what diff ratio??
Is there anything in the tune that can help gas mileage?
Is there anything in the tune that can help gas mileage?
There are variables, such as tire size and engine power.
For best mpg, I wouldn't go beyond a 3.23 or 3.42
For rpm range, it depends on how much power you have, and how you will be driving the car.
After all, no one I know just cruises around at 1800rpm all day...
....even this old guy.

Is your a stock engine?
haha yeah I don't plan to just cruise at 1800rpm all day. I don't want it to be a dog off the line.
A 3.25 is no problem to get, as well as a 3.73 is pretty easy (both in a lsd). I will have to see if I can get something around a 3.4x...
cruising around 75? That would be excellent, not sure if I want a complete dog in both 5th and 6th tho....hmmm
The tire will be a 225/45/17 if it makes a difference
My car will do 2050rpm @ 70mph, in 5th (my only OD gear-.064). This is with a 3.70 rear & 28 inch tires/approx 380hp.
In 5th, there isn't much pull until about 3500. But, who doesn't down shift anyway when you're really looking for some speed.
So, if you're only looking for mpg, I would stick with 3.42 max.
From your stated mods, with 6 gears, and your intention to tap some power, I would go for at least a 3.73 rear, as Andrew said.
You can still cruise the highway at low engine rpm.






