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Buick LM4 specs: 325 ci (5.3L) 8-cylinder, 3.78 x 3.622 in (96 x 92 mm) bore and stroke, 9.5:1 compression. Rated 290 hp, 2004. Used in the Chevrolet SSR.
The Buick 325ci (LM4) is close to square: 3.7795" bore against 3.622" stroke, within 4.3%, which splits the difference between a high-revving layout and a torque layout. The 3.622" stroke puts mean piston speed at 4,000 ft/min around 6,650 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 40.6 ci (666 cc).
9.5:1 is in the range that usually runs on pump premium.
It is one of 2 engines in the Buick 325ci family, all of them 325 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 325 ci / 5.3 L |
|---|---|
| Bore | 3.7795" |
| Stroke | 3.622" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 9.5:1 * |
| Bore/stroke ratio | 1.043 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 290 hp |
| Years | 2004 |
| Year | Version | HP @ rpm | Torque @ rpm | Comp. |
|---|---|---|---|---|
| 2004 | LM4 net | 290 @ 5200 | 325 lb-ft @ 4000 | — |
Factory specification sheet.
| Bore/stroke character | 1.043 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,622 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 40.6 ci |
| Static compression | 9.5:1 — in the range that usually runs on pump premium |
Each link opens the calculator with this engine's specs already filled in.
4 factory vehicles, 2003–2004. Each year opens that model's engine table.