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BMW S50B32 specs: 3.2L (195.2 ci) 6-cylinder, 86.4 x 91 mm (3.4016 x 3.5827 in) bore and stroke, 11.3:1 compression. Rated 321 hp. Rod ratio and piston speed.
The BMW S50B32 is undersquare — the 3.5827" stroke exceeds the 3.4016" bore by 5.1% — a layout that trades peak RPM for leverage and torque low in the range. The 3.5827" stroke puts mean piston speed at 4,000 ft/min around 6,700 RPM, which is where a production bottom end is generally considered at its limit. Each of the 6 cylinders displaces 32.5 ci (533 cc).
11.3:1 on aluminum heads is high enough that pump premium or better is normally required.
It is one of 5 engines in the S5x family, the largest at 195.2 ci. Factory fitments include the BMW E36 M3 (Euro-spec), BMW Z3 M Roadster/Coupe (Euro-spec).
| Displacement | 195.2 ci / 3.2 L |
|---|---|
| Bore | 3.4016" |
| Stroke | 3.5827" |
| Cylinders | 6 |
| Compression ratio | 11.3:1 |
| Bore/stroke ratio | 0.949 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 321 hp |
| Bore/stroke character | 0.949 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,583 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 32.5 ci |
| Static compression | 11.3:1 — high enough that pump premium or better is normally required |
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