AN important clause in the regulations for the Ulster T.T. lays down that “only fuel which the Club considers can be obtained in the ordinary way in most parts of the country may be used.” The T.T. is not a race for racing cars. In essentials every car entered must be a production model, running on a “production “fuel such as private owners may buy from any pump. ‘At Brooklands and other race meetings open to racing cars without restriction on design it is of course common practice to Use special racing fuels prepared to a special prescription, as it were, for a particular engine and even for a particular event. These fuels are doped to prevent

premature ignition, which is the cause of what is generally known as ” knocking ” or ” pinking ” ; but although excellent for racing purposes they are not always suitable for ordinary engines ; and in any case even if they were, few owners could afford their prohibitive cost, and it would be almost impossible to obtain regular supplies. Knocking” or ” pinking ” is, of course, experienced in private cars as well as in racing models. The basic cause is high compression, and the tendency of present-day development is to raise the compression ratio of the engine still higher. This development presents special difficulties in the case of many petrols,

for they will not stand high compression. They ignite too soon, and thus cause the engine to pink.

he demand to-day is for a spirit that will successfully withstand very high compression. Certain petrols, it is claimed, possess this quality. It is possessed too, to a high degree by benzole, the motor spirit nationally derived from coal. Benzole can be subjected to great compression without causing knocking or pinking, and can further transmit this anti-knock property to fuels with which it is blended. It has a higher specific gravity than petrol, giving, it is claimed, greater mileage to the gallon, and another valuable feature is its slow burning which increases the power output.

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