difference in mileage

[bryan28]

Don't have a Ram yet but plan to have one this year (4x4 qc). All i currently tow is a 17' aluminum boat. The highway speeds here are 70mph and i usually put it on cruise between 75 and 80. What would be the approximate difference in gas mileage between 3.21 and 3.92 with the hemi and 8 speed transmission? I drive probably 80% highway to 20% city.

 

[Ratket]

Flat roads or hilly? I'd opt for the 392"s to get the most out of the mds.

 

[MyOhFive]

MDS MAY not engage at those hwy speeds with a 3.92 tho.

If you run flat ground and those percentages are accurate, you would see better MPG with a 3.21. That said, I strongly suggest test driving both because I think you'll generally like the 3.92 better.

 

[RLJ10X]

If there is certifiable hard data that proves that 3.21s get better gas mileage than 3.92s, I have not seen it. So, what you read is opinion. I think that opinion is a hold over from the past, before Overdrive and Double Overdrive.

I went fro 3.55s to 4.10s in the 5/6RFE. if I drive the same, there is no noticable difference in fuel economy. But the 4.10s are sooo much more satisfying.

I have 2 friends with Ford diesel pick ups. They're turning aprox 2000 rpm @ 70 mph. Thats what my 4.10s in my gas Hemi does. Your 3.92s are going to be spinning the engine slower than a Ford Diesel. Why on earth would any one want anything taller? Get the 3.92s, please!

 

[Goatman91]

The wife has 3.21, I have 3.92..... she likes my truck better just saying. Lol get the 3.92s

 

[clh1220]

The wife has 3.21, I have 3.92..... she likes my truck better just saying. Lol get the 3.92s

If neither one of your trucks have the 8 speed it doesn't mean anything. The 8.speed changes every thing. My 3.21 8 speed will run with your 5 or 6 speed 3.92. just saying

 

[Jerry1984]

At those speeds I would say 3.21. I have 3.92 and at 70 I'm real close to 2000rpm. Not too many 75 mph speeds around me except for when I go on vacations.

 

[thad8403]

If there is certifiable hard data that proves that 3.21s get better gas mileage than 3.92s, I have not seen it. So, what you read is opinion. I think that opinion is a hold over from the past, before Overdrive and Double Overdrive.

I went fro 3.55s to 4.10s in the 5/6RFE. if I drive the same, there is no noticable difference in fuel economy. But the 4.10s are sooo much more satisfying.

I have 2 friends with Ford diesel pick ups. They're turning aprox 2000 rpm @ 70 mph. Thats what my 4.10s in my gas Hemi does. Your 3.92s are going to be spinning the engine slower than a Ford Diesel. Why on earth would any one want anything taller? Get the 3.92s, please!

I have a 14 ram cc with an 8 speed. When I had 3.21s at 65 mph my rpms were at 1400 rpm and now at 65 mph with 4.10s I'm at around 1800-1900 rpm. That's why fuel mileage is worse with gears on the highway. You stay at a higher rpm while cruising. I'd say I probably lost 2 mpgs at least on the highway.

 

[bryan28]

Got my Ram. It's a 2014 Sport and has the 3.21 gears. I had gone to the dealer to order one and would've got the 3.92 if i hadn't struck a deal for this truck. After driving it i have no doubts it'll work for me just fine.

 

[Crianor]

If your looking at fuel mileage only, go with 3.21s. Looking at pure math and science, 3.21s will almost always result in better gas mileage as the engine will be spinning at lower RPM's. The only caveat is this... if you are running at a speed that means the tranny needs to drop down a gear or two to hold the speed, the advantage can quickly go away. And at 75 or 80 mph I think you will be close.

There's always a trade-off between performance and fuel mileage. That's why they have different gearing. So yes there is absolutely proof that different gears result in different mileage.

If all you will be towing is a small boat, go with the 3.21s.