From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Foreword to a booklet explaining the benefits and fuel economy of an automatic overdrive system, with test results from a Chrysler Imperial.
| Identifier | ExFiles\Box 125\2\ scan0112 | |
| Date | 2nd November 1936 guessed | |
| FOREWORD THE purpose of this booklet is to tell you about the Chrysler automatic overdrive, one of the exclusive features of your car. The Airflow type of car has made possible higher road speeds than in the past. This, of course, means higher engine speeds. By using an overdrive which drives the axle over the engine speed, it is possible to get high road speeds with low engine speeds. The lower engine speeds show a marked saving in fuel, oil and engine wear and consequently greatly reduces the noise and disturbance so that an entirely new sensation in driving is produced. We believe that you will profit immensely by reading this booklet; first that you may know how properly to take fullest advantage of the overdrive and second that you may inform yourself on the why and wherefore of the device that is going to contribute so greatly to the pleasure and economy of your driving. it would take 8 horsepower at 4,000 revolutions per minute. Thus a thirty per cent. reduction in engine speed effected by the use of the overdrive means a reduction of 50 to 60 per cent. in such parasitic losses at a given car speed. [GRAPH] Y-axis: MILES PER GALLON, with values from 10 to 17. X-axis: MILES PER HOUR, with values from 10 to 60. Lines: The top line is labeled 'OVERDRIVE', the bottom line is labeled 'CONVENTIONAL DRIVE'. Tests conducted by Chrysler engineers have established a remarkable fuel economy factor for the overdrive. Using the Chrysler Imperial, a car of 323.5 inches cubic piston displacement, 130 horsepower, and 8 cylinders 3¼ by 4½ inches without overdrive, it was found possible to get 14.9 miles to the gallon at 20 miles an hour; 14.4 miles at 30 miles an hour; 13.7 miles at 40 miles an hour and 13.1 miles at 50 miles an hour. Demands on horsepower are very large at speeds of upwards of 50 miles an hour and the curve drops sharply. Nevertheless at 60 miles an hour the Imperial got 11.8 miles per gallon. With the Chrysler overdrive, the first test was conducted at 40 miles an hour. The remarkable figure of 16.9 miles per gallon was obtained at this speed, or two miles a gallon more than at 20 miles in conventional drive. At 50 miles an hour the reading was 15.9 miles per gallon, still considerably higher than at 20 miles without the overdrive. At 60 miles an hour, a speed that “eats up” fuel in conventional drive, the Chrysler Imperial got 14.3 miles per gallon with the . 11 . | ||