3.31 gearing
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From: Chicago
3.31 gearing
I have been dying to ask this question.
How does this engine pull grades under a load with the 3.31 Diff, as compared to the 3.73?
I'm looking to maximize fuel economy.
What kind of RPM's are you running at highway speeds.
Thanks.
How does this engine pull grades under a load with the 3.31 Diff, as compared to the 3.73?
I'm looking to maximize fuel economy.
What kind of RPM's are you running at highway speeds.
Thanks.
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Joined: Aug 2003
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From: Isanti, MN
It somewhat depends on what you're towing and how fast, but most reports are that it's just as good as the 3.55s due to the 6-speed transmission being nearly always able to put the engine exactly where it needs to be.
I think this is the reason the towing capacity is identical between both ratios. I had the 3.55s and wished I had the 3.31s!
I think this is the reason the towing capacity is identical between both ratios. I had the 3.55s and wished I had the 3.31s!
Elder User
Joined: Jul 2010
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From: herriman utah
I think 3:31's are a great gear, if the truck needs to downshift it puts me at a really nice RPM for maintaining 70-75 mph, but keep in mind I have the stock 245's on 17" wheels, I would say if you wanna run over size tires get the 3:55's otherwise check back with me in a month or so after I add 275/70 18's
Lead Driver
Joined: Jan 2010
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I have the 3.31 with 18 inch wheels and I don't see how I could overload my 3.31 gearing staying within the legal limits of an F-250.
I'm certain it would fail me if I tried to move 25,000 lbs up a mountain but that's because my F-250 isn't rated for that type of weight.
55 MPH empty in 6th is about 1,200 RPM to give you an idea.
If you plan to go F-350 SRW, get the 3.55.
The MPG difference isn't much from the numbers I see posted here.
I'm certain it would fail me if I tried to move 25,000 lbs up a mountain but that's because my F-250 isn't rated for that type of weight.
55 MPH empty in 6th is about 1,200 RPM to give you an idea.
If you plan to go F-350 SRW, get the 3.55.
The MPG difference isn't much from the numbers I see posted here.
Senior User
Joined: Jun 2009
Posts: 136
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I have the 3.31 gears and it depends on what speed you like to pull at. I found running 63 to 65 pulling about a 10,000 lb 5er that it works well. Doesn't drop to 5th except for big hills with lots of wind and the best fuel mileage. If I ran at 55 to 60 then it was dropping into 5th more often and to me it seemed to lug more.
According to other posters here 70+ works good too.
The 3.31's are really nice empty, I find I can run 70+ and get some good fuel economy.
According to other posters here 70+ works good too.
The 3.31's are really nice empty, I find I can run 70+ and get some good fuel economy.
Tuned
Joined: Dec 2010
Posts: 460
Likes: 51
From: Washington state
I have 331's with 18 inch wheels and I pull a 11,000 pound 5th wheel with ease. I run at around 62 MPH with the same results as Whiteline. At around 70-74 MPH empty I get 18 miles per gallon. I am very happy with the gear and tire combination.
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From: Chicago
Thanks everyone who responded.
I'll be pulling a 5er, probably 12-15000 loaded. I don't expect to race up hills without loosing speed or dropping down gears.
I would only be pulling the trailer about 10-20% of the time, so the rest of my miles I want to maximize my fuel economy. So it's a trade off.
I just wanted some real world info on how these trucks really pull.
I've run every steep grade in america in tractor trailers, 10, 13 and 18 speed, but never an automatic. So thanks for your help.
I have to confess that I don't really understand the tire size issue...17 vs. 18 inches though. Duhhh!!!
I'll be pulling a 5er, probably 12-15000 loaded. I don't expect to race up hills without loosing speed or dropping down gears.
I would only be pulling the trailer about 10-20% of the time, so the rest of my miles I want to maximize my fuel economy. So it's a trade off.
I just wanted some real world info on how these trucks really pull.
I've run every steep grade in america in tractor trailers, 10, 13 and 18 speed, but never an automatic. So thanks for your help.
I have to confess that I don't really understand the tire size issue...17 vs. 18 inches though. Duhhh!!!
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From: Central Illinois
It somewhat depends on what you're towing and how fast, but most reports are that it's just as good as the 3.55s due to the 6-speed transmission being nearly always able to put the engine exactly where it needs to be.
I think this is the reason the towing capacity is identical between both ratios. I had the 3.55s and wished I had the 3.31s!
I think this is the reason the towing capacity is identical between both ratios. I had the 3.55s and wished I had the 3.31s!
Super Moderator
Joined: Aug 2003
Posts: 25,479
Likes: 738
From: Isanti, MN
Thanks everyone who responded.
I'll be pulling a 5er, probably 12-15000 loaded. I don't expect to race up hills without loosing speed or dropping down gears.
I would only be pulling the trailer about 10-20% of the time, so the rest of my miles I want to maximize my fuel economy. So it's a trade off.
I just wanted some real world info on how these trucks really pull.
I've run every steep grade in america in tractor trailers, 10, 13 and 18 speed, but never an automatic. So thanks for your help.
I'll be pulling a 5er, probably 12-15000 loaded. I don't expect to race up hills without loosing speed or dropping down gears.
I would only be pulling the trailer about 10-20% of the time, so the rest of my miles I want to maximize my fuel economy. So it's a trade off.
I just wanted some real world info on how these trucks really pull.
I've run every steep grade in america in tractor trailers, 10, 13 and 18 speed, but never an automatic. So thanks for your help.
It's funny you mention that, Gavin! As much as I made fun of my 17" wheels I never really thought much about it. And then it hit me: My wife's Sienna has 18" wheels, and my F350 had 17s....Not much for that "macho" look, but it makes for some nice and cheap tires. Unlike the van and it's damn run-flats...
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