So I found this 2012 E-350 Ext with a V10 and a factory tow pkcg (a combo which is becoming incredibly rare -- at least in my experience the last few years)... it was essentially loaded with Sync, rear air, 15-passenger config, power everything, etc... and only 17k miles.

I'm getting 12 mpg with this bad boy V10, but here's the really disappointing part: because my truck has the 3.73 rear, Ford only rates it for about 8,300 lbs worth of towing.

What. A. Dis. A. Point. Ment.

Shame on me for not checking the rear diff before I bought. A 4.10 would've gotten me to 10k. I bought the truck to take a 9,500 lb RV travel trailer to Yellowstone in July. I'm going to use it anyway and hope I don't shred the gears.

(Sigh)

 

It won't damage the gears. I guarantee it, or I will gladly refund all of the money you paid me for this opinion.

The tow rating is based on many things. I'm not sure that I know all of them, but I do know some of them.

1.Stopping ability is one. The brakes are the same regardless of axle ratio.
2.Cooling is another. The 4.10 will cool the trans better than the 3.73 because the trans doesn't work as hard. The engine will spin faster, which tends to drive up the temps more than the reduced load decreases them. Overall this is a wash.
3. Performance. It has to not drop below 2nd gear and maintain a certain speed (I don't remember the number) on a certain grade. If you are good with exceeding this, the van can pull it.

I had a 2002 E-350 extended V10. I had the 3.73 ratio and mine was also rated less than if I had the 4.10. My travel trailer scaled at 9100 pounds. I never dragged it over the continental divide, but I did encounter some steep grades at times. It did fine.

 

Thanks, Mark. Your words do make me feel better. I'll let you know how my 5spd auto with tow/haul manages!

 

If you've not already visited the FTE V10 forums do so quickly, look for anything relating to Mike @ 5 Star Tunes. In fact he has a "I Love Mike" sticky thread there---do yourself a towing favor and read there.

That too should be salve for you gear shredding concerns.

 

I don't think reaching for more power or torque is really the correct path. The V10 has the goods. It's just twisting too tall a gear.

It's like thinking that giving more steroids to a young Arnold Schwarzeneger will make him accelerate a 12-speed bike from rest (in 12th gear) faster.

It might. But shifting down to 1st gear would make more sense.

 

Ok, engineer's question:

with a 3.73 rear diff, what size tires (ie: diameter) would I have to put on my E-350 to approximate a 4.10 rear diff?

 

10% smaller radius.

 

If you want to play engineer you should be able to use Excel and understand the formula for tire sizes (sorry but one good rant deserves another)....

You need tires that are 3.73/4.10 the diameter of your stockers which is 90.98%.

If you have 245/75x16's you are at 30.47" diameter on a theoretical basis (actual tires will vary slightly). To mathematically get to the right size you multiply 30.47" times 90.98% which results in 27.72".

I've got a spreadsheet that calculates tire sizes and it looks like 245/60x16" will get you 27.57" which is close to where you want to be.

VERY unlikely that you will find any tire in a 60 series that will give you adequate load capacity. I could run lots of other combinations but I don't think you'll get where you want to be with tire sizes....

My best suggestion is to simply install 4.10 (or even 4.30) gears in your van. Seems like that would address the problem very directly. I bought my new '02 E150 out of dealer stock at a good price, and paid to have a limited slip unit put in the rear axle when it was brand new... Just put in what you need. You might also look into a huge trans cooler, etc, if you don't have one already.

What I would do if I were in your position is to put on the huge trans cooler (and make all other towing prep you need) and try out your existing combination to see how it feels with your actual load and your actual terrain. People have abused trucks and vans far more than your proposal... If you want a LOT more towing oomph, then go to the 4.30 gears instead of the 4.10 but expect your gas mileage to suffer accordingly.

George

 

fwiw.
Back in 1992 I was provided with a 91 Explorer for my company vehicle (bought for a VP who ended up not liking it), I wanted to tow my Tiger on a trailer, so thought that I was all set
Then I read the "fine print" - this was a rear-wheel drive XLT (open rear, too - bad news in the winter here) with a 3.00 gear, according to the manual it was rated to tow 1800 lbs - vs about 5000 for the same vehicle with the higher (I think it was 3.73 gear)
I talked to dealers, service guys, etc. It already had a nice trans cooler, all hp, brake, and gvw capacities were the same across the board. I came to the conclusion that the low rating was based on [lack of] ability to climb mountains.
We ended up taking a number of trips with the trailer (about 4000 lbs) around the mid-atlantic/east coast area over the years, never had a problem. Of course, no mountains needed to be climbed.
One of the guys bought that vehicle from the company, last I heard it ran to over 200K with original engine and trans.
Possible key factors in your decisions could be the amount of towing (% of use and total miles?) and the terrain to be encountered (mountains?).
Good luck with everything,

 

I agree with YoGeorge. I would go with the 4.30's and a Gear Vendors unit. http://www.gearvendors.com/ag4s.html. They even make a money back guarantee that your mileage will increase by a certain percentage. I have a Gear Vendor in my 79 E350 Class C. It makes my C6 3 speed a 6 speed with overdrive.My top cruising speed used to be 55 now I can cruise at 70-80 if I want.