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Engine Epic Part 6 - Jaguar

Here's the sixth installment of our series on modern hi-po engines. This week, we've focussed on Jaguar motors ranging from 2.4 to 6.0 litres capacity. That covers engines up to 276kW

By John Littler, additional research by Michael Knowling

Click on pics to view larger images

Jaguar has always been renowned for their class and the generally upper-level refinement of their cars and engines. Built from a foundation exhibiting a strong motorsport influence, it has always been Jaguar's expectation to provide their customers a piece of the action, giving them highly engineered engines capable of often out-performing larger capacity competitors. You'll notice this when you read on...

Note that in instances where power varied across markets, we've used the higher figure (the Euro engines were usually higher spec than US versions).


1949-1987 (limited production continued to 1992)

2.4/2.8/3.4/3.8/4.2 litre versions

The DOHC inline 'hemi' 6 cylinder was first released in the XK120 of 1949 in 3449cc form (83 x 96mm bore/stroke). It featured a cast iron block and aluminium alloy head. It continued - in one form or another - to power all Jaguars in the '50s and '60s. Initially, the plan was to also use the same engine in a shortened form as the XK4 (2 litre 4 cylinder) to power an XK100, however production demand was so great for the 6 cylinder that waiting lists for the XK120 continued through its entire production life. Hence, no spare capacity was available for the production of a 4 cylinder variant.

The '120' part of the roadster's model name was an indication of its top speed -120 mph (192 km/h). In proving this claim to journalists at Jabekke in Belgium, a stock XK120 achieved 132 mph (211 km/h). A later mildly modified XK120 (rego plate NUB120) achieved an amazing 173 mph (276 km/h!) in 1950. The modifications were limited only to a Perspex bubble over the driver to improve aerodynamics, a higher ratio diff (2.77 from the original 3.31) and some carb and head modifications to maximise the top end. So this 50 year old engine could certainly perform...

The 3.4 (and later 3.8) engine went on to power four Le Mans winners (1951, '53, '56 and '57). In 1958, the 3.8 litre version was released; the 3½ litre was then rebadged as 3.4 litres (although the block continued to have 3½ L cast into the side!). Racing success continued, with the 3.8 litre powering Bob Jane's multi Bathurst winning MkII (among other notable victories) with the manual version of the 3.8 litre MkII holding the crown of "fastest (4 door) production sedan" for a few years in the early '60s. Australia's Bob Jane was also the first to successfully enlarge the 3.8XK to 4.2 litres, with which he staved off a big 420cid (7 litre) V8 Ford Galaxy to win the Bathurst 500 again in 1964 and '65. The Jaguar factory started production of the 4.2 with the Series 2 E-type in 1964; this version also went into the MkX/420G (a large saloon) and 420 (medium size saloon - successor to the S-type). However, the 4.2 is best known for powering the long-running XJ6.

Introduced in 1969, the 4.2 litre XJ6 was the replacement for the medium-sized 420 and also, in 2.8 litre form, a replacement for the smaller MKII (by that stage badged as a 240 (2.4 litre) or 340 (3.4 litre) according to engine capacity). Note that while the 4.2 is an excellent engine, the 2.8 suffered from piston failures (carbon built up on the pistons if the car driven gently, which ended up burning holes through them - the problem never arose during testing as the test drivers gave it too much of a workout!) Relatively few 2.8s were sold; most of those now remaining have had a 4.2 transplant. The XJ6 was never intended to replace the 420G (large saloon) and was originally only offered in a SWB (same length as the 420/Stype) format.

Unfortunately Jaguar's founder (Sir William Lyons) sold the group to British Leyland in 1970 in a bid to gain the capital necessary to modernise. The move proved disastrous, as the BL board was riddled with incompetence and labour relations at the Jaguar factory went from "one big family" to strike-riddled and combative. The 420G was pulled from production without a replacement and the LWB XJ6 was born to fill the gap; in 1973 the XJ12 was released as a somewhat more appropriate successor. However, in 1972 work was started on the "ground-up new design XJ6" (promise of capital for its development being one of the primary factors that swung the sale to BL).

This car (now known as the XJ40 version of the XJ6) was originally slated for release in 1979 and included a new 6 cylinder designed from scratch - the AJ6. Design and production difficulties ensured that the release date was much delayed, with the XJ40 finally seeing the light of day in 1987 (although the AJ6 engine was first released into the XJS in 1984). As such, the XK6 engine continued in production far longer than Jaguar had intended, ceasing mainstream production in 1987, when the XJ40 was finally introduced. Limited production for British army light tanks and scout vehicles (as well as the Daimler DS420 limousine) continued until 1992.

