This 2-door sports car used an updated version of the overhead camshaft, crossflow engine, used in the 1928 Morris Minor and Wolseley 10 and previously fitted in the MG M-type Midget of 1929 to 1932, driving the rear wheels through a four-speed non-synchromesh gearbox.

The chassis was from the D-Type with suspension by half-elliptic springs and Hartford friction shock-absorbers all round with rigid front and rear axles.

Most cars were open two-seaters, but a closed salonette version of the J1 was also made, and some chassis were supplied to external coachbuilders.

The J3 was a racing version with the engine capacity reduced to 746 cc by shortening the stroke from 83 to 73 mm[1] and fitted with a Powerplus supercharger.

[3] The J4 was a pure racing version with lightweight body work and the J3 engine, but using more boost from the supercharger to obtain 72 bhp (54 kW).