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 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.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.
Engine & Transmission
Type S-4 OHV 8 valves total 2 valves per cylinder Bore × stroke 69.00mm × 100.00mm 2.72 in × 3.94 in Bore/Stroke ratio 0.69 Displacement 1496 cc (91.292 cu in) Unitary capacity 374 cc/cylinder Compression ratio 5.80:1 Fuel system 1 SU carb Aspiration Normal Compressor type N/A Intercooler None Catalytic Converter N Max. output 50.7 PS (50.0 bhp) (37.3 kW) @4250 rpm Coolant Water Specific output 33.4 bhp/litre 0.55 bhp/cu in performance Note: A value of -1 means that the car cannot attain that speed. 0-50mph (80 km/h) 19.00s 0-100mph -1.00s 0-Quarter-mile 25.00s Top speed 116 km/h Power-to-weight 37.88 bhp/ton chassis Engine location Front Engine alignment Longitudinal Suspension Front LA.SE. Rear LA.SE. Transmission 4M Drive RWD