POWER TO WEIGHT

Evening Post, Volume CXXI, Issue 115, 16 May 1936, Page 30

POWER TO WEIGHT

THE PETROL BILL

A small engine is riot necessarily much more economical than a larger power unit, and a car purchaser may easily sacrifice the desirable attributes of power for hill-climbing and highcruising speed in the fallacious belief that at least he will make considerable savings in his petrol bill. Many cases can be cited of cars with small engines whose petrol consumption is excessive. The reason is that reasonable economy combined with a reasonably good performance is only obtained by striking a shappy balance between engine size add car weight,,so that.the engine rarely, if ever, is operating with wide open throttle and is nearly always running quietly, well within its limits. If the engine is so small in regard to the weight of the car as to upset this balance (which is .very hard to define in words), it will.be found that in order to obtain a performance comparable with that of the larger-engined vehicle it-will be running for a surprising amount of its time with the throttle either wide open or nearly so. Thus in accelerating away from rest, it wili be found that, the accelerator, will be pushed to the floorboards and-that in fast cruising the throttle will be nearly wide open, whereas,,in similar circumstances and at a similar speed, the engine of the larger car willbe running on. no more than quarter throttle. It has been found that petrol consumption is governed very largely by normal throttle opening, and that is why, in this regard, small engines are often very hungry when it comes to the consumption of petrol. An engine which always runs well within its limits lasts, longer without overhaul*