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I have been racking my brains over the gear ratio change. I am trying to find the "best" ratio for me and my driving.

IIRC, the 198mm ratios available are 2.87 3.06 3.64 & 3.90

If you change to RT axles the 3.73 & 3.90 are available.

Inertia Motorsports has given me two different recommendations over the last 6 months. First was a 3.23 ratio (after market gears) and the second was the 3.73 RT.

The dilemma I am facing is the fact I commute 80+ miles per day with a 60/40 hwy/city driving.

Currently I am running shorter height tires (26.7'' vs 28'') which changes the ''effective'' gear ratio by 1.05 which roughly equals a 3.01 rear axle. The change raised my rpms by 100 at hwy speeds. I have been very amazed with the increase in take off and drivability this relatively small change produced. But I would like more...:)

If I change the rear gear from the 2.87 to a 3.06 (198mm) then my effective ratio with the tires would be 3.20 which is close to the first recommendation of 3.23 gears.

My concerns with going to the 3.64 or 3.73 gears are mpgs and road noise (exhaust) in the car a hwy speeds. I have driven around some with the autostick in 4th gear with the rpms around 2500. The extra exhaust noise gives me a headache after a while. This concerns me since my commute is 1-1.5 hours each way.

Any thoughts...?
 

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I beleive Matrix and SS Dodge have several posts on this subject.
 

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actually, it is a 3.07 gear and not 3.06 that is 198mm. i recommend the 3.07. i know it is a small jump in size, but it puts the motor in the peak power band better than the other gears.
 

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I have the 3.64 gears in my SE. They run around 2600 rpm at 70 mph. Gas mileage doesn't suffer unless you do mostly city driving. They will give you a headache from the noise. I just turn up the radio. I changed from 2.87 to 3.64 because I drag race my car. Very powerful off the line and great passing on the street.
 

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Considering that you are driving 80 miles a day, some compromise is in order. Tony (SS Dodge ) has the proper suggestion, use the 198 mm 3.07 gears. If you poke around you can get the complete replacement gear kit and have someone put it in unless you are familiar with crush sleeves etc. You will also need new pinion bearings.
However, the simpler route is to get a pulled carrier, take the rear cover off and clean it up. Put on new axle seals and for goodness sakes leave the pinion nut alone. You should be all set. You will need a predator to set the axle ratio and tire diameter to get the proper data to the pcm and transmission controller.

You didn't indicate if cost was an issue. If you are trying to conserve cash I would not even consider changing axles.

One caveat, I had both a gear set and a pulled carrier. The carrier had chipped spider gears, fortunately I got my money back after a series of pics and it got scrapped. I with a friend who works on Mercedes used his shop and lift and just swapped the 3.90 in. It took us about 4 hours and I did the busy work with his instructions. I had a much greater benefit as it allowed the centri blower to spool faster and build bost. Realize that the 2009 had the 42RLE transmission.

With the NAG1 and 80 miles/day and you want quiet, put in the 3.07.
Everything is relative as you indicated you wanted to suit your needs that were loosely defined.
 

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I followed Hemiwoman's route and installed the 3.64 gears. Actaully just installed them lastnight so I've only gotten to have a little fun, but if you can find a carrier assembly, that's the way to go. I work at a dealership so fortunately I had access to lifts and the entire install took about an hour and a half.
 
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