Jaguar Engines' Through the Years

Jaguar began its life in 1922 as Swallow Side Cars and did not adopt the Jaguar company name until 1945. It took a further 4 years for Jaguar to start manufacturing cars with its own engine, the XK. Up to that point the company had used a variety of engines from the Standard Motor Company. To date, over a 75 year period, Jaguar has designed and put into production 5 engine families; the XK, the V12, the AJ6, the AJ26 and the Ingenium, with 15 years separating them on average. In this article I will explore the reasons why the engines came to be designed and put into production.

I will also try to explain why this has happened. Jaguar has also used a number of engines from other companies, primarily Ford, but I am not going to discuss these in any detail, restricting myself those designed and developed in-house.

The first in-house Jaguar production engine was the 6 cylinder XK. In Wally Haynes’ IMechE technical paper of 1952 he titled it “The Jaguar Engine” which is a somewhat bold statement in an otherwise modest account of the engines development given it had already won its first Le Mans 24 hour race (the first of 5 when Jaguar dominated the event in the 1950’s). This engine had the longest production run of any Jaguar engine, from 1949 to 1992, a period of 43 years which will not be exceeded by any modern engine. The second Jaguar engine was the V12, which again with a little lack of modesty never had a name other than “The Jaguar V12”, as V12’s were so unusual in the 1970’s that none was needed. This engine lasted from 1971 to 1996, a period of “only” 25 years. The XK was finally replaced by the 3rd Jaguar engine, the AJ6 which was in production from 1983 to 1997, a much shorter period of 14 years. Both the V12 and AJ6 were replaced by the V8 AJ26 which later evolved into the AJ133, which was in production for Jaguar (and Land Rover) from 1996 and is expected to cease production this year, which will be a period of 24 years. The 5th and final engine is the current day Ingenium, a family of “state of the art” 3, 4 and 6 cylinder Petrol and Diesel engines which started production in 2016 and will I believe continue to power JLR vehicles for many years to come.

Given that new engines typically only come along every 10~30 years, each one is a major event and also there needs to be a really good reason for the company to want to take the risk of the cost and work of creating an all new engine rather than to continue to hone and refine the one it has.

Given that new engines typically only come along every 10~30 years, each one is a major event and also there needs to be a really good reason for the company to want to take the risk of the cost and work of creating an all new engine rather than to continue to hone and refine the one it has. It is interesting to consider the reasons why these engines were created and fortunately the technical papers written at or around the launch of each engine gives good indications as to the thinking and motivation of the company at the time.

Taking them in order with the XK engine first, until 1949 the company had been using side valve and overhead valve pushrod engines from “The Standard” to power its vehicles. What is evident in Wally Haynes’ paper is that the company wanted more power. The Standard engines could not rev with their pushrod valvetrains and this fundamentally limited them. The company needed more power both to satisfy its desire to succeed at racing and also for the critical US market. This led the engine to be designed to rev to a then “unheard of” 6000 RPM with max power at around 5250 RPM, numbers that are totally normal today but were a real challenge in the 1940’s. Other things that were important were durability, cost and servicability; the engines had to last without the failure of major components, be economic to manufacture and easy and affordable to maintain. The fact that “re-grinding of valves to their seats” was considered as a normal service operation is another interesting illustration of how things have changed over the years. Other current considerations like emissions and fuel economy did not even get a mention.

Figure 1– The production years of Jaguar’s in-house engines

Moving on to the V12 engine, designed primarily in the 1960’s and things had not changed a great deal. The main reason for the original creation of the V12 was to have a competitive engine for racing. By this time the XK could not compete with the V8’s and V12’s of other companies and Jaguar wanted the power needed to go back racing. The original 5.0 litre V12 was equipped with double overhead cams (DOHC) similar to the XK and was a purpose designed racing engine able to output 502 BHP at a then heady 7600 RPM. Unfortunately the company decided against a return to racing at that time and the engine was simplified to the single overhead cam design that went into production in 1971. This was needed to allow the engine to fit into the company’s road cars without major modifications as well as making the engine cheaper and simpler to manufacture and maintain. During the evolution from racing engine to road engine, the emphasis had shifted from high power to adequate power, coupled with excellent quietness for Jaguar’s push into luxury motoring. At the time of design, fuel economy was of low priority although shortly after going on sale this suddenly changed with the oil crisis of 1973 and an urgent re-design to the HE version with the May combustion chamber followed. Interestingly the subsequent racing versions of the engine used to great effect in the 1980’s at Le Mans and in Group C Endurance, were large displacement versions with the original flat head combustion chamber as this was considerably more suitable for high power than the May chamber.

Next up was the AJ6 and here we see fuel economy being a priority for the first time whilst also needing to produce competitive power and good durability. The engine featured an aluminium block and a 4 valve/cyl head, both of which were very advanced at the time and helped improve the fuel economy of the XJ40 through reducing the engine weight and reducing the engine displacement from 4.2l to 3.6l whilst simultaneously improving power and vehicle performance.

