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Triumph FC specs: 70 ci 4-cylinder, 69.3 x 75.9 mm (2.7300 x 2.9900 in) bore and stroke, 9:1 compression. Rated 63 hp, 1963–1967.
The Triumph 70ci (FC) is undersquare — the 2.99" stroke exceeds the 2.73" bore by 8.7% — a layout that trades peak RPM for leverage and torque low in the range. The 2.99" stroke does not reach 4,000 ft/min of mean piston speed until about 8,050 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 4 cylinders displaces 17.5 ci (287 cc).
9:1 is low by modern standards and generally happy on regular pump fuel.
5 factory variants share these dimensions, rated at 63 hp across 1963–1967.
| Displacement | 70 ci |
|---|---|
| Bore | 2.73" |
| Stroke | 2.99" |
| Cylinders | 4 |
| Configuration | I4 |
| Compression ratio | 9:1 * |
| Bore/stroke ratio | 0.913 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 63 hp |
| Years | 1963–1967 |
| Bore/stroke character | 0.913 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 2,990 ft/min — conservative for a street engine |
| Displacement per cylinder | 17.5 ci |
| Static compression | 9:1 — low by modern standards, generally happy on regular pump fuel |
Each link opens the calculator with this engine's specs already filled in.
These records share identical bore, stroke, displacement and compression. They differ by model year and factory power rating.
| Year | Advertised HP | Code |
|---|---|---|
| 1963 | 63 hp | FC |
| 1964 | 63 hp | FC |
| 1965 | — | FC |
| 1966 | — | FC |
| 1967 | — | FC |
1 factory vehicle, 1963–1967. Each year opens that model's engine table.