XK6 DOHC, inline 6s:

  2.4 3.4 3.8 4.2
Bore 83mm 83mm 87mm 93mm
Stroke 76.5mm 106mm 106mm 106mm
HP (SAE) claimed 133 @ 5750 210 @ 5500rpm 245 @ 5500 240 (2 x SUs), 265 (3 x SU), 265 (EFI) @ 5000rpm
Model Mk1, Mk2, 240 XK120, XK140,
XK150, MkVII, MkVIII, MkII, 340, S-Type, C-Type, XJ6
XK150, Mk2, MkIX, Mk X, E-Type, S-Type, XKSS, D-Type 420, 420G, E-Type,XJ6


The Series 3 XJ6 (1979-87) was the final result of 30-odd years of tweaking and tuning, with much race and road experience. The only way you'll gain much increase in hp from the post '79 engines will be either through the use of forced induction, an increase in capacity, or changes that will noticeably compromise the street driveability. For real world usage, the most noticeable difference will be seen by a conversion to a manual gearbox, and the use of an aftermarket harmonic balancer (along with appropriate valvetrain changes) will allow it to rev more easily past the 5500 rpm redline.

Terry Handley in Bathurst (Australia) offers XK6's in 4.4 and 4.9 litre formats - the increase in capacity providing considerably more power and torque. He also offers some high performance heads and cams that can make a discernible difference. The 3.8 motors are only in 60's era Jags however, and most people are more likely to be modifying the comparatively inexpensive and more numerous XJ6.

The XJ6's 4.2 can be blown, however careful attention needs to be paid to cooling. Overheating will result in dropped valve seats, and ensure that a modern composite head gasket is in place if it's a Series 1 (the early cars used metal gaskets). Low comp 7:1 pistons are widely available for all XK capacities, which will allow significant boost to be used. If you have a Series 1 or Series 2 XJ6 (or any other early 4.2 lire XK6 engine), swapping to a Series 3 head is an easy modification to obtain more power - it has slightly larger intake ports, slightly better gas flow and improved cams.

Fuel injection from the Series 3 can also be easily retrofitted using a donor Series 3 head (and electricals) to almost any XK6 (although the very early 3.4's might be problematic due to coolant passage changes). The 2.4 litre motor from the 60's MkII loves to rev and would be perfect for turbocharging - and 2.4 litre MkIIs are relatively quite inexpensive compared to the 3.4 and 3.8 litre models. The 4.2 is an under-square motor and hence less suitable for turbocharging (it doesn't really like to rev as hard). Walkers in Sydney and Spiteri in Melbourne (both in Australia) have turbo manifolds available for the V12 and AJ6 engines and may be able to provide XK6 versions.

Daimler 2.5L V8 /4.5L V8

Alloy SOHC V8


A design that predated Jaguar's takeover of Daimler-Lanchester in 1959, the 4.5 litre survived only until the end of the Majestic Major production (2 years after takeover). The 2.5 litre continued to be produced right through until 1971 in the MkII-bodied Daimler. (Daimler 2.5 litre - later badged Daimler 250 at the same time as the MkIIs were renamed to Jaguar 240 and 340). It was rumoured that Lyons killed the planned production of the 4.5 litre V8 in the MkII body as he didn't want the Daimler version to be faster than the Jaguar version, leading to a hasty swap to the 2.5 litre V8 out of the Daimler Dart (also known as SP250). Hearsay has it that the 2.5 litre is only a destroked 4.5 litre and hence a 4.5 litre Daimler "MkII" could be a relatively simple modification if the appropriate components can be sourced!


1971 - 1996

5.3 litre (7.8:1,9:1 and 10:1 compression pre-HE, 11.5 and 12.5: HE) and 6.0 litre production

4.4, 5.3, 6.0, 7.3, 8.0 litre race homologation production

Originally designed in a 4.4 litre quad cam all-alloy form in 1963 to power another attempt at Le Mans in the XJ13, the project was shelved (despite fantastic performance from the engine). It was felt that the car wouldn't be competitive due to the amount of work that would be required to make the handling and aerodynamics good enough to beat Ford's GT40. Lyon's avowed rule for racing was never to compete unless Jaguar were sure they could win. Ironically, later testing showed that minor modifications would indeed have made it a quite competitive entrant. However, it has been theorised that Jaguar simply didn't have the funds to make the attempt - all available capital was being used in production development. And the company certainly didn't need any assistance with profile to lift sales - waiting lists were again in existence for both the E-Type and 3.8 litre MkII.

