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im looking for about 22mpg or better

4K views 23 replies 11 participants last post by  secondarychaos 
#1 ·
i got a 2001 f350 4x4 at 373 gears 285-70-16 tires anyways i dont pull much
if i did it would be about 3000 max could i go with the 331 gears ive seen
only thing is i cant seem to find out witch rear end it is
 
#3 ·
i noticed after i got my stage 1 injectors installed and custom tunes i was getting mid 20s on highway. im interested to see what my 238cc injectors will do
 
#4 ·
This is what the wife's pickup is getting right now, if you hand calculate it pretty damn close to lie-o-meter

 
#7 ·
I know that my truck tows fine with 3.55's, and I've towed ~8K. a little sluggish like that, but still perfectly manageable. 3.31's should tow up to 5k without issue, and a little heavier with a good, gentle driver LOL
 
#10 ·
is your speedo recalibrated?
the larger wheels and tires will hurt you, and I'll take back what I said about towing heavy. 3.31's would be real hard on an automatic with bigger tires and towing...
 
#17 ·
If all you do is 60 mph you are going to be running too low of a rpm with a 3.31 gear, esp with a 33" tire. The slightest hill will make it want to lug & down shift all the time. I had 4.10s, went to 3.55s but found that I had to drive 60-65mph to keep it in it's power band.They rocked on the highway doing 65-70mph+ but in the 55mph zones it was little under geared. Most of my driving is city, country roads (55mph) & I cruise 65mph on the highway so I went back to 4.10s.
If all your driveing is 60mph I wouldn't waste money re gearing. I know people with 4.10s that can get over 20mpg if they go 60-65mph. Gotta remember these trucks don't have the low end of a Cummins. Keep em in the power band & they are happier.
 
#18 ·
I don't understand what you wrote here. If I read it as you wrote it, everything is a waste of time and money.

Also, what is the powerband that we are trying to cruise at? I know that above 2000 RPM things get worse but are we talking 1800?
 
#15 ·
I found that with a chip and a valvebody I gained like 1.5-2 mpg after the break in period from the truck running better.

Mind, we don't have roads that you can go much faster then 45-55 ish on with these kind of trucks, with all the potholes and sharp corners you're likely to bounce right into the ditch if you try going much faster LOL

Anyway, I have a fairly consistent 15 mpg going 10-20 miles in town, and a 19-23ish long distance, depending on where in the country I'm at, and if I'm driving daytime or night time.
 
#16 ·
:doh:
I mixed up who I was talking to...
with stock-ish sized wheels and tires, I'd try 3.31's or 3.55's.
with 35's, I'd go with 3.73's or it's going to be a total dog.
 
#23 ·
Cat Rebel is probably right. I doubt that an automatic can tolerate 3.08 gears (1700 RPM @ 70 MPH).

Get your gearing right and clean up your aero.

Nothing else works more than a trivial amount.

Did free-flowing air filter and exhaust years ago. No improvement.
 
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