Fuel mileage difference with the factory gears? - Ford Powerstroke Diesel Forum
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post #1 of 11 Old 07-02-2012, 05:38 AM Thread Starter
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Fuel mileage difference with the factory gears?

fellas, I don't really need needa big superduty, but I'm looking hard at a few 6.7 3/4 tons and a few 1 tons. SRW only, crew only, 4x4 only etc. one of the few option differences I see is one has a 3.31 and the other has a 3.55 rear gear. I do a lot of highway driving with no load at all, how much better would the fuel economy be on the highway with the 3.31 rear? also, I don't tow anything more then an enclosed bumper pull car trailer (will never weigh more then 9k lbs) if I tow a gooseneck it won't be a severely heavy load and won't be often at all.

I currently have a 6.0 gasser 1/2 ton chevy, it pulls good but has a 4 speed transmission and 3.73 gears and I only get about 14 mpg doing 75ish all oklahoma/texas driving. I love my silverado as it has been bullet proof, but the mileage, and only having an extended cab is kind of putting me off after some time. and I figure when I tow my trailer behind it I only get 7-8. obviously there is money to be saved there. I'm thinking a short box should be fine for what I'm doing as well. at most it might have my brute force in the bed.
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post #2 of 11 Old 07-02-2012, 06:33 AM
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The 331s are doing about 2.5 - 3mpg better than the 355s are. The 6.7 torque output makes towing with either a level field.

Sounds like you need to be looking at F150s though??? Better mileage on cheaper fuel.

just sayin


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post #3 of 11 Old 07-02-2012, 06:41 AM Thread Starter
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Quote:
Originally Posted by mowdoc View Post
The 331s are doing about 2.5 - 3mpg better than the 355s are. The 6.7 torque output makes towing with either a level field.

Sounds like you need to be looking at F150s though??? Better mileage on cheaper fuel.

just sayin

with my tastes in trucks, I hate the new F150s....the way my truck would be outfitted, it will still be a 50k dollar truck. might as well have that capability if I need it. plus I don't want to have to buy another truck for many many many years to come. and I have driven the new 150s...still not impressed at all. my silverado handles better and for the most part takes all F-150's minus the eco-boost straight line. driven all matters of 1/2 ton trucks including the wanna-bes (honda, nissan etc.) Ford takes a second, dodge a third, then toyota, then nissan then honda.....who should just stop trying. horrible truck

plus I might need it for a fifth or goose pull later on. at this point I have a goose, but I also have a 6.0 dually that only gets used when it comes out. trying to sell that trailer currently.
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post #4 of 11 Old 07-03-2012, 05:43 AM
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Originally Posted by virginiavenom View Post
with my tastes in trucks, I hate the new F150s....the way my truck would be outfitted, it will still be a 50k dollar truck. might as well have that capability if I need it. plus I don't want to have to buy another truck for many many many years to come. and I have driven the new 150s...still not impressed at all. my silverado handles better and for the most part takes all F-150's minus the eco-boost straight line. driven all matters of 1/2 ton trucks including the wanna-bes (honda, nissan etc.) Ford takes a second, dodge a third, then toyota, then nissan then honda.....who should just stop trying. horrible truck

plus I might need it for a fifth or goose pull later on. at this point I have a goose, but I also have a 6.0 dually that only gets used when it comes out. trying to sell that trailer currently.
I couldn't agree more. I mean, I know the f150 is a great selling vehicle, but for the amount you spend on a loaded platinum model, you could have a 6.7 powerstroke f250.

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post #5 of 11 Old 07-03-2012, 08:14 AM
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First off the 3.31 is not getting 1-3 mpg better than the 3.55's. It all depends on tire size with the gears. 3.31 with 33"s vs 3.55 with 34.5"s about the same. The bigger the tire the more weight you need to spin. That said if your looking at putting a 35" tire on it the 3.55 would be best. If your going to stay stock both will work great. And Ford puts the 3.55 with the 34.5" AT tire with 20" wheels. And 3.31 with the 18" wheels unless you get the camper or some other HD package.

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post #6 of 11 Old 07-03-2012, 09:22 AM Thread Starter
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I'm not looking at anything different tire size wise. just the 3.31 gears same size tires as the 3.55 trucks I'm looking at.
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post #7 of 11 Old 07-03-2012, 10:39 AM
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I like the 3.55 gears because you get the 20" wheels if you want it which makes the truck site higher.
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post #8 of 11 Old 07-03-2012, 03:43 PM
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I don't think you can order 3.31 with the same OD tires from Ford. That being said, I drove the 3.31 with 18" wheel package and 3.55 with 20" wheel package and the RPM at 60 was the same as far as I could tell. I have the long bed with 3.55 - see my info - and I get 15.6-16.3 around town (7 miles one way to work, then around town stop go). On a recent trip with all road I was at 18.8 mpg over a 640 mile run - one tank - 60-75mph. Hand Calculated. On the return trip I pulled 18.4 mpg but was stop n go a bit more. I think the 3.31 with a bigger tire would turn less, but I also think you'd downshift into 5th on steeper grades. I can pull them in 6th all day but sometimes she's boosting pretty good and a little less rpm and I'd be downshifting.

These are awesome trucks. I come from a line of Tundras and loved the 3 I've owned. So, saying this Ford is awesome is saying something. So capable, comfortable, posh......

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post #9 of 11 Old 07-03-2012, 08:56 PM
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I've driven several of both rear ends across the country. 3.31 with 18" or 3.55 with the 20" and you will get about 18 mpg at 80 mph or 21-22 mpg at 65 mph

I just don't think it makes much difference on fuel economy. Like the gentleman above said, The difference is negated by the tire size.

If you think you might pull a 5ver or GN. Then get the F350. Not much differnce in price or ride. And fuel mileage is the same.

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post #10 of 11 Old 07-04-2012, 01:38 PM
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Wrong if you order a Lariat/Camper pkg it will be with 18" wheels and 3:55 gears the diference is about 200 rpm at 65mph if memory serves me correct
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