The 1000hp Sunbeam

The first car in the world to travel at over 200mph

Text and pics: Julian Edgar

It’s the 29th of March, 1927. The location is the long stretch of sand at Daytona Beach, Florida. The car, the like of which has never been seen before, is an ultra-streamlined machine of imposing length – all 6 metres (20ft) of it. Under the skin there are two enormous engines, each a V12 of over 22 litres (1343 cubic inches) capacity. Power? Nearly 750kW (1000hp). The man behind the large, thin-rimmed steering wheel is Major H O D Segrave.

And he is about to go faster than anyone has ever driven a car…

The 1000hp Sunbeam – otherwise known as Mystery – was designed by Louis Coatalen, chief engineer of Sunbeam, a major car manufacturer in the United Kingdom. Detail design work and construction were left to Captain J S Irving – a name that was to be well associated with later Land Speed Record cars.

The Sunbeam was a radical departure from previous Land Speed Record cars. Its all-enveloping, low-drag body was so different that it was given the unkind nickname of ‘The Slug’ – but it was a slug that topped 200mph (320km/h). Here it is pictured at the British Motor Museum at Gaydon, UK.

Two 22-litre engines

The new record contender aimed to achieve success through two main technical approaches – a lot of power achieved through the use of two engines, and low aerodynamic drag achieved through all-enveloping streamlining.

The engines comprised Sunbeam Matabele aircraft engines. The 12 cylinders were cast in blocks of three and arranged in a V angle with an included angle of 60 degrees. Bore was 122mm (4.8in) and stroke 160mm (6.3in). Each cylinder used four valves, operated by overhead camshafts, and each cylinder used two spark plugs. Four six-cylinder magnetos were used on each engine to provide ignition. Carburetion was by two Claude-Hobson carburettors positioned within the vee. Power output was 373kW (500hp) at just 2000 rpm. The rear engine straddled the rear axle, while the front engine was placed just behind the front axle. Each engine had its own radiator positioned ahead of it, and each engine was mounted in a subframe that in turn was mounted to the main chassis by three ball joints.

The engines were mounted back to back, with the small flywheels pointing towards the driver. A system of clutches allowed the front engine to be used to start the rear engine. To reduce the size of the frictional clutches and gearbox, engine speed was increased by 2.5 times to reduce the required torque handling. Following the 3-speed gearbox, the speed was reduced by further gearing before final drive was made to the rear wheels by two chains. During development, the car was placed on a custom axle dynamometer that used Heenan and Froude retarders. Contemporary accounts say that over 1000hp was measured by the dyno.

This contemporary drawing clearly shows the mechanical make-up of the car. Each of the two 22-litre engines was enormous.

Mechanical drum brakes

The chassis of the car used two longitudinal deep-channel girders, braced with channel section cross-members. The longitudinal chassis members were 355mm (14in) deep, spaced 1.08m (42?in) apart in the middle of the car but tapering in plan view at each end. Given the large external dimensions, the wheelbase and track of the car were relatively small at 3.58m (11 feet 9 inches) and 1.57m (5 feet 2 inches), respectively. Half-elliptic springs and solid axles were used front and back, with the rear axle kinked downwards in its middle to avoid the engine above. Four-wheel mechanical Dewandre drum brakes were fitted and four Hartford friction dampers were used per axle.

The shape of the car was extraordinarily unusual. The top of the bodywork was only 1170mm (46in) above the ground. The air intake for the front radiator was through a rectangular opening let into the otherwise curved front. Openings in the side of the bodywork provided air exits for the front radiator, while scoop inlets were used for the rear radiator and engine. The body shape was developed through the use of models tested in the Vickers aircraft wind tunnel at Weybridge. These tests indicated that on the full-size car, aerodynamic downforce at the front could reach 320kg (700lb) while there would be 90kg (200lb) of lift at the rear. (However, other sources suggest that the rear diffuser was designed to provide rear downforce – so these figures may have been reversed over time.) The body was made of aluminium. Complete with fluids, the car weighed 4 tons. At the time, the car’s shape led to a rather irreverent nickname – the “Slug”.

An enormous single tachometer and duplicated instruments for the two engines, all behind a thin wood-rimmed steering wheel. 

30,0000 watched the record being broken

When the car reached Daytona, it had never been driven at high speed – there was no suitable test surface available in the UK. A crown of 30,000 lined the dunes on Tuesday, March 29, 1927. At 9.30am, Segrave started his first run, driving north into the wind. As with all Land Speed record breakers of the time, Segreve changed up the gears as he went – at 145km/h (90mph) changing into second, and at 217kmh (135mph) into third. Side winds pushed the car around and he knocked over some marker flags; the car was slow to respond to the steering inputs. Reaching the end of the course, Segrave braked – but little happened. To slow sufficiently, he had to steer into the sea, the shallow water achieving what the brakes had not. On the return run, the wind again blew the car around, but he was able to hold the car on course.

Note the long, aerodynamically sophisticated tail that includes a rear diffuser. The car was wind-tunnel developed. 

The timing officials checked their calculations and then announced a new Land Speed Record: over the flying two-way mile, a speed of 327.97km/h (203.79mph). It was the first time anyone had exceeded 200mph – 322 km/h. However, Segrave’s record stood for only 11 months before it was beaten by Malcolm Campbell, again on Daytona Beach. 

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