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HandWiki. Triumph I4. Encyclopedia. Available online: (accessed on 17 June 2024).
HandWiki. Triumph I4. Encyclopedia. Available at: Accessed June 17, 2024.
HandWiki. "Triumph I4" Encyclopedia, (accessed June 17, 2024).
HandWiki. (2022, November 22). Triumph I4. In Encyclopedia.
HandWiki. "Triumph I4." Encyclopedia. Web. 22 November, 2022.
Triumph I4

The Triumph Four Cylinder or Triumph I4 engine is a cast-iron overhead valve straight-four engine produced by Standard Triumph. Introduced in their Standard Eight in 1953, it was used in a wide range of Triumph vehicles, including the Triumph Herald, Triumph Spitfire and certain Dolomites.

dolomites straight-four cast-iron

1. Origin

1.1. Standard Eight Engine

The Triumph inline four was first used in the Standard Eight in 1953. With a displacement of 803 cc the engine produced 26 bhp at 4500 rpm, by 1957 power has increased to 30 bhp at 5000 rpm.

1.2. Standard 10

In 1954 the Ten was introduced as a larger-engined, better-appointed version of the Standard Eight, though sharing a similar frame and transmission. The engine was a enlarged version of the inline 4 displacing 948 cc. A tail-finned (with optional two-tone paint schemes) version of the Ten, the Standard Pennant was launched in October 1957. This version of the engine had power increased to 37 bhp.

2. Triumph Herald & Spitfire

Most of the development of the engine happened in its run within the Herald and Spitfire range.

2.1. Herald & Herald S (948cc)

The initial engine used in the Triumph Herald was the Standard Pennant's 4-cylinder 948 cc OHV. Power was claimed as 34.5 bhp (25.7 kW).[1]

2.2. Herald 1200

Standard-Triumph experienced financial difficulties at the beginning of the 1960s and was taken over by Leyland Motors Ltd in 1961. This released new resources to develop the Herald and the car was re-launched in April 1961 with an 1147 cc engine as the Herald 1200. To gain the extra deplacement the cylinders were placed out of centre which cleared the studs so that a bigger bore could be used. This move gave a capacity of 1147 cc.[2] Twin carburettors were no longer fitted to any of the range as standard although they remained an option, the standard being a single down-draught Solex carburettor. Claimed maximum power of the Herald 1200 was 39 bhp (29 kW).[1] An upmarket version, the Herald 12/50, was offered from 1963 to 1967. It featured a tuned engine with a claimed output of 51 bhp (38 kW)[3]

2.3. Spitfire 4

The 1147 cc version of the engine was used in the first model of the Triumph Spitfire. Mildly tuned and fed by twin SU carburettors, in UK specification the in-line four produced 63 bhp (47 kW) at 5,750 rpm, and 67 lb⋅ft (91 N⋅m) of torque at 3,500 rpm.[4]

2.4. Further Boring

In 1965 The 1,147 cc engine was replaced with a bored-out 1,296 cc unit (the bore increasing from 69.3 mm (2.73 in) to 73.7 mm (2.90 in), stroke retained at 76 mm (3.0 in)), this was fitted on the new Triumph Herald 13/60 and Triumph 1300 saloons. First appearing in the Triumph 1300 it developed 61 hp (45 kW) with the single Stromberg CD150 carburettor, later in 1967 the Mk3 Spitfire utilised the engine in SU twin-carburettor form, putting out a claimed 75 bhp (56 kW) at 6,000 rpm, and 75 lb⋅ft (102 N⋅m) of torque at 4,000 rpm.

In 1970 with the introduction of the MK4 spitfire the 75 horsepower engine was now rated at 63 horsepower (for UK market employing the 9:1 compression ratio and twin SU HS2 carburetors; the less powerful North American version still used a single Zenith Stromberg carburetor and an 8.5:1 compression ratio) due to the German DIN system; the actual output was the same for the early Mark IV.The engine continued at 1296 cc, but in 1973 was modified with larger big-end bearings to rationalize production with the TR6 2.5 litre engines, which somewhat decreased its high revving nature. There was some detuning as well to meet new emissions laws.

2.5. Triumph 1500

The largest modification to the Triumph inline 4 came in 1970 when its stroke was increased from 76 mm (3.0 in) to 87.5 mm (3.44 in), expanding the displacement to 1493 cc. First used in the FWD Triumph 1500 with a single SU carburettor it had a power output of 61 bhp (45 kW; 62 PS). Later used in The Triumph Spitfire 1500, the final incarnation of the engine was rather rough and more prone to failure than the earlier units, though torque was greatly increased[5] While the rest of the world saw Spitfire 1500s with the compression ratio reduced to 8.0:1, the American market model was fitted with a single Zenith-Stromberg carburettor and a compression ratio reduced to 7.5:1 to allow it to run on lower octane unleaded fuel, and after adding a catalytic converter and exhaust gas recirculating system, the engine only delivered 53 bhp (40 kW) (DIN) . The notable exception to this was the 1976 model year, where the compression ratio was raised to 9.1:1. This improvement was short-lived, however, as the ratio was again reduced to 7.5:1 for the remaining years of production.

