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Chevrolet Duramax specs: 403 ci (6.6L) 8-cylinder, 4.055 x 3.898 in (103 x 99 mm) bore and stroke, 17.5:1 compression. Rated 300-310 hp. OHV.
The Chevrolet Duramax is close to square: 4.0551" bore against 3.8976" stroke, within 4.0%, which splits the difference between a high-revving layout and a torque layout. The 3.8976" stroke puts mean piston speed at 4,000 ft/min around 6,150 RPM, which is where a production bottom end is generally considered at its limit. Each of the 8 cylinders displaces 50.4 ci (825 cc).
At 17.5:1 this is a compression-ignition engine: the ratio is the heat source that lights the fuel, not a knock limit to be managed.
It is one of 13 engines in the Duramax family, the largest at 403 ci. 2 factory variants share these dimensions, rated from 300 to 310 hp. Factory fitments include the Chevrolet Silverado 2500HD/3500HD, GMC Sierra 2500HD/3500HD, Chevrolet Express Van and 1 other.
| Displacement | 403 ci / 6.6 L |
|---|---|
| Bore | 4.0551" |
| Stroke | 3.8976" |
| Cylinders | 8 |
| Compression ratio | 17.5:1 |
| Bore/stroke ratio | 1.04 |
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | OHV |
| Fuel type | diesel |
| Advertised HP | 300–310 hp |
| Bore/stroke character | 1.040 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,898 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 50.4 ci |
| Static compression | 17.5:1 — high enough that pump premium or better is normally required |
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 |
|---|---|---|
| — | 300 hp | LB7 |
| — | 310 hp | LLY |