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GMC LFX specs: 217 ci (3.6L) 6-cylinder, 3.701 x 3.37 in (94 x 85.6 mm) bore and stroke, 11.5:1 compression. Rated 323 hp. DOHC. Rod ratio and piston speed.
The GMC High Feature V6 (LFX) is oversquare — the 3.7008" bore exceeds the 3.3701" stroke by 9.8% — a layout that favors airflow and RPM over leverage at the crank. The 3.3701" stroke does not reach 4,000 ft/min of mean piston speed until about 7,100 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 36.2 ci (593 cc).
11.5:1 on aluminum heads is high for a production gasoline engine; running a ratio like that on pump fuel depends on chamber design and fuel delivery rather than the number alone.
It is one of 6 engines in the High Feature V6 family, sitting between the 169 ci and 222.7 ci members. Factory fitments include the Cadillac ATS, Cadillac CTS, Chevrolet Camaro and 2 others.
| Displacement | 217 ci / 3.6 L |
|---|---|
| Bore | 3.7008" |
| Stroke | 3.3701" |
| Cylinders | 6 |
| Compression ratio | 11.5:1 |
| Bore/stroke ratio | 1.098 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 323 hp |
| Bore/stroke character | 1.098 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,370 ft/min — conservative for a street engine |
| Displacement per cylinder | 36.2 ci |
| Static compression | 11.5:1 — high enough that pump premium or better is normally required |
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