Ford 6.7 ratios?

gearhead · 07-29-2015, 05:01 AM

I could get off the recliner and go visit dealers but I thought I would try this first.
I'm looking at Ford's website on building a F350 dually. My current truck has a 3.55 rear end. When towing at about 55 mph it will get down around 1400 rpm. I know that's about where max torque is, but it just feels too low. I usually downshift to lock out 6th gear and keep the rpm's above 1500. Anything around 65mph I let it run in 6th.
Fords website shows if you order the FX4 package you get 4.30 gears. I think I prefer 3.73. I can get that by ordering a 4x4 and not the FX4 package.
All that said, for those that have 4.30 gears, are you happy? I'm wondering about rpm's and mileage while unloaded. Do you recall what rpm you are running at 65mph?

Seabee · 07-29-2015, 06:23 AM

Why visit a dealer? Use this calculator: http://www.apexgarage.com/tech/gear_ratios.shtml

Bolter303 · 07-30-2015, 09:09 AM

I have a new 2015 F350 DRW with the 4.3. At 65 and in 6th I am at 2000-2100 rpm. I only have about 1K miles on it and I got 10.2 mpg pulling a 40 foot Montana at 14,200 lbs. some mild grades and some wind. Going back home with out the trailer at 70 mph and 2400-2500 passing semi's ago 80-85 I got 13.9 mpg. Will get better. Now when I left Vegas in a thunderstorm I hit 30+ mph cross winds with rain. I dropped to 55 mph and the truck held firm as as well as the trailer. The trailer did wag in the gust but never rolled side to side. The 4.3 gears gives you the wider front axel from the F-450. Look at the pictures of the two trucks you will see a wider fender flair up front. The 4.3 increases you towing ability guide a bit. This truck is my last, will retire in a few years and if I get a bigger heavier trailer this truck will pull it. Any other questions let me know

gearhead · 08-06-2015, 03:08 PM

^^^all good info.
I usually get 10.5-11.5 mpg towing the 5th which usually is about 11,700#, depending on her shoe count of course.
Freeway running empty from Houston area to Tulsa 17.8 mpg. Usually 3 mph over posted limit.
Sounds like the 4.30 wouldn't be a big issue in the grand scheme of things, but the 3.73 may fit my needs better.
Do you get the driveshaft shudder in 1st gear?

Javi · 08-06-2015, 04:56 PM

My dually is doing just fine with the 3:73's.. Unless I was hauling a 16K plus trailer I see no need of the 4:30's..

**JRTJH** · 08-06-2015, 08:36 PM

Gearhead,

Your 2013 F350 has the "first generation" 6.7L in it. Remember that the 2015 introduced the second generation engine with increased torque/HP. Like Javi said, unless you're looking at towing significantly more than your HC, the 4.30 gearing would probably be overkill.

I'd think the 3.73 is all you'll need and when driving solo, you'll still be able to stay below "redline" at 75-80. With the 4.30 gearing, you'll be winding the engine up pretty tight just to get above 75. That probably would decrease your solo MPG and wouldn't improve your trailer towing performance enough to justify the gearing selection.

jtyphoid · 08-07-2015, 05:41 PM

I'm happy with our 2015 F350 6.7 4x2 dually with 3.73 rear end, both solo and when towing our 15.5K Raptor. It has all the get up and go that I need (and I use it when merging into Houston freeway traffic with the Raptor in tow).

I would have liked the wide-track front axle that I understand comes with the 4.30, but a few extra back-and-forths have sufficed to get me in and out of all of the tight spots that I've run into so far.

Javi · 08-09-2015, 11:06 AM

Just a note about RPM.. With stock tires my truck (see sig) is setting on 2K at 75mph

I'll tell you that anything over 65 empty will suck the fuel down in a hurry. Pulling my trailer 62-62 seems to be the upper limit for suckage to really kick in..

It's ridiculous how much power this thing has.. even on short ramps this thing will pull 65 to merge before the run-out starts..

Best case towing is 11.5 mpg worse case 9.75mpg..
Best case empty highway has been 16ish and worse case 15ish..
In town is 13ish empty...

Overall for 7K miles is 13.5mpg about 28% towing

SteveC7010 · 08-09-2015, 11:32 AM

Quote:

Originally Posted by Javi

Just a note about RPM.. With stock tires my truck (see sig) is setting on 2K at 75mph

I'll tell you that anything over 65 empty will suck the fuel down in a hurry. Pulling my trailer 62-62 seems to be the upper limit for suckage to really kick in..

It's ridiculous how much power this thing has.. even on short ramps this thing will pull 65 to merge before the run-out starts..

