I'm wondering how hot it ran...
Boat engines are a lot like aircraft engines. They are run under heavy load for long periods of time and that's why they typically don't make big power numbers given their displacement. Power produces heat and heat has to be dissipated by the cooling system. More power = more heat. Utility engines aren't even supposed to be run at their full rated power but intermittently. 80-85% load is often the maximum continuous that won't void a warranty.
Now think about increasing the power/heat by 50-100% and running it at 100% load for long periods. That's why people who mod their mud motors often blow them up.