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Nissan RB25DE specs: 2.5L (152.4 ci) 6-cylinder, 86 x 71.7 mm (3.3858 x 2.8228 in) bore and stroke, 10:1 compression. Rated 178 hp. DOHC.
The Nissan RB25DE 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).
10:1 on aluminum heads is in the range that usually runs on pump premium; aluminum sheds heat faster than iron, which makes the same number a little more forgiving.
It is one of 11 engines in the RB family, sitting between the 121.8 ci and 182.7 ci members. Factory fitments include the Nissan Skyline R32, Nissan Skyline R33, Nissan Laurel C33 and 2 others.
| Displacement | 152.4 ci / 2.5 L |
|---|---|
| Bore | 3.3858" |
| Stroke | 2.8228" |
| Cylinders | 6 |
| Compression ratio | 10:1 |
| Bore/stroke ratio | 1.199 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 178 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 | 10:1 — in the range that usually runs on pump premium |
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