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Chevrolet 153ci specs: 153 ci (2.5L) 4-cylinder, 3.875 x 3.25 in (98.4 x 82.6 mm) bore and stroke, 8.5:1 compression. Rated 90 hp, 1965–1970.
The Chevrolet 153ci is oversquare — the 3.875" bore exceeds the 3.25" stroke by 19.2% — a layout that favors airflow and RPM over leverage at the crank. The 3.25" stroke does not reach 4,000 ft/min of mean piston speed until about 7,400 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. A rod ratio of 1.754 is long by production standards — less side-load on the cylinder wall and gentler piston acceleration around TDC, the geometry that tolerates high RPM. Each of the 4 cylinders displaces 38.3 ci (627 cc).
8.5:1 is low by modern standards and generally happy on regular pump fuel.
It is one of 2 engines in the Chevrolet 153ci family, all of them 153 ci — the differences between them are in compression, heads and rating, not displacement. 6 factory variants share these dimensions, rated at 90 hp across 1965–1970.
| Displacement | 153 ci / 2.5 L |
|---|---|
| Bore | 3.875" |
| Stroke | 3.25" |
| Cylinders | 4 |
| Compression ratio | 8.5:1 |
| Rod length | 5.7" |
| Rod ratio | 1.754 |
| Bore/stroke ratio | 1.192 |
| Piston deck clearance | 0.011" |
| Induction | 1-1 |
|---|---|
| Advertised HP | 90 hp |
| Years | 1965–1970 |
| Bore/stroke character | 1.192 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,250 ft/min — conservative for a street engine |
| Rod ratio | 1.754 — long — less side loading on the cylinder wall, favours high RPM |
| Displacement per cylinder | 38.3 ci |
| Static compression | 8.5:1 — low by modern standards, generally happy on regular pump fuel |
| Intake valve diameter | 1.725" |
|---|---|
| Exhaust valve diameter | 1.505" |
| Chamber volume | 69.6 cc |
| Rocker ratio | 1.75:1 |
| Lifter type | hydraulic |
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 |
|---|---|---|
| 1965 | 90 hp | — |
| 1966 | 90 hp | — |
| 1967 | 90 hp | — |
| 1968 | 90 hp | — |
| 1969 | 90 hp | — |
| 1970 | 90 hp | — |