Emphasis On Sports Cars—
THE LOTUS -AUSTIN
ATER building the successful Fordengined Lotus trials car, now driven by Michael Lawson, Cohn Chapman started to build another trials car. Then the 750 Club announced its revised Formula Racing for Austin Sevens and Colin, in syndicate with the Aliens, Michael and Nigel, decided to start on a team of three of the new Austin Specials but modified for the dual role of ” Formulae ” racing in summer and trials in the winter. Last November, a 1930 Austin Seven saloon was bought for £15 and this formed the basis ofthe first car, which was racing early the following season and which has proved to be something quite outstanding amongst amateur built specials.
When we say that the car was completed in under six months, was rendered completely race-worthy during its first season, is driven to and from meetings and, handled by a variety of drivers including Chapman’s friend, Hazel Williams, has set up the following lap-timesSilverstone Club Circuit 1 min. 58 sec., Boreham 2 min. 26 sec., Gamston 1 min. 83 sec., lbsley 1 min. 58 see., Castle Combe (early stages) 1 min. 43 sec.— readers will appreciate why we hastened the Plus Four to Alexandra Park to examine this car. To those not conversant with lap times, we have only to say that the Lotus is a scientifically-designed, very handsome unblown 750 c.c. road-equipped two-seater which has done a s.s. quarter mile in 17 sec., 0-50 m.p.h. in 6.6 see. Its builders claim that so far it has cost them less than S:200. The princip2e on which Chapman worked was to put nothing into the Lotus which had not been
carefully weighed first. ” Simplicate and add lightness” was his motto, rather than drill everything full of holes afterwards.
The chassis is Austin Seven, of ft. 9 in. wheelbase. The side-members are boxed in and two 14-gauge tubular crossmembers replace the originals. An extension at the rear, in 20-gauge steel, serves as a mounting for the Newton shock-absorber struts and will carry the alternative trials back besides carrying a 1930 Austin Seven petrol tank, cut away to clear the axle casing. The rear springs, mounted normally within the side-members, are fiat set and considerably softer than standard. The wide-track backaxle has the 4.9 to 1 ratio. The propeller-shaft is late-type Ruby.
Going to the front of the car you observe a tubular pyramid around the engine and thereby hangs a most interesting story. Originally the Lotus would take Beckett’s Corner at 75 m.p.h. Its owners noticed that the crankcase studs of the rigidly-mounted two-bearing. engine were pulling out, so rubbermountings were substituted, using 3s. Ford rubbers. The cornering speed was now 5 m.p.h. down. Clearly, chassis flexion was to blame for both these
short-comings, hence the aforesaid structure. It is properly-stressed and bolted together with h.t. bolts, so that it can be dismantled for complete engine removal, and has restored and improved on the original cruising speed. In addition to this elaborate bracing, a 15-gauge tube encircles the scuttle, acting as an anchorage for the steering. cohunn and enhancing the safety-factor. So rigid is this that the firewall further forward is merely a sheet of alloy attached to the sides of the body shell.
The front. axle is a Ford Eight beam, divided in the middle for i.f.s. The spring is above it and Silentbloe bushes arc liberally dispersed here and there about the rest of the chassis. The track is 4 ft., the axle 21 lb. heavier than an Austin axle but more durable in its king-pins. Ford radius arms anchored on Silentblocs and Newton struts damp the soft transverse spring. The steering column is extended forward to an Austin Seven steering box laid on its side ahead of the axle so that its drop arm can operate a transverse drag link coupled to separate track rods. The column incorporates a fabric joint and is adjustable. ‘fhe steering wheel, of sprung type, can be adjusted for ” spring ” and is a beautiful thing, made by the Aliens’ and Chapman’s girl-friends. The brakes have light alloy back-plates and are Lockheed hydraulic from a new Morris Minor, 2LS at the front, using the stiffer Girling drums. The wire wheels were made up by the West London Repair Co. and feature special light centres which do not shroud the brake drums as Austin wheels would. They weigh 9 lb. 10 oz., against over
13 lb. for the Austin wheel, or 21 lbcomplete with tyre and tube ; 4.00-15 front and 4.50 or 5.00-15 rear tyres are used, depending on requirement’s.
Throughout, the builders of the Lotus have carried a tiny 25-1b. spring-balance; and any component that brings this to its full reading is regarded with very deep distaste indeed ! So we find a front wing, complete with rigid 24-gauge struts and sidelamps, weighing a mere 10 oz., and the beautiful little polished aluminium body shell only 65 lb. complete with hoops.
Turning to the engine, from which such wonderful results have been obtained, originally a two-bearing unit was used. This was at times taken up to 6,500 r.p.m., but the standard Austin Seven rods bent into quite astonishing shapes. ” Ulster ” rods were substituted, retaining the 1 a–in. crankshaft, and then big-ends started to run. This explains why the Lotus started on three cylinders at the Eight Clubs Meeting. Chapman was criticised unfairly in some quarters for going flat-out on three pots ; unfortunately the crank broke in shear nevertheless.
