Like I said, my speedo compared to my gps is only off by 3mph at 80

 

Right, so then your baseline MPG calculations weren't correct with 3.55s.

One or the other isn't accurate...you can't change gear ratios, but calculate MPG changes without also changing your speedo calibration. The math doesn't add up.

Either way, most folks report little change in MPG but a big increase in performance, which equates to a great mod in my book

 

I gotcha! Didnt think of the "before" I agree, i probably gained a little mpg then, but a huge increase in acceleration without sacrificing mpg

 

To steal a phrase I saw on this site...
I wish more folks wouldn't "fear the gear"

These trucks are geared very tall from the factory, so a jump to 4.10s or shorter isn't the same as it was back in the day, where your car would be screaming at redline doing 80mph.

I tow with my 4.10s, keep the truck locked in third on the highway (overdrive off), and at 65MPH I'm still under 3,000rpm.

 

I currently have 3.73's in my expedition. I rarely tow and i have stock tires. I just want it a bit quicker and responsive. I was looking at 4.10 gears. Would I notice the difference or would i have to go up to 4.56's. At the same time i dont want the mpg to decrease. What do you guys think?

 

dont get 456's unless you have 35's or bigger tires. I just didnt want to pay to have the gears done, but I did it my self, and id do it again rather than pay a shop $400 in labor...

 

Built, when are you taking it to the track to test them out?

 

Looks like july 3rd or 10th. That is the next day I can make it.

 

So there would be a good amount of difference from 3.73 to 4.10 keeping everything else stock.

 

I'm not sure if that would be worthwhile.
Usually a two-ratio jump makes the most sense.

What size tires do you have?

 

i couldnt imagine my truck with stock size tires on it.... I think 4.10's on a stock f150 would be too much. But Im not sure with 3.73's as stock

 

Nah...lots of guys on this iste run 4.10s with stock-sized tires, including me.
It's also popular among the Lightning crowd.

Same deal - great performance, no MPG penalty.

 

Yeah I've got 33s on mine and I'm probably going from 3.55LS to 4.10s.... I'd like it to remain under $500. Is that possible?

 

I've heard this from different sources. However, I went with 4.10's and am running the stock wheels. I don't think I've made the wrong choice at all. In fact, I have myself second guessing thinking I shouldve considered 4.56's.

I will say, though, my engine is a 4.6, not a 5.4 . There's a small difference there.

Joe

 

about how long does a gear changed take to do if i was going to do it myself? i have plenty of tools and any help i need.