Engines : Jaguar AJ-V8

Taking Jaguar forward into the 21st century inevitably meant weaning it off its love affair with the straight-six, and taking the company in a whole new V8-powered direction. The AJV8 engine was the result of this radical thinking.

Ralph Hosier tells the story of its birth…


A change in direction…

THERE WAS a time when ‘Jaguar’ and ‘V8’ could not be uttered in the same breath, which is odd when you consider the majesty of the Daimler 2.5- and 4.5-litre V8s used since the ’60s. But by the end of the ’80s it was becoming clear that the weight of the gorgeous Jaguar V12 was just too much, plus its enormous physical size was hampering car design, particularly for crash performance where you need some crumple zone rather than solid engine.

The engine was revolutionary in the ’60s, but in the ’80s the labour intensive assembly and expensive parts was costing the company more than it was making. For the last years of the XJS the V12 was not even on the official brochures, it was only its legend that was keeping sales alive. The AJ6 and AJ16 six-cylinder engines were making almost the same power and saved about 120kg which made a huge difference to the cars handling. But even this engine was showing its age.

New shorter engines were needed in order to allow sufficient room for an effective crumple zone. The engines needed to warm up more quickly, for both customer comfort and the ever tightening emissions regulations. This needs more precise cooling in the heads and block plus the use of considerably less metal. The piston ring system needed to control the oil much more accurately and piston friction had to be lowered. Indeed, friction throughout the engine needed to be reduced to meet the fuel economy targets and emissions targets.

With these issues in mind, a number of alternatives were looked at including a V12 derived V6 with the lost power being returned by using a brace of turbos. Another V6, an Orbital two-stroke engine which gave the same number of power strokes per rev as the old V12 engine, was looked at but oil control and refinement never quite met the targets. They even looked at a number of engines from other companies, which could be bought in without the huge cost of developing their own engine.

During the BL days there had been some discussion of using the Buick-derived Rover V8, which had substantial advantages in terms of weight (in fact it weighed half as much as the V12), cost and size. Unfortunately, most of the advantage came from the fact that it was relatively thin walled and so suffered in refinement a little. But in reality this could have been developed out, as was the case in the final fling of the Rover V8 inside the P38a Range Rovers.

But that venerable V8 was itself a relic of the ’60s and ultimately suffered from the same issues as the old Jaguar engines, in terms of efficiency and emissions. It also struggled to meet the power demands of modern cars, the 4.6-litre version only putting out 220bhp.

A new design decision

So, in the late ’80s, the bold decision was made to design a completely new Jaguar engine, one that would meet the forthcoming challenges of regulations and customer expectations. Originally code named the AJ12, the project used a single cylinder research engine to examine a number of different combustion chamber, cylinder head/ port and cam options. This data showed that a 500cc cylinder with 26 degree ports and a four-valve configuration gave the best economy and performance for Jaguar applications.

Although AJ12 never resulted in a physical engine, the data was used to study a modular engine design, concentrating on a 4-litre eight-cylinder and a 3-litre six-cylinder, but also looking at a 2-litre four-cylinder, a 5-litre 10-cylinder and a 6-litre 12-cylinder engine. This would require some rather sophisticated machinery to be able to make all those variants, sharing common components such as piston and valves but little else. As the analysis data grew, it became clear that the complexity of doing all those variants would be crippling, so it was decided to concentrate on six, eight and 12-cylinder Vee-engines. Thus the project now became known as AJ26, 26 being the sum of six, eight and 12.

But this would be hugely expensive, the fuel bill alone for testing engines runs into millions of pounds per year. At this time Jaguar was privately owned and as such there was simply not enough spare cash to invest in new products. What was needed was an owner who could suffer the financial hit in the long period between investment and return.

The Ford Factor

When Ford became interested in buying Jaguar, it was only natural to see if one of their many engines would fit the bill. Indeed it was not uncommon for Jaguar owners in the USA to retro fit a Yank V8 so there was some precedence for this already.

But work had already started on the fledgling Jaguar V8 and the Whitley team, lead by Dave Shutzpack, were passionate about seeing it through, they had looked at all the requirements and designed something that would give the legendary levels of Jaguar refinement and powerful whilst being small, light and efficient. But there would be a long road to go from a concept to a fully customer ready production engine. Typically it takes around seven years, that’s a long time to ask an investor to wait for a return.

Ford looked at the arguments for both Ford engines and for the new Jaguar engines, after all the data was analysed and the requirements understood, they decided to invest the millions needed by Jaguar to make their own new engine. But this would be dedicated tooling for just the V8, all other variants were not to be.

The first year had been largely given over to defining the requirements, the specifications for each part of the engine such as how much heat goes into the coolant and the oil, how much force is needed to turn the engine over, valve train stiffness, noise levels as well as the major things like the power and torque levels.

This had lead to the basic design, this was put into the new computers and virtual tests run to establish the best coolant flow paths, the best inlet and exhaust port shape, the cam profiles and the such. A huge amount of data was produced and analysed, without making a single engine. Somewhat different to the early days of the V12 when development was a matter of calculated guess work and then lots of test engines proving it all out.