The 2.9l version of the engine featured a 2 valve/cyl cylinderhead, very similar to the V12 and was intended as a high value entry engine. The AJ6 was the first Jaguar engine designed without racing as a priority but instead with fuel economy and emissions being important and balanced with all the other needs. The ultimate version of the AJ6 family was the 322 HP supercharged version of the 4.0l AJ16, which in manual X300 XJR form realised a sub 6 second 0 to 60 MPH time; highly competitive with the German competition of the time.

THE FIVE IN-HOUSE JAGUAR ENGINES

The AJ26 followed and by now things were starting to get quite complicated; the company wanted more power, better fuel economy, lower emissions, more cylinders for smoothness, more compact for crash worthiness, high reliability and (at the same time) able to replace both the AJ6 and V12. The planned solution is in the name, the engine was called AJ26 with 26 being the sum of the 6, 8 and 12 cylinder engines planned, all to use a common cylinder (piston, rod, valves, porting, cooling jackets ...) with the 6 and 12 being 60 deg V engines and the V8 a 90 deg engine. Many other parts were modular with a common accessory belt drive arrangement and the cam chain parts were to be identical, just orientated differently for the 60 deg vs 90 deg engines. Sadly, this plan never came to pass. The 6 and 12 were cancelled and were effectively replaced with the 3.2l V8 and 4.0l supercharged V8. During the V8’s life it was twice upgraded with the 2nd upgrade to 5.0l being a very major one with considerable technology added as well as the increase in displacement. This allowed the power to be increased by nearly 50% permitting the engine to be competitive for a further 10 years with up to 600 BHP being realised from its 5.0 litres.

Figure 2 – The ever expanding design requirements over the era’s

Last, but definitely not least, the Ingenium family is Jaguar’s most complex engine family ever. 3, 4 and 6 cylinder engines in both petrol and diesel form. The first diesel engines designed in-house by Jaguar and also a return to JLR manufacturing in their own factory under their own control. This indeed was one of the prime drivers for the engine as well as needing further enhancements to fuel economy, emissions and NVH compared to the Ford and Ford manufactured engines that JLR was using at the time. The sale of JLR to Tata in 2008 included agreements for the on-going supply of engines to JLR from multiple factories but it meant that JLR was only able to manufacture cars which the contract with Ford catered for. This meant that in periods of high market demand there were occasions were Ford was unable to supply as many engines as JLR wanted.

Figure 3 – Engine specific power (BHP/litre) through the years

This was intensely frustrating for the JLR management as with self-control over engine production they could have responded to market demand more effectively. Born out of this problem, the Ingenium family was conceived to replace almost all of JLRs engines

with a modern highly capable, modular range of engines built on a common flexible production facility allowing great responsiveness to changes in market demand. I am sure that this has proven a very wise decision as the European market has moved away from diesel engines and back to petrol ones. Without this in-built flexibility this could have been very difficult indeed. The real challenge for the Ingenium designers was that they

had to provide this modular flexibility at the same time as also delivering world class petrol and diesel engines with little or no compromises. This I think clearly illustrates the growing challenges faced by engine designers over the years. The requirements needing to be delivered have increased decade after decade and none of the old requirements have gone away except for the need for the engines to be raced.

One thing that sadly has been lost over the years is a handsome looking engine. Wally Haynes commented in 1952 as follows: “... which automobile designers (on both sides of the Atlantic) as a general rule ignore – and that is the styling of the external design of the engine so that it looks the high-speed efficiency unit that it is, and conveys to the layman some idea of the thought and care that had been expended on the design ” This design ethos was upheld with the AJ6 and AJ26 but sadly by the AJ133, and subsequently the Ingenium, the complexity of design, coupled with other competing pressures meant that the decision was taken to cover the engine with a large plastic cover as done by most companies in the world.

I will close this first article with a quick comparison of the specific performance of the generations of Jaguar engines (Fig 3) and observe with interest how with the passage of time and the growth of knowledge and engineering tools (particularly Computer Aided Analysis since the 1990’s) how the specific performance of the engines has grown and that engines designed purely for the road with a focus on emissions, quietness and economy in fact have substantially higher performance than their racing fore-fathers . Of particular note is that it took 30 years to match the racing XK with the AJ26 NA, then 20 years to match the racing V12 with the Supercharged AJ133 and then just 10 years to match the racing AJ26 with the Ingenium P300 supercharged and turbocharged engine.

You can see the remarkable advances in engine performance achieved over the years, now delivered with emissions at a tiny percentage of those in prior era’s and fuel economy improved by 30~50% . In future articles I will discuss the individual engines, details of their performance, economy and other attributes and then discuss the technologies that have delivered the advances seen.

Story taken from Xclusively Jaguar Magazine - September 2020 issue.

Read the full issue here.