Triumph slant-four engine

Triumph Motor Company

Industry	Automotive
Headquarters	United Kingdom
Products	Automobiles, engines (including Triumph Slant-Four)

Template:Infobox engine

The Triumph Slant-Four is a petrol-powered inline-four engine designed by the Triumph Motor Company. It made its debut in 1968 under the bonnet of the Saab 99. Triumph’s own vehicles did not feature this engine until 1972. Initially launched with a displacement of 1.7 litres, the engine's capacity was gradually increased to 2.0 litres. Production by Triumph ceased in 1981.

History

In 1963, Triumph’s Chief Engine Designer Lewis Dawtrey delivered an in-depth report analyzing forthcoming trends in engine technology alongside Triumph’s projected requirements. After considering various configurations such as rotary, horizontally opposed, V4, and V6 engines, Dawtrey advocated for a family of overhead camshaft (OHC) engines comprising both inline-four and V8 variants. These were intended to be manufactured using identical tooling. This new engine series was planned to cover displacements ranging from 1.5 litres to 3.0 litres, ultimately replacing both the four-cylinder Standard SC engine and the derivative Triumph I6 engines, which traced their origins back to the 1953 Standard Eight. The proposal was approved, leading to in-house development at Triumph under the leadership of Dawtrey and Harry Webster. The initial focus was on creating a 1.5 litre inline-four unit.

Concurrently, Saab Automobile was engaged in designing prototype inline-four engines producing 55 horsepower at 1.2 litres and 68 horsepower at 1.5 litres for their forthcoming Saab 99 model. Although Ricardo, a UK-based engineering consultancy, was not directly involved with the slant-four's development, they maintained an overall engine development contract with Triumph and were aware of their progress. When Saab concluded that independently developing an engine would be prohibitively costly and risky, Ricardo facilitated contact between Saab and Triumph.

Triumph committed to supplying Saab with 50,000 slant-four engines annually for the new Saab 99. By this time, displacement had increased from the original 1.5 litres to 1.7 litres. Saab held exclusive rights to use the slant-four during its initial production years. Saab retained its existing transaxle, which was designed to be driven from the front of the engine. This arrangement required rotating the slant-four by 180°, positioning the clutch and flywheel at the front. As a result, the water pump originally mounted at the front faced the firewall/bulkhead and became inaccessible, necessitating its relocation atop the cylinder block.

The first Triumph vehicle to incorporate this engine was the Triumph Dolomite 1850 launched in 1972. The standard Dolomite featured the 1.85 litre version, while the sportier Triumph Dolomite Sprint, introduced in June 1973, received both a redesigned cylinder head and an enlarged displacement of 2.0 litres. The slant-four also powered Panther Westwinds’ Dolomite-based Panther Rio from 1975 to 1977. The Triumph TR7, released in 1975, employed a 2.0 litre engine equipped with an eight-valve cylinder head. A limited number of pre-production Triumph TR7 Sprint cars were fitted with the sportier Sprint version of this engine in 1977. Production of the slant-four by Triumph ended when the TR7 was discontinued in 1981.

The V8 variant within this engine family debuted in a Triumph vehicle two years prior to the slant-four’s introduction, appearing in a model released in 1970. Development of this V8 continued throughout the mid- to late-1960s with early versions displacing approximately 2.5 litres. When Charles Spencer King (commonly known as Spen King) succeeded Webster as Head of Engineering, he approved ongoing development of the Triumph V8 and played a key role in bringing its associated vehicle, the Triumph Stag, into production. The production version of this V8 had a displacement of three litres.

Technical specifications

The slant-four engine block is constructed from cast iron, sometimes referred to as chrome iron in certain sources. Its cylinders are tilted at a 45° angle relative to the vertical axis. This configuration enabled the use of the same manufacturing equipment designed for V8 engines and contributed to a reduced engine height, allowing for lower hood lines. The crankshaft was supported by five main bearings. The pistons, made of aluminium, featured three rings. Every slant-four engine is oversquare, with larger displacement models exhibiting an even greater oversquare ratio due to an increase in bore size while maintaining the same stroke length.

The cylinder head was crafted from aluminium alloy and incorporated wedge-shaped combustion chambers. A single overhead camshaft operated the valves, driven by a single-row 3⁄8 in (9.5 mm) chain. There were eight valves total—two per cylinder—aligned inline and actuated by the camshaft through bucket tappets adjusted with shims.

Sprint 16-valve engine

File:Dolomite Sprint Valves Section.jpg

Cross-section of Dolomite Sprint cylinder head, illustrating the single camshaft controlling both intake and exhaust valves.

File:1974 Triumph Dolomite Sprint - Flickr - The Car Spy (21).jpg

Triumph Dolomite Sprint powerplant

In 1973, Triumph introduced an innovative 16-valve cylinder head on the slant-four engine for the Dolomite Sprint model. At that time within British Leyland (BL), both Harry Mundy—involved in Jaguar’s engine development—and Walter Hassan, who oversaw engine technology at BL and Jaguar, collaborated by sharing research on four-valve cylinder heads with King.

Under King’s leadership, and with assistance from Harry Mundy and engineers at Coventry Climax, a 4-valve-per-cylinder head was engineered where all valves were actuated by a single camshaft, diverging from the more typical DOHC layout. The valves were arranged in two rows of eight, inclined at 27° from vertical. Inlet valves measured 1.38 in (35.05 mm) in diameter and were directly operated through bucket tappets by the camshaft lobes; exhaust valves were 1.21 in (30.73 mm) in diameter and driven via rocker arms. This cylinder head design earned a British Design Council award in 1974.

