Jaguar AJ6 engine

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Jaguar AJ6
ManufacturerJaguar Cars
PredecessorJaguar XK6
SuccessorJaguar AJ-V6
Jaguar AJ-V8

The AJ6 (Advanced Jaguar 6-cylinder), and the similar AJ16, was an inline-6 piston engine used by Jaguar in the 1980s and 1990s. It was designed to replace the much-loved Jaguar XK6 engine, and was introduced in 1984. The AJ6 was only the third engine ever designed by the company. The AJ16 was replaced in 1996 with the Jaguar developed Jaguar AJ-V8 engine.

Jaguar had considered cutting the V12 in half to build a V6, or possibly a V8, but chose instead to develop a new inline-6. The cylinders are inclined, as in a slant-6, by 22 degrees. It is uses an aluminum block to reduce weight, and has an optional DOHC head for higher efficiency and power.


The original engines were the DOHC 3.6 and the SOHC 2.9. The DOHC 3.6 was revised and enlarged to 4.0 in 1990. It is still essentially an "AJ6", however. This was, as per usual, offered for the XJ-S before it was built into the XJ40 saloon.


The 3.6 was the first AJ6 engine, debuting in 1983 on the XJS. It had DOHC 4-valve heads with a 91 mm bore and 92 mm stroke. Power was 165 kW (221 hp) with 325 N m (240 ft·lbf of torque. Power was reduced to 201 hp (150 kW) for versions having catalytic exhaust system. Early versions of the 3.6L AJ6 as used in the 1984 - 1987 XJS cars had a conventional distributor type of ignition system with electronics within the distributor body. This early AJ6 ignition system is nearly identical to the system used on the XK engine in the Series III XJ6 cars. The Lucas fuel injection system on the 3.6L AJ6 engines in these early XJS cars sensed engine load using a Manifold Air Pressure (MAP) sensor just like the V12 cars from the same era. Later 3.6L AJ6 engines as used in the 1986-1989 XJ40 cars had a crank sensor type of ignition system with a bare distributor that only carried the spinning ignition rotor inside the distributor cap. The fuel injection system used on the later 3.6L AJ6 engines used a hot wire Mass Air Flow sensor to determine engine load.

Vehicles using the 3.6 were:


The 2.9 used a SOHC head from the Jaguar V12 engine, and was prone to failure. The block is the same as the 3.6, with the crankshaft and pistons lowering the stroke to 74.8 mm. Only the 1984-1989 Jaguar XJ6 used the 2.9. It was used for the entry-level XJ6 in Britain and Europe but rarely, if ever, seen in models exported to the US. The SOHC 2.9, which was generally considered somewhat underpowered for such a large car, was discontinued in 1990 (Actually 3.2 starts with a J-plate, so late 90 2.9 is possible) and replaced with a DOHC 3.2 (essentially identical to the DOHC 4.0).

The 2.9 Engine was, as in earlier years the 2.8 XK-engine, sized to match road-tax regulations in some European Countries like Italy or France. In France cars with more than 3 litres of engine size had to pay a luxury tax.

4.0 (1989-1994)

The 24 valve DOHC 4.0 L (3980 cc) version replaced the 3.6 L AJ6 in 1989. It featured a longer 102 mm stroke, and generated 183 kW (235 hp) power and 392 N m (290 ft·lbf of torque. The 4.0L engines as used in the 1990-1994 XJ40 cars continued with the crank sensor and empty distributor type of ignition system and the hot wire Mass Air Flow sensor type of fuel injection control system as the 1988-1989 3.6L XJ40 cars.

TWR modified Xj40's the result was the XJR. Jaguarsport name was also formed, as a partnership between TWR and Jaguar. The first XJR the XJR 3.6L had extensive appearance changes coupled with stiffer suspension, anti-roll bar/links, power steering valve that reduced efficiency by 40% and a LSD but no performance enhancements. Interior wise it included special stitching, "spor t" or "XJR" embossed front headrests, Jaguarsport speedo labels and tread-plates. Side

1990 XJR's had the upgraded 4L engine with the old style bodykits, and appearance changers.

XJR 4.0L's 1990+ Had all of the 3.6xjr handling upgrades and benefits from engine enhancements such as high lift cams, improved inlet/outlet manifolds etc.. They were sent directly after being produced to TWR in Coventry to be modified.

Exterior also changed again for last generation of the XJ40 XJR MY-91+. Bodykit was resculptured and the boot spoiler was deleted. Side moudlings were now added, with the smaller "XJR" badge embedded in them. Engine now had a plauqe saying "Jaguarsport XJR 4L" on the rocker cover. XJR badge size was decreased on the boot (had previously ranged from XJR-3.6, XJR-4L, 4-liter and "XJR". The later one ("XJR") is most common and the only badge you could choose on the boot infil panel models. A "spor t" one on the front with in its own unique XJR grill. In this unique grill a "spor t" badge was installed. Interior even had XJR specific wood (SPB part number).

Total XJ40 cars built was 208,733 and supposedly 500 JaguarSport cars built, 200 of the round headlight versions and then about 300 with the square headlights like the Sovereigns and Daimler's. 1990+ XJR power output is around 250bhp/288lbf.

Other significant modified Xj40's; Chasseur Xj40's had twin turbo convesions done by turbo technics. Bhp was around 340 on the 3.6L AJ6. A more powerful 4L model was also made. Janspeed also did a twin turbo conversions. The Bhp is around 305-320 again from the 3.6 AJ6. Arden also did special bodykits and wheels/badging.

3.2 (1990-1994)

A 24 valve DOHC 3.2 L, essentially a shorter-stroke (83 mm) 4.0 L, replaced the 12 valve SOHC 2.9 in 1990. It produced 149 kW of power and 298 N m of torque, and proved a popular engine in Europe (sales outnumbered 4.0 L saloons roughly 4:1) but was not exported to America.

Following the launch of the Aston Martin DB7, a car based on Jaguar's original replacement platform for the XJ-S (which was discarded in favour of the XK8 based on the X300 platform, note the traditional Jaguar 6-dial dashboard and ski-slope), the Jaguar AJ6 was used by Aston Martin as well. This version featured an Eaton supercharger.

Cars using the 4.0 and 3.2 included:


Both the 3.2 and 4.0 were substantially revised for the 1995 launch of the new X300 saloon. These are the "AJ16" engines, both now featuring coil-on-plug distributorless ignition, new engine management systems, magnesium alloy valve covers, revised pistons and other detail changes. The AJ16 was discontinued with the launch of the AJ-V8 (XK8 and XJ8 in 1996/7). Even now in 2007, it is becoming difficult to find internal engine parts such as bearing shells and pistons for these AJ16 engines so rebuilds a few years down the line may be challenging.

4.0 / 3.2 (1994-1997)

For the launch of the new X300 saloon for 1995, substantial revisions were made to the 4.0 L and 3.2 L AJ6 engines. The new design was called the AJ16 to reflect the major differences between it and the original AJ6.

Cars using the 4.0 and 3.2 included:


A supercharged version of the 4.0 L AJ16 was released in 1994 in the Jaguar XJR which used an Eaton M90 blower to boost output to 240 kW and 512 N m (322 hp) and 377 ft.lbf

See also