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Nissan RB specs: 2.5L (152.4 ci) 6-cylinder, 86 x 71.7 mm (3.3858 x 2.8228 in) bore and stroke, 9:1 compression. Rated 245-276 hp. Rod ratio and piston speed.
The Nissan RB is oversquare — the 3.3858" bore exceeds the 2.8228" stroke by 19.9% — a layout that favors airflow and RPM over leverage at the crank. The 2.8228" stroke does not reach 4,000 ft/min of mean piston speed until about 8,500 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 25.4 ci (416 cc).
9:1 on aluminum heads is low by modern standards and generally happy on regular pump fuel.
It is one of 11 engines in the RB family, sitting between the 121.8 ci and 182.7 ci members. 2 factory variants share these dimensions, rated from 245 to 276 hp. Factory fitments include the Nissan Skyline R33 GTS25t, Nissan Laurel C34, Nissan Cefiro A32 and 3 others.
| Displacement | 152.4 ci / 2.5 L |
|---|---|
| Bore | 3.3858" |
| Stroke | 2.8228" |
| Cylinders | 6 |
| Compression ratio | 9:1 |
| Bore/stroke ratio | 1.199 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 245–276 hp |
| Bore/stroke character | 1.199 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,823 ft/min — conservative for a street engine |
| Displacement per cylinder | 25.4 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
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 |
|---|---|---|
| — | 245 hp | RB25DET |
| — | 276 hp | RB25DET NEO |