I just found this site and there is so much usefull info on here. Thanks to all the car gods on here that supply all the knowledge. I have an 02 f-150 with the 5.4 in it. I have done the headers, 3 inch flowmaster system, cold air intake, transgo reprograming kit, throttle body, tornado fuel system and underdrive pulleys.Now I am looking to do a bigger gear. I am not sure what size bellhousing is in my truck so if anyone knows please tell me. I am also not sure about what size gear to do. I do mainly city driving but some freeway on the weekends. I have the 3:55 in my truck right now and on the freeway at 80mph it only tacs to about 2100 since I have the overdrive. Should I go 4:11 or bigger? I dont want to get killed on gas milleage but I am looking for more off the line performance. So if anyone can help me please let me know.
Thanks
Ian

 

Well working backwards in the math it comes out that you have 265/70/17 or 265/75/16 (same tire size). Going to 4.11 gears you will run at 2450 rpms give or take at 80mph. This will give you a better low end grunt, but will hurt you some at the top end obviously. The other thing to think about will be fuel economy. It might improve it slightly but it will take a long time to make up the cost of a gear swap in fuel savings. You're looking at around $500-600 for a 2wd, and $1000-1100 for a 4x4 to do this swap.

Its not called a bellhousing, thats what goes on the front of your transmission. You have a 9.75 rear axle since you have a 5.4L, and you have a reverse rotation 8.8 IFS front axle IF you have a 4x4. If its 2wd you don't have to touch it.

 

I previously had 4.30 gears and they were not that bad. The ones I had were a little noisy so I changed to 4.10 Ford racing gears and am very happy with the gears and also where the rpm's are on the highway.
My rear is the 8.8. I know you have the 5.4 but some have the 8.8 rear, most have the 9.75. I think someone here will tell you how to read the tab on the rear and also the tag in your door to tell what rear you have.

 

Today I checked and at exactly 2000 rpm I was doing 64MPH. If I get a chance in the next couple of days I will take it up to 80 and see what the tach says.

 

Some of the very early F150s had the 8.8 and 5.4L. All the new ones get 9.75s.


Its easy to tell the difference between the 8.8 and 9.75 visually. The 8.8 has a 10 bolt diff cover and is somewhat round shaped. The 9.75 has 12 bolts and is more pear shaped. The diff shape is reminicent of the D44 and D60 housings.

 

Just an update.
With 4.10 gears, auto overdrive at 80MPH yesterday on very slight upgrade and TQ locked, the tach read 2550 RPM.

 

Thanks for all the info I recieved. I am going to do the 4:10 in my truck and will post to see how it runs.