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GMC 327 specs: 327 ci (5.4L) 8-cylinder, 4.00 x 3.25 in (101.6 x 82.6 mm) bore and stroke, 10.5:1 compression. Rated 250 hp. OHV. Rod ratio and piston speed.
The GMC Small Block Chevy (327) is oversquare — the 4" bore exceeds the 3.25" stroke by 23.1% — a layout that favors airflow and RPM over leverage at the crank. The 3.25" stroke does not reach 4,000 ft/min of mean piston speed until about 7,400 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 8 cylinders displaces 40.9 ci (670 cc).
10.5:1 on iron heads is in the range that usually runs on pump premium; iron holds heat, so treat it as the less forgiving side of that range.
It is one of 23 engines in the Small Block Chevy family, sitting between the 265 ci and 400 ci members. Factory fitments include the GMC C/K Series, GMC Suburban, GMC Handi-Van.
| Displacement | 327 ci / 5.4 L |
|---|---|
| Bore | 4" |
| Stroke | 3.25" |
| Cylinders | 8 |
| Compression ratio | 10.5:1 |
| Bore/stroke ratio | 1.231 |
| Piston deck clearance | 0.089" |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 250 hp |
| Bore/stroke character | 1.231 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,250 ft/min — conservative for a street engine |
| Displacement per cylinder | 40.9 ci |
| Static compression | 10.5:1 — in the range that usually runs on pump premium |
| Intake valve diameter | 1.787" |
|---|---|
| Exhaust valve diameter | 1.406" |
| Chamber volume | 60.5 cc |
| Rocker ratio | 1.5:1 |
| Lifter type | hydraulic |
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