Engine Classes
| Letter | Cubic Inch Displacement | Approximate Liter Equiv. |
| AA | 501 cid and over | 8.21 liters and over |
| A | 440 thru 500 | 7.21 to 8.19 |
| B | 373 thru 439 | 6.11 to 7.19 |
| C | 306 thru 372 | 5.01 to 6.10 |
| D | 261 thru 305 | 4.27 to 5.00 |
| E | 184 thru 260 | 3.01 to 4.26 |
| F | 123 thru 183 | 2.01 to 3.00 |
| G | 93 thru 122 | 1.51 to 2.00 |
| H | 62 thru 92 | 1.01 to 1.50 |
| I | 46 thru 61 | 0.76 to 1.00 |
| J | 31 thru 45 | 0.51 to 0.75 |
| K | 30 cid and under | 0.50 and under |