Best case towing is 11.5 mpg worse case 9.75mpg..
Best case empty highway has been 16ish and worse case 15ish..
In town is 13ish empty...

Overall for 7K miles is 13.5mpg about 28% towing

My '12 has 3.31 gears. Our towing has been almost exclusively in the Adirondacks where there are no level roads. It's always uphill or downhill.

Like you, I'm a bit in awe of the power that the 6.7 has. It walks right up to 60 or 65 quite effortlessly with the trailer in tow. But I am seeing different mileage numbers. Admittedly, I'm just using the on-board computer's results, but here they are:

Towing: High is right around 14.0 MPG; low about 11. In the Adirondacks. We haven't made any real trips outside of the park yet so I haven't had a chance to see if the mileage will creep higher in flatter country on the two lane roads.

Just the truck: If I keep the speed at 65 or a bit slower on the interstates, I can nudge it up to 21 MPG providing I'm not in really hilly country. The uphills pull the MPG down quite noticeably at speed. On even short trips, it never dips below 18 MPG. Now around town is really where it drops off. I live in a small village, and except for infrequent trips to other towns (15 to 30 miles), the mileage drops way off, mostly because of start and stop driving. The grocery and drug stores are not even a mile away. A lot of times I'll take the truck to other local places even though I could walk because my tools and such are in it.

I'm not sure about the accuracy of the on-board computer so I may start running my own numbers for comparison.

Javi · 08-09-2015, 11:39 AM

Quote:

Originally Posted by SteveC7010

My '12 has 3.31 gears. Our towing has been almost exclusively in the Adirondacks where there are no level roads. It's always uphill or downhill.

Like you, I'm a bit in awe of the power that the 6.7 has. It walks right up to 60 or 65 quite effortlessly with the trailer in tow. But I am seeing different mileage numbers. Admittedly, I'm just using the on-board computer's results, but here they are:

Towing: High is right around 14.0 MPG; low about 11. In the Adirondacks. We haven't made any real trips outside of the park yet so I haven't had a chance to see if the mileage will creep higher in flatter country on the two lane roads.

Just the truck: If I keep the speed at 65 or a bit slower on the interstates, I can nudge it up to 21 MPG providing I'm not in really hilly country. The uphills pull the MPG down quite noticeably at speed. On even short trips, it never dips below 18 MPG. Now around town is really where it drops off. I live in a small village, and except for infrequent trips to other towns (15 to 30 miles), the mileage drops way off, mostly because of start and stop driving. The grocery and drug stores are not even a mile away. A lot of times I'll take the truck to other local places even though I could walk because my tools and such are in it.

I'm not sure about the accuracy of the on-board computer so I may start running my own numbers for comparison.

Those are about the same numbers I got with my '12 SRW however there really is a huge difference in perceived power between the '12 with 3:31 and the '15 with 3:73.. the '12 isn't even in the same league... stability while towing is also a huge difference..

C130 · 08-10-2015, 12:36 PM

My 2015 F450 with 4.3 also turns 2000 RPM's at 65 mph. Gas mileage suffers quite a bit if going over 70 mph. It really seems to like 65-67 mph for gas mileage and will get around 18 mpg at those speeds. Anything over 70 mph and it's around 15 mpg.

Towing, the 4.3 is great and I averaged about 10 mpg traveling from Houston to East Tennessee and back and towed at around 70 mph most of the time. Same with my 2011 F250 as far as mileage, I got 10 mpg. For daily use though I'd prefer the 3.73 for sure and not sure the 4.3 is really needed much of the time. I think it really depends on where you are going to be towing and how much towing you're going to be doing. Saying that, the 4.3 tows incredibly well and I was amazed at how little it shifted in the hills. I'm not sure I helped any but for towing the 4.3 is awesome, daily driving the 3.73 is better. I use my F450 as a daily driver , driving 38 miles each way. 65 mph is the magic number for my F450 for sure as a daily driver.

gearhead · 08-10-2015, 03:45 PM

I'm thinking the 3.73 is where I would be going.
Decisions, decisions.
Wait for the aluminum body 2017, or get a "deal" on a "old style" 2016. Leave a new $60,000 truck sitting outside, or sell the Corvette to make garage room. Wife doesn't want me to sell the hotrod..."you'll just want something else". Yep, probably with just 2 wheels on it too. (Triumph Thruxton)
Son wants the current F350. I have 2 wanting to buy the Vette.
ARGH.........

**JRTJH** · 08-10-2015, 03:59 PM

Hell, just build a bigger garage

gearhead · 08-10-2015, 06:38 PM

I need a barn. But I have a HOA. I need to buy a cheap lot somewhere else in town and build a barn, I'm full here.

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