Both have the same displacement. Differences appear to be in the ignitions (PCM555 Digital Inductive vs Modular CDI w/computer control), alternator systems (60 vs 40 amps), induction systems (2 stage direct fuel injection vs loop charged (EFI)etc. fuel injection), oil injections electronic multipoint vs standard), dry weights (443 vs 416 pounds), and list price of $12,180 vs $10,225). Has anyone seen performance test data for these outboard engines or have any other thoughts about the Optimax being worth $2,000 more than the EFI engine for the same hp for use in fresh water?