The calculation gave most of the answers, but some elements still required real world testing. To this end some elements of the new engine were experimented on in isolation, using a current production ‘slave’ engine as a base, giving rise to some odd reports in the press of the new engine being based on this that and the other engine. For example, in order to try different bore and stroke combinations on the single cylinder rig, the engineers looked about for existing parts from all sorts of manufacturers, at one point it was using a Peugeot piston and a Mazda con rod!

V8 running

The first V8 engines were run on test beds in late ’89 and the first car to receive one was an XJ-S, one of the cars that had just finished being used to evaluate the twin turbo AJ16 in fact. As is always the way with the first ever engine installation, nothing fits, mounts, hoses, air intake and exhaust manifolds all had to be fabricated for the job. Steve, one of the mechanics on the job, recalls ‘they gave me a bag full of exhaust tube and various bends and told me to get on with it’. At the end of ’90, after a couple of weeks of trial and error fitting work the first 4 litre V8 Jag burbled into life and was universally admired by the small select audience of management privileged enough to see it, particularly in America which was a crucial market.

It weighed about the same as the old six-cylinder but had more power and a greater spread of torque, thanks to the new variable cam timing system. But there was a small problem, it didn’t sound like a ‘Jaguar’. Although very appealing, the V8 burble sounded like any normal mid size car in the USA and part of the Jaguar magic was the very high levels of refinement and quietness. Sound is such an emotive thing and much debate was had as to what the new engine should sound like, eventually the decision was made to make it quiet and an enormous amount of work went into designing complex intake and exhaust systems. It is interesting to note how this has changed now such that the current XKR even has a device built into the bulkhead to help you hear the engine’s magnificent growl.

The first car I drove with the new V8 was an XJ40 in about ’93 at the Ford research centre in Dunton, Essex. The car was based on the XJ12 body, code named XJ81, which had completely new metal work in front of the bulkhead in order to accept a V engine. The car was bristling with new technology, it had one of the first electronic throttle systems and this particular car had a manual gearbox but with an automatic clutch. As you shifted gear the systems would move the throttle and clutch so as to give you smooth gear shifts. It was marvellous to drive but ultimately it was easier to just use one of the excellent ZF five-speed auto gearboxes instead.

It’s interesting to note how Jaguar has had a history of technological innovation, and how right from the start how Jaguar was showing Ford new things. In return Ford showed Jaguar how to massively improve production processes, improving quality and reducing costs. This relationship is continuing to this day, I am pleased to say, with both sides benefiting.

As the engine developed, the early tunes were used to check and refine the basic performance and emissions characteristics. Then cars were used to tune the transient response, that is to say how the engine responds to acceleration, deceleration and gear shifts. This is always a very difficult balance between good drivability and good emissions, a slightly rich fuelling on acceleration give very good drivability but will fail emission completely on hydrocarbons alone.

Part of the solution was to ensure the automatic gearbox control system ‘talked’ to the engine control system. This kept the throttle, fuel and spark precisely in tune with the change in engine speed during the shift, allowing the engine to anticipate the changes rather than have to react to them after the fact.

After the engine had received a good stable tune, it was time to test it in all the harsh climates it would face in the real world. Traditionally this involves driving it in the Arctic and in the deserts of Arizona or Africa. But now tests could also be done in Fords climatic test chambers which drastically cuts down the development time and expense. As well as cold and hot climate tests, the new cars had to be tested in extremes of damp to check the corrosion resistance of the components and all the wiring. Then there is the rough road testing, both on specially prepared test track with a range of harsh surfaces, and on shake rigs where computer controlled hydraulic rams try to shake the car to pieces. In short a lifetime of use and abuse is concentrated into a matter of months. By the end of ’94 a huge amount of data had been produced and all the necessary changes had been made, the results were looking very good indeed.

After this year of climate and durability tests, the final tweaks could be made and then it was time to start running the cars at government approved test centres to get the various certifications needed to sell a new car. At the same time further tests were re-run in house just to confirm that the final version was working as expected.

In parallel to all this development, the production plant was tooling up. First prototype tooling is made and the whole assembly process is tested, any special tools or assembly methods are identified and the first set of people are trained. The first few test cars were built this way, as were the cars eventually used for the journalists to drive at the launch in ‘95.

The cost of production tooling is huge, the Bridgend AJV8 plant cost Ford £125 million. So it was vital to be certain that everything was right before the orders were placed, this could only happen when all the test data was in and all the tweaks had been tested. This is still true today and is one of the reasons it takes so long to get a new idea into production.

So, in ’97, eight years after the project started, the first XK8s were sold with the all new, entirely Jaguar, V8 engines. A new era had begun.

Keith Adams

About the Author:

Created www.austin-rover.co.uk in 2001 and watched it steadily grow into AROnline. Is the Editor of Classic Car Weekly, and has contributed to various motoring titles including Octane, Evo, Honest John, CAR magazine, Autocar, Diesel Car, Practical Performance Car, Performance French Car, Car Mechanics, Jaguar World Monthly, Classic Car Weekly, MG Enthusiast, Modern MINI, Practical Classics, Fifth Gear Website, and the the Motoring Independent... Likes 'conditionally challenged' motors and taking them on unfeasable adventures all across Europe.

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