3.92 and fuel economy
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Joined: Jan 2009
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Jack,
The 09 with 20 and the 3.21 is a D-O-G. You need to drive one with a 3.92 or 4.10, no wait, don't because you will want to trade your truck. Some people get the 3.21 looking for better mileage and it will actually get worse if you tow/haul or drive much in town.
The 09 with 20 and the 3.21 is a D-O-G. You need to drive one with a 3.92 or 4.10, no wait, don't because you will want to trade your truck. Some people get the 3.21 looking for better mileage and it will actually get worse if you tow/haul or drive much in town.
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Amateur
Joined: Nov 2009
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3.92 will get better mileage than 3.55 with 20's if you drive alot in town or haul/tow.
It is all about torque. Use the search button on this forum. I wrote a detailed explaination on this topic several months ago. Stay away from the 3.21 axle with 20's unless you want a dog and a lugging engine. The 3.92 is limited slip and the 3.55 is open. I have the 3.55 on my 09 sport CC because it was a great deal as a demo, but I would never order or buy one of the lot that was not 3.92 or 4.10 on these trucks unless you are wanting the 17 inch tires.
It is all about torque. Use the search button on this forum. I wrote a detailed explaination on this topic several months ago. Stay away from the 3.21 axle with 20's unless you want a dog and a lugging engine. The 3.92 is limited slip and the 3.55 is open. I have the 3.55 on my 09 sport CC because it was a great deal as a demo, but I would never order or buy one of the lot that was not 3.92 or 4.10 on these trucks unless you are wanting the 17 inch tires.
NC
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The 20s are still taller than the 17s and thus create a higher gearing. If you want a bad A$$ truck, get 4.10 gearing with 17 inch tires. You won't have to look very hard to find a 3.92 truck and you will be much happier than if you had the 3.55 or 3.21. At 70mph, the hemi is happier at 1900 than it is at 1700. It will not drop down a gear nearly as often to maintain speed saving tranny wear. Don't worry about the RPMs with the 20s, on the 3rd gen back in 02/03, 4.10 were required by the factory if you ordered 20 inch tires.
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Joined: Mar 2009
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From: Houston, TX
I just returned from a ~900 road trip with the EVIC stating 20.6 mpg. Like another poster, I seem to get the best mileage cruising @ 72-73 mph. I have a 2wd Laramie w/ 3.92 gears. I can't see a 4x4 breaking 20.
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Joined: Aug 2007
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From: HOUSTON,TEXAS
My truck has 3:21. and it doesnt downshift going up and down hills, and it does get better mileage, 22.9---23.0 mpg(hand calc) and as far as a DOG....I ran 14.8--14.9 all night long at the track, when I started it ran 15.1 till I figured how to launch , a Crew Cab with 20's, no engine is phisically happier at higher RPM. When the programmer gets here, I will be really pleased with the extra mileage,and power, all with 3:21's.
Also, when I read about 3:92.s getting over 21/22 MPG, I go back over to my neighbors house and ask him again , what he gets, with his Crew CAB 4x4 and 3:92's--he only gets 17 at the most, at 70mph, he has tried every kind of driving technique, so he must be doing something wrong.............
Also, when I read about 3:92.s getting over 21/22 MPG, I go back over to my neighbors house and ask him again , what he gets, with his Crew CAB 4x4 and 3:92's--he only gets 17 at the most, at 70mph, he has tried every kind of driving technique, so he must be doing something wrong.............
Last edited by BULLRAM; Jan 26, 2010 at 11:52 AM.
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Any engine due to design harmonics will have a RPM that is its sweet spot and 1500-1600 is NOT the best RPM for the 5.7. It likes 1750-1900 much more. There are some very annoying vibrations in the 1200-1500 range on most 5.7 hemis. Read the gas pedal and seat vibration threads.
Being a dog can be relative to what it is being compared to. 3.21 gearing does make the truck slower than the same truck with better "lower" gearing. I have a sport with 3.55 gears and I get 20.X mpg on the highway at 70 mph. I will assure you that a 3.92 truck is quicker than a 3.21 and it will get better mileage in town and on the highway if you are towing.
Being a dog can be relative to what it is being compared to. 3.21 gearing does make the truck slower than the same truck with better "lower" gearing. I have a sport with 3.55 gears and I get 20.X mpg on the highway at 70 mph. I will assure you that a 3.92 truck is quicker than a 3.21 and it will get better mileage in town and on the highway if you are towing.
Professional
Joined: Sep 2009
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From: Houston
My truck has 3:21. and it doesnt downshift going up and down hills, and it does get better mileage, 22.9---23.0 mpg(hand calc) and as far as a DOG....I ran 14.8--14.9 all night long at the track, when I started it ran 15.1 till I figured how to launch , a Crew Cab with 20's, no engine is phisically happier at higher RPM. When the programmer gets here, I will be really pleased with the extra mileage,and power, all with 3:21's.
Also, when I read about 3:92.s getting over 21/22 MPG, I go back over to my neighbors house and ask him again , what he gets, with his Crew CAB 4x4 and 3:92's--he only gets 17 at the most, at 70mph, he has tried every kind of driving technique, so he must be doing something wrong.............
Also, when I read about 3:92.s getting over 21/22 MPG, I go back over to my neighbors house and ask him again , what he gets, with his Crew CAB 4x4 and 3:92's--he only gets 17 at the most, at 70mph, he has tried every kind of driving technique, so he must be doing something wrong.............
City driving in Houston, I'm getting about 16.5 EVIC and 15.5 Hand calc. Wish I was getting that kind of mileage.
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Joined: Aug 2007
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From: HOUSTON,TEXAS
I totally understand the towing factor, when towing it will NOT compare to the 3:92's my point is like you stated it is not a DOG on accleration, to some....
OOSIK, I run 65/70 to San Antonio, all the time, i have NEVER gotten lees than 20 hand calc,my book is full of 20 plus readings, it is all relative to your driving, in town ,I get less because of stop and go, i am not alone on the mileage,
OOSIK, I run 65/70 to San Antonio, all the time, i have NEVER gotten lees than 20 hand calc,my book is full of 20 plus readings, it is all relative to your driving, in town ,I get less because of stop and go, i am not alone on the mileage,
