Triumph Stag - Engineering

Engineering

The initial Stag design was based around the saloon's 2.5-litre engine, and Harry Webster intended the Stag, large saloons and estate cars to use a new Triumph-designed overhead cam (OHC) 2.5-litre fuel injected (PI) V8. Under the direction of Harry Webster's successor, Spen King in 1968, the new Triumph OHC 2.5 PI V8 was enlarged to 2997 cc (3.0 litres) to increase torque. To meet emission standards in the USA, a key target market, the troublesome mechanical fuel injection was dropped in favour of dual Zenith-Stromberg 175 CDSE carburettors. A key aim of Triumph's engineering strategy at the time was to create a family of engines of different size around a common crankshaft. This would enable the production of power plants of capacity between 1.5 and 4 litres, sharing many parts, and hence offering economies of manufacturing scale and of mechanic training. A number of iterations of this design went into production, notably a slant-four cylinder engine used in the later Triumph Dolomite and Triumph TR7, and a V4 variant manufactured by StanPart that was initially used in the Saab 99. The Stag's V8 was the first of these engines into production. Sometimes described as two four-cylinder engines Siamesed together, it is more correct to say that the later four-cylinder versions were half a Stag engine (the left half in the case of the Triumph engines and the rear half in the case of the Saab). It has sometimes been alleged that Triumph were instructed to use the proven all-aluminium Rover V8, originally designed by Buick, but claimed that it would not fit. Although there was a factory attempt by Triumph to fit a Rover engine, which was pronounced unsuccessful, the decision to go with the Triumph V8 was probably driven more by the wider engineering strategy and by the fact that the Buick's different weight and torque characteristics would have entailed substantial re-engineering of the Stag when it was almost ready to go on sale. Furthermore Rover, also owned by British Leyland, could not necessarily have supplied the numbers of V8 engines to match the anticipated production of the Stag anyway.

As in the Triumph 2000 model line, monocoque construction was employed, as was fully independent suspension – MacPherson struts in front, semi-trailing arms at the rear. Braking was by front disc and rear drum brakes, while steering was power-assisted rack and pinion.