QDMQDMQDM
The formula I was taught to calculate fuel burn for an aircraft engine was: 3/4 pint per HP/HR ( using US gallons ). Depending upon how much power was used ( % of max rated power ) in any flight regime, you could approximate the fuel consumed in an hour. The T-6, for example, had a 600hp engine and in cruise we burned around 25-30 USG per hour depending on the cruise power setting used. Perhaps with a modified car engine; however, this formula would not be accurate.