JAGUAR XK ENGINES

A key element in the character of a sports car is its engine. The new Jaguar XK will be launched with a powerful four-cam naturally aspirated 4.2 litre AJ-V8 powerplant. This compact, lightweight engine is based on that fitted to the latest generation Jaguar XJ saloon and has undergone significant development compared with the engine used in the previous Jaguar XK, including new fuel-injection technology. The latest 4.2 litre engine satisfies Euro 4 emissions requirements as well as stringent US emissions regulations.

The naturally aspirated 4.2 litre V8 engine produces 300bhp SAE (298 PS EEC) and develops maximum torque of 303 lb ft (411Nm) EEC at 4,100rpm. Again, the spread of torque is an important ingredient in the Jaguar XK's effortlessly sporty character, and this engine delivers more than 85 percent of torque all the way from 2,000 to 6,000rpm. Yet it still offers fine fuel economy and low emissions figures, with a drop in CO2 emissions of 5 percent over the previous Jaguar XK.

The naturally aspirated 4.2 litre V8 XK Coupe has an electronically limited maximum speed of 155mph and a 0-60mph time of 5.9 seconds, plus instant throttle response and broad flexibility for punchy performance across the range. With the all-new XK's weight savings, the new naturally aspirated 4.2's standing quarter-mile time of 14.4 seconds is less than half a second off the pace of the previous supercharged 4.2 XKR.

The latest AJ-V8 engine was developed to satisfy Euro 4 emissions requirements. Compared to the Euro 3 requirements, that meant a 50 percent reduction in hydrocarbons (HC) and oxides of nitrogen (NOx) and a 60 percent reduction in carbon monoxide (CO) emissions. The new engine also satisfies more stringent American regulations requiring a 50 percent reduction in HC emissions. It features Exhaust Gas Recirculation and the latest generation of catalyst cores with thinner coatings of higher density catalysing material - which reduces exhaust gas restriction and is more efficient.

The compact AJ-V8 engine has very stiff but lightweight all-aluminium construction, with eight cylinders in a 90-degree vee. The combination of strength and lightness begins with a ribbed cylinder block and cylinder heads. The 4.2 litre version has bore and stroke of 86.0x90.3mm for a capacity of 4196cc. The fully balanced four-throw, six-counterweight crankshaft is supported in five main bearings. The connecting rods use split-fractured big-end journals for strength with light weight and perfect balance. Each cylinder head carries two chain-driven overhead camshafts, which are hollow, to save weight and improve performance by allowing higher engine speeds. The camshafts operate four valves (two inlet and two exhaust) in each pentroof combustion chamber, around a central spark plug. An unusually narrow 28 degree included valve angle allows a compact combustion chamber shape and narrower heads, which benefits overall packaging.

The inlet camshafts allow variable inlet valve timing, with VCP Variable Camshaft Phasing, which is controlled by three-dimensional digital maps stored in the Engine Management System, on the basis of engine speed, throttle position and oil temperature data gathered from a series of sensors in the engine. The phase of the inlet camshafts is varied hydraulically and continuously (advancing the opening of the inlet valves at high engine speeds to allow the combustion process to start earlier). That delivers faster throttle response at all engine speeds, and gives optimum performance at all speeds and under all loads - with more torque at low speeds and maximum power at high speeds, while optimising fuel consumption. The VCP system has the added advantage of providing a degree of internal exhaust gas recirculation - which reduces emissions of NOx by slowing the combustion rate, and of hydrocarbons by re-burning some of the exhaust gases.

The major difference between this engine and the previous generation 4.2 litre XK engine is in the fuel injection technology. This latest V8 now uses multi-hole injectors, which improve the fuel spray pattern in the combustion chambers, improving both power and fuel efficiency.

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