THE V-TWIN FOR SPRINT WORK

THE V-TWIN FOR SPRINT WORK Continued from page 125

So there is some basis for considering the air-cooled V-twin as a sprint job and for believing in its continued development after the war. It may Well be that the research work on air-cooled aeroengines now in hand will especially focus the enthusiasts’ attention on the simple engine when speed trials return, and enable even more than um b.h.p., from 1,100 c.c. to be realised, with further reduction in weight, when, if adhesion problems can be lined up, the conventional racing job with lots of little boosted pots and shaft transmission will not look so modern. the driver. The steering is rack and pinion from a pre-1914 Morgan. The “Freikaiserwagen ” runs on straight dope and weighs under 6-1 cwt. It has had some Outstanding successes and does 50, 65, and 90 m.p.h. cm the indirect gears, and crossed the line at Syston at 102 m.p.h. in top gear, still accelerating. The writer has often exceeded 1(a) m.p.h. in ordinary cars, but David Fry must experience very much accentuated emotions at this speed ill the nose of his very light vehicle I Another very potent V-twin is Gerald Sumner’s Suniner-j.A.P. It started as the G.N. ” Gehenna,” driven. by Charles Martin and others. in 1935 E. C. Baragwanath designed a special push-rod 998 c.c. J..A.P. sprint engine, of which only three were built. This engine had duralumin-filled push-rods to obviate distortion, and a No. 8 Cozette compressor mounted behind the near side cylinder, blowing at 14 lbs. per square inch, and drawing from a special Amal carburetter, of which only two were made. The G.N. frame was extensively drilled, and fitted with this engine. During the winter of 1936 the chain transmission was replaced by a ” 2.3″ Bugatti gearbox in a Brescia Bugatti shell, driving to a 2-litre Bugatti rear axle. The rear brakes are Bugatti and the clutch a Borg and Beek. A Special tubular front axle, with M.G. brakes, is sprung on quarter-elliptic springs, with radius arms below and friction Shockabsorbers beside the leaves. The rear axle is sprung on quarter-elliptics. Doubtless this resulted in increased weight, permissible because the engine was now giving about 90 b.h.p. per litre; assuming the ratios were correct. The G.N. transmission hasto be strengthened to transmit such power, and chain-breakages while changing speed becom„? increasingly troublesome, but it does score in low weight, speed of change and rear -axle adhesion, and in easy selection of useful ratios for

different venues. Baragwanath raised the compression-ratio to 7.25 to 1 for thae cylinder and 6.5 to 1 for the other, and 89 b.h.p. was realised at 5,300 r.p.m. In July, 1938, a decent body was fitted, with cowled nose, the oil-tank being so shaped as to direct air on to the cylinders. There is a 4i gallon fuel tank in the t ail. Remarkably noisy, the Suniner-.1 .A. P. can do about 112 m.p.h. and clocked 21.91 sees. at Lewes in 1938. It crashed rather badly at the last Prescott meeting of 1938. Of more normal G.N. development is E. G. M. Wilkes’s Wilkes-G.N. Wilkes started racing a stripped G.N. known as ” The Maggot” at Dancer’s End in 1932, but as this car—rumour says it was bought for 6/9 l—was an almost standard i.o.e. touring G.N. it was not terribly impressive; it would possibly have been a better policy to have run it with road equipment and original body. In 1935 Wilkes acquired a ” Mowgli ” engine from Sumner and, proceeded to overhaul both this engine and his original chassis. The rear springs were flattened and mounted on 2″ oak blocks, and new radius arms fitted, The front axle is tubular with Austin Seven brakes and king-pin assemblies welded to the tube, and rod brake operation. Later the front springs were flattened and placed above

the frame. The engine was steadily

developed, the valve timing being modified SO that the inlet valves opened just before T. 1).C., and two single-cylinder B.T.H. magnetos fitted. The inlet ports were welded up to 1.25″, tapering towards the valves, and the exhaust ports ground out. Two Antal Type 6 needle-jet singlefloat carburetters were fitted. To combat chain breakages, the transmission was rebuilt, and a new rear axle made up from a tubular shaft and M.G. brake components. The Wilkes-G.N. carries no body, but there is an oak facia before the driver and the -car is beautifully turned out. Although not. considered quite rapid enough for Shelsley, it has done extnlnely well at Dancer’s End,

lieechwood and Poole. Extensions to the exhaust pipe improved acceleration at the last-named Venue. Another car now very highly developed is C. R. Instone’s G.N. ” Martyr.” in 1929 historic, along Vitb two friends, acquired an early G.N. with push-rod engine. Throughout the winter much modification took place, twin magnetos firing two plugs per cylinder, and two carburetters being incorporated. Pat Thompson was the brainy gent, according to Rupert, and when his theory and science failed him he went on working— with a 3 lb. Brtuumagen screwdriver and tiat enormous crowbar, so that the rest of the team prayed a little something might be left as a souvenir. In 1931 two disasters occurred. Pat returned to Ireland, and the engine blew up most of its valve gear. A new j.A.. push-rod engine was then installed, but, in spite of a modified clutch, it merely tied the frame in knots. At Shelsley it proved quite impossible to get out of third speed, and the entire climb had to be made on that ratio. The frame was accordingly braced up, and other mods. completed. Then the bevel-drive -Shaft and axle bent. So the entire transmission WAS overhauled, the shafts all being replaced in special materials, with the exception of the propeller shaft. The ” Martyr “, now climbed Shelsley in 49.8 secs. although subsequent inspection showed that the prop. shaft had broken in the bell housing and was driving on the serration of its fracture :mly ! A new clutch and propeller shaft were put in, and. only the original side-members remained of the former U.N. A quite reasonable body Was fitted, and wheelspin defeated by the use of Dunlop E.L.P. 5.75″ x16” rear tyres. Later still, the engine was Zoller supercharged, and after overturning in practice ;It Sheisley last year, it took Rupert up in 48.0 secs., winning the supercharged 1,100 c.C. class. Even now we have not exhausted

all the V-twin Specials. There are the Blackburn-engined Killick and the CarlMark J.A.P., both with engines behind the driver, and the converted three-wheeler Morgans of Lones (” Tiger-Cat “) and Barry ‘Woodall (” Chatterbox “), and a liumbelof other G.N. developments. Tlase V-twin specials that have been raced of recent times are likely to run against conventional racing-ears again after the war. Although they mostly date from the early G.N. days, their subsequent development has been a highly specialised business, on modern

It is hoped that the foregoing survey, if incomplete, will at least bs, of interest to those who seek individual descriptions of such ears, and that it may provide some applicable information to those who are working on V-twin sprint cars at the present time. To install a multi-cylinder engine in the simple chassis has been done times without; number, and eventually was resorted to commercially by G.N. themselves. But it imposes great stress on the transmission if a useful power-gain is achieved, and if extra power in some abundance is not forthcoming, there is a loss on account of greater weight Of block, head, crankshaft and cooling elements, etc. (Continued on page 119)