The 1921 S.T.D. 'Works' Grand Prix chassis was built to the three-litre and minimum weight of 800 kilogrammes formula for that year's Indianapolis 500 and French Grand Prix de l’A.C.F. These team cars were modified by the Sunbeam Experimental department in Wolverhampton for the 1922 Isle of Man Tourist Trophy, which was won by one of the cars. A few months later, and with 1916 4.9-litre engines, two of the T.T. cars competed in the Coppa Florio, Sicily and gained second and fourth position.
The cars also participated in local events including Brooklands and hillclimbs. They are notable for obtaining the first significant international motor-racing success for Britain after the Great War and having "the best run of success by any Brooklands' car in such a period". Of the five constructed, four survive: one as a single-seater, two as standard T.T. and one as a resurrected T.T.
Background Sunbeam emerged from the Great War well poised to amalgamate with two other firms. Together with Talbot and Darracq they formed the S.T.D. Combine. S.T.D. was to become a dominant player in Land Speed Records, Grand Prix and Voiturette racing both in Britain and abroad.The Encyclopedia of Motor Sport Edited by G N Georgano 1971 pp. 607–608 S.T.D. race cars using identical chassis and engines were to be designated variously as Sunbeam, Talbot or Talbot Darracq in response to the different events or countries they took part in. These zero tolerance racing cars were milled, as it were, from solid billet.The Auto Car 1921 July 9 pp. 74–75 Racing program was extensive; tailor-made alternative lightweight bodies, specific axle ratios and engines to suit each event were formed. The driving force behind the S.T.D. and its racing program was the charismatic and ingenious Breton Louis Coatalen. Designer, engineer and racer Coatalen was inspired by the belief that "Racing improves the breed".
Whilst catapulting S.T.D. to the highest echelons of the sport, the costly racing policy may have ultimately led to the demise of the S.T.D. Combine. Its subsequent merger with the Rootes Group did not help matters. Conversely it may be that S.T.D.'s loss of direction and withdrawal from racing in the late Vintage period was the real source of their demise.
Coatalen maintained that reducing engine weight significantly reduced overall vehicle weight. This design philosophy, combined with precise balancing, cooling, and lubrication, resulted in highly regarded engine designs.\({}^{}\) His chassis engineering improved vehicle handling, which, alongside technical support and prominent drivers, led to a period of consistent racing success for the company.\({}^{}\)
During its pre 1930s heyday S.T.D. was consistently and fully committed to international racing at the highest level and was synonymous with British Racing.
Design 1920 November 3, S.T.D. Experimental Department Order EXP.273 (4 nos. Grand Prix Chassis) and EXP. 271 (7 nos. straight-eight-cylinder engines).Experimental I.P.s'. 6-5-21 EXP/271 and EXP/273 both dated 3/11/20, EXP/305 dated 14/12/20 EXP/412 dated 20/4/21 at the Heal Archive Project cost £50,000 (about £5,000,000 in 2010). These were the first new post Great War Grand Prix chassis to be constructed by S.T.D.
Designed by the S.T.D. Experimental Department possibly in both Wolverhampton and Sureness,The British Competition Car, Cyril Posthumus, 1959 p. 52 the highly advanced 1921 straight-eight engine is unmistakably influenced by Ernest Henry's pre-war work for Peugeot and his immediate post-war work for Ballot where the resemblance is particularly noticeable.
The flexible chassis, was likewise the latest in design and benefited from Louis Coatalen's understanding.Motor Sport 1948 March, Cecil Clutton p. 78 Presaging the future of racing, these were the first British racing cars ever to be fitted with brakes on all four wheels.
These 1921 Grand Prix chassis were amenable to changes of both engine and body. Two engines were used in competitions; the 1921 3-litre straight-eight dohc and the 1916 4.9-litre. Body types included two-seaters and single-seater with pointed tails, slanted tails or exposed fuel tank. Bonnets were adjusted according to the type of carburettors and engines used. In addition, radiators and badges of the three firms constituting S.T.D. were interchangeable. The Works selected the most appropriate combination of body, engine and radiator for each speed event. The cockpit arrangement as well as car dimensions were arranged according to each pilot's specific requirements; resulting in tailor-made cars for the Works team drivers.
