THE HEART OF A JAGUAR
Chief engineer Malcolm Sandford talks through the focus on detail that makes Jaguar’s 5-litre AJ-V8 Gen III engine the benchmark in its class.
TORQUE-ACTUATED VARIABLE CAMSHAFT TIMING UNIT
Sharpens throttle response
Conventional variable camshaft timing systems use engine oil pressure to change the phasing of the camshaft. This requires a large oil pump and a lot of energy. For the AJ-V8 Gen III that sits at the heart of a modern Jaguar, Jaguar chief engineer Malcolm Sandford led a team that developed a breakthrough technology that uses the free energy from the intake and exhaust valve springs as they open and close. The response rate of this new torque-actuated variable camshaft timing system is up to three times faster, delivering a more immediate engine response to the driver’s demand. “This is a major reason why the responsiveness of both our naturally aspirated and supercharged V8s set the benchmark
in their class,” says Sandford.
ALUMINIUM CYLINDER BLOCK
Each Jaguar 5-litre AJ-V8 Gen III engine is built around an extremely stiff, all-new, aluminium cylinder block, with cast-iron liners and cross-bolted main bearing caps to reduce noise, vibration and harshness. “The cylinder block itself is a beautiful piece of engineering,” says Sandford. “It’s constructed using high-pressure die-casting techniques – a first for Jaguar. The block is extremely stiff and rigid, significantly enhancing engine refinement.” The block also features what’s called an open-deck design, which allows the engine coolant to flow all the way to the top of the engine, reducing weight while improving cooling at the top of the cylinder liners.
OIL-PUMP PRESSURE-RELIEF VALVE
Improves fuel economy
Jaguar’s intelligent oil-pump pressure-relief valve typifies the brilliant engineering that has gone into creating the third-generation AJ-V8. Usually, the relief valve is set for high engine speed and high-temperature conditions. That can result in a compromise where, in warming up from cold, the oil pump is pumping more oil than the engine needs. What the Jaguar pressure-relief valve does is sense oil pressure deep in the engine’s heart, in its oil galleries, to accurately control oil-pump delivery. “As a result, oil-pump frictional losses are dramatically reduced during the warm-up period. That means improved fuel economy and lower emissions,” explains Sandford.
DIRECT-FEED FUEL INJECTOR
It was a world first for Jaguar – a truly innovative spray-guided fuel injection system that positions this multi-hole, direct-feed injector right in the centre of each of the engine’s eight cylinders. With fuel delivered at a pressure of up to 150 bar, the injector turns it into a precisely metered fine mist that’s sprayed directly into the centre of the combustion chamber. The result is accurate air-fuel control under all conditions, improving fuel economy and reducing CO2 emissions to just 262g/km on naturally aspirated vehicles and 292g/km on supercharged vehicles. For the driver, there’s another reward – sensational low-speed response. “There’s just an explosion of controllable power,” explains Sandford. “The design of this injector helps move the Jaguar driving experience on to a whole new level.”
SWITCHABLE INLET TAPPET
Positioned between each of the engine’s inlet-side three-lobe camshafts and the top of each inlet valve is this ingenious, hydraulically actuated, switchable two-piece tappet. Most engine tappets are solid, one-piece parts, but on the naturally aspirated AJ-V8 Gen III Engine the tappet is made of two pieces. Depending on how aggressively the car is being driven, a solenoid on the back of the cylinder head triggers an oil pressure signal that engages or disengages a tiny pin in the tappet. At lower engine speeds, the pin disengages to give a short valve opening for stronger mid-range torque. Step on the throttle and as the revs increase to 2800rpm, the pin engages and the valve stays open longer, allowing greater airflow for higher power.
FOUR-LOBE SUPERCHARGER ROTOR
Open up the new twin vortex supercharger unit fitted to Jaguar’s 510PS and 470PS supercharged AJ-V8 Gen III engines and you’ll find two high-twist, four-lobe rotors. These rotors counter-rotate, compressing air and force-feeding it into the engine’s combustion chamber to boost power. Meshing together, with less than the width of a human hair separating them, the precision-engineered lobes spin at speeds of up to 15,000rpm. “This is our sixth, and our most advanced, generation of supercharger at Jaguar,” explains Sandford. “This latest version uses four lobes instead of three and a lot more twist to create a smoother, more efficient flow of air into the engine, and with almost non-existent supercharger whine.”
The legendary Jaguar XK engine powered some of the world’s most evocative cars
Jaguar has always created engines that push boundaries. The XK engine powered cars such as the XK120, the E-type, the Mark II and XJ6. It sped racing Jaguars, such as the C-type and D-type, to five historic victories in the Le Mans 24 Hours. And, from its debut in 1949, it continued in production for more than four decades up to 1992. It was probably one of the greatest car engines ever created. Conceived by Jaguar founder William Lyons during the last years of World War II, it was a revelation when it made its debut in the sleek, lightweight body of the then all-new XK120 at the London Motor Show in October 1948. With its dual overhead camshafts and hemispherical combustion chambers, this race-inspired 3.4-litre in-line six cylinder delivered sensational performance. Continuously refined and developed through its life, one of its highpoints was when its capacity was enlarged to 4.2-litres in 1964, setting both a performance benchmark in the E-type and a new standard in luxury and refinement four years later with the all-new XJ6.
Photography by Patrick Llewelyn-Davies