Alvis went further up-market in 1935 with the 3½ Litre (SA 25.63). This used a new six-cylinder engine of 82 x 110 mm, 3571 cc. The separate iron block and aluminium crankcase were retained, but the crankshaft was more robust and carried in seven main bearings. Wheelbase was extended to 10'7"; otherwise design and layout followed the SC Speed 20, including use of the incomparable all-synchromesh gearbox and the independent front suspension. Bhp rose to 102 with great silence and refinement. This chassis was not offered with standard bodywork, and all of the cars made differ to some degree in this respect. Saloons, dropheads, tourers and at least one sedança are to be found. Top speed of this heavy car was over 90 mph. Only about 60 were produced.

1935 3½ Litre Charlesworth saloon

In 1936 the Speed 25 (SB 25.63) was introduced, virtually the same chassis and engine but with the wheelbase shortened by 3" to 10'4", i.e. the same as the Speed 20 which it superseded, and with standardised, series-built coachwork.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.

1935 3½ Litre Gurney Nutting saloon

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..

The 4.3 litre (SA, SB & SC 31.48) came out in 1937, following on from the 3½ Litre. Two chassis lengths were offered, with wheelbases of 10'7" (same as the 3½ Litre) and 10'4" (same as the Speed 25).

1937 SB Speed 25 Charlesworth saloon

The engine was similar to the Speed 25, but with the bore increased to 92 mm for 4387 cc and 137 bhp. This unit was very powerful, but had lost some of the smoothness of the Speed 25. Centralised chassis lubrication was retained, but additions included the DWS built-in hydraulic jacking system and a Clayton Dewandré vacuum brake servo. This last named was a welcome addition, nowadays the mind boggles at the thought of stopping a laden weight of over two tons from 100 mph with cable operated drum brakes powered by foot pressure only!

1938 SC Speed 25 Charlesworth DHC

A variety of different coachwork adorned this superb chassis: Charlesworth did the standard saloon and drophead coupé, but van den Plas made a pillarless saloon and some dropheads. Offord also made a series of dropheads. Many other coachbuilders made one-offs. One of the most sought after Alvises is the van den Plas tourer on the short chassis. Only twelve of these were made, and eleven survive today - in fact all the bodies survive, one having been mounted on another chassis after an accident. There are also some replicas - caveat emptor! Maximum speed was 105 mph in this form, and under test 0 - 60 mph was achieved in 11.3 seconds.

1937 4.3 Litre short chassis van den Plas tourer

Neat and purposeful, the short chassis 4.3 van den Plas tourer was one of the greatest achievements of the pre-war British motor industry. Even the vast Charlesworth saloon 4.3 Litre would exceed 100. For many, the 3½ Litre/Speed 25/4.3 Litre cars represent the peak of Alvis' car-building achievements. Total 4.3 production numbered nearly 200 examples. It is fascinating to speculate on what direction development might have taken had not war intervened, or if post-war conditions had favoured re-introduction of some of these models.

1937 4.3 Litre Charlesworth saloon

1939 4.3 Litre short chassis van den Plas tourer