COMPRESSION RATIOS

Evening Star, Issue 23498, 12 February 1940, Page 11

COMPRESSION RATIOS

One of the most important developments in the modern automobile engine has been the raising of compression ratios, thereby increasing borse-powor developed by about 80 per cent., without any appreciable increase in weight of power unit. Take, for instance, some of the American or Canadian cars operating on New Zealand roads. Fifteen years ago they had engines which, on the average, bad a displacement, of 2521 n and developed in the region of 60 h.p. ‘The lates models average about 25uin displacement, almost’ identical with the engines of 15 years ago, yet they can develop on the average over 100 h.p. This increase in power output, which applies equally to cars of British and Continental origin, has been gained by increasing the pressure on the petrol-air mixture_ in the combustion chambers before it is burned, which, in effect, squeezes more power and more milqs out of each drop of petrol used. Since 1931 the average compression pressure in passenger car engines Jins increased from between 901 b and 1001 b per square inch up to between 1-101 b and 1501 b per square inch. How the compression ratios in cars have been raised is shown by the fact that, in 1925, they averaged around 4.5 to 1; in 1931 they had risen to about 5.25 to 1; to-day some models have ratios as high as 6.28 to 1, with oven higher ratios optional. The net result is more power and greater economy; in fact, a better automobile.