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GMC 6V53 specs: 318 ci (5.2L) 6-cylinder, 3.875 x 4.50 in (98.4 x 114.3 mm) bore and stroke, 17:1 compression. Rated 185 hp. OHV. Rod ratio and piston speed.
The GMC 6V53 is undersquare — the 4.5" stroke exceeds the 3.875" bore by 13.9% — a layout that trades peak RPM for leverage and torque low in the range. With a 4.5" stroke, mean piston speed reaches 4,000 ft/min at only 5,350 RPM — the practical ceiling for a production bottom end — which is why a stroke this long makes its power low and runs out of safe revs early. Each of the 6 cylinders displaces 53.0 ci (869 cc).
At 17:1 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 5 engines in the Detroit Diesel V8 (Two-Stroke) family, the smallest at 318 ci. Factory fitments include the GMC General, GMC Brigadier, Various medium-duty trucks and 1 other.
| Displacement | 318 ci / 5.2 L |
|---|---|
| Bore | 3.875" |
| Stroke | 4.5" |
| Cylinders | 6 |
| Compression ratio | 17:1 |
| Bore/stroke ratio | 0.861 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | diesel |
| Advertised HP | 185 hp |
| Bore/stroke character | 0.861 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,500 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 53.0 ci |
| Static compression | 17:1 — high enough that pump premium or better is normally required |
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