Originally Posted by
blawknox977
wow thankyou seminaryranger!! that gives me a lot to think about.
i have the auto transmission, tire size: 285/75/16r i have the standard 4.1:1 ratio gears everything is stock.
i know im not going to get dramatic changes in MPG but i was just looking for an improvement around +2 or so. i drive on the highway a good amount, couple times a week i drive about 60 miles round trip.
with that size tire a 4.56:1 ratio and considering the year and how weak the motor is maybe thats not to bad a combo.
anything else you need to know to help figer out a good combo?
and i have replaced most of those thing suggested, what are COD's and zerks??
You can use the RPM Calculator (link below) to determine if you want to change the gears in your axles. The automatic transmission (4R100) in your Super Duty has a "Transmission High Gear Ratio" of .71. Your 285/75R16 tires have a diameter of 32.76" or 33" rounded. If you enter the following values into the RPM Calculator, you can determine the RPM's at a given speed.
Miles Per Hour:
70
Tire Diameter in Inches:
33
Axle Ratio:
4.10
Transmission High Gear Ratio:
.71
RPM:
2,077
If you change to 4.30 gears, the new RPM's would be 2,177. If it were me, I would not invest the money to change your 4.10 gears unless you plan to run taller tires (35" or 37") in the future.
RPM Calculator
COP = Coil On Plug - There should be a COP attached to each of the spark plugs on your engine. Sometimes these fail due to age and/or heat. They can be tested.
Zerk's - These are the "nipples" that are used to inject grease into ball joints, u-joints, etc. to keep the suspension and drivetrain from binding.
Also, look at the "Combo's" offered at 5 Star Tuning... Specifically, there is Combo 3 and Combo 4 that applies to your Super Duty. See link below for details.
http://www.5startuning.com/combodeals/