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Ram Pentastar specs: 220 ci (3.6L) 6-cylinder, 3.78 x 3.268 in (96 x 83 mm) bore and stroke, 11.3:1 compression. Rated 305 hp. Rod ratio and piston speed.
The Ram Pentastar is oversquare — the 3.7795" bore exceeds the 3.2677" stroke by 15.7% — a layout that favors airflow and RPM over leverage at the crank. The 3.2677" stroke does not reach 4,000 ft/min of mean piston speed until about 7,350 RPM, so piston speed is not what limits this engine's revs — valvetrain and breathing are. Each of the 6 cylinders displaces 36.7 ci (601 cc).
11.3:1 on aluminum heads is high enough that pump premium or better is normally required.
It is one of 4 engines in the Pentastar family, all of them 220 ci — the differences between them are in compression, heads and rating, not displacement. 2 factory variants share these dimensions, rated at 305 hp. Factory fitments include the Ram 1500, Ram ProMaster.
| Displacement | 220 ci / 3.6 L |
|---|---|
| Bore | 3.7795" |
| Stroke | 3.2677" |
| Cylinders | 6 |
| Compression ratio | 11.3:1 |
| Bore/stroke ratio | 1.157 |
| Block material | aluminum |
|---|---|
| Head material | aluminum |
| Valvetrain | DOHC |
| Fuel type | gas |
| Advertised HP | 305 hp |
| Bore/stroke character | 1.157 — oversquare — bore exceeds stroke, which favours higher RPM and larger valves |
|---|---|
| Mean piston speed at 6,000 RPM | 3,268 ft/min — conservative for a street engine |
| Displacement per cylinder | 36.7 ci |
| Static compression | 11.3:1 — 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 |
|---|---|---|
| — | 305 hp | ERB (Upgraded) |
| — | 305 hp | ERB (Upgrade) |