• 1950 Jaguar XK 120 Alloy Roadster

The ’Leaping Cat’ that established Jaguar as a sports car manufacturer

The Jaguar XK120 was a turning point in Jaguar’s history and a sign of things to come. It was the fastest car in the whole world at the time of its launch in 1948 and remains one of the most beautiful British cars ever made.

First showcased at the 1948 London Auto Show held at the Earls Court, the XK120 was cheerfully received by an enthusiastic crowd who fell in love with the curvaceous and streamlined bodywork which covered the new XK inline-6 engine which promised never-before-seen performance on the road.

The first 242 XK120s were built with an alloy body until demand became so great that Jaguar switched to a different plant and began mass production in mid-1950. The XK120 spawned the XK140 and XK150 models which were successful evolutions of the concept and lasted in production all the way to the dawn of the ‘60s.

1950 Jaguar XK 120 Alloy Roadster Exterior

1950 Jaguar XK 120 Alloy Roadster
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The Jaguar XK120 was the result of Sir William Lyons’ team’s desire of building a rigid, flexible, and powerful engine shortly after the end of World War II.

The company, formerly known as SS Cars Ltd. had only changed its name to ‘Jaguar’ in 1945 before serious development work began on the construction of a new engine.

Prior to the global altercation, the SS works put together an SS Jaguar 100 sports car fitted with an experimental engine with of 3.5-liter capacity that churned out little over 160-horsepower using special racing fuel and a 15:1 compression ratio. This was to be the number that the Jaguar engineers looked to match with their future design.

The first double overhead-cam engine to come as part of this new project, codenamed ‘X’, was the XF 4-cylinder 1.36-liter unit that was mildly successful on the bank but was followed by a traditional pushrod design known as the XG. The small 1.75-liter engine was followed by the XJ which was built as both a 4-cylinder and as a 6-cylinder engine. The 6-cylinder XJ engine had its stroke increased for a capacity of 3.4-liters and was named XK.

1950 Jaguar XK 120 Alloy Roadster
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This was the engine that found its way under the streamlined body of the XK120 at the 1948 London Auto Show. The ‘120’ in the name stood for the estimated top speed of the new car, which proved to be quite an understatement. Meanwhile, the bodywork itself was the result of the joint effort of Sir Lyons and chief engineer William Heynes who was hired by Lyons to lead the engineering department in 1946. He oversaw the production and design of all of the Jaguar cars up until the Series III E-Type.

The XK120 looked incredibly modern with its covered rear wheels, front fenders that were incorporated in the bodywork and the overall simple line.

The front end is dominated by the elongated chromed grille, which became a signature design element in years that followed, which is framed by the hood itself that opens up with the grille itself. The two-piece bumper is attached to the body without any sort of over-riders and, below them, there are two air vents. The round single-lamp headlights, incorporated into the fenders, peer from between the spherical wheel arches and the slightly hoisted hood line. The indicators are fitted on the top of the fenders, thus above the headlights.

1950 Jaguar XK 120 Alloy Roadster
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The elegant profile of the car is dominated by two major design lines: the line of the hood which extends back towards the middle of the car until it meets the two-piece chromed slightly rounded windshield and the line of the fender which protrudes outward from the midsection and then goes straight across the doors blending with the rear fender. The rear wheel covers are detachable and the car often ran in competition without them to aid cooling. You’ll notice the rubber seals on the back quarter panel that seal the rear fenders to the bodywork.

The 16-inch steel rims are covered by full-size hubcaps in the color of the body with a chromed central piece.

The car’s line is only broken when the soft top goes up as it looks like an improperly attached hat, rather than a roof.

All of the Alloy-body XK120s were sold in Roadster specification although an FHC (fixed-head coupe) and drophead coupe version followed.

1950 Jaguar XK 120 Alloy Roadster
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The rear end of the XK120 is a simple affair.

The round taillights are attached to the sloping rear bodywork inside two chromed aerodynamic slots on either side of the trunk. The car doesn’t have a full-size bumper at the back, instead going for two over-sized over-riders.

