Beginning in March, 1936, a 4¼ Litre version of the car was offered as replacement for the 3½ Litre, in order to offset the increasing weight of coachwork and maintain the car’s sporting image in the face of stiff competition. The engine was bored to 3½ in (88.9 mm) for a total of 4.3 L (4257 cc/259 in³). From 1938 the MR and MX series cars featured Marles steering and an overdrive gearbox. The model was replaced in 1939 by the MkV.

1234 4¼ Litre cars were built, with Park Ward remaining the most popular coachbuilder. Many cars were bodied in steel rather than the previous, more expensive, aluminium over ash frame construction.

A Drophead 4¼ Litre was featured as James Bond’s car in the 1983 movie Never Say Never Again