Jaguar XK-120 (1948-1954)
Article by Mark Trotta
Originally designed to showcase Jaguar's new twin-cam motor, the XK120 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, with the Jaguar XK120 becoming a huge influence in the next few decades of sports car history.
Described by many as "jewel-like", the XK motor was built under direction of William Heynes. The under-square 3.4 litre size was derived by an 83 mm bore by 106 mm stroke. Underneath the polished covers were a pair of chain-driven camshafts, which sat atop an aluminum-alloy head.
Hemispherical combustion chambers allowed use of larger valves, with domed cast-aluminum pistons boosting the compression ratio up to 8.0:1. With a pair of sidedraft carburetors, output was 160-horsepower and an equally impressive 195 lb/ft of torque. Able to reach 120 miles-per-hour, the Jaguar XK120 was the fastest production car of its day.
The XK dual-cam motor was a marvel of engineering, and would power Jaguars for another two decades, including the 1961-1969 Jaguar XKE.
With intentions of making just a few hundred cars, the first run of XK120's were aluminum-bodied, but overwhelming demand quickly prompted the switch to pressed steel.
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 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. Though not as responsive as rack and pinion (as would come on the XK140), most drivers felt the recirculating-ball steering system felt light and smooth. All-wheel drum brakes were marginal at best.
A closed version of the XK120 joined the roadster in 1951. Deluxe accoutrements in the fixed-head coupe included wood-veneer dashboard and door tops, with both models getting leather seats. The nearly vertical steering column was telescopically adjustable to suit shorter or taller drivers. A second roadster model, the drophead coupe, was offered in 1953, and featured a padded, folding top with roll-up side windows.
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.
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.
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. Over 12,000 XK120's were built in the seven years produced.
In an effort to compete with rivals BMW and Mercedes-Benz, Jaguar replaced the XK120 with the XK140 in 1955, then a final rendition as the XK150 in 1957.
Read: Sports Car History