounds (2.5 kg) over the weight of a comparable aluminum intake. It also has a comparatively small radiated surface area to help it maintain excellent noise and vibration characteristics.
An integrated cylinder head/exhaust manifold design saves approximately 13 pounds (6 kg) per engine when compared with a comparable engine with separate head/manifold assemblies.
The cylinder heads include four valves per cylinder, with a dual overhead camshaft design incorporating infinitely variable cam phasing.
A forged steel crankshaft provides optimal strength in the bottom end, while the connecting rods are made of powdered metal that features a higher ratio of copper, which makes them stronger and enables them to be lighter.
The pistons are made of lightweight cast aluminum and feature a friction-reducing polymer coating on the skirts , as well as fully floating wrist pins, which also help reduce friction. Less weight in the pistons means less reciprocating mass in the engine, which in turn means less inertia and greater operating efficiency.
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. Cast aluminum dampens internal engine noise better than a conventional stamped steel pan and is structurally stiffer.
Optimized-flow fuel injectors and the integrated exhaust manifolds/cylinder heads promote lower emissions.

To help achieve their performance goals, the Cadillac SRX's engineers redesigned the exhaust system with dual runners from the engine to a collection point farther rearward in the vehicle. The diameter and length of the pipes were specifically tuned to improve low-end torque from 1,200 to 3,000 rpm.

High-pressure exhaust pulses from each of the cylinders in the engine are timed to arrive at this collection point so that they phase together in a precise way. This tuning effect, which is called scavenging, literally pulls exhaust gases out of the engine by synchronizing high and low pressure pulses from each cylinder. Peak torque now occurs at a very low 2,400 rpm and remains high all the way through 5,300 rpm. The torque and power improvements were achieved while maintaining quiet performance.

"No stone was left unturned when it came to optimizing the airflow of the LFX, from the moment it enters the engine until it is expelled through the muffler," said Pilibosian. "The exceptional airflow qualities enabled us to exceed the 300-horsepower target, while careful calibration of the dual continuously variable valve timing system and the exhaust system contribute to the engine's great low-end torque."

The LFX engine is paired with the Hydra-Matic 6T70 electronically controlled six-speed automatic transmission, with tap up/tap down driver control. A wide overall ratio spread of 6.04:1 allows a "steep" first gear, as well as a "tall" overdrive top gear for low-rpm highway cruising. Acceleration is maximized, as is fuel economy. Engine noise is also lower during cruising. Because of the wide ratio spread (6.04:1), first gear is a very high ratio, which provides brisk acceleration from a stop. Sixth, however, is an overdrive ratio, which keeps the engine revolutions as low as possible for highway cruising, reducing engine friction losses and improving fuel economy.

A driver-selectable Eco feature alters the shift points of the 6T70 to enhance fuel economy by up to 1 mpg. A clutch was added to the variable displacement air conditioning compressor to enhance fuel economy. The compressor is only run when needed and provides no drag when turned off.

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