Need help with gas mileage

[Irish_Alley]

I know this is hard to do in our trucks and I’m referring to my 04 impala. But I was getting 22 mpg diving it like crazy. I put a cold air intake on her, and changed my driving habits completely by getting on the gas a lot less and driving like grandpa when it comes to acceleration. Keeping under 65 and costing to stops trying to use my brakes as little as possible mpg jumped up to 29

[Edahall]

I was able to gather some data from my tach, tape measure and speedo. Then I handed that data to my engineer brother and voila, figured out that my rear end is a 4.56. The 3.73 rear ends are very numerous at the junk yard and that would put my revs down at somewhere near 2400. I'll be doing that for sure.

In other news, my last two fill ups gave me mileage of over 13 mpg. I'm not sure what's going on there, but I'll cross my fingers and hope for more of that.

Find a 3.08  3/4 ton rear axle out of a 1st generation Dodge truck.  The truck most likely would have had a Cummins would most likely be an 88-90 model.  Next thing, find a torque converter for you TH400 with the lowest stall speed you can find to reduce slippage.  This setup would give you just under 2000 rpm's at 60 mph.

[Isaac3384]

I am really glad someone everyone is posting info on this; I need to get my fuel milage up too. I had considered doing a manual trans swap and reworking the gears, but it sounds like I can get a decent increase just by doing the gears.

[Irish_Alley]

yes but if you go too short then the amount of work it takes to reach 60 will counter react the mpgs you will be saving at 60 unless you have a motor or transmission that will work with the short gears

[Isaac3384]

Right, that's why I was considering going with either an OD trans, or a 5 speed; it would give me a wider range of gears to help compensate for the shorter rear end gears; depending on how the tranny was set up. In what little spare time I have, I'll do some research aswell and post any valuable info I find.

[Irish_Alley]

when your looking for one with od also keep in mind what each gear ratio is for the trans. how well the truck will still function

[roadrage41]

I'm getting 11, swap to a turbocharged 5.3