My says to put a holley 500 cfm 2 barrel on what you have and be surprised by throttle response and gas mileage of a properly tuned carb. I ran this combo on a 70 dart with 318 and stock 2 barrel intake with 2.94 road gear and got 20+ mpg. Any changes to the amount of air you put into the chamber is gonna = less fuel economy in most every case. At least that is the way I figure if you are gonna keep the fuel air ratio at optimum.