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 Works 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.
Sunbeam, the only British manufacturer committed to international racing emerged from the Great War well poised to amalgamate with two other firms of notable racing pedigree. 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. 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. The highly evolved Experimental Departments in Wolverhampton and Suresnes cooperated on the meticulous development and construction of these fine wholly hand-crafted machines. These zero tolerance racing cars were milled, as it were, from solid billet. 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 with numerous successes still legendary today, the costly racing policy may have ultimately led to the demise of the once mighty S.T.D. Combine. Its subsequent merger with the Rootes Group was less than glorious. 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 famously held that ounces off the engine translate to pounds off the car; this simple design principal together with fastidious balancing, cooling and lubrication produced truly elegant engines. Coatalen's chassis behavior is near magical and this together with sophisticated technical support and the greatest racing talents had led the company to a golden age of racing successes, the likes of which were not to be seen in Britain for many decades.
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.
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). 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 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 highly flexible chassis, was likewise the latest in design and benefited from Louis Coatalen's profound understanding. Presaging the future of racing, these were the first British racing cars ever to be fitted with brakes on all four wheel, a feature which no doubt contributed to their successes.
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 and slanted tails) and T.T. type (exposed tank).
Frame is upswept over front and back axles to achieve lower centre of gravity. Underslung front and rear axles machined from solid billet (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.
Chassis dimensions of surviving cars vary indicating specificity in body fitting.
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 Shelsley Walsh Hillclimb - 1921 3-litre straight eight.
Credited to Coatalen the design is an Ernest Henry type straight eight in line twin overhead camshaft. 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.)
"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.
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