These models are grouped together because they are based on almost identical 9'10½" wheelbase chassis and running gear, the frame being double-dropped as on the SA Speed 20. Beam axles were used, with the standard Alvis 14" drum brakes, cable operated. Coachwork consisted of saloons by Cross & Ellis and Holbrook, plus tourers and dropheads also by Cross & Ellis. The Firefly engine was of 69x100 mm, 1496 cc, essentially the Speed 20 less the front two cylinders with the bore reduced to bring the capacity under 1½ litres and give the familiar 11.9 hp RAC rating. The timing chain was still at the rear of the engine, and a single SU carburettor sufficed. A unit mounting gearbox externally identical to the SA Speed 20 but with different ratios was used on the earlier Fireflies (SA 11.9), whilst for 1933 and 1934 (SB 11.9) ENV preselector units were listed.

1932 Firefly SA Cross & Ellis Tourer

The Firefly continued the high quality four-cylinder tradition and has long been derided in some books for being overweight. The writer suspects that some of these opinions are carried on from one author to the next and that those repeating them have never actually driven the cars. In fact they go very well indeed by comparison with others of the era, and at least one Firefly is currently campaigned with great success at the tough, competitive end of historic rallying. The Firefly was a particularly good-looking, small (by Alvis standards) car, and deservedly enjoys an enthusiastic following. The lowered chassis and relatively wide track confer excellent roadholding qualities and the willing little engine is easy to work on.

1933 Firefly SB Cross & Ellis DHC

For 1935 the Firefly became the Firebird (SA 13.22). Mechanical modifications paralleled the Speed 20 SC: bore up to 73 mm, stroke to 110 mm for 1842 cc. The all-synchromesh gearbox was fitted, the chassis being modified to take it. The radiator shell was now slightly pointed instead of flat. Saloon bodywork was by Cross & Ellis, or to the same design by Holbrook, rather more commodious than the Firefly saloon despite no increase in track or wheelbase. The open bodies, tourer and drophead, also by Cross & Ellis, were much prettier than the saloon, and consequently more desirable now. Running gear was virtually unaltered from the Firefly, but chassis lubrication was by grease nipples grouped on the sides of the scuttle under the bonnet instead of by the "one shot" method of the larger cars.

1935 Firebird Holbrook saloon

The Sixteen (SF 16.95) came out in 1934, essentially a six cylinder Firefly.. It had a version of the early Speed 20/Crested Eagle engine with the familiar dimensions of 67.5 x 100 mm for 2148 cc, whilst the Silver Eagle name was revived for 1935 with the engine stroke increased to 110 mm for 2362 cc (SG 16.95). Both cars used the all-synchromesh gearbox.. A longer bonnet was fitted to accommodate the six-cylinder engine, resulting in improved proportions, especially on the saloon. The combination of the all-synchro box and the small six renders these cars particularly smooth, but little if any faster than their four cylinder sisters. A few cars had very pretty non-standard coachwork, otherwise Holbrook and Cross & Ellis provided the same range as for the Firebird.

1936 Silver Eagle SG Cross & Ellis DHC

These cars typify the "parts bin" approach to car manufacture adopted by Alvis in the 1930s, sharing many components with other models. The four cylinder cars must have cost nearly as much to make as the six cylinder versions, yet sold for much less. Nevertheless some economies of scale would have allowed unit costs to be reduced and overheads amortised over larger production numbers. Sales-wise, these were very successful models. The Firefly sold some 900 units, the Firebird 450, plus over 650 of their six-cylinder sisters.

1936 Silver Eagle SG Holbrook saloon