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Austin-Healey 29D specs: 178 ci 6-cylinder, 83.3 x 88.9 mm (3.2811 x 3.5000 in) bore and stroke, 9.03:1 compression. Rated 124 hp, 1959–1961.
The Austin-Healey 178ci (29D) is undersquare — the 3.5" stroke exceeds the 3.2811" bore by 6.3% — a layout that trades peak RPM for leverage and torque low in the range. The 3.5" stroke puts mean piston speed at 4,000 ft/min around 6,850 RPM, which is where a production bottom end is generally considered at its limit. Each of the 6 cylinders displaces 29.7 ci (486 cc).
9.03:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 3 engines in the Austin-Healey 178ci family, all of them 178 ci — the differences between them are in compression, heads and rating, not displacement. 3 factory variants share these dimensions, rated at 124 hp across 1959–1961.
| Displacement | 178 ci |
|---|---|
| Bore | 3.2811" |
| Stroke | 3.5" |
| Cylinders | 6 |
| Configuration | I6 |
| Compression ratio | 9.03:1 * |
| Bore/stroke ratio | 0.937 |
* Compression ratio from a single source; not yet cross-verified.
| Fuel type | gas |
|---|---|
| Advertised HP | 124 hp |
| Years | 1959–1961 |
| Bore/stroke character | 0.937 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 3,500 ft/min — conservative for a street engine |
| Displacement per cylinder | 29.7 ci |
| Static compression | 9.03:1 — 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 |
|---|---|---|
| 1959 | 124 hp | 29D |
| 1960 | 124 hp | 29D |
| 1961 | 124 hp | 29D |
1 factory vehicle, 1959–1961. Each year opens that model's engine table.