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Nissan U20 specs: 122 ci 4-cylinder, 87.2 x 83 mm (3.4331 x 3.2677 in) bore and stroke, 9.5:1 compression. Rated 135 hp, 1967–1970.
The Nissan 122ci (U20) is oversquare — the 3.4331" bore exceeds the 3.2677" stroke by 5.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.2677" stroke does not reach 4,000 ft/min of mean piston speed until about 7,350 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 30.5 ci (500 cc).
9.5:1 is in the range that usually runs on pump premium.
It is one of 6 engines in the Nissan 122ci family, all of them 122 ci — the differences between them are in compression, heads and rating, not displacement. 4 factory variants share these dimensions, rated at 135 hp across 1967–1970.
| Displacement | 122 ci |
|---|---|
| Bore | 3.4331" |
| Stroke | 3.2677" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 9.5:1 |
| Bore/stroke ratio | 1.051 |
| Fuel type | gas |
|---|---|
| Advertised HP | 135 hp |
| Years | 1967–1970 |
| Bore/stroke character | 1.051 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,268 ft/min — conservative for a street engine |
| Displacement per cylinder | 30.5 ci |
| Static compression | 9.5:1 — in the range that usually runs on pump premium |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1967 | 135 hp | U20 |
| 1968 | 135 hp | U20 |
| 1969 | 135 hp | U20 |
| 1970 | 135 hp | U20 |
1 factory vehicle, 1967–1970. Each year opens that model's engine table.