Seven made by Lotus between 1957 - 1973
by John Watson
The Mark III
The 750 Formula set out to be one of the least expensive in the sport of car racing and in order to keep costs down the regulations made it compulsory to use many Austin Seven parts like chassis, rear axle, engine gearbox and propshaft etc. In addition, the cars had to be road worthy and capable of being driven to and from the circuit. Selling the Mark II to trials driver Mike Lawson as well as dispossing of the Mark I, Colin was in funds enough to buy an Austin Seven saloon for the basis of the Mark III, and have money to start on the new project in Vic Williams’s lock-up. No sooner had he started than he met the Allen brothers, Michael and Nigel, two dental students who were neighbours of Hazel's and whose parents had a very well-equipped garage. In no time at all, Colin had convinced them that what they wanted to do most was to make themselves a Mark III Lotus each, to be built at the same time as Colin’s own, in their garage!
Chassis
The Mark III chassis was to be much stiffer than the earlier cars having, instead of flat aluminium bonded plywood, additional tubes welded to form a triangulated ‘cage’ bolted to the front ‘A’ frame. This cage needed to be removed before any serious work could be done to the engine but this, as it turned out, was a small price to pay for what was to be streets ahead in chassis design terms, compared with the rest of the competition in the 1951 750 Formula championship. As with the previous cars there was a split Ford Eight beam axle with a flattened semi eliptical spring providing independent swing-axle front suspension. A great deal of care was taken to ensure that everything was as light as possible; in fact the completed car only weighed 815lbs (370Kg).
Trick engine
Whilst the body and chassis were far ahead of the other competitors, the real success lay with the performance of the engine. By this, his third year of competition, Colin realised that interpretation of the regulations was all important in order to make a winning car. The 750 Formula rules required the use of a standard Austin Seven side-valve cylinder block with its ‘siamesed’ inlet ports. In other words the four cylinders and four inlet valves were served by only two inlet ports. From a technical point of view this was inefficient because with a 1-3-4-2 firing order the two adjacent cylinders fired immediately after one another and would rob each other of the correct amount of incoming fuel/air mixture.
Colin’s answer was to ‘de-siamese’ the ports, not by altering the side-valve block, but by using a specially made four-piped but two-branch manifold. Fabricated of sheet steel, the two rectangular-sectioned pipes were each divided into two and this division protruded into the two enlarged ‘siamese’ inlet ports within the block where they were ‘sealed’ in with asbestos strip. A hugh twin-choke Stromberg carburettor from a Ford V8 was fitted! So to the casual eye it looked like a modified two-pipe inlet manifold. Although no power output was ever documented, the results were devastating as the Mark III simply ran away from everything in it’s class that year. With a top speed of around 90 mph from a crude 749cc side-valve engine designed in 1922, most 5 to 10 lap races were won by half a lap.
At the end of the season the inevitable happened; the rules got changed and the following year ‘de-siamesed’ ports were banned! Successes on the track meant that Michael and Nigel Allen’s cars were not going to be completed as any progress on them was thwarted to keep Colin on the track. It had been decided that Colin would be the driver in all the 750 Formula Championship races whilst Michael, Nigel and occasionally Hazel would drive in non-championship events. By the end of the season it was clear that the arrangement they had wasn’t going to work and Nigel decided to concentrate on dentistry.
Move to Hornsey
Success in competition brought other 750 Formula racers along to have special bits made for their cars. One even wanted a Mark III replica and soon it became apparent that the Allen’s garage wasn’t going to be suitable. Stanley Chapman’s public house in Tottenham Lane Hornsey, The Railway Hotel, had old stables where empty bottles were stored. Although small, this was four times the size of a typical lock-up garage and soon the fledgling car-maker took a lease from Chapman Senior and moved in there. At the same time it was decided to place the business on a more formal footing and the Lotus Engineering Co was started on 1st January 1952. Michael Allen worked full time and Colin, whilst still at his job with British Aluminium Company during the day, worked at Tottenham Lane evenings and weekends.
The Mark IIIB
The first job for the Lotus Engineering Co was to complete the ‘replica’ Mk III which was ordered by Adam Currie. The chassis had been one of those intended for the Allens and this time it was very different being fitted with a E93A Ford Ten side-valve engine and designated the Lotus Mark IIIb.
The Mark IV
The other car to be constructed that Winter was designed for Trials and had been ordered by Mike Lawson who owned the Mark II. Whilst the Mark II had been successful in the hands of Mike Lawson, things had moved on a bit and a more upto date machine was required. As before an Austin Seven chassis frame was used but this time the power unit was from a Ford Ten. In addition Mike wished the car to be for road use as well and it was made a little more roomy for this purpose. It also had special front suspension similar to that found on farm tractors which allowed great amounts of travel over rough ground. On smoother road conditions this system, nicknamed the ‘jelly joint’ could be locked. Up until now only one example of each model had been made. This was soon to change . . .
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