MOTOR HORSEPOWER
S. A. E. Scale
FOUR-CYCLE HORSEPOWER RATING
| Bore | 1 cyl. | 2 cyl. | 4 cyl. | 6 cyl. | |
|---|---|---|---|---|---|
| 2 | 3⁄4 | 3.00 | 6.00 | 12.00 | 18.00 |
| 2 | 7⁄8 | 3.00 | 6.50 | 13.00 | 20.00 |
| 3 | .00 | 3.50 | 7.00 | 14.50 | 21.50 |
| 3 | 1⁄4 | 4.00 | 8.50 | 17.00 | 25.50 |
| 3 | 1⁄2 | 5.00 | 10.00 | 20.00 | 29.50 |
| 3 | 3⁄4 | 5.50 | 11.00 | 22.50 | 34.00 |
| 4 | .00 | 6.50 | 13.00 | 25.50 | 38.50 |
| 4 | 1⁄4 | 7.00 | 14.50 | 29.00 | 43.50 |
| 4 | 1⁄2 | 8.00 | 16.00 | 32.50 | 48.50 |
| 4 | 3⁄4 | 9.00 | 18.00 | 36.00 | 54.00 |
| 5 | .00 | 10.00 | 20.00 | 40.00 | 60.00 |
| 5 | 1⁄4 | 11.00 | 22.00 | 44.00 | 66.00 |
| 5 | 1⁄2 | 12.00 | 24.00 | 48.00 | 73.00 |
| 5 | 3⁄4 | 13.00 | 26.50 | 53.00 | 79.50 |
| 6 | .00 | 14.50 | 29.00 | 57.50 | 86.50 |
This scale gives the nearest equivalent to the whole or half horsepower, as is required by State where licenses are paid at so much per horsepower.
Formula—S. A. E. D2 times N 2.5 equals horsepower.
For sleeve valve timing see [Chapter II] on Valves.
DISPLACEMENT
There are probably few men operating cars to-day who fully understand what is meant by the term displacement, often used in referring to automobile races. It is one of the main factors or points in determining the class in which a car is qualified to enter under the laws that govern races. In looking over a race program, you will note that there are usually two or more classes, one of which is open, and another with a limited piston displacement, which gives the smaller cars a competing chance in their class.
Consequently piston displacement is merely the volume displaced by all the piston in moving the full length of the stroke. The volume of a single cylinder is equal to the area of the bore multiplied by the length of the stroke, and the total displacement of a four cylinder motor will be four times this and that of a six cylinder motor, six times this.
Piston displacement:
D2 times S times N times 3.14 4