The V12 sat dormant until 1968, when the design was re-examined for use as the powerplant for a planned limousine (a replacement for the 420G). The design criteria were primarily quietness of operation, smoothness across all the rev range, bundles of low-end torque to allow effortless take off in what was expected to be a large and heavy car (the 420G was used as the testbed - it weighed well over 2 tons...). Oh yes, and sufficient power for the Jaguar slogan "Grace, Pace and Space" to ring true.

It was quickly determined that the DOHC layout - while a winner on the 6 cylinder - didn't offer sufficient advantage over a SOHC layout to warrant the additional noise and weight it added. It was also really only an advantage in power output when the car was revved hard. While the significantly under-square layout (70mm stroke x 90mm bore) allowed the engine to comfortably obtain high revs (8000 rpm was the original redline), the DOHC layout gave noticeable additional power only at the top end of the rev range. Because the design criteria valued low-end torque more highly than peak power, it was reluctantly decided to move away from a DOHC configuration for which Jaguar had become well known.

The eventual design was an all-alloy 5.3 litre V12 in SOHC 2 valve layout with a near flat chambered head and dished piston. The induction system was deliberately manufactured to a comparatively small diameter to enhance intake velocity at low revs and hence maximise bottom-end torque. With an undersquare layout making it very able to rev hard, redline was set to 6500 rpm for the simple reason that the engine simply couldn't suck enough air to make it worth revving it any harder! Softer valve springs and lower lift were also utilised to minimise valvetrain noise.

The end result was a mere 240kW (322hp) peak power but a massive 420Nm of torque, in a nice - nearly flat - line across the rev range. The engine had been designed with a large amount of space between each cylinder, resulting in such quiet operation at idle that 12 months into production they had to fit a starter lockout to prevent owners trying to restart an already running engine! Of course at redline it still made that characteristic V12 yowl!

The engine was first made available on the Series 3 E-Type in quad Stromberg format (the more traditional-for-Jaguar SU's wouldn't fit under the E-Type's bonnet!). The original release date was delayed by 2 years while engineers tried to work the bugs out of the electrical injection system they had always intended to use in production (the test engines used mechanical injection). The delays, however, became costly and the carburetted version was released also in the first XJ12 in '72.

In 1975 the bugs were finally ironed out in time for the release of the XJS which came in injected form - originally Lucas-modified Bosch D Jetronic, then later digital K-Jetronic, P-Jetronic and then Zytek. The XJ12 sedans received the injected engine in 1977. EFI made a noticeable improvement to fuel efficiency, but not enough to stop sales of the V12 sliding downwards due to the on-going ramifications of the OPEC fuel crisis. (While most of the traditional Jaguar buyers could afford the grossly inflated fuel prices, in many countries it became politically incorrect to drive a gas guzzler. In the UK, many XJ12 owners removed the V12 badges and replaced them with XJ6 badges to avoid vandalism and abuse!)

In 1980, Swiss engineer Michael Mays (best known for his work with Porsche) was hired to redesign the heads to improve fuel economy. His design became known as the HE (for High Efficiency), and it went into production in 1982. It was a quite effective improvement, lifting fuel economy from the low teens (12-13) to 18-20 mpg. The design involved a "swirl" being induced to the air/fuel mixture, allowing more efficient combustion and hence allowing significantly leaner fuel mixtures to be employed. This was created by a different combustion chamber and piston design, with higher compression ratios of 11.5:1 and 12.5:1. HE heads and pistons are therefore not interchangeable with pre-HE heads and pistons. Note, though, that the block remained identical, so a HE can be converted to pre-HE and vice versa via changing the head, the pistons and crank (rods are the same). In 1989 the 5.3 was stroked to 6.0 litres in order to compensate for the power loss caused by pollution requirements. It's fairly widely acknowledged that the 6 litre isn't as smooth a power plant as the 5.3; however it was still a very refined unit.

All alloy SOHC V12s:

  5.3 5.3 HE 6.0 HE
Bore (mm) 90 90 90
Stroke 70 70 78.5
Power (kW) 240 @ 5500 217@ 5500 234@ 5400
Torque (Nm) 420 @ 3500 430 @ 3000 463@3750
Models E-Type, XJS, XJ12 (Series 1 and 2) XJ12 (Series 3), XJS XJS, XJSC, XJ12 (XJ40) XJ12 (X300)


Due its original design criteria, the V12 is well suited to modification - if you don't mind a little more engine noise, you can massively increase the power output. Note, however, that the engine will generally still remain more refined than an average pushrod V8, even in heavily modified form. Induction manifold changes will liberate hp at the top end while losing some of the bottom end torque - it's a good idea to combine that with a manual gearbox or higher stall speed torque converter so you can keep the engine in the power band.

