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Shelby 428ci specs: 7.0L (428 ci) 8-cylinder, 105 x 101.2 mm (4.1320 x 3.9840 in) bore and stroke, 12.25:1 compression. Rated 390 hp, 1967.
The Shelby 428ci is close to square: 4.132" bore against 3.984" stroke, within 3.7%, which splits the difference between a high-revving layout and a torque layout. The 3.984" stroke puts mean piston speed at 4,000 ft/min around 6,000 RPM, which is where a production bottom end is generally considered at its limit. A rod ratio of 1.629 is in the range most production engines fall in. Each of the 8 cylinders displaces 53.5 ci (877 cc).
12.25:1 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 2 engines in the Shelby 428ci family, all of them 428 ci — the differences between them are in compression, heads and rating, not displacement.
| Displacement | 428 ci / 7 L |
|---|---|
| Bore | 4.132" |
| Stroke | 3.984" |
| Cylinders | 8 |
| Compression ratio | 12.25:1 |
| Rod length | 6.488" |
| Rod ratio | 1.629 |
| Bore/stroke ratio | 1.037 |
| Piston deck clearance | 0.005" |
| Induction | 2-4 |
|---|---|
| Advertised HP | 390 hp |
| Years | 1967 |
| Bore/stroke character | 1.037 — square — bore and stroke are within 5%, a balanced compromise |
|---|---|
| Mean piston speed at 6,000 RPM | 3,984 ft/min — in the range typical of performance street engines |
| Rod ratio | 1.629 — moderate — the range most production V8s fall in |
| Displacement per cylinder | 53.5 ci |
| Static compression | 12.25:1 — high enough that pump premium or better is normally required |
| Intake valve diameter | 2.037" |
|---|---|
| Exhaust valve diameter | 1.566" |
| Chamber volume | 65 cc |
| Rocker ratio | 1.73:1 |
| Lifter type | mechanical |
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