I have an 08, 4.7, QC, 2WD. It has a rated mpg of 14/18. I was looking at the specs for a 2013, 4.7, QC, 2WD. It has a rate of 14/20. My 08 has a 545RFE transmission, where the 2013 uses a 65RFE. As far as I can tell, the both transmissions use the same gear ratios. So what makes the difference? Was there different tuning in the newer 4.7's?

 

In 2008 they revamped the 4.7, taking cues from the Hemi. The new 4.7 has higher compression and 2 plugs per cylinder (a hand down from the Hemi). The 2013 4.7 should be the same as the 2008. As far as I read, the 4.7 was discontinued at the end of 2013, so there shouldn't be a new and improved version. It's possible your 2008 was one of the change over period that got the older 3rd gen engine though. But to answer your question, I'd say the 2 plugs per cylnder and the more power helps improve the MPGs. This is a good case of where a little more HP and torque means you ride the engine a little more gently and get better MPGs

 

I think the body style improved the highway mileage a bit. I think they reduced the about of air going into the engine compartment in the 4th gen.

 

The stock 3.21 gears would have a contribution.

 

Ewww thats terrible.

 

I agree, but it would yield an extra MPG or two on the interstate. Would be hell trying to pass someone uphill though, LOL...


The second plug in each cylinder does allow for a more efficient burn of the fuel.

 

Same exact transmissions. The 65RFE just has a newer software program that allows use of all 6 forward gears when ERS is enabled. Otherwise, the upshift will use 2nd OR 2nd-prime(never both) when disabled.
The 65RFE also uses a diff Torque Converter which may help slightly.

and I think they are phasing out the 4.7L for 2015. Just using up current inventory for 2014. That was a rumor though.

 

I would say most if any real gains are probably due to aerodynamics to allow these bricks to rolls down the highway a little easier. I don't know about Dodge but you have to be careful before jumping all over on rear end ratios on the new trannies. I know Chubbie's 6 speed with a 3.42 ratio or whatever yields a final drive ratio similar to what the old 4 speed and 3.73 had but at least you've got 2 or 3 highway gears to work with. You don't need the rear end ## we're all used to if the gearing before it is adjusted accordingly. And yes I have 4.56's but that's because I can't lockout my OD's on my '04. Otherwise I would have gladly kept my 3.55's.