Stiffer valve springs to prevent valve float will allow you to take advantage of that 8,000 redline potential. However, you will probably need to look at the ignition - 12 cylinders at 8,000 rpm requires a spark every millisecond and a standard coil isn't be able to provide enough current. Jaguar moved to twin coils later in production, and these can be easily retrofitted to earlier cars. Also don't forget to upgrade the exhaust so you can get the gas back out again! The XJ and XJS came standard with 2-inch duals (massive by 70's standards!) but a 3 inch pipe will help.

There are two suppliers of pistons, cranks and rods that will allow the 5.3 pre-HE to be stroked to 7.3 litres(!); you can also bolt a standard 6 litre crank out of a later car straight into a 5.3 litre HE to create a 6.0. The pre-HE is well suited to forced induction with its standard 7.8:1 or 9:1 compression ratios (the 10:1 isn't suitable but it is very rare). The HE cannot be supercharged without a reduction in the compression ratio - the 12.5:1 is constantly on the verge of pinging with anything less than 97 RON fuel (UK 4 star) and really requires 100 RON (UK 5star) for hard use. Unfortunately, this is a higher octane than even Australia's Premium ULP (95-96RON).

The 11.5:1 runs fine on Super or PULP but there's no margin there - even a couple of psi boost on Aussie pump fuel will see the start of knocking. Decompression to around 8.5-9:1 is required for any useful amount of boost. Note, however, that twin turbocharged pre-HE's have seen estimated 1000hp outputs in boats, and a twin Lysholm screw HE in an XJS in the US (decompressed to 9:1) recently saw the dyno go off the scale (it maxed at 700hp at the rear wheels!!).

Similarly, the BL Broadspeed racing coupes (XJ12C) in '76 and '77 were estimated to be outputting around 600-700hp from a naturally aspirated pre-HE V12. These cars were British Leyland's (unsuccessful) tilt at Le Mans (without Jaguar approval or backing - don't you love corporate politics J ). The XJR7, 11 and 15 were very successful (with 3 Le Mans wins) and also ran modified versions of the standard 12 - the XJR15 was stroked and sleeved to 8 Litres (naturally aspirated). Five valve, DOHC heads are now available aftermarket which can allow V12s set up to rev hard to achieve much higher peak power outputs.... particularly in combination with forced induction!


2.9/3.6/3.2/4.0 litres


All alloy DOHC inline 6, AJ6 4 valve, AJ16 4valve

The "new from the ground up" XJ40 also got a wholly new engine - the AJ6 inline 6 cylinder was originally released in 2.9 and 3.6 litre formats. The 3.6, in true Jaguar tradition (as had been done with both the XK6 and V12), was first released in the 2door (XJS) before hitting production in the mainstay four doors. However, only a small number of XJSs were sold in 6 cylinder versions, with most buyers preferring the silky V12.

The new 3.6 in all alloy with 4 valve DOHC and a variant of the Mays head was quite fuel efficient, as well as having a good power to capacity ratio. The earliest US models used a compression ratio of 8.2:1 and a cat converter, while the European engines sported a 9.6:1 ratio. Due to these factors, the Stateside engine was down to 130kW (DIN) at 4750 rpm, and 300Nm of torque. However, later on in around 1989, the US model then received the more efficient 9.6:1 compression ratio, which boosted power up to 146kW (DIN) at 5000 revs. The 2.9, on the other hand, used the conventional SOHC 2 valve V12 HE head. This motor had very poor power for its 2.9 litres, and was also prone to many points of failure. Fortunately very few were produced! The block, however, is identical to the 3.6 and hence can be used as a donor for parts for a 3.6 rebuild.

In late 1989, the 3.6 was superseded by the 4.0 litre - the extra capacity being gained in both stroke and bore. The 2.9 was dropped altogether, later being superseded by the 3.2 in '92 - a far superior mill to its predecessor. Using the 4valve DOHC construction, it was essentially a destroked 4.0. The 3.2 capacity block was also used in the Aston Martin DB7.

Click for larger image

In 1990 there was also another significant milestone - Jaguar released the XJR. An Eaton (alloy twin rotor Roots blower) supercharged version of the 4.0 AJ16. Available in the UK and Germany in both 5 speed manual and auto, in Australia and the US it was only available in auto form. This means, of course, you can very simply obtain engineer's certification for supercharging any XJ40 if you use the correct manifold and blower (and the ECU will need to be remapped). There were no engineering differences between the XJR and other XJ6's (although there were trim and badging differences), hence it should not be difficult to obtain certification and insurance.


