KNOCKING AND ENGINE PERFORMANCE.

King Country Chronicle, Volume XXXI, Issue 4953, 9 February 1937, Page 3

KNOCKING AND ENGINE PERFORMANCE.

For some years now automotive and fuel engineers have been very conscious of the harmful effects of knocking brought about by the use of ordinary petrols in cars of high compression ratio. Until recent years, the average motorist was not greatly concerned about the effect of “knocking”; compression ratios then were relatively low. But to-day it is vastly different. In the modern car, with its high compression engine, the most unobservant motorist cannot fail to be conscious of the sharp “pinking” sound that occurs in an engine running on ordinary petrol during hill climbing in top gear, or when the accelerator is suddenly pressed down to care for some traffic emergency. “Knocking” becomes more accentuated after a few thousand miles of running when carbon deposits increase the already high compression of the engine. “Knocking” is definitely ruinous to engine performance. Power is lost immediately, and the sharp explosive blow on moving parts combined with the over-heating which invariably accompanies knocking, is very damaging to plugs, valves, pistons, and bearings.

“Knocking” can be stopped by retarding the spark, or, if it occurs on hills, by changing to a lower gear. But either of these methods is false economy—simply shutting the stable door after the horse-power is gone. There is only one sound method of stopping “knocking,” and that is to remove its first cause, and on the subject of causes there is complete agreement amongst technical men the world over. “Knocking” is caused by the use of a petrol of low anti-knock property. Therefore, to stop “knocking” a high anti-knock petrol must be used, because only high anti-knock petrol can develop full knockless power in the car of to-day.