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Chevrolet LLY / LMM specs: 403 ci (6.6L) 8-cylinder, 4.055 x 3.898 in (103 x 99 mm) bore and stroke, 16.8:1 compression. Built 2007.
The Chevrolet LLY / LMM 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. A rod ratio of 1.646 is in the range most production engines fall in. Each of the 8 cylinders displaces 50.4 ci (825 cc).
At 16.8:1 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 17 engines in the Duramax family, the largest at 403 ci.
| Displacement | 403 ci / 6.6 L |
|---|---|
| Bore | 4.0551" |
| Stroke | 3.8976" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 16.8:1 * |
| Rod length | 6.417" |
| Rod ratio | 1.646 |
| Bore/stroke ratio | 1.04 |
* Compression ratio from a single source; not yet cross-verified.
| Block material | cast iron |
|---|---|
| Head material | aluminum |
| Valvetrain | OHV |
| Fuel type | diesel |
| Firing order | 1-2-7-8-4-5-6-3 |
| Years | 2007 |
| 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 |
| Rod ratio | 1.646 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 50.4 ci |
| Static compression | 16.8:1 — high enough that pump premium or better is normally required |
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1 factory vehicle, 2007. Each year opens that model's engine table.