Triumph I6
The Triumph Six Cylinder or Triumph I6 engine is a cast-iron overhead valve straight-six engine produced by Standard Triumph. It is an evolution of the Standard Motor Company's inline-4 SC engine originally designed for the Standard Eight, with the addition of two cylinders and a larger displacement.
Introduced in their Standard Vanguard Six in 1960, it was used in a wide range of Triumph vehicles, including the Triumph TR5, TR250, and TR6.
Origin
Standard Six engine
The six cylinder engine was developed from the Standard SC four and was first used in 1960 in the Standard Vanguard Six, in which it had a bore and a stroke, giving a capacity of 1998 cc. It was also used in the Eight and the Ten.The engine was next used in the Triumph Vitesse, a sports saloon based on the Herald, in 1962. In this application, the engine had a bore, reducing displacement to 1596 cc. The Vitesse was given the two-litre engine with the 74.6 mm bore in 1966.
The Triumph 2000 replaced the Vanguard Six in 1963 when Leyland discontinued the Standard marque. The two-litre six was later used in the Spitfire-based GT6 coupé from 1966 to 1974.
Beginning in 1967, the engine was used in the Triumph TR5 and TR250 sports cars, replacing the Standard inline-four engine used in TRs from the TR2 to the TR4A. For this application, the stroke was increased to, giving 2498 cc. When equipped with the Lucas mechanical fuel injection system in the TR5, this new 2.5-litre version gave a claimed at 5500 rpm. When tested on dynamometers, 110 to 130bhp at the crankshaft is more usual, and may explain Triumph's decision to fit the TR7 with a 2-litre slant-four engine, whose power output and hence performance were in fact similar to those of the earlier and ostensibly more powerful engine. The TR250 was sold in the US with Stromberg carburettors to avoid the need for additional emissions control systems; this reduced the power to at 4500 rpm. The TR6, made from 1969 to 1975, used the TR5's engine, detuned to in 1973. with a 106 hp version of the TR250's engine in the United States.
The fuel-injected 2.5 litre engine became available in the 2000 unit body as the 2.5 PI in 1968; this was supplanted by the twin-carburettor 2500 TC in 1974. The 2000 and 2500 TC were discontinued in 1977.
Technical
A partial chart of Triumph engine numbers is posted on the "Spitfire & GT6 magazine" site. However the capacity appears not to match the bore/stroke, or that published on other sites including the GT6 Ezine, hence the corrections in the tables below.Engine Applications Chart
| Engine No. Prefix | Capacity | Car |
| HB | 1596 cc | Vitesse 6 |
| HC | 1998 cc | Vitesse 2 Litre |
| KC | 1998 cc | GT6 Mk1/2 |
| KD | 1998 cc | GT6 Mk1/2 |
| KE | 1998 cc | GT6 Mk3 |
| KF | 1998 cc | GT6 Mk3 |
| KG | 1998 cc | GT6 Mk3 |
| MB | 1998 cc | 2000 Mk1 |
| MB | 1998 cc | 2000 Mk1 |
| MG, MM, MN | 2498 cc | 2500 |
| ME, ML | 1998 cc | 2000 Mk2 |
| CC | 2498 cc | TR250 & TR6 |
| CF | 2498 cc | TR6 |
| CP, CR | 2498 cc | TR6 and TR5PI |
Factory Quoted Power Chart
| Model | Quoted power at rpm | Quoted torque at rpm | Capacity |
| TR5 | at 5500 | at 3500 | 2498 cc |
| TR250 | at 4500 | at 3000 | 2498 cc |
| TR6 | at 5500 | at 3500 | 2498 cc |
| TR6 | at 5000 | at 3500 | 2498 cc |
| TR6 | at 4500 | at 3000 | 2498 cc |
| 2.5 PI Mk1 & Mk2 | at 5500 | at 2000 | 2498 cc |
| 2500 Mk2 | at 4700 | at 3000 | 2498 cc |
| 2500 TC | at 4700 | at 3000 | 2498 cc |
| 2000 Mk1 | at 5000 | at 2900 | 1998 cc |
| 2000 Mk2 | at 5000 | at 2900 | 1998 cc |
| 2000 TC | at 4750 | at 3300 | 1998 cc |
| GT6 Mk1 | at 5000 | at 3000 | 1998 cc |
| GT6 Mk2 | at 5300 | at 3000 | 1998 cc |
| GT6+ | at 4700 | at 3400 | 1998 cc |
| Vitesse 6 | at 5000 | at 2800 | 1596 cc |
| Vitesse 2L | at 5000 | at 3000 | 1998 cc |
| Vitesse Mk2 | at 5300 | at 3000 | 1998 cc |