XJR FOR 1997: JAGUAR ELEGANCE WITH SUPERCHARGED POWER
Now in its third model year, XJR affirms the Jaguar heritage: elegance -- embodied in its quiet, impeccably appointed cabin -- combined with exciting performance and refined handling.
The XJR is powered by the first artificially aspirated engine ever built by Jaguar for a production car. Developing 322 horsepower, the supercharged powerplant adds a stirring dimension to a line of sedans already renowned for performance and luxury. Sales of the XJR surpassed targets by considerable margins during its first two years.
The soul of the XJR is its supercharged, intercooled AJ16 engine. This aluminum in-line six-cylinder engine delivers outstanding power and torque across a broad range of engine speeds. The smooth, refined engine reaches its maximum output of 322 horsepower at 5000 rpm and develops an exceptional 378 pounds-feet of torque at a low 3050 rpm.
Roots-Type Supercharger: Immediate Response, Designed for Durability
The pressurized induction of artificially aspirated engines, whether turbocharged or supercharged, provides higher power output through more efficient combustion of the air-fuel mixture. The advantage of a supercharger is immediate response to throttle openings at any engine speed because it is belt-driven by the engine crankshaft. Turbochargers, driven by engine exhaust flow, have an inherent lag in throttle response at low engine speeds.
The XJR’s Roots-type supercharger, made by the Eaton Corporation, pumps air into the engine with two close-fitting rotors turned by gears inside the supercharger housing. The design is especially durable due to the absence of contacting surfaces and the resultant reduction in friction and heat.
AJ16 Engine: Designed to be Supercharged
The robust 4.0-liter AJ16 engine was designed from the start to be supercharged with very few modifications. The naturally aspirated versions also benefited from the upgrades needed to absorb the heavy stresses imposed by the supercharged application. Such things as additional internal ribbing for the cylinder head, a new head gasket with increased clamp load and a seven-bolt exhaust manifold add to the durability and refinement of all AJ16 engines.
Other components of the supercharged engine differ only slightly from the naturally aspirated version. The cast aluminum pistons, for example, are very similar on both engines.
To compensate for the higher combustion pressures and to provide the optimum balance between performance and economy, the supercharged engine's compression ratio is lowered from the standard engine's 10.0:1 to 8.5:1.
During development, the supercharged engine proved to be relatively insensitive to inlet valve timing at full throttle. Consequently, Jaguar retained the standard camshaft profiles and re-timed the valve motion to ensure no overlap, thus preventing any blow-through of unburned charge at high-load conditions and promoting good idle quality.
An unusual inlet system, unique among Jaguars, incorporates the intercooler’s heat exchanger into the inlet manifold. This eliminates the need for a plenum chamber and interconnecting pipe and results in a very compact throttle volume -- the airflow path is no longer than the naturally aspirated engine -- in the inlet system, enhancing engine performance.
The only other notable modification made to the base engine was the addition of a drive to the supercharger.
A charge cooler is fitted between the blower and engine to increase the charge density, again allowing for better combustion. Jaguar engineers selected an air intercooler that was unique among passenger cars. It provides superior full-throttle response, refined operation and compact packaging, as well as improved fuel economy and tailpipe emissions at full throttle.
Sports-Car Performance in a Luxury Sedan
The AJ16 supercharged engine endows the XJR sedan with exhilarating performance with no loss of refinement. With the four-speed electronic automatic transmission, acceleration from rest to 60 mph takes but 6.7 seconds, and top speed is 155 mph. Output is a full 77 horsepower higher than the normally aspirated version that powers other Jaguar sedans.
Compared to the normally aspirated AJ16, the supercharged version has higher overall gearing, which partially compensates for its higher specific fuel consumption. This provides the customer with good real-world fuel-economy potential, dependent upon driving style.
The XJR rides on 17-inch wheels with eight-inch rims fitted with Z-rated Pirelli P Zero tires. Jaguar's sport suspension settings are standard, and the steering is specially tuned to suit the tire and chassis characteristics of the vehicle.