The engine’s displacement was increased to 1,998 cc (122 cu in), accompanied by fitting larger HS6 SU carburettors. Additional modifications included a duplex timing chain and an aluminium timing cover. The big-end journals were also cross-drilled for improved lubrication.

Initially, the engine was projected to deliver 135 bhp, but King returned from vacation to discover an engine test bed producing 150 bhp on its first build. The original plan was to market it as the 'Dolomite 135', but this was changed to 'Dolomite Sprint'. Various explanations exist for this renaming; a common belief is that production variability prevented consistent 135 bhp output. However, according to Matthew Vale, the power measurement standard shifted during development from imperial (SAE) to metric (DIN), resulting in approximately 5% lower published figures—the equivalent of 135 bhp SAE translating to 127 bhp DIN.

The Dolomite Sprint has been recognized as "the world's first mass-produced multi-valve car". While multi-valve engines date back to 1912 and more recent examples before the Sprint included the Cosworth BDA, Nissan S20 (1969), and Lotus 907 (1972), these had not been implemented in mass-market vehicles until after the Dolomite Sprint’s debut.

This 16-valve 2.0 L powerplant was also installed in a limited number of prototype and pre-production TR7 Sprint models manufactured at Triumph’s Speke facility during 1977.

Saab B engine

Main article: Saab B engine

In 1972, Saab shifted the manufacturing of the 1.85 L slant-four engine to their own Scania division, operating out of a plant located in Södertälje. An unverified letter published in Motor Sport magazine cites a Saab press release from July 1970, suggesting that this internal production plan was intended from the beginning. After this transition, Saab undertook a redesign which led to the creation of the Saab B engine. The engine's displacement was increased to 2.0 L; however, its bore diameter was reduced by approximately 0.3 mm (0.012 in) compared to the enlarged Triumph variant, resulting in a total volume of 1,985 cc (121.1 cu in).

The Saab B engine retained many characteristics of the original Triumph design, including bore spacing and bearing configurations, but addressed previous issues by redesigning components such as the water pump and its sealing system.

Slant-four variants

Displacement	Bore	Stroke	Compression ratio	Induction	Power	Torque	Year(s)	Notes
1,709 cc (104.3 cu in)	83.5 mm (3.3 in)	78 mm (3.1 in)	8.8:1	1x Zenith-Stromberg 175 CD	80 hp (59.7 kW) at 5200 rpm	94 ft⋅lb (127.4 N⋅m) at 3000 rpm	1969-1971	Saab 99 - single carburettor
			9.0:1	Bosch D-Jetronic fuel injection	87 hp (64.9 kW) at 5200 rpm	129 ft⋅lb (174.9 N⋅m) at 3000 rpm	1970	Fuel-injected Saab 99 1.7 L
1,854 cc (113.1 cu in)	87 mm (3.4 in)	78 mm (3.1 in)	9.0:1	2x SU HS4 carburettors	92 hp (68.6 kW) at 5200 rpm	108 ft⋅lb (146.4 N⋅m) at 3500 rpm	1972 - 1980	Triumph Dolomite 1850
			9.0:1	1x Zenith-Stromberg 175 CD carburettor	88 hp (65.6 kW) at 5000 rpm	147 ft⋅lb (199.3 N⋅m) at 3000 rpm	1971-1974	Saab 99 - single carburettor version
			9.0:1	Bosch D-Jetronic injection	95–97 hp (70.8–72.3 kW) at 5000 rpm	147 ft⋅lb (199.3 N⋅m) at 3500 rpm	1971 - 1972	Fuel-injected Saab 99 1.85 L
1,998 cc (121.9 cu in)	90.3 mm (3.6 in)	78 mm (3.1 in)	9.5:1	2x SU HS6 carburettors	127 hp (94.7 kW) at 5700 rpm	122 ft⋅lb (165.4 N⋅m) at 4500 rpm	1972 - 1980	Sprint 16V engine
			9.25:1	2x SU HS6 carburettors	105 hp (78.3 kW) at 5500 rpm	119 ft⋅lb (161.3 N⋅m) at 3500 rpm	1975 - 1981	TR7 model

Motorsports

The Dolomite Sprint's sixteen-valve engine competed in FIA Group 1 and Group 2 events, prepared by Leyland Special Tuning based in Abingdon. Their debut racing season was in 1974, during which they failed to finish any races. In the following year, upgrades including larger carburettors and a modified camshaft enabled them to complete their first event, finishing seventh at the Mintex Rally. Subsequent results included second place in the Avon Tour of Britain and third position at the Lindisfarne Rally. At the Wales Rally GB#Lombard RAC Rally Lombard RAC Rally, the Dolomite Sprint secured victory in both the two-litre category and Group 1 overall, finishing sixteenth overall in the standings. By the year after, attention shifted primarily towards the TR7 model—initially utilizing the Sprint engine—and by 1978 all efforts were concentrated on developing the TR8.

The independent Broadspeed team, led by Ralph Broad, conducted extensive enhancements on the Sprint engine, reportedly increasing output to approximately Template:Cvt 174 bhp kW 1. Broadspeed-powered Sprints captured the Manufacturer's Championship in ’74 and earned the driver's championship title in ’75. In ’76, they achieved second place in their two-litre class and reclaimed class victory again in ’78.

Additionally, the Sprint engine found application in Formula Three, installed within chassis from Anson Cars and March Engineering. The March car equipped with this engine attained eighth place in the ’76 season standings. In ’79, two March vehicles piloted by Nigel Mansell and Brett Riley finished fifth and eighth respectively in the F3 championship, with each driver securing a race win during the British Formula Three International Series#Vandervell British F3 Championship season.