The standard horse-power rating, formerly known as the A. L. A. M. Rating, has been officially adopted by the National Automobile Chamber of Commerce, Inc.
The formula adopted is
D is the cylinder bore in inches, N the number of cylinders, and 2.5 a constant, based on the average view of eminent engineers as to a fair, conservative rating for a four-cycle motor at one thousand feet per minute piston speed.
TABLE OF HORSE-POWER FOR USUAL SIZES OF MOTORS
 |
2 CYLS. | 4 CYLS. | 6 CYLS. | 8 CYLS. | 12 CYLS. |
 |
5.00 | 10.00 | 15.00 | 20.00 | 30.00 |
 |
5.50 | 11.03 | 16.54 | 22.05 | 33.08 |
 |
6.00 | 12.10 | 18.15 | 24.20 | 36.30 |
 |
0.62 | 13.23 | 19.84 | 26.45 | 39.68 |
 |
7.20 | 14.40 | 21.60 | 28.80 | 43.20 |
 |
7.81 | 15.63 | 23.44 | 31.25 | 46.88 |
 |
8.50 | 16.90 | 25.35 | 33.80 | 50.70 |
 |
9.12 | 18.23 | 27.34 | 36.45 | 54.68 |
 |
9.80 | 19.60 | 29.40 | 39.20 | 58.80 |
 |
10.50 | 21.03 | 31.54 | 42.05 | 63.08 |
 |
11.25 | 22.50 | 33.75 | 45.00 | 67.50 |
 |
12.00 | 24.03 | 36.04 | 48.05 | 72.08 |
 |
12.80 | 25.60 | 38.40 | 51.20 | 76. SO |
 |
13.62 | 27.23 | 40.84 | 54.45 | 81.68 |
 |
14.50 | 28.90 | 43.35 | 57.80 | 86.70 |
 |
15.31 | 30.63 | 45.94 | 61.25 | 91.88 |
 |
16.20 | 32.40 | 48.60 | 64.80 | 97.20 |
 |
17.12 | 34.23 | 51.34 | 68.45 | 102.68 |
 |
18.00 | 36.10 | 54.15 | 72.20 | 108.30 |
 |
19.00 | 38.03 | 57.04 | 76.05 | 114.08 |
 |
20.00 | 40.00 | 60.00 | 80.00 | 120.00 |
 |
21.00 | 42.03 | 63.04 | 84.05 | 126.08 |
 |
22.00 | 44.10 | 66.15 | 88.20 | 132.30 |
 |
23.00 | 46.23 | 69.34 | 92.45 | 138.68 |
 |
24.20 | 48.40 | 72.60 | 96.80 | 145.20 |
 |
25.31 | 50.63 | 75.94 | 101.25 | 151.88 |
 |
26.50 | 52.90 | 79.35 | 105.80 | 158.70 |
 |
27.62 | 55.23 | 82.84 | 110.45 | 165.68 |
 |
28.80 | 57.60 | 86.40 | 115.20 | 172.80 |
