The Jaguar XK120 is a sports car manufactured by Jaguar between 1948 and 1954. It was Jaguar's first sports car since SS 100 production ended in 1939.

History

The XK120 was launched in open two-seater or (US) roadster form at the 1948 London Motor Show as a testbed and show car for the new Jaguar XK engine designed by Jaguar Chief Engineer William Heynes. The display car was the first prototype, chassis number 660001. It looked almost identical to the production cars except that the straight outer pillars of its windscreen were curved on the production version. The sports car caused a sensation, which persuaded Jaguar founder and Chairman William Lyons to put it into production. Beginning in 1948, the first 242 cars were wood-framed open 2-seater bodies with aluminium panels. Production switched to the 1cwt or 112 lb heavier all-steel in early 1950. The "120" in the name referred to the aluminium car's 120 mph top speed (faster with the windscreen removed), which made it the world's fastest production car at the time of its launch. In 1949 the first production car, chassis number 670003, was delivered to Clark Gable. The XK120 was ultimately available in three body styles, all two-seaters and available either as Left (LHD) or Right Hand Drive (RHD): an open 2-seater described in the US market as a roadster (OTS); a fixed head coupé (FHC) from 1951; and a drophead coupé (DHC) from 1953. Certain Special Equipment roadster and fixed head coupe cars were produced were sold between 1948 and 1949 as an early production build for enthusiasts, denoted by an 'S' preceding the chassis number. A version with a smaller engine (2-litre 4-cylinder) designated the XK100 and intended for the UK market was cancelled prior to production. On 30 May 1949, on the empty Ostend-Jabbeke motorway in Belgium, a prototype XK120 timed by the officials of the Royal Automobile Club of Belgium achieved an average of runs in opposing directions of 132.6 mph with the windscreen replaced by just one small aero screen and a catalogued alternative top gear ratio, and 135 mph with a passenger-side tonneau cover in place. In 1950 and 1951, at Autodrome de Linas-Montlhéry, a banked oval track in France, open XK120s averaged over 100 mph for 24 hours and over 130 mph for an hour. In 1952 a fixed-head coupé took numerous world records for speed and distance when it averaged 100 mph for a week. XK120s were also highly successful in racing and rallying. In 2016, Bonhams sold a matching numbers left-hand-drive alloy-bodied roadster – one of only 184 – for $396,000 (£302,566). This marks the highest price achieved for an XK120 at auction thus far.

Construction

The first 242 production XK120s, hand-built with aluminium bodies on ash framing, were constructed between late 1948 and early 1950. To meet demand, and beginning with the 1950 model year, all subsequent XK120s were mass-produced with pressed-steel bodies. Aluminium doors, bonnet, and boot lid were retained. The DHC and FHC versions, more luxuriously appointed than the constantly exposed open cars, had wind-up windows and wood veneers on the dashboard and interior door caps. The XK120’s steel chassis was mostly copied from the Jaguar Mark V, using many of the same parts. The dual overhead-cam 3.4 L straight-6 XK engine was highly advanced for a mass-produced unit of the time, featuring a high-temperature, high-strength aluminum alloy cylinder head, hemispherical combustion chambers, inclined valves, and twin side-draft SU carburetors. Using 80 octane fuel a standard 8:1 compression ratio developed 160 bhp. Most of the early cars were exported; a 7:1 low-compression version, with commensurately reduced performance, was reserved for the UK market, where the post-war austerity measures then in force restricted buyers to 70 octane "Pool petrol". The Jaguar factory's access to 80 octane fuel allowed it to provide cars with the higher compression ratio to the press, enabling journalists to test the model's optimum performance in Belgium, on a long, straight stretch of road between Jabbeke and Ostend. The XK engine's basic design by William Heynes, later modified into 3.8 and 4.2-litre versions, survived until 1992. All XK120s had independent Heynes designed torsion bar front suspension, semi-elliptic leaf springs at the rear, recirculating ball steering, telescopically adjustable steering column, and all-round 12-inch drum brakes which were prone to fade. Some cars were fitted with Alfin (ALuminium FINned) brake drums to help overcome the fade. The open two-seater provided little weather protection. Its lightweight folding canvas top and detachable sidescreens stowed out of sight behind the seats. The doors had no external handles; they were opened by an interior pull-cord, accessed through a flap in the sidescreens when the weather equipment was in place. The windscreen could be removed for aeroscreens to be fitted. The drophead coupé (DHC) had a padded, lined canvas top, which folded onto the rear deck behind the seats when retracted, and roll-up windows with opening quarter lights. The flat glass two-piece windscreen was set in a steel frame that was integrated with the body and painted the same colour. Dashboards and door-caps in both the DHC and the closed coupé (FHC) were wood-veneered, whereas the open cars were leather-trimmed. All models had removable spats ("fender skirts" in America) covering the rear wheel arches, which enhanced the streamlined look. On cars fitted with optional centre-lock wire wheels (available from 1951), the spats were omitted as they gave insufficient clearance for the chromed, two-eared Rudge-Whitworth knockoff hubs. Chromium-plated wire wheels were optional from 1953. Factory standard 6.00 × 16-inch cross ply tyres were fitted on 16 × 5K solid wheels (Pre–1951), with 185VR16 Pirelli Cinturato radial tyres available as a later option. In addition to wire wheels, upgrades on the Special Equipment (SE) version (called the M version for Modified in the United States) included increased power, stiffer suspension and dual exhaust system.

Engine specifications

Performance

The Motor magazine road-tested an XK120 in November 1949. This pre-production car, chassis number 660001, road-registered as HKV 455, was the first prototype built. It was also the 1948 London Motor Show display model, and had been driven by Prince Bira in the 1949 Silverstone Production Car Race. When tested, it had the 8:1 compression ratio, was fitted with an aerodynamic undertray, and ran with hood and sidescreens in place. The magazine reported a top speed of 124.6 mph, acceleration from 0–60 mph in 10.0 seconds and fuel consumption of 19.8 mpgimp. The car as tested cost £1263 including taxes. The XK120 M for US market accelerated from 0–60 mph in 8.7 seconds, top speed was 132 mph by the speedometer, but actual top speed was about 120 mph.

Racing and rallying

XK120s were active in racing and rallying:

1949

1950

In 1950 Jaguar allocated six alloy-bodied XK120s to drivers Leslie Johnson, Peter Walker, Nick Haines, Clemente Biondetti, Ian Appleyard and Tommy Wisdom.

1951

1952

1954

High-speed runs and records

1949

1950

1951

1952

1953

Production

XK100 development

A 2-litre four-cylinder version of the twin cam XK engine was to have powered an XK100 variant of the XK120 for the UK market. Details of the model were included in an "Advance Particulars" brochure for the XK but Jaguar's managers were dissatisfied with the engine and the project was cancelled prior to production.