I swapped my gears for 4.10s, I had 3.55s. If you have done this swap, how has your mileage been. It seems to be that my mileage has gone down dramatically(I know, I know, I havent been driving around like Reese Millen Drifting in his GTO), even cruising around town seems to drain my tank or in traffic is the same. I'm stumped. What do you guys think?

Thanks
M V

 

What size tires? If you went to bigger tires, a gear swap should help mileage, at least a little. If you have stock tires, then yes it will give you worse mileage. I have 4.10's with a 4.6 auto and 33" tires and I get around 14 in the city and 16 on the highway. What are you getting now and what were you getting???

 

is your speedo calibrated for your new gear setup?, if not you dont know if your milage went up or down since your speedo is off, get it calibrated and you will be able to get a more acurate reading, good luck

 

I just got 4.56s put in my truck last Friday and spent the weekend breaking them in for 500 miles. My speedometer is very off but I calculated my mileage in this way. On the freeway it listed a road in 3 miles, so when I reaced the road, I checked the odometer and it said I had traveled 3.9 miles. Therefore, for every mile I drive, my odometer is recording 1.3 miles traveled. I am running 20 inch rims with 32 inch tires. With my stock 3.55 gearing I was getting 13 mpg consistantly with 90% city driving. Since the 4.56s, my mileage has gone up to 15.7 mpg, 90% city driving. This is better than my stock wheel/gearing setup so I am pleased. And even better, the speedometer inaccuracy gives me an excuse to pick up a tuner!

 

Its kinda wierd, the Tech who swapped for me said he had a hard time with re-calibrating everything. Since Ford does'nt have 4.10s in its computer system (they only went up to 3.73s) to re-cal. it he ended up using 3.73 settings, then he changed the tire size to one size smaller to try and make up for any inaccuracy. I still have stock tires though, so I dont know what that will do. He said there is a chance for an engine light to come on. Another recommendation was to get a Tuner, so I guess thats what would fix everything. Now I have an excuse to geta Tuner to .
Hopefully that will help, at least get all of the settings to there correct points.

Thanks guys
Later
M V

 

a very easy way to find out how far your speedo is off is to use a hand held GPS unit, using this method you can find out exactly how far it is off, good luck