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BMW B46B20 specs: 2.0L (122 ci) 4-cylinder, 82 x 94.6 mm (3.2280 x 3.7240 in) bore and stroke, 10.2:1 compression. Rated 248-288 hp, 2018–2023.
The BMW B46B20 is undersquare — the 3.724" stroke exceeds the 3.228" bore by 13.3% — a layout that trades peak RPM for leverage and torque low in the range. The 3.724" stroke puts mean piston speed at 4,000 ft/min around 6,450 RPM, which is where a production bottom end is generally considered at its limit. Each of the 4 cylinders displaces 30.5 ci (500 cc).
10.2:1 is in the range that usually runs on pump premium.
It is one of 7 engines in the BMW 122ci family, all of them 122 ci — the differences between them are in compression, heads and rating, not displacement. 6 factory variants share these dimensions, rated from 248 to 288 hp across 2018–2023.
| Displacement | 122 ci / 2 L |
|---|---|
| Bore | 3.228" |
| Stroke | 3.724" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 10.2:1 |
| Bore/stroke ratio | 0.867 |
| Fuel type | gas |
|---|---|
| Advertised HP | 248–288 hp |
| Years | 2018–2023 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 2018 | B46B20O1 net | 248 @ 5200 | 258 lb-ft @ 1450 | 10.2:1 |
| 2019 | B46B20O1 net | 248 @ 5200 | 258 lb-ft @ 1450 | 10.2:1 |
| 2020 | B46B20O1 net | 248 @ 5200 | 258 lb-ft @ 1450 | 10.2:1 |
Factory specification sheet.
| Bore/stroke character | 0.867 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,724 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 30.5 ci |
| Static compression | 10.2:1 — in the range that usually runs on pump premium |
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 |
|---|---|---|
| 2018 | 248 hp | B46B20 |
| 2019 | 248 hp | B46B20 |
| 2020 | 248 hp | B46B20 |
| 2021 | 288 hp | B46B20 |
| 2022 | 288 hp | B46B20 |
| 2023 | 288 hp | B46B20 |
1 factory vehicle, 2017–2023. Each year opens that model's engine table.