Smaller venturis consume less fuel, all things being equal. Depends on fuel, needle setting, prop, weight and drag of the plane and ambient temp, perhaps even barometric pressure. Running a large vanturi with a free flowing muffler and a prop similar to an apc 101/2x41/2, I have seen a nice Gieseke Nobler do the pattern needing 4 1/2 ounces when there was a chill in the air. This using Powermast 5%, 22% (50/50). In the heat of the summer the consumption fell to a hair bellow 4 ounces. Definitely true for this plane. Since early in the season, when practicing, my friend had to cut the pattern a bit short with a 4 ounce tank. When temps hit 70 and above, not a problem. Some of my best running profiles needed similar amounts of fuel when I used a large venturi. These days I use .272 and smaller venturis. .272 is midway between the small, .257 (kinda) and the large .283. I often use less than 3.75 ounces when set up like this.