| 1 |
All cars up to and including 1400cc |
| 2 |
All cars from 1401cc to 1650cc with up to two valves per cylinder |
| 3 |
All cars from 1401cc to 1650cc with more than two valves per cylinder |
| 4 |
All cars from 1651cc to 2100cc with up to two valves per cylinder |
| 5 |
All cars from 1651cc to 2100cc with more than two valves per cylinder |
| 6 |
All other eligible cars |