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Mazda KJ-ZEM specs: 2.3L (138 ci) 6-cylinder, 80.3 x 74.2 mm (3.1614 x 2.9213 in) bore and stroke. Rated 210 hp, 1995–2002. Used in the Mazda Millenia.
The Mazda KJ-ZEM is oversquare — the 3.1614" bore exceeds the 2.9213" stroke by 8.2% — a layout that favors airflow and RPM over leverage at the crank. The 2.9213" stroke does not reach 4,000 ft/min of mean piston speed until about 8,200 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 23.0 ci (377 cc).
8 factory variants share these dimensions, rated at 210 hp across 1995–2002.
| Displacement | 138 ci / 2.3 L |
|---|---|
| Bore | 3.1614" |
| Stroke | 2.9213" |
| Cylinders | 6 |
| Configuration | V6 |
| Compression ratio | 8–10:1 (published figures vary) |
| Bore/stroke ratio | 1.082 |
| Fuel type | gas |
|---|---|
| Advertised HP | 210 hp |
| Years | 1995–2002 |
| Bore/stroke character | 1.082 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 2,921 ft/min — conservative for a street engine |
| Displacement per cylinder | 23.0 ci |
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 |
|---|---|---|
| 1995 | 210 hp | KJ-ZEM |
| 1996 | 210 hp | KJ-ZEM |
| 1997 | 210 hp | KJ-ZEM |
| 1998 | 210 hp | KJ-ZEM |
| 1999 | 210 hp | KJ-ZEM |
| 2000 | 210 hp | KJ-ZEM |
| 2001 | 210 hp | KJ-ZEM |
| 2002 | 210 hp | KJ-ZEM |
1 factory vehicle, 1995–2002. Each year opens that model's engine table.