Gearing confusion..... Please help my poor head

[OKCIS]

Ive got an 08 F-150 SC FX4 6 inch procomp lift with 35's. The truck gets 8mpg sometimes 10 if im highway only. Other then this stuff its stock im about to order an intake, exhaust and a programmer for it. I was looking into a gearing change on the truck also but I guess it just doesn't make sense to me for some reason.

Right now i have 3.73's in the truck. If i jumped to 4.10's or 4.56's how would this effect my rpm's on the highway? My thought is the truck tops out sooner so running at 75mph currently at 2200 rpms if i jump to say a 4.56 wouldn't my rpm's jump to around 3000?

Currently the truck just feels like it has no power. It seems like it takes half throttle just to get the thing moving and i would really like to correct that so that's why i was looking at gears. The only problem is ill just live with it if its going to net a lower MPG. The ratio of cost of gears to savings in gas make no difference to me i don't leave anything stock that I own so i never even consider that stuff. I just don't want to pay more money at the pump then im already paying. In turn id like to see the truck get up and start moving without having to give it so much throttle.

Hopefully one of you can shed some light on all this for me.

[05_sprcrw]

A regear would definitely help you get back some of the power you "lost".
I would definitely not do anything less then 4.56 gears.

A simple formula to help you find the new rpms would be.

New RPMS = (New Gear Size) * (Old RPMS) / (Old Gear Size)

So using what you have provided if you went 4.56 it would look like this

approx. 2670 rpms = (4.56)*(2200) / 3.73

Here is a link to help you with all the info you need. The second page is were most of the info on selecting them will be found.

http://www.f150online.com/forums/oth...p-rev-1-a.html

Hope this helps.

[bluejay432000]

I assume you did recalibrate the speedometer with the taller tires?

[05_sprcrw]

Originally Posted by bluejay432000

I assume you did recalibrate the speedometer with the taller tires?

I was wondering the same thing to me 2200 rpms sounds a little high for 75.

[bluejay432000]

Originally Posted by 05_sprcrw

I was wondering the same thing to me 2200 rpms sounds a little high for 75.

Since he does not yet have a programmer, I doubt he did. If that's the case, his speedometer is registering much slower than his actual speed and he is not recording all his miles, so gas mileage is better than his calulation.

[OKCIS]

The dealership told me it has been recalibrated. I am having second thoughts on this issue though cause while 8mpg seems horrible it doesnt sound too out of the question right now. The biggest thing that has me questioning if its been done or not is ive been driving the same stretch of road to and from work now for 10 years. Speed limit is 70mph and ive always done 75mph and rarely ever pass anyone. Since i got the truck im passing everyone and ive got the cruise set between 72-75 everyday.

my brother in law has a hypertech hes not using anymore so im going to test it out just for the recalibration and see what if it makes any difference.

Thanks for the input maybe i can make more sense of this now.