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Ford IDI specs: 444 ci (7.3L) 8-cylinder, 4.051 x 4.358 in (102.9 x 110.7 mm) bore and stroke, 21.5:1 compression. Built 1988–1994.
The Ford Power Stroke 7.3 (IDI) is undersquare — the 4.3583" stroke exceeds the 4.0512" bore by 7.0% — a layout that trades peak RPM for leverage and torque low in the range. With a 4.3583" 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 55.5 ci (909 cc).
At 21.5:1 this is a compression-ignition engine: the ratio is the heat source that lights the fuel, not a knock limit to be managed.
It is one of 5 engines in the Power Stroke 7.3 family, all of them 444 ci — the differences between them are in compression, heads and rating, not displacement. 7 factory variants share these dimensions across 1988–1994.
| Displacement | 444 ci / 7.3 L |
|---|---|
| Bore | 4.0512" |
| Stroke | 4.3583" |
| Cylinders | 8 |
| Configuration | V8 |
| Compression ratio | 21.5:1 |
| Bore/stroke ratio | 0.93 |
| Block material | cast iron |
|---|---|
| Head material | cast iron |
| Valvetrain | OHV |
| Fuel type | diesel |
| Years | 1988–1994 |
| Bore/stroke character | 0.930 — undersquare — stroke exceeds bore, which favours low-end torque |
|---|---|
| Mean piston speed at 6,000 RPM | 4,358 ft/min — in the range typical of performance street engines |
| Displacement per cylinder | 55.5 ci |
| Static compression | 21.5:1 — high enough that pump premium or better is normally required |
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 |
|---|---|---|
| 1988 | — | IDI |
| 1989 | — | IDI |
| 1990 | — | IDI |
| 1991 | — | IDI |
| 1992 | — | IDI |
| 1993 | — | IDI |
| 1994 | — | IDI |
1 factory vehicle, 1988–1994. Each year opens that model's engine table.