So, in spite of much prejudice against it, a three-bearing engine was installed. This had the advantage that a brand-new crankshaft and rods were obtainable, the latter for a mere 22s. 6d. each, and that the rods had thin-shell bearings, enabling rapid replacements to be made if bearing trouble intruded, and of course eliminated the inevitable whip of the two-bearing crank. Chapman believed that threebearing cranks broke only because, due to poor crankcase breathing, corrosion
set in, causing wear in the rear main bearing and consequent Hexing of the shaft about its centre bearing. To overcome this he decided to tit a Hoffman type rear-main race and to incorporate a Fram filter in the lubrication system. This filter feeds oil back over the timing gears and a tap cuts it out during racing, in ease a pipe should break.
The cylinder block is over-bored 0.050 in. and the inlet valves enlarged to 1 h. in., to accommodate which the exhaust valves have been reduced to .31.2 in. less than standard. The bores are carefully radiused to assist gas flow and an alloy head has been modified to give the desired shape and the highest possible compression-ratio. The combustion spaces have been cleverly built-up by aluminium welding.
Up to the last Boreham Meeting the compression-ratio was 0.1 to 1, but it is now up to 7.2 to 1, which, with a new inlet system, gives an additional 500 r.p.m. in top gear. A normal C. and A. ” Ruby” gasket is used. The engine will run on Pool, but now prefers 80 octane petrol.
The mrburetter is a downdraught pump-type, twin-choke Stromberg from a 30-h.p. Ford V8, on a square-section V-manifold, asbestos-lagged to obviate heat conduction from the exhaust pipes. Fuel feed is by normal Austin Seven pump. The external exhaust system consists of square-section off-takes for Nos. 2 and 3 ports and ordinary small-bore pipes from Nos. 1 and 4, leading into a double Servais-type silencer, the whole planned to provide an extractor effect. A ” Nippy ” camshaft is used with ” Ulster ” springs and the latter, being seeondhand, have broken rather frequently due to fatigue, new springs being on order. So line is the clearance between valves that a template was made to determine the optimum sizes that could be used, while so close do the pistons come to the head that crankcase whip as on the earlier engine would cause contact between these components I I
The pistons are modified solid-skirt Covitto, with two 11,-in. compression anti one h-in. seraper ring.
Cooling is looked after very thoroughly, a Stuart Turner water pump being driven from the front of the camshaft and a three-branch off-take taking water from the head. The radiator is milditied Austin Seven, converted to filth-type by the John Lancaster Radiator Co. It operates under pressure and is (fowled by a featherweight shell incorporating two close-set la teas pass-lamps as headlamps. The fan is retained but cut down. Oil (Shell) is contained in a ” Nippy ” sump.
Ignition is by a Scintilla Vertex magneto driven from the dynamo and inclined rearwards to clear the bonnet. The engine takes normal automatic advance (8 deg. at magneto, 16 deg. at engine), but a hand control is also fitted, and 14-mot, plugs are used. The rev.-counter drive is Laken from the magneto drive. No support has been found necessary for the magneto, but a east-iron end easing is used on the dynamo.
The flywheel Was lightened to reduce torsional loading on the crankshaft on the over-run rather than to humour pickup. It now weighs 16.i lb. The standard clutch, with springs 1 gauge heavier and mechanical advantage in the pedal linkage, has given no trouble. It is lined with Mintex of the kind supplied for two purposes–racing, and to the Ministry of Works for their lady drivers I The gearbox is ” Nippy,” with remote control. A Morris Minor
handbrake is fitted, with enclosed cable linkage to the rear brakes. The very handsome two-seater body is nicely upholstered, has a lightweight hood, and a 22-gauge undershield runs the length of the car. A pleasing detail, typical of Bic care that. has gone into the whole of the Lotus, is the use of tiny ballbearings for the fold-flat, windscreen I
The performance of this car is truly outstanding and far surpasses that of other 750 Formula contenders. Indeed, owners of the most potent Ford l’en specials, Meadows II.R.G.S, and even larger ears are apt. to find the Lotus harrying them along the Straights and as likely as not passing out of the corners I Very few ” 500s ” can live with this astonishing Austin Seven in its present form, and it must, be giving more b.h.p. than blown ” Ulsters “of happy memory. 5,500 r.p.m. is adhered to in the lower gears and 5,900 r.p.m. has been held in top, equal to 88 m.p.h. Chapman puts the genuine maximum in road trim, with screen down, as 84,85 m.p.h. and the acceleration . . The roadholding is entirely in keeping, making the Lotus a most formidable sports/racing car. And, to and from Meetings, it does 50 m.p.g., indicating how freely it breathes. It is a great credit to its builders, of whom Michael Allen has done most of the engine work, Nigel that on the chassis, with Chapman responsible for the design, development and general construction.
That such a car has been built so economically in a small garage is an enormous tribute to this keen team, and to the tolerance of their plixents and girlfriends ! The Lotus is a fine example to would-be special-builders willing to approach such work scientifically and barn gallons of midnight oil.—W. B.
As editor I wish to apologise to historical archivists and those with long memories who noticed some inaccurate and odd items in the piece published last month about former MCC…
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