1950 Jaguar XK 120 Alloy Roadster Exterior Dimensions

Wheelbase 102 inches
Length 173 inches
Width 61.5 inches
Height 52.5 inches

1950 Jaguar XK 120 Alloy Roadster Interior

1950 Jaguar XK 120 Alloy Roadster
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The leather-lined interior of the XK120 personified if that can be said when talking about a car, simplicity. The bus-like four-spoke steering wheel with the Jaguar logo in the middle sticks right out of the dash. On the dash, there’s a center section that sticks out which is where you’ll find all of the necessary dials and switches, of which there is a handful.

There are two big dials on either side of the mid-section. The one on the left is the tachometer while the odometer is on the right.

Some racing versions had their gauges inverted according to the position of the wheel and the needs of the driver. Also, some competition models came with bucket seats that offered more side support than the normal plush ones.

On the passenger’s side, there’s a handle that should help for ingress and egress. The gear shifter is positioned in the middle with the handbrake in the passenger’s footwell on the right-hand side of the transmission tunnel.


1950 Jaguar XK 120 Alloy Roadster
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Essentially, the XK120 was built as a test bed for the large-capacity 6-cylinder XK engine. Originally, the smaller XJ engine variety, which was updated and given the XK designation as well, was also supposed to go into production in the Jaguar XK100.

The model was announced at Earl’s Court at the same time with the XK120s presentation but, ultimately, the 2.0-liter 4-cylinder 107-horsepower Jaguar was shelved.

The reason for the cancellation was the public’s overwhelming interest in the more powerful inline-6 option. Indeed, the engine developed 162-horsepower at 5,000 rpm and 193 pound-feet of torque at 2,400 rpm which was quite special 70 years ago. The engine had a high-tensile alloy cylinder head with hemispherical combustion chambers, chrome-iron cylinder block, alloy pistons, and steel connecting rods.

The chassis in which it was nestled was, originally, made out of ash wood (on the 242 alloy-body cars). The box-section design proved to be very rigid due to the cross-members.

1950 Jaguar XK 120 Alloy Roadster
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The suspension was independent at the front with transverse wishbones and torsion bars controlled by telescopic dampers. At the back, there were steel semi-elliptic springs controlled by piston-type Girling dampers, connected to a live axle.

The synchromesh single helical 4-speed gearbox was fitted with a Borg & Beck 10-inch clutch.

The drum brakes were from Lockheed and measured 12 inches in diameter on the XK120. Burman recirculating ball steering is what controls the movements of the front wheels.

With the light bodywork and partially-wooden chassis, the XK120 in its original form weighed just 2,855 pounds.

1950 Jaguar XK 120 Alloy Roadster
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The high power output coupled with the low weight and aerodynamic body made the XK120 very quick. Indeed, on May 30th, 1949, on an empty stretch of highway between Ostende and Jabbeke, in Belgium, an XK120 timed by the RACB (Royal Automobile Club Of Belgium) achieved an average speed over two runs of 132.6 mph with a small aero screen in place of the stock windscreen. Two more mph were gathered when the passenger side was covered by an alloy tonneau.

The XK120 went on to record many world records for speed and distance during its lifetime, as well as being ultra-successful in sprint sports car racing, endurance racing, and rally racing even after Jaguar switched its focus to the purpose-built C-Type in 1951.

