If you have one built right and tuned- They are awesome!! carbs (750-900+ cfm) Demon-sizzler in GA (he built mine) or Scott Smith Harms in Spokane, both build these carb to run. I have a 416 sb and if I keep my foot off it, you will get fair/decent mileage..and if you stomp it (no bog with mine) my rear tires go up in smoke..big power!