TUNING THE AUSTIN SEVEN
SOME NOTES GLEANED DURING AN INTERVIEW WITH Mr. WILLIAMS OF MESSRS. AUTO-CONVERSIONS pRHAPS the Austin Seven has been the subject of more special conversions by enthusiastic homebuilders than any other make. The reasons are not far to seek. The Austin Seven has been on the market for fifteen years, so examples are available secondhand from the proverbial ” fiver ” upwards. Then, in all these fifteen years the fundamental design has remained largely unchanged, so that various combinations of engine and chassis are possible. A friend of ours has a 1935 engine and 4-speed gearbox in a 1926 chassis, which merely entailed
shortening the propeller shaft. This universal inter-changeability makes the spares problem a very simple one, e specially as new spares are available in every large town, ” replacement ” spares are offered by several big dealers, and almost every breaker can find Austin bits. Before considering the question of increasing performance it must be emphasised that there are limits to what may be done with a 747 c.c. two-bearing side-valve engine, without courting serious unreliability. If sheer speed is required, it will be as well to experiment with a different engine from that used in the road-car, a procedure which the interchangeability factor and. low price of secondhand engines makes practicable. Even then, do not be too optimistic as to results. All the ultra-fast Austin Sevens of recent years have been supercharged. It is true that in the 1923 200-Mile Race E. C. Gordon England finished second in the 1,100 c.c. class, two up in his Austin Seven, at an average of 76.84 m.p.h., and that in 1924 Capt. Waite took the flying start kilometre record at Brook lands at nearly 86 m.p.h. However, while we believe that England used a standard crankshaft and con-rods, we also believe that a very high compressionratio was employed in conjunction with a Ricardo head and that a special camshaft was used. Twin carburetters were cer tainly used. Also, it should be remem bered that England had a brand-new engine very carefully assembled, which is rather different from using a somewhat worn unit. Certainly England put the ” Brooklands ” model into production in 1924 and guaranteed 75 m.p.h. But this was without hood, screen, and wings, the fitting of which brought the speed down to 65 to 70 m.p.h. Moreover, the specification included a 30 mm. Solex carburetter (or twin 80 H.K. Zeniths on
pre-1926 models), K.E. valves, special tappets, double valve springs, high compression head, light pistons, modified. timing gears, drilled crankshaft ad forcefeed lubrication, three-branch external exhaust manifold, special crown wheel giving ratios of 4.4, 8.17 and 14.5 to 1 (30, 55 and 75 m.p.h. on gears at 5,000 r.p.m.) and. fully-faired bodywork. The price was £265 without equipment. Thus, while these early performances show what a 750 c.c. engine can do, and speak very well indeed for the reliability of standard Austin components, in this article we shall he more concerned with raising the 45 to 55 m.p.h. maximum to 55 to 65 m.p.h., and improving the acceleration, while retaining reliability and economy, rather than with the attainment of ultrahigh speeds. In the notes which follow the differences between the various years from the tuning viewpoint become evident. But we can now briefly emphasise the main distinctions to assist those buying secondhand cars for purposes of modification. The Austin Seven was born in 1922 and the first production model had a bore and stroke of 54 x 76 mm. (697 c.c.), and, we believe, coil ignition. It was thus of
7 h.p. R.A.C. rating. For 1923 it was increased in size to 56×76 mm. (747.5 c.c.), and remains so to this day, supplemented by the rather different ” Big Seven” of 5.77×88.9 mm (900 c.c.), with which we are not now concerned. Its outstanding design features were the triangular frame, transverse front spring, quarter-elliptic rear springs, four-cylinder side-valve engine with magneto ignition and separate block, roller-bearing crankshaft and jet lubrication, single-plate clutch, three speed and reverse gearbox and two-piece semi-enclosed propeller shaft. The ” Chummy ” tourer cost £225 in 1922 and £149 in 1926. In 1927 solid hubs replaced the original hollow hubs—an easy identification point. In 1928 came coil ignition. In 1929 the opengate gear-change gave way to a ball gate and longer leVer. Detail changes made about 1929-31 included longer steering column with flat wheel, grubscrews locking brake drums to hub, higher nickel radiator, shelves in instrument hoard, heavier gauge wheel spokes, Triplex glass and chromium plating. The engine now gave 10.5 b.h.p. at 2,400 r.p.m. (and 12 b.p.h. at 2,600 r.p.m. about 1932), the ratios were 4.9, 9.0 and 16.0 to 1, and the tyre size 26″ x a”. 1929 models had larger, better brakes. In 1930 the foot-brake operated on all wheels, whereas previously it had operated the rear brakes, with the hand lever working the front brakes. In 1932, a four-speed twin-top gearbox and better facia were incor porated. In 1933 came synchromesh on third and top, and dipping lamps and rear fuel tank, and in 1934 automatic ignition control, and synchromesh on
second, third and top.. Later models had improved engine with combined manifolding and a horizontal Zenith carburetter, and existing models have Girling brakes and three-bearing crankshaft. By 1937 the standard engine gave 17 b.h.p. at 3,800 r.p.m. The later models pulled an axle-ratio of 5.6 to 1, in place of the former 4.9 to 1 axle, so there is a
choice for experimenters. The later rear tank cars have a wheelbase of 6′ 9″, 6′ larger than pre-1932 models, and a track 3ff wider at the back than at the front. The weight has naturally increased from the original figure of approx. 7 cwt. Turning to the production sports models, the first, apart from the Gordon England 75 m.p.h. ” Brooklands ” model already mentioned and officially backed by the Austin firm, was Austin’s own pointed
tail two-seater of 1925-6. Reminiscent
of the tourer with a tiny pointed tail stuck on behind the two seats, it was, we believe, untuned, did about 50 m.p.h.
and cost :.10 more than the tourer in 1926. We saw one in use quite recently.
The remainder of this article will be concluded in our December issue.