The Evolution of Jaguar’s XK Six: Iconic Engine Produced for 43 Years

The origins of the British brand date back to 1922, when two motorcycle enthusiasts, William Lyons and William Walmsley, founded the Swallow Sidecar Company. In the following years they began to develop passenger car bodies in addition to motorcycle sidecars, and in 1935 the company, renamed SS Cars, introduced the first in-house developed sedan. In 1936 a two-seater sports car named the SS Jaguar 100 hit the streets, but at the start of World War II three years later vehicle production ceased and the nickname SS took on much more connotation. sinister. This led to a rebranding of the company which became Jaguar Cars in 1945.

During WWII, work at the Foleshill factory in Coventry revolved around repairing Whitley bombers and making sidecars or trailers for the armed forces, but President William Lyons did not give up his original company. In absolute secrecy, he tasked the engineering team led by Bill Heynes to develop a new set of engines that would help revive the company after the war was over.

As the British Isles were bombarded by Nazi forces, Heynes along with fellow engineers Walter Hassan and Claude Baily were assigned fire watch duties. It was during those long hours on the factory roof that the foundations for the XK engines were laid.

As soon as the war ended and the name of the company changed, the engineering team began to refine two prototype units that they had secretly built over the past two years.

One was a four-cylinder intended for smaller sedans, while the other was a six-cylinder that would serve as Jaguar’s flagship engine. The latter was more promising and benefited from most of the development work in the years that followed.

The goal was to create a powertrain that was not only reliable, but also powerful enough for a sports sedan that could reach a top speed of 100 mph (161 km / h). To achieve this, engineers used innovative design features such as hemispherical combustion chambers or dual overhead camshafts (DOHC), a configuration that was rarely used on mass-produced engines at the time.

On September 15, 1947, an advanced production candidate of the new XJ six-cylinder was launched for the first time. Built on a cast iron block with a lightweight aluminum head, it had a bore and stroke of 83 x 98 mm (3.26 x 3.85 in), moved 3.2 liters (195 ci) and produced 142 hp at 5,000 rpm. This was not a major increase over the Standard Motor Company’s inline-six used by the company in the previous decade, so the stroke was lengthened to 106mm (4.17 inches). This increased the volume to 3.4 liters (210 ci), while power increased to 160 hp at 5,000 rpm.

Jaguar now had the powerful and supple engine they had envisioned, but the sports sedan it was intended for was far from over. For the 1948 London Motor Show – which kicked off just over a month after the final engine shape was ready – the automaker surprised everyone by unveiling a gorgeous two-seater roadster called the XK120.

Hastily conceived as a test bed and show car for the new engine, it was an instant success, with the public and the press praising its exquisite design, a reaction that encouraged Jaguar to start more production. late in the year. In the early 1950s, the XK120 was one of the most popular sports cars in the world.

The XK six-cylinder was praised for its smoothness, unmistakable sound, and raw power. In May 1949, on the empty Ostend-Jabbeke motorway in Belgium, a slightly modified XK120 reached an average speed of 132.6 mph (213.4 km / h), a feat that made it one of the cars of fastest mass-produced sport on the planet. at the time. It would go on to break numerous world records for speed and distance, becoming a big hit in race car form and increasing Jaguar sales in legal form.

In the mid-1950s, the company finally abandoned development of the four-cylinder XK, because engineers could not achieve the same results from smooth operation of the six-cylinder. This was a major problem since the plans for a compact sedan were well advanced. The solution came in the form of a smaller displacement straight-six built around a shorter block. This new version which produced around 112bhp using twin Solex carburettors became the heart of the new model called the 2.4-liter Jaguar (later designated Mark 1).

In 1958, ten years after the original XK six-cylinder entered production, a new 3.8-liter variant was introduced, initially for the XK 150 model line and the Mark IX sedan. It retained the 106mm (4.217in) stroke of the 3.4 but was reamed to 87mm (3.4in) and fitted with dry liners. It could produce up to 265 hp when fitted with a straight port head.

In the early 1960s, Jaguar made significant improvements to the engine, developing a wide range of racing components that could be ordered through the company’s dealer networks. It also offered no less than five individual heads, most of which were color coded and offered distinct performance enhancements.

In many cases, owners who used their Jaguars for racing bored the 3.8-4.2 liters (256 ci.), A modification that led to significant performance gains. This practice ultimately resulted in the last major factory upgrade for the XK.

Introduced in 1964 and based on a redesigned block, the 4.2-liter would become the oldest and most widely used version of the iconic six-cylinder. Although the industry has now caught up in terms of technological advancements and hemispherical chambers or the DOHC configuration have become widespread, the venerable powertrain still performed well.

The 3.8 and 4.2 were the engines under the hood of the E-Type (XK-E for the North American market), arguably the best production vehicle Jaguar has ever built. Horsepower was the same, coming in at 265 hp, as were 0-60 mph (0-97 km / h) acceleration times of 6.4 seconds, but the 4.2-liter hit peak power earlier. in the rev range, which means much better throttle response. This made the E-Type one of the fastest production cars of the 1960s and, combined with its excellent chassis, exquisite styling and affordability, it also became one of the most popular vehicles of the years. 1960, especially in Europe.

In the late 1960s all other displacement versions were discontinued, meaning the 4.2 was the only XK remaining until 1975 when a revised 159bhp 3.4-liter was introduced. Both versions were starting to feel heavy and underpowered compared to newer engines, but the XK’s reign was far from over. Jaguar continued to use it in most of its models, including the cars it marketed under the British brand Daimler (acquired in 1960). It continued as a Jaguar engine until 1987, with the XJ6 being the last model to feature it, but continued to be manufactured for the Daimler DS420 Limousine until 1992.

Designed in the 1940s and produced for 43 years, the XK six-cylinder is one of the most successful engines in history and one of the few automotive units to have seen production spanning six consecutive decades.

Although the British manufacturer has created much more powerful engines throughout its history, the XK will be remembered as the best. It was used by the C-Type and D-Type racing cars which helped Jaguar win five of their seven titles at Le Mans. Plus, it was the engine that made the XK120 and E-Type one of the best sports cars of the 1950s and 1960s, a period when the company flourished.

Thanks to YouTube user Tedward, you can hear the sound of a 1954 version of the XK in the video below.

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