When this question popped into my head recently, I quickly realized there would likely be a delightfully broad spectrum of answers.
The largest displacement engine I have owned was the 460 cubic inch (7.5 liter) V8 in my 1975 Ford Thunderbird. While defanged due to pollution controls, it still pumped out a terrific amount of torque and was simply unfazed my hills of any nature.
As for operating, I briefly drove a Kenworth T-800 road tractor around my office complex one Friday afternoon. It was rated at 475 horsepower or thereabouts, so it’s likely in the 15 liter range.
So, what is the largest displacement internal combustion engine you have operated? Better still, what was it in?