Time between overhauls on a stern drive is inversely proportional to the amount of torque put through it over time. If you spend a lot of time with the throttle wide open and have a high torque engine, the drive will wear much more quickly than and identical drive that has been gently operated with a small engine. Those old Volvo Penta drives backed with little 2.1 liter 4 cylinder engines seem to last forever.
You may notice I did not mention Horsepower. It's torque that kills a stern drive, not necessarily HP, though they typically go hand in hand. Diesels are a perfect example of an exception to this rule though. A 300 HP diesel can kill a drive much quicker than a 300 HP gas engine because they typically make substantially more torque and run larger pitch props with slower prop RPM. this really loads the drive and wears it quickly.
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