The V8's get 3.45 and the V6's get 3.09 (at least what I see for '12). The lower the number, the better mileage in exchange for reduced performance and towing.

What would happen if somehow a V8 could be changed to a 3.09? How much would mileage go up and how much performance and towing would be lost? Can it even be done? Or is it just not worth it?

 

If I'm not mistaken the R/T has 3.88's

 

No the R/T has the 3.45 just as all the other Hemi equipped Durangos. And to answer your question is that the 3.09 gear ratio transmission isn't set up to be connected to the Hemi, but yes you would expect to see mpg gain of a 2-4 mpg with a 3.09 ratio rather than 3.45, but you would lose towing ability quite a bit.

 

seems to me it's time for someone to invent a dual ratio setup that a driver could switch? Have an eco button to engage 3.09?

 

They already have......and you already have it. It's your standard overdrive transmission. Today it has 5 or 6 gears in the D. Some day it will have 8 or 9. Automatic transmissions used to only have 3 gears....they keep adding them. I seem to remember something about Mercedes coming out with an 11 speed?

 

I thought the final axle ratio was the way to "reset" one single transmission model (and every speed within that tranmission) up or down for the engine. But if one had a dual ratio (or two speed, or even multi speed) final drive ratio transmission, then that would offer even more flexibility. By just adding two final drive ratios along with a 5 spd transmission, one now has ten gears. Kind of like how road bikes will have 1,2 or 3 crank gears and 9-11 rear drive gears.

I thought overdrive was basically a "fake" gear in that the transmission locks up and power is no longer being transferred by transmission fluid and this only happens at highways speeds after the highest gear is reached?

 

I'm going to be changing to a 4.11 sometime soon anyway.

 

How and where are you getting this done?

How much does it cost?

Does it void the warranty?

How will this affect the performance? The R/T is listed as 0-60 in 7.3 seconds.....can you calculate how much that time will improve?

I'm interested in doing this to my 2012 R/T also but I'm not sure how/where to get started.

 

It will be done by a shop, costs around 750-1,000 USD for it to be done properly. Makes 0-60 a lot better but also makes your top speed lower.

 

not true at all OD is just a lower gear ratio than drive (lower in the sense that it makes the engine spin lower and the driveshaft/wheels spin faster.

what you are referring to is torque converter lockup, and it will happen in lower gears under the right conditions (no it doesnt happen often)