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3.31 Rear axle ratio?

8K views 14 replies 11 participants last post by  Dim Sum 
#1 ·
Anyone have a truck with a 3.31 rear axle ratio? I'm looking at a bunch of 2010 trucks and some have 3.31's and some have 3.55's. Is there any noticeable difference between the two when it comes to acceleration or MPG's. I would think MPG's would be a little bit better but these trucks vary so much from one to the other I'm not sure it would matter. DPF delete will happen shortly after purchase and down the road I will add a levelling kit and some 35's.
 
#2 ·
I didnt know you could get a 6.4 with 3.31's
 
#3 ·
I didn't either until I started looking at window stickers... They are XLT models with 17" wheels so that might be the reason why. I think the 18" wheels have 3.55's and the 20" wheels have 3.73's.
 
#4 ·
3.31's would be awesome on a RC/LB race truck with like 28-30" race tires. I can't imagine them being good on a CC/SB though, but who knows? I want 3.55's in my truck, but I can't justify the cost of doing for the benefit in MPG and track times.
 
#10 ·
3.31's would be awesome on a RC/LB race truck with like 28-30" race tires. I can't imagine them being good on a CC/SB though, but who knows? I want 3.55's in my truck, but I can't justify the cost of doing for the benefit in MPG and track times.
Huh?? Don't you breath and live the track Jeff!! :rolleyes:
 
#5 ·
I'm never going to tow heavy with this truck and the biggest tire I'll throw at it is a 35, but it is a CC/SB. I'm basically deciding between a XLT with the FX4 package and 3.55's, or an XLT with the XLT convenience package and leather with a 3.31 rear. I can always get Katzkin leather for the first truck for $645 off ebay so either one will work. I'm going from a V6 F150 work truck so it's a HUGE upgrade either way.
 
#6 ·
I have the 20" wheels and I have the 3.55 gears too....I have a 2010 f-250. I'm not sure the 3.55's get you that much better fuel economy? Maybe on the flats for long runs, but overall, I don't see much of a gain.
 
#12 ·
Bought a new 2010 F250 FX4 3 weeks ago. It had the 17 inch wheels like previously stated and 3.31 gears. With stock wheels, it averaged 15.4 mpg mix of hwy & city (work and back everyday is 120 miles). Now have Pro Comp 20x9 with Nitto 34x12.5 Terra Grapplers. Also installed a ReadyLift leveling kit. Checked with a GPS, the speedo is exactly 10% off at any speed. Last tank, it showed 14.9 mpg so adding in the 10%, goes to 16.39 mpg. The truck has enough torque that the gear ratio is properly compensated and you will not notice the difference except at the pump. Driven F250's with 3.55 and 3.73 and can't tell the difference...
 
#13 ·
3.55s

I have a 2010 with factory 20s. I can run 75 mph and still be below 2000 RPMs, which is recommended for reasonable MPG. The sweetspot for MPG with 3.55s seems to be 62-65 MPH. The stock 6.4 is somewhat of a dog off of the line so I am not sure I'd want anything lower than 3.55s when running a 34" or 35" tire.

I wasn't aware that the 2008-2010 F250/F350 came with anything smaller than 18s". What style wheels are the 17s" as I am looking for some wither wheels. I assume all sizes come with TPMS?


Thanks...
 
#14 ·
No longer have the wheels and tires. They looked just like the stock 18 inch ones with all terrain bfgs. The local tire dealer took them as a trade since they had only 1600 miles on them. Every stock 6.4L, no matter what the gearing is a "dog" off the line. When I bought mine I wanted styling and the best mpg possible. The 08-10 F250 is the BEST looking truck ever made, IMHO. So, I opted for the higher gear ratio to squeeze every mile out of a tank of gas. At 75mph, it cruises at 1650rpms with the boost steady at about 5 on level ground of course. As soon as the factory warranty expires I will be getting a Spartan tuner even though I TOTALLY disagree with the way Spartan does business, charging folks to "un" VIN lock a DD. Might even buy a used vin locked one just to see if I can "unlock" it in the interim. Additional accessories will be a full AFE exhaust and stage II intake. Will probably do the stage II intake now and hope for another half an mpg...
 
#15 ·
The 6.4 is no dog once you tune it :). Different animal.

I've said this before, tuning the truck makes the twin turbos deliver performance that you expected when you first sat in the truck and was disappointed by the lag.
 
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