It really depends on what rpm the engine is running and what load you have it under. Do you know your pulley ratios? On 'average' a gallon or so per hour is a good rule of thumb. Some machines burn alot more though.. I have a GM 6.0 and run it between 12-1500 rpm depending on how I set it. That's with a 47@15hg max spinning around 27-2800 rpm. It idles along nice at that speed and doesn't burn too much fuel. If you run it much over 1600rpm you'll notice it on the gas gauge.. The engine runs really hot as well.Especially in the summertime.. I wouldn't run it much over 1600...