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Hyundai 25 specs: 2.5L (152.6 ci) 6-cylinder, 81 x 80 mm (3.1890 x 3.1496 in) bore and stroke, 10:1 compression. Rated 170 hp. Rod ratio and piston speed.
The Hyundai Delta (25) is close to square: 3.189" bore against 3.1496" stroke, within 1.3%, which splits the difference between a high-revving layout and a torque layout. The 3.1496" stroke does not reach 4,000 ft/min of mean piston speed until about 7,600 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 (417 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 3 engines in the Delta family, the smallest at 152.6 ci. Factory fitments include the Hyundai Sonata, Hyundai Santa Fe, Hyundai H-1 and 2 others.
| Displacement | 152.6 ci / 2.5 L |
|---|---|
| Bore | 3.189" |
| Stroke | 3.1496" |
| Cylinders | 6 |
| Compression ratio | 10:1 |
| Bore/stroke ratio | 1.013 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 170 hp |
| Bore/stroke character | 1.013 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,150 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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