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Mitsubishi 4D56 specs: 2.5L (151 ci) 4-cylinder, 91.1 x 95 mm (3.5866 x 3.7402 in) bore and stroke, 21:1 compression. Rated 74 hp. Rod ratio and piston speed.
The Mitsubishi 4D56 is close to square: 3.5866" bore against 3.7402" stroke, within 4.1%, which splits the difference between a high-revving layout and a torque layout. The 3.7402" stroke puts mean piston speed at 4,000 ft/min around 6,400 RPM, which is where a production bottom end is generally considered at its limit. Each of the 4 cylinders displaces 37.8 ci (619 cc).
At 21:1 this is a compression-ignition engine: the ratio is the heat source that lights the fuel, not a knock limit to be managed.
It is one of 3 engines in the Astron family, the smallest at 151 ci. Factory fitments include the L200, Pajero, Delica.
| Displacement | 151 ci / 2.5 L |
|---|---|
| Bore | 3.5866" |
| Stroke | 3.7402" |
| Cylinders | 4 |
| Compression ratio | 21:1 |
| Bore/stroke ratio | 0.959 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | SOHC |
| Fuel type | diesel |
| Advertised HP | 74 hp |
| Bore/stroke character | 0.959 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,740 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 37.8 ci |
| Static compression | 21:1 — high enough that pump premium or better is normally required |
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