The chassis in all these permutations is the same and can be called the 1921 G.P. chassis. Body type can be called G.P. type (pointed & slanted tails) and T.T. type (exposed tank).
Colour/trim Body: 1921 French G.P. Talbot – 'British Racing Green'; Talbot Darracq – blue 1921 Shelsley Walsh – 'British Racing Green' 1922 IoM T.T. 'Sunbeam Dreadnought Grey' 1922 Coppa Florio 'Sunbeam Dreadnought Grey' Wheels: Black Upholstery: Sprung squab with fluted seat back in embossed veg-tan leather The TASO Mathieson & K Taylor Photographic and Document Archive courtesy Keith Taylor – DA6521 & DA6752 at WolverhamptonRapiditas Vol5 1922–1923 p. 59
Chassis Frame is upswept over front and back axles to achieve lower centre of gravity.Carbooks Volume 21 1922, Michael Frostick (editor) p. 24 Underslung front and rear axles machined from solid billetAutomobillia 1921 p. 17 (back axle to 3mm thickness). Front axle H-section. U- shape sub-frame carries the engine, clutch and gearbox and mounted on the chassis at three points. Alignment of front end of crankshaft is below the centre line of the rear axle; as such the line of crankshaft, the transmission and the propeller shaft slopes downwards towards front in order to keep centre of gravity as low as possible.
Dimensions and weight Chassis dimensions of surviving cars vary indicating specificity in body fitting. Wheelbase 8 ft 9 in, Track 4 ft 7in Weight: 1921 Grand Prix de l’A.C.F. – 19.5 cwt 1922 IoM T.T.: K Lee Guinness – 21 cwt 99 lb H.O.D. Segrave – 22 cwt 31 lb J. Chassagne – 22 cwt 10 lb (2,474 lb) Engine weight dry 520 lb.
Engine Two race engine types were used with the 1921 Grand Prix chassis depending on event regulations, a 1921 3-litre straight-eight and a 1916 6-cylinder 4.9-litre. 1921 Indianapolis – 1921 3-litre straight-eight; four horizontal Claudel Hobson 1921 Grand Prix de l’A.C.F – 1921 3-litre straight-eight; four Zenith carburettors 1921 Shelsley Walsh Hillclimb – 1921 3-litre straight-eight. 1922 Isle of Man Tourist Trophy – 1921 3-litre straight-eight (modified and compression raised); two racing CZC vertical Claudel Hobson carburettors 1922 Coppa Florio Sicily – 1916 6-cylinder 4.9-litre. Brooklands – both engine types Hillclimbs – both engine types
The 1921 3-litre straight-eight Credited to Coatalen the design is an Ernest Henry type straight-eight inline twin overhead camshaft.Motor Sport 1948 March, Cecil Clutton p. 75 Bore and stroke 65x112mm, Capacity 2973cc. Lightweight aluminum alloy cylinder blocks and crankcase. Block cast in two blocks of four; non-detachable head cast in one. Shrunk-in steel liners and screwed- in phosphor-bronze valve seats. Crankshaft of nickel-chrome forging, machined from a single billet; plain bearings. Hollow five main journals and eight crankpins. Each crank throw is counterbalanced. No flywheel. Camshaft driven by train of straight-tooth pinions at the front. Rotation viewed from above anti-clockwise both inlet and exhaust. Pistons are aluminium domed- head carrying three compression rings and an oil groove in the skirt serving instead of scraper ring. Piston clearance 0.015’’ to 0.018’’. Groves 1/16’’. Connecting rods H-section, white metal big end bearings. Four tulip-shape overhead valves (twin inlet and twin outlet) per cylinder (32 in total) inclined at 60 degrees operated by two overhead camshafts through inverted cup-style tappets. Valve clearance (cold) inlet 0.010, exhaust 0.015. Valve timing varies between chassis and in time viz. in 1922 open 12 degrees BBDC close 55 degrees ATDC; 1960 – chassis II: inlet opens 5 degrees BTC and closes 35 degrees ABC. Exhaust opens 45 degrees BBC and closes 10 degrees ATC. Compression 1921 French G.P. was 5.7 to 1, increased for the 1922 IoM T.T. to 6.3 to 1. Output 112bhp at a maximum 4,700rpm. (See footnote below.)
