I thought I would post this information for all those considering a rear gear change specifically for towing. See my signature for truck info. Original Gear Ratio was 3.73, 11.5”, 14 bolt. Now 4:10. Don’t think there is much difference in MPG with the 4:10’s when not towing based on what I saw with both ratio’s.

The tow was a 26’x 10’6” Passenger Carrying Alumitech, Inc. Airboat. (Tour Boat) Trailer and Boat estimated at 7000 pounds. Airboats tow like Parachutes. It catches the wind from all directions. There are 3 rows of seats with backs up front 10ft wide. Then there is the operators stand, and behind that is engine, prop, gage around all that.



When towing my 14,000 GVW fifth wheel I averaged 11 mpg with the 3:73’s.

The tow route was the same when the Airboat was being towed. 360 miles from Orlando, Fl to Panama City, Florida all three times.

In March I towed this to Panama City with the 3:73 gears.

I had 4:10’s installed on the 10th of May.

I picked it up on 11 May and brought it back to Orlando. Blown Engine. I took it back to Panama City, Florida on 14 May.

The Engine and Tranny info was provided by an Edge Insight Monitor. Fuel burn info was provided by the Trax II Transfer Flow system. Fuel Capacity with truck tank is 105 gallons. Total round trip from Melbourne to Orlando to Panama City and back to Melbourne via Orlando, varied depending on the route traveled without the airboat on the trailer.

March Trip May 11th May 14th

Air Temp 72 (day) 70 (night) 91 (day)
Speed 65 65 65
RPM’s 1750 1950 1950
EGT’s 1150-1250 980-1050 980-1050
Boost, Flat Road 27 psi 17 psi 17 psi
Engine Water 198-200 198-200 198-205
Tranny Temps 192-195 192-195 200-207
Engine Load 65-70% 53-56% 53-56%
Fuel Burn 49 gallons 43 gallons 43 gallons
MPG Tow 7.34 8.37 8.37

Round Trip (Miles) 888 817 878
Total Fuel Burn 77 gals 72 gals 76gals
Avg MPG 11.5 11.3 11.5

Load Reduction 14% with 4:10’s

I tried 4 times to post the temps etc without them running together. Sorry I can't see to get it so its easier to read.

Anyway it was obvious to me the 4:10's are a better choice for heavy towing than the 3:73's. I really did not believe 200 rpm's would make that much difference. I wanted 4:30 gears which would have put the tow at 2250 rpm at 65mph. No one makes them. 4:56 is the next availible and that was way to much for non towing hyw use.

 

for an auto yea but with a stick and the g56 tranny the 3;73's are the way to go

 

I'm sure I will get a smack down on this one..

but start the boat motor for a push down the road

 

Brrrrilliant!

 

G56 with 3:73's is the same as my set up at 65mph. 2000 rpm's. 4:10's with the 56 is 2200 at 65 mph. If I were a commercial driver with a 3500, I would want the 4:10 and G-56. Hard to slow the cummins down running 2200.

http://www.powerspec.cummins.com/sit...ng/gearing.htm

 

Sounds like fuel assisted wind reduction system or client fuel surtax.

 

Last time I towed my 15k lb5ver with the 04.5 4x4 NV5600 3.73 gears I got 10.5-11.5 MPG depending on the hurry I was in going over the eastern mtns.
Now my tow rig has 4.44s and I would hate to drive it without my aux trans. Lock in OD the aux lets me turn 2k rpm at 70. A much better combo running empty with the G56. If I was deadheading alot profesionaly I believe I would get 3.42 gears and tow in 5th gear and use OD to get home. This way you could capitalize on the empty MPG with a 6.7L while having RPM loaded for the interstate.

 

I had to go back and get the boat one more time, on 3 June. I deceided to install the Juice with Attitude for the tow back with the boat. Hope the moderator will not have a problem with this as it may belong in the high performance section. It is related to what I have posted on this thread already.

I used position one for running lite with no tow and position 2 for towing with the juice.

There was no difference in fuel mileage for the round trip on the 11th of June at 845 miles using 74 gallons of fuel. 11.4 mpg. Towing the boat was just a little less at 8 mpg. I was getting 8.3 in stock format. It was 99 degrees outside on State Route 20 just south of I-10 during the afternoon. I had to pull it back to 57 mpg to keep the engine and tranny around 203-205.

We don't have very many hills in Florida, except, in the panhandle and along the Florida Turnpike between Orlando and Wildwood. Some are 4-5% grade a mile long. Before, with the cruise control on,the truck would downshift about 3/4's the way up the hill with the Airboat at 65mph. With the Juice, there was no downshifts on any of the hills with the cruise control on. EGT's were not very much higher than running stock while doing the hills. I was impressed with that. I had a little more engine temp going up the hill.

The Airboat Engine was computer controlled (figures) and was causing all kinds of problems with the first two engines. A differant type was used this time. I later learned the wiring harness was chaffing causing the computer to screw up on the first two engines.

 

I agree on the 4.1s. My 03 gets the same mpg pulling a 31' 5er that my 97 did with 3.54 pulling a 25' 5er and the 4.1s do everything easier. The downside of the 3.42 would be losing the nice slow granny and the wide splits between gears. Those were the 2 best things about going from the 5sp/3.54 to the 6 sp/4.1. Craig