I had a customer call up when the 400hp outboards were first released. Needed to get 4 on the back of his boat to replace the 350s. He asked about fuel useage. I mentioned an old rule of thumb, outdated but still kind of close, is 10% of HP/hour at WOT. He lost his mind. He said he only has 500 gallons on board and that is 160 gallons per hour and only has 3 hours of fuel! I said, sir, you have 1,600hp, you will be in another country if running wide open for 3 hours....where are you going? Back off to a cruise speed....