In the UK the 9:1 compression ratio, less restrictive emissions control equipment, and the Type HS2 SU carburettors now being replaced with larger Type HS4 models, led to the most powerful variant to date. The 1500 Spitfire now produced 71 hp (DIN) at 5,500 rpm, and produced 82 lb⋅ft (111 N⋅m) of torque at 3,000 rpm

3. Technical

Factory Quoted Power Chart
Model Quoted power @rpm Quoted torque @rpm Capacity Fueling System Year
Standard 8 26 bhp @ 4,500 rpm   803 cc   1953
Standard 10     948 cc   1954
Standard 8 30 bhp @ 5,000 rpm   803 cc   1957
Standard Pennan 37 bhp   948 cc   1957
Triumph Herald 34.5 bhp   948 cc   1959
Triumph Herald S 34.5 bhp   948 cc   1961
Triumph Herald 1200 39 bhp   1147 cc Single down-draught Solex carburettor 1961
Triumph Spitfire 4 63 bhp @ 5,750 rpm 67 lb⋅ft @ 3,500 rpm 1147cc Twin SU carburetors 1962
Triumph Herald 12/50 51 bhp   1147 cc   1963
Bond Equipe GT 63 bhp   1147 cc   1963
Bond Equipe GT4S 67 bhp   1147 cc   1964
Triumph 1300 61 bhp   1296 cc Single Stromberg CD150 carburettor 1965
Triumph Spitfire Mark II 67 bhp @ 6,000 rpm   1147 cc   1965
Triumph Herald 13/60 61 bhp   1296 cc Single Stromberg CD150 carburettor 1967
Bond Equipe GT4S 1300 75 bhp   1296   1967
Spitfire Mark III 75 bhp @ 6,000 rpm 75 lb⋅ft @ 4,000 rpm 1296 cc Twin SU carburettors 1967
Triumph 1300TC 75 bhp   1296 cc Twin SU carburetors 1968
Triumph 1500 61 bhp   1493 cc   1970
Triumph Toledo 58 bhp   1296 cc   1970
Triumph Spitfire Mark IV (UK) 63 bhp (DIN)   1296 cc Twin SU HS2 carburetor 1970
Triumph Spitfire Mark IV (US)     1296 cc Single Zenith Stromberg carburetor 1970
Triumph Toledo special export 61 bhp   1493 cc   1971
Triumph Toledo special export TC 64 bhp   1493 cc   1971
Triumph 1500TC     1493 cc Twin SU carburettors 1973
Triumph Spitfire 1500 (UK) 71 bhp (DIN)   1493 cc Twin SU HS4 carburettors 1974
Triumph Spitfire 1500 (US) 53 bhp   1493 cc Single Zenith-Stromberg carburettor 1974
MG Midget 1500 (UK) 64 bhp   1493 cc   1974
MG Midget 1500 (US) 50 bhp @ 5,000 RPM 67 lb⋅ft @ 2,500 RPM 1493 cc single Zenith-Stromberg 150 CD4T[6] 1974
Triumph Dolomite 1300     1296 cc   1976
Triumph Dolomite 1500     1493 cc Twin SU carburettors 1976
Triumph Dolomite 1500HL     1493 cc Twin SU carburettors 1976

4. Inline 6

A six cylinder engine was developed from the four used in the Eight and the Ten.[2] It was first used in 1960 in the Standard Vanguard Six, in which it had a 74.6 mm (2.9 in) bore and a 76 mm (3.0 in) stroke, giving a capacity of 1998 cc.

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 66.75 mm (2.6 in) 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.

The inline 6 version was loosely developed into the Leyland PE166 engine.[2]

5. Replacement

Though never directly replaced (the 1500 version powered the last Triumph Spitfire) the Triumph slant-four became the premier Triumph 4 cylinder unit, being used instead of the OHV unit the higher specification Dolomites.


  1. "News Summary". Practical Motorist. 7 (nbr 83): 1187. July 1961. 
  2. "Rover six cylinder, The Triumph connection". 
  3. Michael Sedgwick & Mark Gillies. A-Z of Cars 1945-1970. pp. 203. 
  4. 1936-, Robson, Graham, (1982). Triumph spitfire and GT6 : spitfire 1,2,3,IV,1500 ; GT6 1,2,3. London: Osprey. pp. 187. ISBN 0850454522. OCLC 9761666. 
  5. 1936-, Robson, Graham, (1982). Triumph spitfire and GT6 : spitfire 1,2,3,IV,1500 ; GT6 1,2,3. London: Osprey. pp. 187. ISBN 0850454522. OCLC 9761666. 
  6. 1500 workshop manual. British Leyland UK limited. 
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