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GMC 455 specs: 455 ci (7.5L) 8-cylinder, 4.06 x 4.38 in (103.1 x 111.2 mm) bore and stroke, 8.2:1 compression. Rated 370 hp. OHV. Rod ratio and piston speed.
The GMC Pontiac V8 (455) is undersquare — the 4.3799" stroke exceeds the 4.0598" bore by 7.3% — a layout that trades peak RPM for leverage and torque low in the range. With a 4.3799" stroke, mean piston speed reaches 4,000 ft/min at only 5,500 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 8 cylinders displaces 56.9 ci (932 cc).
8.2:1 on iron heads is low by modern standards and generally happy on regular pump fuel.
It is one of 9 engines in the Pontiac V8 family, the largest at 455 ci. Factory fitments include the Pontiac GTO, Pontiac Firebird Trans Am, Pontiac Grand Prix and 9 others.
| Displacement | 455 ci / 7.5 L |
|---|---|
| Bore | 4.0598" |
| Stroke | 4.3799" |
| Cylinders | 8 |
| Compression ratio | 8.2:1 |
| Bore/stroke ratio | 0.927 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | gas |
| Advertised HP | 370 hp |
| Bore/stroke character | 0.927 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,380 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 56.9 ci |
| Static compression | 8.2:1 — low by modern standards, generally happy on regular pump fuel |
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