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Compression ratio depends on the engine:
300 (4.9) or 460 (7.5).....8.4 : 1
302 (5.0) or 351 (5.8).....8.2 : 1
Deisel...........................20.7 : 1
I don't know which one your 250 has, could have either 460 (which mine has) or i think 351. If you have the VIN i could tell for sure.