Jaguar XK120 History
Article by Mark Trotta
Originally designed to showcase Jaguar's new twin-cam motor, the XK120 sports car was an immediate hit when it debuted in October of 1948. Strong public reaction convinced company founder William Lyons to put the streamlined roadster into production.
Initially produced as roadster only, the XK120 featured a split windscreen, cut-down doors, canvas roof and detachable side screens. When removed, the roof and side screens were stored behind the seats.
There were no exterior door handles; entry was made via a pull-cord. When the top and side screens were on, the pull-cords were accessed through a flap in the screens.
With intentions of making just a few hundred cars, the first run of Jaguar XK120's were aluminum-bodied, but overwhelming demand quickly prompted the switch to pressed steel.
In May 1950, the first predominantly steel bodied XK120 rolled off the production line. Only the hood, doors and trunk remained aluminium.
Chassis and Suspension
Borrowed from Jaguar's big sedans, the modified frame was actually sturdier than needed, making the XK heavier than other sports cars of the day.
Riding on 16" x 6" tires, the XK chassis featured torsion-bar independent front suspension with ball joints, and semi-elliptic leaf springs in the rear. The car was narrow, tracking 51 inches at the front and 50 inches in the rear.
XK120 Roadster Dimensions
- Wheelbase: 102 inches
- Total Length: 176 inches
- Vehicle Weight: About 2950 pounds
XK120 Steering and Brakes
Though not as responsive as rack and pinion (as would come on the XK140), drivers of the day considered the recirculating-ball steering system to be light and smooth. All-wheel drum brakes were marginal at best.
Described by many as "jewel-like", the dual overhead cam (DOHC) motor was built under direction of William Heynes. The under-square 3.4 litre size was derived by an 83mm bore by 106mm stroke.
Underneath the polished valve covers were a pair of chain-driven camshafts, which sat atop an aluminum-alloy head. Hemispherical-shaped combustion chambers allowed use of larger valves. Induction was supplied by a pair of SU H6 side-draft carburetors.
When fitted with domed cast-aluminum pistons, engine compression ratio was 8.0:1. In this configuration, peak output was 160 horsepower with 195 lb/ft of torque. For some markets, the compression ratio was dropped to 7.0:1. This was due to the fact that only 70 octane fuel was available in several post WW2 countries.
The only transmission offered was a four-speed manual gearbox.
Able to reach 120 miles-per-hour, the Jaguar XK120 was the fastest production car of its day. The dual-cam motor was a marvel of engineering, and would power Jaguars for another two decades, including the 1961-1969 Jaguar XKE.
XK120 Fixed-Head Coupe
A closed steel top version of the XK120 joined the roadster in 1951. Deluxe accoutrements of the fixed-head coupe (FHC) included wood-veneer dashboard and door tops, and leather seats. The nearly vertical steering column was telescopically adjustable to suit shorter or taller drivers.
XK120 Drophead Coupe
A second roadster model, the drophead coupe, was offered in 1953, and featured a padded, folding top with roll-up side windows. Both the FHC and DHC models had lockable doors.
Orders for the Jaguar XK came from every continent, with nearly 60% of them being exported to America. This went a long way to help England, still recovering from five terrible years of war.
XK120 Influence On American Sports Cars
In the early fifties, when GM engineers started work on their upcoming Corvette sports car, an XK120 roadster was rolled into the design studio and studied. The long nose-short tail was copied, as well as its 102-inch wheelbase.
After Ford Motor Company heard about their rival's eminent new sports car, they too used the Jaguar's dimensions for their forth-coming two-seat Thunderbird.
From 1948 through 1954, over 12,000 XK120's were produced.
- Roadsters: 7612 (1175 right-hand drive and 6437 left-hand drive)*
- Fixed Head Coupes: 2678 (194 right-hand drive and 2484 left-hand drive)
- Drop Head Coupes: 1765 (294 right-hand drive and 1471 left-hand drive)*
* Various reports show figures +/- 10 or 20 units.
In an effort to be more competitive with rivals BMW and Mercedes-Benz, Jaguar replaced the XK120 with the XK140 in 1955, then a final rendition as the XK150 in 1957.
Jaguar XK120 In Competition
A race-prepared XK120 finished first in class at the 1951 Le Mans race, Jaguar's first win there since 1935.
One of the more impressive of its many records was the grueling "Seven Days and Seven Nights" competition of 1952. A fixed-head XK120, near the end of the event, broke a spring, and was still able to finish and set a new record with an average speed of 100.31 mph.
Jaguar Wins NASCAR Race
In June of 1954, NASCAR staged their first road-course race. The event, held at Linden Airport, New Jersey, was open to both American stock cars and foreign sports cars.
Driver Al Keller drove his #4 Jaguar XK120 to victory, becoming the first and only driver in the history of NASCAR's premier series to win a race in a foreign-made car.
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