The Armstong Siddeley engine may have seemed an odd choice, but more power was obtained by the fitting of a high-lift camshaft, three double-choke Weber carburetors and a free-flowing, six-branch exhaust system. The crankshaft was specially designed to withstand the increased power output (227bhp @ 5100rpm), the car being run on 100-RON petrol which could withstand the 9.5:1 compression ratio. The high power output and well-balanced J2R Chassis brought it success in four races in 1954 against cars such as Jaguar C-types, XK120s, Allards and Aston Martin DB3Ss, among many others.
The Sphinx made its debut at Goodwood on March 27th 1954 winning second place to a Jaguar XK120 C in one race. The team backing Sopwith’s Sphinx was called ‘Equipe Endeavour’, named after his father’s racing yachts, which competed in the America Cup Race in the 1930s. Although he was not an official sponsor of Tommy and the Sphinx because a race team was hardly Armstrong Siddeleys style, staff from the Armstrong Siddeley factory devoted their spare time to working on the car. Sopwith's head mechanic that helped him design and work on the Sphinx was John Crosthwaite. Interestingly, Crosthwaite went on to work with John Cooper of Cooper Cars after his season with the Sphinx, supervising production and final design of Equipe Endeavour's sports cars on Sopwith’s behalf.
After its BARC Goodwood debut, the Sphinx ran in many other races in 1954 including: National Castle Combe, British Empire Trophy, National Silverstone, Ibsley, National Davidstow, National Snetterton, Snetterton International and Goodwood International,. It took part in a total of 17 races in the 1954 season, placing first in four races, once at Silverstone, once at Snetterton, and twice at Davidstow. After the 1954 season, Sopwith decided to move on to other cars and retired the Sphinx.
