In 1936 the Speed 25 (SB 25.63) was introduced, using virtually the same chassis and engine as the 3 1/2 Litre but with the wheelbase shortened by 3" to 10'4", i.e. the same as the Speed 20 which it supplanted, and with standardised, series-built coachwork. The most common body was a sports saloon by Charlesworth, who also did the drophead coupés, whilst Cross & Ellis provided the tourer. The Speed 25 was a popular model, and a few had one-off coachwork. Changes made during the run mainly concerned the bodywork, running boards disappearing from saloon and drophead for 1939 (SC 25.63), after 1937 the drophead had a larger boot.
The later tourers were made by Mulliner after Cross & Ellis went out of business. Mechanical changes included a new dual exhaust system with six silencers for 1939, coil ignition only instead of magneto/coil. Vacuum servo assistance for the brakes was added - already fitted on the 4.3 Litre. The Speed 25 was a very fast car, top speed being some 95 mph. Nearly 400 left the Holyhead Road works.
Source: Alvis Cars - Alvis Owner Club