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Custom Dodge Ram Performance Mods - Engine - 4.7 Liter V8 Discuss modifying your Dodge Ram with Performance Parts and Accessories!
Factory Spec: 4.7-liter V8 engine - 310 horsepower, 330 lb-ft of torque.


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  #11  
Old 08-20-2013, 07:25 PM
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Example: I changed from the stock 3.92 to 4.56. My around town mileage went up a bit (when I can keep my foot of it...) because the engine isn't working as hard to get the truck moving. When I get out on the highway, mileage suffers because now to maintain the same speed I did before, the engine is spinning faster (higher rpm). It's always a trade off, unless you can adapt another OD gear to it lol.
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Old 08-28-2013, 12:09 PM
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Basically you need to decide if you care about mpg or not, and if so, how much do you care?

3.55 give pretty good mpg on the highway. 3.92/4.10's won't be horrible at 70mph but you will likely lose a little mpg. Now if you cruise at 80 or higher with that gearing you will get bad mpg. 4.56 mpg on the highway really suffers, and if you cruise at 80+ you'd be getting terrible mpg.

With my 3.55, I can cruise at 70mpg and get over 20mpg easily. At 80 mph I can still sometimes get 20mpg, depending on conditions. And even at 85, 90 mpg(yes I sometimes drive that fast) I will still get anywhere from 17-20mpg again depending on conditions(mainly how windy it is). Keep in mind too this is all unloaded, not hauling or towing any weight. At 70mph though, the truck can feel a bit sluggish cruising when you pass someone, sometimes it has to kick down a gear to really get up and go.

I've experimented locking out the 6th gear and cruising around with the 5th gear on the highway, which is effectively the same as having 3.92 or 4.10 in the 6th gear(don't remember which one off hand without doing the math). What I found was that probably 75% of the time I still got 20mpg or higher pretty easily, unless it was very windy. When you start going over 70mph, mpg drops off pretty quickly. The truck had way more power on demand though, which I really liked.

Personally, I would never go as high as 4.56's, but I drive on the highway occasionally. I don't do highway driving a lot, but we go half way across the country a few times a year, and that gearing would really put a damper on those trips. If I was only around town, then yeah I'd regear to 4.56, as it's only going to help. If you do highway driving, I wouldn't recommend anything higher than 4.10, and even with that you're limited to around 70mph cruising if you want to see any decent mpg.
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