Swallow Sidecars had announced its SS1 car at the 1931 Olympia Motor Show. This was based on the Standard 16 Ensign car, but it had its own chassis from Rubery Owen, even though it used Standard mechanics and 2,054cc and 2,552cc six cylinder engines. In 1935 SS Cars produced a new chassis, and engines were upgraded to 2,143cc and 2,664cc in line with Standard production changes. A new SS II with 1,343cc and later 1,608cc engines was introduced. SS also produced a 3,485cc six cylinder engine from 1937 for its own 3.5-litre cars; this was not given to Standard Cars. From 1935 SS Cars were given Standard engines fitted with swallow's own Weslake-designed overhead valve cylinder head. SS-swallow cars were given steel saloon bodies from 1938 and were sold as 1.5-litre (1,608cc and then 1,776cc), 2.5-litre (2,664cc) and 3.5-litre (3,485cc). The smaller car was built on a 112.5-inch wheelbase and measured 173-inches long, whereas the bigger cars had a wheelbase of 120 inches (after 1937), length of 186 inches and were wider by half-an-inch at 66 inches.