  2.9 3.6 3.2 4.0 4.0 S/charged
Bore (mm) 91 91 91 91 91
Stroke 74.8 92 83 102 102
Power (kW) 123(DIN) 165(DIN) 149@5250 183@4750 240@ 5000 (10.5 psi boost)
Torque (Nm) 239 @ 4000 325@4000 298@4000 392@4000 512@3050
Models XJ6 XJ-S, XJ6, XJ6 Sovereign, Daimler XJ6 XJ6Sport, XJ6 Sovereign XJS, XJ6, XJ6 Sov, XJ6 Sport, Daimler XJR

* Note that maximum power and torque dropped in later vehicles due to pollution regulations.

Current Cats....


Click for larger image

1996 - present

4.0 litre 4valveDOHC all-alloy V8

The 4.0 litre AJV8 was the replacement for the AJ16, and it was first released in the 2-door XK8 (XJS replacement). A little later it replaced the AJ16 in the 4-door XJ model. It was the first Jaguar V8 since the 60's, when production of the Daimler 2.5 and 4.5L V8s stopped.

The all-new 3996cc litre engine (which is still current) features electronic throttle control for maximum response and precision, and a linear variable camshaft phasing system for a wide spread of torque across the rev range. Improved combustion efficiency is also achieved through the use of air-assisted injection, whereby air is introduced with fuel into the injector itself. Exhaust emissions and oil consumption is reduced by the use of Nikasil-plated cylinder bores, leading up to a pent-roof combustion chamber. Maximum power is listed at 216kW at an engine speed of 6100 rpm, while a torque peak of 393Nm is available at 4300 rpm. Its all-aluminium construction helps it claim the right to being the lightest engine in its class. Built up from ultra-modern manufacturing techniques, this engine has an extraordinary level of NVH and it is one of the most flexible engines you are ever likely to drive.

Click for larger image

Following the success of this engine, two more versions have become available - the supercharged 4.0 and the naturally aspirated 3.2 litre V8. The supercharged model is simply awesome, featuring dual compact water-to-air intercoolers to reduce the air intake temperatures from the blower from around 160 degrees C to 60 degrees. It is boosted to 12 psi above atmospheric to deliver a stomping total of 525Nm of torque and an adrenaline-pumping 276kW at full power! The static compression ratio has also been reduced to cope with the force of the Eaton supercharger.

The more sedate 3.2 litre comes fitted to the S-type and XJ saloon and has the same refinement as the more powerful AJ8s. Its smaller capacity, however, lets peak power drop slightly to 179kW, and there's an accompanying reduction in peak torque - down to 316Nm. As with the other V8s, the 3.2 litre features a hydraulic front engine mount to reduce vibration and uses cylinder-specific ignition control.


Click for larger image

1999- present

3.0 litre 4 valve DOHC all alloy V6

This block is common to the Ford Mondeo and the Lincoln LS6 (Jaguar is now owned by Ford), but all other parts are of Jaguar design. It is the second V6 in Jaguar's history (not the first as is commonly suggested) - the first V6 was actually fitted to the XJ220 (instead of the V12 the potential purchasers thought they were getting!).

This very compact 3.0 litre V6 is currently in service under the stylish bonnet of the new S-type, and it is capable of producing 175kW (238bhp) at 6800 rpm complimented with 293Nm of torque at 4500 rpm. Jaguar has opted for a relatively high compression ratio (at 10.5:1), which would indicate this engine has had a lot of development time spent in the area of the combustion chamber and engine management. Its all-aluminium construction gives it extraordinary strength with minimal weight, and the lightweight theme extends to the specially-developed valve gear, which uses 5.5 millimetre valve stems. A two-position variable cam timing system is linked to this gear to provide an even spread of torque. As in the AJV8, electronic throttle control is also employed for its high level of precision.

Current AJ engines:

  AJV6 3.0 AJV8 3.2 AJV8 4.0 AJV8 supercharged
Bore (mm) 89.0 86.0 86 86
Stroke (mm) 79.5 70.0 86 86
Power (kW) 175 179 216 276
Torque (Nm) 293 316 393 525
Models S-type XJ S-type, XJ, XK8, Daimler V8 XJ, XK8, Daimler Super V8

The next installment of our Engine Epic is coming soon, but we'll give you a little time to take all of this in first!

Engine Epic Part 8 - Mitsubishi Engines
Engine Epic Part 7 - Mazda and Honda
Engine Epic Part 5 - Aussie Engines
Engine Epic Part 4 - Subaru, Daihatsu, Suzuki and Isuzu
Engine Epic Part 3 - BMW
Engine Epic Part 2 - Toyotas
Engine Epic Part 1 - Nissans

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