Transmission
1. Better Gear Ratio in the upper 3 Gears
For the performance characteristics of a race engine, the gear ratios of engine types 351/352 in the upper three gears are not close enough together. Since engine type 521/522 the upper 3 gears are in closer steps. Gear shafts of 351, 352, 521, 522 are interchangeable.
Transmission gradiation
| gear | 351/352 | 521/522/1A2/31k/1WW |
| 1 | 2,57 | 2,57 |
| 2 | 1,78 | 1,78 |
| 3 | 1,32 | 1,32 |
| 4 | 1,04 | 1,08 |
| 5 | 0,89 | 0,96 |
| 6 | 0,79 | 0,89 |
1.2 The primary transmission ratio of the RD 350 and the RD 250 aircooled are different
Primary transmission gradiation RD250: 21:68
Primary transmission gradiation RD350: 23:66
Oil pump transmission RD250 21:22
Oil pump transmission RD350/400: 23:21
To convert a RD 250 engine to the primary transmission ratio of a RD 350 the following parts needs to be changed:
- Plastic wheel oil pump (21 teeth RD350 - Part Number 278-13178-00 RD250 22 teeth )
- Plastic wheel tachometer drive (20 teeth RD350 - Part Number 278-17851-00, (RD250, 18 teeth )
- For 350cc cylinder you need longer studs Part Number 248-11361-00 or tinker as described here