Convert 392 to 355???

Convert 392 to 355???

This is a discussion on Convert 392 to 355??? within the RAM 1500 Diesel General Discussion forums, part of the RAM 1500 EcoDiesel Forum category; how much fuel economy do I lose going 3.92 instead of 3.55??? I drive 70/30 city/hwy,,,,dont tow but always have about 400lb in bed and ...

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Thread: Convert 392 to 355???

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    RAM Rookie Virgilio's Avatar
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    Convert 392 to 355???

    how much fuel economy do I lose going 3.92 instead of 3.55??? I drive 70/30 city/hwy,,,,dont tow but always have about 400lb in bed and im running 33"x13" wide terra grapplers.
    Is it possible to convert my longhorn to 3.55??? Should I???
    Thanks in advance for input.

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    RAM Guru Bigfoot's Avatar
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    Quote Originally Posted by Virgilio View Post
    how much fuel economy do I lose going 3.92 instead of 3.55??? I drive 70/30 city/hwy,,,,dont tow but always have about 400lb in bed and im running 33"x13" wide terra grapplers.
    Is it possible to convert my longhorn to 3.55??? Should I???
    Thanks in advance for input.
    You probably would not gain much in the long run, certainly not worth the conversion cost. Fuel economy comes from many factors, rear axle ratio being one of the middling ones. The large tires are a stronger influence and their mass and diameter argue for keeping 3.92. Your final drive ratio with the 33" tires is actually close to 3.55 compared to stock 31" tires. Driving style counts for a lot, too.
    Last edited by Bigfoot; 07-28-2014 at 07:18 AM.
    "The avalanche has already started; it is too late for the pebbles to vote." - Kosh Naranek

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    RAM Sr Member Crappie man's Avatar
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    Quote Originally Posted by Virgilio View Post
    how much fuel economy do I lose going 3.92 instead of 3.55??? I drive 70/30 city/hwy,,,,dont tow but always have about 400lb in bed and im running 33"x13" wide terra grapplers.
    Is it possible to convert my longhorn to 3.55??? Should I???
    Thanks in advance for input.
    if you don't tow and you plan on keeping this truck at least 100000 miles or more then it would be worth it but not unless you kept it that long. I think id keep it like it is and maybe in a year you can trade if you want the 3.55 gears because I really believe the trade value will be good on these. Or maybe in two years. Me I put 30k a year on so I lose a lot of money due to miles but will trade at 60k in two years and hope to trade at a $12k difference. That is what I am shooting for in my truck. My boss trades his every 2 years at 13k difference on a gmc Denali 1500 gas engine with the 6.0 engine all wheel drive. he puts 50k on it. I would hope being diesel on my Laramie and 4x4 I hope to do the same at 60K.

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    RAM Rookie Virgilio's Avatar
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    tnx guys

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    RAM Wizard jeffjcalweb's Avatar
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    hi - pretty funny, i actually checked to convert from 3.55 to 3.92 and i can help with the answer.

    first, the answer is yes you can. you can (should) be able to do this at a Ram dealer. my local dealer (Northern CA area) was able to get a part list, availability and price for me.... to convert my 4x4 Laramie CC it was $4,960 ... so there's your number to go the other way as well.

    the aftermarket (ie differential shop) in my area said they could not do this for the '14 as parts were not available to them yet.

    in the end, the price was not worth it. if you REALLY had to make a change, quite honestly you'd be better off taking that $4K (if you were willing to spend it) and start over with a new truck and use the $4K to offset any trade-in/equity balances.

    hope that helps. and believe me i REALLY searched on this topic because i was so adamant to needing 3.92's instead of my 3.55's.
    Virgilio likes this.

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    RAM Regular CG98x's Avatar
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    ^^^^^ you guys should just trade axles then you would just need your speedos corrected.
    2014 Ram 1500 Big Horn Crew Cab 4x4 6'4"bed Air suspension, Ramboxes and other cool stuff Build date of 4/2/2014 Avg 24 MPG 52000miles and counting

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    RAM Wizard jeffjcalweb's Avatar
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    @ CG98x - believe me if we were within a geographic distance that we could, i'd do it! great idea!

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    RAM Jr Member Keith G's Avatar
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    food for thought, I have 3.92 axle and my 2nd tank averaged 26.9 mpg, and the 3.92 gives you 1000 lbs more towing capacity, which I need when I pull my TT. I believe your individual driving habits will have more say in your economy instead of what axle to purchase.
    CB919 likes this.

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    RAM Sr Member Crappie man's Avatar
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    I would agree to that. I bought off the lot and it came with 3.55s and id rather have 3.92s if I ever get a TT. But if I do I will wait a couple years then do it and be ready to trade anyway.

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    RAM Rookie Virgilio's Avatar
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    Great input guys!! I guess better to have it and not need it rather than vice a versa.

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