Sunbeam Supercharging

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LAST MONTH D.S.J. made the 4-litre V12 Sunbeam Tiger the subject of his “Racing Car Development” series. He stated that when this famous car took the Land Speed Record on Southport sands early in 1926, driven by Major (later Sir) Henry Segrave it had a large supercharger driven off the front of the crankshaft and as usual he was right. However, that is not quite the whole story, as the accompanying photograph emphasises.

True, when Louis Coatalen dispatched this comparatively-compact Sunbeam, then known for some reason that eludes mean “Ladybird”, on its LSR mission it did have a single large, geared-up supercharger. Incidentally, Coatalen presumably had three reasons for attempting to raise the fastest-ever record with a conventional type of racing car. Firstly, he had sold the 350 h.p. V12 aero-engined Sunbeam to Capt. (later Sir) Malcolm Campbell, who had progressively beaten the Sunbeam Motor Company’s coveted record with it. Second, money could be saved and good publicity gained if the LSR could be wrested from Campbell using a car of modest engine size and wheelbase, employing components from the existing 2-litre GP Sunbeams. Thirdly, the speed necessary to capture the record was such that unless the bid was made abroad, there were no available courses in Britain where it could be safely accomplished unless the car making the timed runs could attain over 150 mph quickly in a short distance, which Coatalen saw as calling for light weight as well as about the same power as the huge aero-engined record-cars were developing. Hence his 4-litre job.

Reverting to its supercharger, this was far from successful. On a practice run at Southport the aluminium casing split after the rotors had distorted and fouled it. The first record attempt had to be abandoned and the Sunbeam returned to Wolverhampton, which must have irked the methodical de Hane Segrave, who would have known that the public had been informed in advance that he would make the runs either at 9 a.m. or 1 p.m. that day depending on the tides and the state of the beach. Capt. Irving, who had designed the car, wanted to fit two smaller superchargers but time was against this, as after the end of March the beach would not again be suitable until the Autumn. Instead he tried modifications to the single supercharger, which he hoped would give it a life of three minutes. Six casings had cracked previous to this and when Segrave returned to Southport a fortnight after his first appearance there, there was clearly not much confidence in the outcome.

The Sunbeam was towed to the start of the timed section to save its delicate supercharger, the radiator was filled with hot water, the car was warmed up by driving it slowly to the Southern end of the course, after which Segrave used only about three-quarters throttle for his first timed-run. He then opened right up for the return run but by then the supercharger was nearing the end of its useful life and when the car struck a gulley and left the ground for some 49 feet, the engine overrevved. the blower must have exceeded 5,000 r.p.m. by quite a margin, and its casing again split open, just after passing the end of the flying kilometre.

However, inspite of his cautious South-North run the Sunbeam had recorded 152.33 m.p.h. for the two-way kilometre, so the LSR was raised, if by only 0.139 sec. The five-mile, ten-mile and equivalent kilo. records which the Sunbeam had also been after were abandoned, and its speed for the two-way mile (149.33 m.p.h.) was not high enough to break that record. Nevertheless the Sunbeam was afterwards put on show at Selfridge’s in London and at premises of George Harvey Lee in Liverpool. . . .

Presumably by the time when the “Southport” Sunbeam ran in the Spanish GP (in July 1926) Irving’s twin superchargers, as seen in the accompanying photograph, had been fitted. It seems likely that Irving used two spare superchargers intended for the 2-litre GP Sunbeams, as these instruments, one per engine, had boosted the GP cars at about the same pressure (71b. sq. in.) as that wanted for the 4-litre V12 power unit. A Solex carburetter fed each supercharger, as on the GP cars. It seems that the original inlet manifolding may have been used, but with the twin blowers it sat lower between the vee of the cylinders, the two superchargers being less high than the single one. It looks as if the single blower may have been set slightly to the o/s of the centre-line of the engine, presumably to accommodate the gearing-up, and that the original hose-joint between it and the inlet pipe was retained in the new installation, with a second riser-pipe, without a hose joint, brazed on and bolted direct to the second, or n/s supercharger, and that then, or later, the opportunity was taken of incorporating blow-off (or pressure-release) valve on the front of this inlet piping, which appears to have been lacking with the single supercharger. The details of the two-blower layout can be studied on the ex-Neil Corner Sunbeam in the Midlands Motor Museum at Bridgnorth, because, as D.S.J. stated, the engines were unchanged when T&T’s (and Reid Raillon) modified the two V12 Sunbeams for Sir Malcolm Campbell in 1931/32.—W.B.

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