I want to swap the gears in my 04' F150 2wd. It has the 5.4 3v with an automatic transmission. I have 3.55 now and was thinking of going with 4.10. What kind of performance and fuel mileage differences am I going to notice? What will my RPMs be at highway speeds 70mph or so? I tried searching the forum but did not find exactly what I was looking for. Thanks for your help.

 

Multiply your current rpms at what ever speed you choose by 1.15 and that will give the rpms with 4.10 gears.

New gear ratio divided by old gear ratio provides the difference proportion of 1.15 (in this case).

Lee

 

Here are my RPM with 285/60R18 tires...31.5-inch street tires...and 4.10 gears:
https://www.f150online.com/forums/sh...d.php?t=263323

MPG change is unnoticeable.
Performance change is very noticeable.
Second-best mod I ever did to my truck...supercharger was the best mod

 

Thanks for the info it was very helpfull in making my decision.