anybody here...have, or had, a a 6.0 with 3.55s or higher in it?

Ive got an 05 6.0 CC 74k with 3.73s and most of my driving I have minimal weight behind me. and a few times a year i have 3-10k behind it....

So I was thinking about putting in 3.55 gearing for a little better mileage along with a few other mods to help in that department.

and i was wondering if anyone has knowledge on this... it seems like these 6.0s really like to run the Rpms up so i am brainstorming ways to help a little because im not going to drive 65 mph on the free way to save 2 bucks by getting better mileage THAT way.

 

You might find it a lot easier to put bigger tires on the truck.

 

I was thinking the same thing!

 

Contrary to popular belief putting larger tires on actually worsens your mileage. Pushing the larger tires plus more surface friction. Usually costs you about 2mpg.

 

Agreed, but I think it will still be cheaper to do that than re-gear (especially if its 4wd), and more easily reversible. The next size bigger won't kill it.

 

I will posts some figures, If your truck had 3.73 gears and 285 tires running 2,000 rpm with a final ratio of .7 your speed would be 75 mph. With 265 tires and a 3.55 rear your speed would be 76 mph. My truck has factory 265 size tires on it with a 3.73 rear and if I wanted to achieve the same roll out ratio as a 3.55 truck with 265 tires, I could go to a 285 size, which is not drastic.

 

i dunno, i did NOT like what 265/75R16 did from my original 235/85R16. and that's only wider...

 

I ran your 235/85R16 through the program and it came out to 72.3 mph at 2,000 rpm vs the 265/75R16 would be 72.12 mph. What was your dislike with the 265 tires?

 

A wider tire would effect mpg's just like lower air pressure.
If you could find a taller tire with the same width and minimal additional weight your gain would be greater.

The cost of gear change will take a very long time to pay for itself ,

 

I installed 285/65/18 on my truck from the original 265/75/16, and I noticed a drop in mpg, I didnt want to believe it, but my hand calculations are coming out to about 1.2 mpg loss. I went back to adding PS into the gas tank to help bring the mpg back up, but have yet to observe any differences. So far I am seeing only about 12.7 mpg... And that sucks, but this was also after the july pcm flash to where my mpg took a huge drop.

 

Read my posts here: Ford Truck Enthusiasts Forums - View Single Post - My EX is back from the shop but...

And here: Ford Truck Enthusiasts Forums - View Single Post - My EX is back from the shop but...

 

I remember reading and posting on that thread, I was heading back to the boneyard to pick up a FICM from an 04 F350, and came to find out, that they are different from the 03-04 and the 05 to curtrent. I guess I am going to have to send mine out for a reprogram and just be down for a couple of days.

 

Sorry, that's something I failed to mention...

But yeah, you'll be down for a few days, but when you get your FICM back, you'll be beyond happy with your truck.

Like I said, if I owned a 6.0 that would be my first mod...