Because of the different years and engines, there were four different harmonic balancers used on the Z31's VG30 engines. Below is a chart to help determine which one you want to use.
| Year | Engine | Aspiration | Part Number | PS Pulley | AC Pulley | H2O/Alt Pulley |
|---|---|---|---|---|---|---|
| 1984-1986 | A/B Series | non-turbo | 12303-V5020 | V-Belt | V-Belt | V-Belt |
| 1984-1986 | A/B Series | turbo | 12303-V5320 | V-Belt | V-Belt | micro-V |
| 1987 | A/B Series | all | 12303-F6100 | micro-V | micro-V | micro-V |
| 1987-1989 | W Series | all | 12303-21V10 | micro-V | micro-V | micro-V |
You can use the A/B series balancers on the W series crankshafts if you get the spacer from Nissan (p/n 12308-V5321).
You should be able to use a W series balancer on an A/B series crankshaft if you get a slightly longer bolt with matching threads.