IGNITION TIMING

Hawke's Bay Tribune, Volume XXII, Issue 272, 1 November 1932, Page 4

IGNITION TIMING

HOW THE SPARK AFFECTS THE POWER. How spark timing affects compression is little understood by the average motorist, yet it is easily explained. Since petrol vapour requires a measurablo period of time to burn, it is customary to time the sprark in the cylinders to ignite tho gas before the pistons reach the top of their compression strokes. With the spark properly advanced, enough of tho gas should start burning to further compress its unburned portion, so that when the pistons start down on their power strokes they do so with greater force. If the spark is too early and too much gas starts burning, the tendency is for the pistons to be prevented from reaching the top of their compression strokes. This causes pronounced knocking, and during cranking results in back-firing. Tho faster the engine runs the more, within limits, the spark can be advanced with safety and efficiency. In this way the igniting of the gas charge itself affects compression and power. This knowledge is elementary, but if owners studied its effects they would obtain better performance from their cars. It should be remembered, too, that tho use of spark plugs that are older than 10,000 miles has a similar effect to retarded ignition, because of the considerably weakened sparks at the plug points being incapable of igniting the cylinder charges efficiently.