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Mitsubishi 4B12 specs: 2.4L (144 ci) 4-cylinder, 88 x 97 mm (3.4646 x 3.8189 in) bore and stroke, 10.5:1 compression. Rated 168 hp. DOHC.
The Mitsubishi 4B12 is undersquare — the 3.8189" stroke exceeds the 3.4646" bore by 9.3% — a layout that trades peak RPM for leverage and torque low in the range. The 3.8189" stroke puts mean piston speed at 4,000 ft/min around 6,300 RPM, which is where a production bottom end is generally considered at its limit. Each of the 4 cylinders displaces 36.0 ci (590 cc).
10.5:1 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 2 engines in the Global Engine family, the largest at 144 ci. Factory fitments include the Lancer, Outlander, Delica.
| Displacement | 144 ci / 2.4 L |
|---|---|
| Bore | 3.4646" |
| Stroke | 3.8189" |
| Cylinders | 4 |
| Compression ratio | 10.5:1 |
| Bore/stroke ratio | 0.907 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 168 hp |
| Bore/stroke character | 0.907 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,819 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 36.0 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
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