Late in 1927, Alvis introduced their first six-cylinder car, the 14.75 hp (TA, later TB 14.75). It was designed to be smoother and more silent than the 12/50, and changes to the chassis were minimal, consisting largely of making the front cross-member removable. The same range of coachwork styles was available as on the four-cylinder car. Output of the 63 x 100 mm, 1870 cc engine was estimated at about 60-62 bhp, it featured a four bearing crankshaft, with a Lanchester type friction balancer at the front. Lowered gearing and the extra weight ensured that it was no faster than the four-cylinder car, but quieter and more flexible. This first six established the standard Alvis practice of taking the camshaft drive from the rear of the engine, using a chain.

1933 Silver Eagle 20 Mayfair All-Weather

The reason for this was that in-line sixes tend to suffer from torsional oscillations of the crankshaft, and positioning the drive at or near the node at the driving end minimises the whip effect oscillations cause on the timing drive. Subsequent exceptions to this rule included the four-cylinder 12/70, its derivative the TA 14, and the Silver Crest. For the first time the induction and exhaust systems were moved to the nearside, and the sparking plugs to the offside. A bronze water pump appeared in place of the simple thermo-syphon cooling system of the older designs, and the oil pump was fitted internally rather than externally at the bottom of the sump. In late 1929 the engine was bored out to 67.5 mm, 2148 cc and the name "Silver Eagle" applied (TA and SA 16.95). Bhp went up to 72.

1933 Silver Eagle 20 engine

This became one of the best known and loved of all Alvis models, marketed in many forms until 1932 (SB, SC, SD, SE, TA, TB and TC 16.95). Chassis lengths of 9'4½" and 9'10½" were used; some were lower and had a wider track. The name was revived later in the 1930s for a quite different car. A marked improvement in performance accompanied the fitting of the bigger engine, and a sports version with three carburettors and higher gearing was offered, capable of 85 mph. Late in 1930 a yet larger engine, 73x100 mm, 2511 cc, 19.82 hp was offered, developing 75 bhp. Most of these chassis were fitted with saloon or limousine coachwork by the better coachbuilders on three different wheelbases (9'10½", 10'3" and 11' as TA, TB and TC 19.82). These cars retained the vintage style chassis frame, using the engine and gearbox as braces, and separate, right hand gate change gearbox.

1932 Silver Eagle 20 Mayfair Carriage Co. 6-light saloon

An improved braking system, again of Alvis patented design, with larger drums and a more sophisticated mechanism was fitted.. For the first time a centralised chassis lubrication system was used, substituting a pedal operated oil pump and miles of copper tubing for the multiplicity of grease nipples on earlier cars. Similar systems were fitted on the more expensive Alvises up to the war. Likewise the later Silver Eagles, and the last 12/60s, saw the first appearance of the Alvis "jelly mould" hub for the knock-on wire wheels. This design used corrugations on the hub mating with similar corrugations on the wheel centre in place of the more usual splines. Although it was an excellent system, so far as is known it was not used by any other maker, and it remained a distinctive feature of 30s Alvises. The Silver Eagle introduced the dual (magneto & coil) ignition, and the triple SU carburettors fitted to many Alvis models up to the late thirties.

1932 Silver Eagle 20 Carbodies

Not many 20 hp Silver Eagles were made (they were very expensive cars) and very few survive. Its significance is that it was the last Vintage high chassis design using the flange mounting engine to stiffen the chassis, with a separate right-hand gate change gearbox. It also retained the vintage style silver face, bevelled glass instruments. Yet it had the revised brakes, central lubrication system and hubs of the subsequent cars. The SA Speed 20 which followed is definitely a post-Vintage design. Approximately 1,600 of the various Silver Eagle models were made. This figure does not include the 1935-6 cars which were also called "Silver Eagle".