Go to 500 Owners Home PageThe 500 c.c. Formula Unsupercharged

The original rules for the national 500cc Formula, published in "Iota" April 1947.

By A.C.H. Harding, Secretary of the Technical Panel.

Engines. Engines may be of any type, any number of cylinders, provided that the capacity does not exceed 500 c.c.

Superchargers will not be permitted.

It was decided that any type engine, up to 500 c.c. capacity, could be employed provided that it is naturally aspirated. This rule was made for several reasons:-

(a)  The use of a supercharger enables the enthusiast with unlimited capital to gain considerable advantage over those less fortunate. Multi-cylinder engines, designed for use with high boost pressure give exceedingly high power output but may easily entail expenditure amounting to thousands of pounds.

(b)  Considerable difficulty is experienced in supercharging single cylinder engines without adding undue weight and cost. Here, again, the advantage is on the side of the more costly multi-cylinder units.

(c)  The availability of power units suitable for use with supercharges amounts to less than five per cent that of the more general type of unit, not to mention the extreme difficulty of obtaining superchargers. Again the advantage would go to builders who are either in the trade or have trade contracts.

(d)  Considerably less difference exists between performance figures of naturally aspirated engines in any one class compared with the results obtained from engines of similar capacity but with differing boost pressures.

The barring of superchargers, for the purpose of the 500 c.c. Formula should, therefore, enable the impecunious enthusiast to compete with the more fortunate on equal terms. To put the whole thing in the simplest way. We may say that power or horse power per litre remains consistent on naturally aspirated engines but increases with Supercharged engines in an ever diminishing proportion to the capital outlay.

Fuel. Any Type of Fuel. The decision not to restrict the fuel was arrived at after exhaustive discussion. There are several excellent fuels obtainable by any competitor at a cost which is not beyond the reach of anyone; the slight extra cost is more than offset by the saving in engine components.

Almost all engines within the capacity of the Formula can run on petrol, petrol-benzol, or alcohol, without much alteration. The use of an alcohol fuel is of the utmost assistance to the builders of cars, especially designs with air cooled rear engines. The evaporation of the fuel in the cylinders of dope engines is extremely useful to the internal combustion engineer, providing internal cooling, preventing detonation and enabling the working pressures to be raised with consequent increase in available horse-power.

The case for a standard pump fuel restriction condemned itself from the outset. Pump fuel would not be cheaper than special fuel if cost in engine components could be considered; and extra supervision which would have to be provided by hard worked organisers of events coupled with the almost impossible question of defining pump fuel made such a restriction pointless.

Fuel Tanks – Fuel tanks to be of one Imperial Gallon Capacity. The use of small capacity tank has a number of advantages which may be summed up as follows:-

(a)  Minimum of risk from fire. Although one gallon of fuel can be extremely dangerous the risk is obviously very small compared with a crashed machine with a full 10-gallon tank.

(b)   The use of a minimum weight of fuel is essential for all types of sprint events and a tank of one gallon capacity is sufficient.

(c)  Racing on circuits can be greatly enhanced by the use of suitable pit accommodation. The employment of a small capacity tank will enforce, at least, one pit stop in a race of 50 miles length if the machine is running on petrol and considerably more if a dope motor is in use. A pit stop takes time and it will readily become obvious that the faster the machine, the greater the horse power output of the engine. Fuel consumption can, therefore, provide an automatic handicap to the machines using alcohol and enable the competitor, using a machine running on petrol to offset the gain in speed and power from the use of an alcohol fuel.

Minimum Weight – A Minimum Weight of 500lbs. Dry. With tyres, but without Fuel and Oil. A minimum weight of 500 pounds will allow builders of 500 c.c. cars to construct wheels, chassis and other highly stressed parts from materials which have been adapted from parts already in existence. There is, of course, nothing to prevent the construction of cars from light alloys; in fact builders are advised to incorporate as much light alloy as possible, always providing that the correct grade is used and that it is handled in the correct manner. This minimum weight was fixed after consideration of facts and figures obtained from specials already in existence. A machine, built down to the limit of 500lbs. will need careful thought and design to ensure that useless material is not left in places where a little extra hard work can effect removal. On the other hand, the limit does; definitely exclude attempts to beat the power weight ration figures by the construction of cars which would endanger the lives of drives and spectators and the sport in general.

It may be stated that a figure of 650 lbs. for a finished car built to the formula would be in line with machines built to really sound engineering standards.

Gearboxes – Any Type of Gearbox may be used and the incorporation of Reverse is optional. No Limit, whatsoever, is put on the transmission of cars built to the Formula. The car, unless built for use on the road, will not normally be influenced by such matters as the laws under the Traffic Act and even if used on the road, they would not be required to be fitted with reverse gear unless the weight exceeds 8 cwts.

Brakes – Brakes must operate on all four wheels with independent hand operation of brakes on one pair of wheels. This rules makes it clear that in addition to the normal brakes operating on all four wheels, a separate hand brake must be provided to ensure that a failure of the foot brakes system does not render the car absolutely devoid of brakes.

It should be stressed that this rule will be most rigidly adhered to by all scrutineers acting on behalf of the Club. Although brakes are such an important item of equipment, the number of cars which come to the line in sprint races with defective brakes is most surprising. The brakes should be regarded as the most important single item of equipment and builders will do well to concentrate on retardation at the expense of a little acceleration. Mistakes in acceleration may be made as many times as the car is moved from rest, but a mistake in the fitting of a brake pin, brake pipe or cable, may possibly prove to be the first and last.

Bodywork and Body – Bodywork is Optional – but desirable. It may be said that a car body has little effect on its performance; that statement is, to some extent true. Included in the term bodywork, such matters as chain guards, seating and general protection to the driver, must be considered.

Too many Specials are apt to just “happen” when it comes to the finishing stage. Too often there is insufficient time to complete anything in the way of seating or protection from the potential dangers of whirling chains, spinning wheels and bare exhaust pipes, to say nothing of the extreme discomfort of the combined results of the elements and track surface.

A workmanlike body is a most desirable asset; it most certainly enhances the appearance of a machine and, what is more, from the public angle, is most essential. From the builders point of view it provides comfort, protection and that sense of satisfaction, derived from the knowledge that a job has been designed, manufactured and above all, finished.

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