1950 Jaguar XK 120 Alloy Roadster Specifications

Configuration XK Straight 6
Location Front, longitudinally mounted
Construction cast iron block, aluminum head
Displacement 3.4-liters
Bore / Stroke 3.3 inches / 4.2 inches
Compression 8.0:1
Valvetrain 2 valves / cylinder, DOHC
Fuel feed 2 SU H6 Carburettors
Aspiration Naturally Aspirated
Power 162-horsepower at 5,000 rpm
Torque 193 pound-feet of torque at 2,500 rpm
Chassis steel body on steel box-type frame
Front suspension wishbones, torsion bars, Newton telescopic dampers, anti-roll bar
Rear suspension live axle, semi-elliptic leaf springs, Girling lever arm dampers
Steering Burman recirculating ball
Brakes Lockheed drums, all-round
Gearbox Moss 4 speed Manual
Drive Rear wheel drive

1950 Jaguar XK 120 Alloy Roadster Pricing

1950 Jaguar XK 120 Alloy Roadster
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The XK120 Alloy Roadster has become a collector’s favorite over the years. The design has a lot to do with the demand and the rising prices, but there’s also the performance of the car and its heritage and importance in the history of the Jaguar brand.

As such, you won’t find one of the original 242 cars built in Holbrook Lane, Coventry, for less than $200,000. The average price for one is, though, a bit higher at around $340,000 with storied examples selling for almost $500,000. It’s worth noting that only 184 of the 242 XK120s are left-hand drive and, originally, not many reached the U.S. shores as exports only began in 1949.

1950 Jaguar XK 120 Alloy Roadster Competition

Ferrari 340 America Barchetta

1951 Ferrari 340 America Barchetta by Touring
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The Ferrari 340 America was the first model in the America series conceived with export in mind, used as a means to increase Ferrari’s footprint in the United States. The 340 featured a brand-new Lampredi V-12 which made its way to Formula 1.

The heavy Lampredi unit produced around 220-horsepower in its detuned endurance-focused version and it propelled the car forward to a top speed of 150 mph. The 340 America, of which only 23 were built in a number of body styles by multiple coachbuilders, weighed just 1,980. As with any limited-run early Ferrari, the 340 America is crazy expensive and, although it played in a bit of a different league compared to the Jaguar, they raced at around the same time in history.

Read our full review on the 1951 Ferrari 340 America Barchetta

Allard J2

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The J2 was another car that raced at Le Mans in the early-’50s. Only 90 units were built until 1951 and, originally, the car came fitted with a 3.6-liter Ford flathead V-8 which was producing under 90-horsepower. But the car’s engine bay was roomy enough to fit a variety of different engines, so all of the cars that were shipped to the U.S. market arrived without an engine installed. Clients then put in Oldsmobile, Chrysler or even Cadillac V-8 engines inside their Allards.

For instance, most of the J2s that raced at Le Mans in 1950 and 1951 ran with a 5.4-liter Cadillac V-8 and ran in the Sports 8.0-liter class. One of these cars came in 3rd overall in the 1950 event. Allard would later introduce the J2X with a redesigned front suspension arrangement which enabled the possibility to move the engine 7 inches forward to improve weight distribution. It came with a 170-horsepower engine which made a top speed of 112 mph possible.

Final Thoughts

1950 Jaguar XK 120 Alloy Roadster
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The Jaguar XK120 Alloy Roadster is a legend in Jaguar’s storied history. It scored innumerable victories even before Jaguar established a dedicated racing department and was the fastest production road car at the time of its release.

What set it apart, beyond the +120-mph top speed, was the gorgeous styling that inspired many other automobiles of the era.

  • Leave it
    • Very few Alloy-body Roadsters left
    • Expensive to buy

Further reading

1951 - 1953 Jaguar C-Type High Resolution Exterior
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Read our full review on the 1951 - 1953 Jaguar C-Type.

1954 - 1957 Jaguar D-Type
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Read our full review on the 1954 - 1957 Jaguar D-Type.

Source: RM Sothebys

Michael Fira
Michael Fira
Associate Editor and Motorsport Expert - fira@topspeed.com
Mihai Fira started out writing about long-distance racing like the famous 24 Hours of Le Mans. As the years went by, his area of interest grew wider and wider and he ever branched beyond the usual confines of an automotive writer. However, his heart is still close to anything car-related and he's most at home retelling the story of some long-since-forgotten moment from the history of auto racing. He'll also take time to explain why the cars of the '60s and '70s are more fascinating than anything on the road today.  Read full bio
About the author

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