Initially installed with the 2,054cc six-cylinder Standard 16 engine, in October 1933 this power unit was enlarged to 2,664cc.
The SS90 two-seat sports appeared in March 1935 when the new chief engineer William Heynes and consultant Harry Weslake designed an ohv head for the 2.7-litre Standard engine, which with twin carburettors boosted power from 84 to 104bhp.
In 1936 the new Jaguar SS100 sports two-seater was introduced with this power unit and in 1938 the model was offered with a further developed 3 1/2-litre engine which produced 125bhp, at last making the SS100 truly capable of just over 100mph. Of the 314 examples built, many had successes in rallying, with class wins in the 1937 and 1938 RAC Rallies, and a Coupe des Alpes win in the 1948 Alpine by Ian Appleyard in the only post war example. To many people the archetypal sports car of the
late 1930s is summed up to perfection by the SS100. Its lengthy bonnet, slab tank tail, louvered bonnet, folding screen, flowing wings, sculpted doors, and fine performance all added up to an amazing car for £395 with 2.5-litres, and only £445 3.5-litre form. With excellent brakes, steering and gearbox, the 3.5-litre propelled the SS100 to 60mph in under 11 seconds. With this formula the model should have been a vast success, but a combination of four factors including the perceived relative youth of the company against more established marques, the intervention of the war, the price – which many believed was too low, since the car attracted a rather flashy image, and lastly SS were still buying in engines rather than producing the whole car themselves. Just 198 2.5-litre and 116 3.5-litre examples were sold, but in later years these rare cars have come to be appreciated for the sensational features the model has, indeed the looks of the SS100 have been much copied by various replica car manufacturers who have based their cars on more modern Jaguar components.