Engineering Wonders of the World
Volume III

THE DEVELOPMENT OF THE RACING MOTOR CAR 331 that used in 1906, at an average speed of over 70 miles an hour. A few months later the rules were again altered, this time in a more practical direction, for the bore of the engine was restricted to 155 millimetres. As the ordinary engine of 1906 and 1907 had a bore of some 180 or 185 millimetres, this was a sub- stantial reduction. It produced some very not- able results ; for the bore having been limited, the stroke of the engine was greatly lengthened by some makers, and in some cases the power obtained far exceeded that which it had been the custom to expect from the racers of the former years. Certainly the Grand Prix cars of 1908 were the fastest road- racing vehicles ever produced, and caused an alteration of ideas concerning the high- speed petrol engine which can almost be called a revolution. In 1909 it had been decided to reduce still further the THE SIX-CYLINDER NAPIER OF 1905. This car was the fastest English road-racer ever built, and still holds a number of world’s records, made by Macdonald at Florida in 1905. It competed in the Gordon-Bennett race of 1905 in the Auvergne. WAGNER, THE WINNER OF THE VANDERBILT CUP OF 1906, ON HIS SUCCESSFUL DARRACQ. It is interesting to compare this car with those of 1904 and 1905. The change- speed lever was placed at the side instead of beneath the steering-column, and detachable rims were fitted. DURAY AT FULL SPEED IN THE GRAND PRIX OF 1907, IN WHICH HE COVERED EIGHT LAPS AT AN AVERAGE SPEED OF OVER SEVENTY MILES AN HOUR.