Standard-Triumph fitted a 1,596 cc version of their traditional straight-6 derived from the engine used in the Standard Vanguard Six, but with a smaller bore diameter of 66.75 mm (2.6 in), compared with the 74.7 mm (2.9 in) bore on the Vanguard, equipped with twin Solex B32PIH semi-downdraught carburettor. These were soon replaced by B321H carburettors, as the accelerator pumps proved a problem. The curious observer will notice a "seam" on the cylinder block between the third & fourth cylinders revealing the humble design beginnings from the 803 cc Standard 8 block of 1953.
The gearbox was strengthened and offered with optional overdrive. Front disc brakes were standard as were larger rear brake drums, and the Herald fuel tank was enlarged, retaining the handy reserve tap of the smaller Herald. The front suspension featured uprated springs to cope with the extra weight of the new engine, but the rear suspension was basically standard Heralda swing-axle transverse-leaf system which quickly proved inadequate for the relatively powerful Vitesse. The chassis was basically the same as the Herald, and the Vitesse was available in convertible and saloon forms; a coupé never got beyond the prototype stage. A handful of Vitesse estates also were assembled to special order at Standard-Triumph's Service Depot at Park Royal in West London.
The interior was much improved over the Herald; wooden door cappings were added to match the wooden dashboard and the car featured better seats and door trims. Optional extras included a fabric, (Webasto), sunroof on saloon models. Exterior trim was also improved with stainless steel side trim and anodised alloy bumper cappings (replacing the white rubber Herald design). The prospective buyer of a classic Vitesse will do well to check that the side flashes are full-length and continue around the radiator grille.
A year or so after the car's launch, the Vitesse received its first facelift; the dashboard was revised with a full range of instruments instead of the large single dial from the Herald, and from September 1965, at commission number HB27986, the twin Solex carburettors were replaced by twin Zenith Stromberg CD 150 carburettors. Power output increased from the original 70 bhp (52 kW) at 5,000 rpm & torque of 92.5 lb·ft (125 N·m), enough to provide a useful performance boost and making the car a much more flexible performer. There was a claimed, although somewhat optimistic increase of 13-14 bhp, and the motoring magazine tested top speed rose to 91 mph (146 km/h), with the 0-80 mph (0-128 km/h) time decreasing from 46.6 seconds to just 33.6 seconds.
The Vitesse 6 sold extremely well for Triumph, and was by some way the most popular Vitesse sold during the model's lifetime. The car was well liked for its performance and reasonable fuel economy, as well as the well appointed interior. The Vitesse had few rivals for the price: able to perform as well as many sports cars, (it was advertised by Triumph as "The Two Seater Beater"), but with room for a family. The convertible in particular was virtually unique in the marketplace and another genuine 4-seater sporting convertible would not reappear from a British manufacturer until the Triumph Stag several years further down the line.Source: Wikipedia.