Jaguar XK120

The XK120 at a glance

From a show car to a production hit

During the war, Jaguar's chief engineer William Heynes and his team worked on a new family of engines. Among them was a 3.4-litre six with two overhead camshafts, a layout then found mainly in racing cars. To show off the engine, company chairman William Lyons had a low, flowing two-seat body built on a shortened saloon chassis. The car was meant as a limited-edition halo model of perhaps 200 units.

At the 1948 London Motor Show, the reaction of the public and dealers changed the plan. Orders far exceeded what the coachbuilt car could deliver. The first 242 cars, built from late 1948 to early 1950, had hand-formed aluminium panels over an ash frame. From the 1950 model year Jaguar switched to pressed-steel bodies, about 51 kg heavier, but kept aluminium doors, bonnet and boot lid. Only then did proper series production begin.

The history of the company behind it is told in Jaguar's history and in our story of how Jaguar was born.

Body styles and production numbers

The open two-seater came first and remained the best seller. A fixed-head coupé with a closed steel roof followed in 1951, and a drophead coupé with wind-up windows and a lined hood arrived in 1953.

The left-hand-drive share shows how much the car depended on exports. American buyers took a large part of the output, and the XK120 helped establish Jaguar as a premium sports brand in the US.

The XK engine and running gear

The XK straight-six measured 3,442 cc, with a bore and stroke of 83 × 106 mm. In standard form, with 8:1 compression on 80-octane fuel, it made 119 kW (160 bhp) at 5,000 rpm. UK cars initially ran 7:1 compression because of low-grade post-war petrol. From mid-1951 the Special Equipment (SE) version, sold as the "M" in the US, added higher-lift camshafts and twin exhausts for 134 kW (180 bhp) at 5,300 rpm. From 1953, a C-Type cylinder head with larger SU carburettors gave 157 kW (210 bhp) at 5,750 rpm.

The engine proved so sound that Jaguar used developments of it until 1992, in models from the E-Type to the XJ6. Many racing classes of the 1950s were won with it.

The chassis had independent front suspension with torsion bars, a live rear axle on semi-elliptic leaf springs and recirculating-ball steering. The drum brakes were the car's weak point: they faded quickly when driven hard, and some cars received finned Alfin drums to cope.

Performance and speed records

In its November 1949 road test, The Motor magazine recorded a top speed of 124.6 mph (200.5 km/h) and 0–60 mph in 10.0 seconds. Fuel consumption was 19.8 mpg (about 14.3 l/100 km). A US-market SE was timed from 0 to 60 mph in 8.7 seconds. That made the XK120 the fastest standard production car on sale at its launch.

Jaguar backed its claims with public record runs:

• 30 May 1949, Jabbeke (Belgium): a prototype averaged 132.6 mph (213.4 km/h) over the flying mile, with test driver Ron Sutton at the wheel.
• 1950–1951, Montlhéry (France): open cars averaged more than 100 mph (161 km/h) for 24 hours and over 130 mph (209 km/h) for one hour.
• 1952, Montlhéry: a fixed-head coupé averaged 100.31 mph (161.4 km/h) for seven days and nights, covering 16,851 miles (27,120 km).
• 21 October 1953, Jabbeke: Norman Dewis reached an average of 172.4 mph (277.5 km/h) in a modified car.

For a sense of scale, the 1cars fastest-cars ranking shows how far top speeds have climbed since: today's leaders are more than twice as fast.

Racing and rally results

The XK120 won its first race at Silverstone in 1949 with Leslie Johnson. In the 1950 Le Mans 24 Hours, three modified cars started. Johnson's car ran as high as second before clutch failure in the 21st hour, while the others finished 12th and 15th. Jaguar then built a dedicated racer, the XK120C or C-Type, which won Le Mans in 1951.

In rallying, Ian Appleyard and his wife Pat won the Alpine Rally twice in their white roadster NUB 120. On their third start they finished without a penalty point and took the first Coupe d'Or, and they also won the Tulip Rally. Stirling Moss led a 1–2–3 finish in the Tourist Trophy, and Johnson took fifth in the 1950 Mille Miglia. On 13 June 1954 Al Keller won the first NASCAR Grand National road race in an XK120 coupé.

Rivals and its place in sports-car history

The XK120 rivalled far more expensive cars on speed. The Mercedes-Benz 300 SL of 1954 was faster but cost much more and was built in smaller numbers. Compared with the 300 SL, the standard XK120 had 39 kW less power, yet it reached buyers six years earlier. Aston Martin's DB2 offered similar pace with a more exclusive image.

Specialists later used Jaguar engines in their own racers, such as the Lister Jaguar Costin roadster. Other cars of the period are collected in the 1cars classics of the 1950s, and later Jaguar sports cars appear among the best sports cars.

Buying a Jaguar XK120 today

Early alloy roadsters are the rarest and most valuable, followed by steel roadsters with SE specification. Fixed-head and drophead coupés usually cost less, and they suit buyers who want a classic for touring rather than for shows. Matching chassis and engine numbers, documented history and a Jaguar Heritage certificate matter more than shine.

On a test drive, check for brake pull and fade, oil leaks from the twin-cam engine, and corrosion in the steel body and the chassis outriggers. Many cars have been upgraded with disc brakes, five-speed gearboxes and better cooling; these changes make touring easier but can lower the value for purist buyers. All Jaguar models in our database, old and new, are in the Jaguar catalogue.