Well I've been thinking about changing the gears in my truck, 07 5.4 fx4. But I have a few things to think about and could use some opinions from others as food for thought.
I have 33" mud tires, which I use to be able to smoke until I put the longtube headers on and my low end power went bye bye. Well I miss the low end/take off power. The problem is I think it will be a waste of money to upgrade to 4.10, and the next step is 4.56. But im concerned that might absolutely kill my hwy mileage. I messed with the rpm calculators and I would be running about 2250rpm @ 70mph, which doesn't seem to bad. Just not sure what the mileage would look like at that rpm. Right now I get 18-19 hwy at 70. Im stuck on the fence!

 

Tough call. I think 4.56s would be too much for 33s. I have 35s and 4.56s and I think it's about perfect. I wouldn't want to go up to 4.88s with 35s though which is about the same as 4.56s and 33s.

 

I do a good bit of city driving and only average about 12mpg, but I think a lot of people judge their fuel consumption according to their highway mpg and don't take into account just how much fuel they actually burn driving around town day to day. I'm just thinking the amount of fuel I save during my city driving will offset the decrease in my hwy mpg. Just not sure because I don't think anyone has this setup. I currently pull 18-19 hwy so I couldn't see it being worse than maybe 15-16 with 4.56 gears? Also when I'm on the highway it's to drive from Lubbock to Abilene, which is "hilly".

 

I travel a "hilly" highway from Modesto to Soulsbyville (120/108) every weekend and I average 13 MPG combined. Most of it is city driving to/from work except a few trips to Oakdale during the week (back roads, average 60-65 MPH) and Soulsbyville on the weekends. I have a pretty heavy foot and my truck is 2wd, 4.6, 32" tires and 4.56 gears. I love the low end my truck now has and I would do it again without hesitation. I thought about 4.30 since I have a 2wd... but then I said F it and went for 4.56.

 

Good insight. I'm leaning toward doing it but just want to see what others have to say, yourself included, before I jump the gun and do it. If my highway mileage is going to be horribly bad it will not make up for fuel saved city driving, and would be costing me more money in the long run by changing the gears. That is the question I'm trying to determine. Maybe ill just have to do the rear gears and experiment first.

 

I've got 4.10s and 31s and spin close to 2200 @70mph and get about 16mpg. If I keep it at 2000rpm (63mph) I can get 18mpg. City driving is about 14mpg

 

This doesn't help the thread salvo, but it's interesting to see these good mpg figures with the 5.4.

I have a 4.6 auto with a 3.08 rear. The tachometer reads 1550 to 1600 on hwy.@ 65 mph.

The best mpg I've seen is 19. The worst is a bit above 16 /city.

 

Blackout, if you are wanting to get 37's just wait a little longer and get the 4.88's when you get your lift and tires.

regearing your truck twice is very expensive.

 

Well I don't think a lift is going to happen for another 3-4 years, pretty busy with college still. Looking to help my tranny out too in the mean time. This past weekend doing 80 something mph turning 2200 rpm, hilly roads, I averaged roughly 14-15 mpg. So doing 70mph turning 2200 shouldn't be any worse since wind resistance will be less. Right? Those numbers would work for me.

 

At this point I'm just looking for some people with experience to tell me if they think the rough guess I came up with looks reasonable? 15-16 hwy at 70 given the mpg I get at the other speeds listed.

 

I would get 4.10s. You will get maybe 16mpg at 70 with 33s and 4.10s can still turn 35s just fine. If you were going to add 37s sooner then 4.56s would be ok, but 3-4 years is a long time and a lot of fuel.

 

i wouldnt even worry about changing gears then if you arent going to get bigger tires for several years. you are only running 33's, i ran 35's on my stock 3.55 gears for 4 years and got around 15mpg

 

Think I'll just save up for some power adders then. I don't think it's worth switching to 4.10. I guess maybe some ud pulleys is the next step. Then from there who knows. Lol

 

get a programmer if you dont already have one.

 

Gryphoned up!