ELIMINATING THE KNOCK

Sun (Auckland), Volume IV, Issue 958, 29 April 1930, Page 6

ELIMINATING THE KNOCK

USE OF THE SPARK IN TOP GEAR WORK Small high-efficiency engines are very liable to knock if the driver attempts to force their speed up from a slow pace in top gear without using his spark lever. The reason for this becomes obvious when one considers the conditions ruling in the inlet manifold and cylinders during acceleration. As the engine is running at low speed on a nearly closed throttle the cylinders are only partially filled and as the gas is mixed by the slow-running jet it is richer and slower burning than the normal supply. When the driver suddenly steps hard on the accelerator the restriction is taken off the incoming gas and the cylinders receive their full quota of fuel. Unfortunately the mixture is by no means homogeneous, and as the air commences to pour into the cylinders before the comparatively heavy petrol vapour has a chance to get under way the mixture is weakened below normal and knocking is set up. If, however, the driver retards the spark just before he pushes the accelerator pedal down, by providing a late spark he counteracts the rapid burning tendencies of the weakened fuel, and thus knocking is avoided. Immediately after the accelerator has been pressed down the driver should commence advancing the spark, moving the lever gradually to .the .advance position to suit the rising speed of the engine. The secret of success in this connection is to make the movement of the spark lever synchronise perfectly with the demands of the engine, and if this control is expertly handled the acceleration will be sweet and astonishingly rapid.

The Avus race track in Berlin was originally a private road from Potsdam to Berlin. It was constructed for the ex-Kaiser Wilhelm, but after the wat* was turned into' a speedway by making banked loops at each end and growing a strip of grass down the middle of the wide track.

Footpaths made up with a greencoloured top-dressing are a feature of some main roads in Shropshire, England. At night it is easier than usual to distinguish between them and the road surface itself.

It is stated that the Ballot, the Mathis and the Hispano-Suiza companies have amalgamated in order to compete with the American invasion of the French market.