well first things first.....the car has a 650 holley spreadbore carb with mechanical secondaries and a 3.90 gear. the speedo is off by fast by about 8 mph. but the other day when i drove 150 miles back to my hometown i got 21 mpg and on the way back to my apartment i got 22 mpg. i know its not a legit number because my speedo is off but its got to be fairly close. with the edelbrock carb i had on there and 3.55 gears and the speedo being off by like 4 mph i was getting 13-14 mpg on the highway. i really need to get my speedo fixed so its correct and recheck my mileage. im hoping it isnt too far off from what it comes out to now though. does anyone know what speedo gear i need? i think its a 23 tooth gear but im unsure because ive got a 21 tooth gear now and thats what i had with the 3.55 but i needed a 20 tooth for the 3.55 and it was fast also. kinda wierd....thanks for any help or input and sorry for the long rambling post....oxycodon does wierd things to my brain