See other engines in this family
Honda B21A1 specs: 2.1L (126 ci) 4-cylinder, 83 x 95 mm (3.2677 x 3.7402 in) bore and stroke. Rated 140 hp, 1990–1991. Used in the Honda Prelude.
The Honda B21A1 is undersquare — the 3.7402" stroke exceeds the 3.2677" bore by 12.6% — a layout that trades peak RPM for leverage and torque low in the range. 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 31.5 ci (516 cc).
2 factory variants share these dimensions, rated at 140 hp across 1990–1991.
| Displacement | 126 ci / 2.1 L |
|---|---|
| Bore | 3.2677" |
| Stroke | 3.7402" |
| Cylinders | 4 |
| Configuration | I4 |
| Bore/stroke ratio | 0.874 |
| Fuel type | gas |
|---|---|
| Advertised HP | 140 hp |
| Years | 1990–1991 |
| Bore/stroke character | 0.874 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,740 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 31.5 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 |
|---|---|---|
| 1990 | 140 hp | B21A1 |
| 1991 | 140 hp | B21A1 |
1 factory vehicle, 1990–1991. Each year opens that model's engine table.