The 1916 4.9-litre 6-cylinder "Coatalen produced the world's first twin-cam Six for the 1916 Indianapolis 500" an Ernest Henry prewar Peugeot type in-line six cylinder 81.5x157 mm, capacity 4,914 cc. Two cast blocks of three; twin overhead camshafts driven by a vertical shaft and gears from the front of the engine; four valve per cylinder (24 in total), 60 degrees included angle. Camshafts castings split horizontally. Pivoted cam followers carried by bronze mountings. Crankshaft in three pieces carried in four large ball bearings; plain big ends. Drilled aluminum pistons – a first for Sunbeam racing car. Dry sump lubrication with two oil pumps – one for the bearings and the other for the camshafts. Mounted on sub-frame articulated with the chassis. Single Bosch magneto ignition driven at ¾ engine speed. Twin CZS Claudel Hobson carburettors mounted on two water-jacketed induction manifolds. Compression ration 5.8:1, 152 bhp at 3,200 rpm. Two speed gearbox was tried but four speed gearbox with cone clutch generally used; Hotchkiss drive with bevel back axle. Revolution counter driven by the camshaft.
The engines mounted in a 1914 G.P. Sunbeam chassis were entered in 1916 in a number of American events; racing having ceased in Europe during the war but continued in America prior to the US entering the conflict. In the careful hands of J Christiaens who suggested their construction, his car regularly finished 'in the Money' winning large prizes including $3,000 (4th) in that year's Indianapolis 300-Mile. The cars also performed well in the hands of Galvin and Louis Chevrolet achieving a number of third places.
In 1919 the 4.9-litre engines were mounted in two 1914 T.T. Sunbeam chassis; Josef Christiaens was killed demonstrating one of the cars at Wolverhampton and they were subsequently entered at that year's Indianapolis 500 for J Chassagne and Dario Resta. In the event, they were withdrawn without explanation said to be in excess of 300 cubic inch limit.
Mounted in the 1921 Grand Prix Sunbeam chassis this engine proved competitive and effective at Brooklands until 1929 and in Southport well into the thirties; indeed William B. Boddy noted that one of the cars had "the best run of successes by any Brooklands car over such a period". Some of the greatest drivers of the period achieved fine results with the combination of the 4.9 L in a 1921 G.P. chassis including HOD Segrave, Malcolm Campbell and Kaye Don.(See footnote below.)
Carburetion (3-litre engine) Various carburettor configurations were used depending on the event, including four horizontal Claudel Hobson (1921 Indianapolis 500), four Zenith carburettors (1921 Grand Prix de l’A.C.F.); however, in the Isle of Man Tourist Trophy two racing CZC vertical Claudel Hobson carburettors 42 choke were used. Claudel Hobson were an S.T.D. Subsidiary.Seventeen Sports Cars 1919–1930, Peter Hull and Nigel Arnold-Foster p. 138 Fabricated inlet manifolds incorporating water jacket to stop icing. Fuel feed by pressure from 30-gallon copper bolster tank at rear was used in the Isle of Man Tourist Trophy and the Coppa Florio; other configurations in other events.
Fuel consumption 7–22 miles per gallon 0.7 pint per bhp/hour at 3,000 rpm, 0.65 pint per bhp/hour at 3,500rpm.
Ignition (3-litre engine)