I have a '99 F-350 V-10 4x4 CC SWB with a 6" pro comp lift, 35" Nitto Terra Grapplers, Flowmaster cat-back, cat-removed, diablosport tuner and a k&n kit. My truck has a 3.73 gear and as I'm reading here, it's not going to work. I don't feel like changing trannys once a year so I'm looking into gears. I tow a 12,000lb TT pretty regularly and can't quite decide what set of gears to install. Some people say 4.30 (I say no) some lean twards 4.56 and I've even heard trading for a diesel (hell no) and I'm thinking more of like 4.88. What is your opinion?

 

Ok, we'll do just a lil math. Back in 99, the best towing gear ratio offered by Ford was 4.30. Stock tire size was 31.6 (265x75R16) At 65mph in OD the rpms would be approx 2080. Getting back to this rpm is the goal. So, with 35" tall tires and 4.56 gears the rpm is 1991. Close. With 4.88 gears, the rpm would be 2131, just a lil high.

If you use your 3.73 ratio, the stock rpms with 31.6" tires is 1804. Here, the 4.56 gears would be best if you wanted to stick with the capabilities of a 3.73 geared truck. In 99, the GCWR of 3.73's was 17,000 pounds while the 4.30's is 20,000.

It seems that the 4.56's may be the best in between choice. If you tow often and have lots of hills the 4.88's may be better. The 4.56 may be a tad easier on fuel. Confused??

http://www.4lo.com/4LoCalc.htm

 

here's another link for gear ratio vs rpm
http://www.amxfiles.com/resource/tech/rpmvs.html

 

here's anouther web site for some gear changing. play with the calculators and see what you come up with

http://www.accuautoparts.com/

i would agree that you are in the right ball park with 4.88's!! A LOT of people under shoot their gear selection. some other thought to gears are tire width (wider tires = larger foot print, whitch means more resistance when turning), then think about weight, obviously a larger tires is going to weigh more. believe it or not there can be a big difference in tire brands that are the same size!! when the calculator says you need a 4.30 gear they don't really calculate for the added weight and width!! so a 4.56 or a 4.88 would make up the difference for the weight over stock tires, and the wider foot print on the ground!!

and something else to think about if you ever get the "bigger tire bug" drop in a set of your 4.88's or 5.13's and you'll be covered up to a 40/42" tire if you ever get that big bug, hahaha!!

 

Thanks alot for the input. I think I might go with the 4.88s as the final ratio will be 4.13 with the tires I have. My truck didn't exactly struggle with the load it just had a little bit of a hard time with hills and whatnot.

 

I would go with at least 4:88s, especially with the weight of your TT.

 

I'll second dkf...with your weight and given that you tow frequently...the 4.88 and those tires will be a good combo.

It will give you a little deeper final drive then 4.30's...but I have 4.30's and I'd actually like maybe 200 RPM's more in 3rd...so you may well hit on the right combo.

BTW...I tow a 9000# 35' hitch to bumper TT...I had 3.73's and the 4.30's make a HUGE towing difference...but like I said...having 200 more RPMs with this stock 2V motor and 4R100 wouldn't be a bad thing...so I think you are making a GREAT choice with those tires...

Good luck and let us know how it works out!

joe.

 

With that rig you'll be lucky to get 5mpg, so you might as well go ahead and get a transferflow replacement tank.

 

post up your truck..............you must be a sales man, cuz that's the same BS that dealers train their monkeys to say to sell diesels.

if you would have read more than just this thread you'd see that most V10's get better than 5mpg..............if you think that go head to the oil burner section, and leave the V10 posts to the OWNERS of the V10's that have actual results.

i got 11mpg on out atv trip last weekend (200miles round trip) running 40's and 4.56's. and despite comments like yours i average between 13-14 on the highway 12-13 around town (unloaded)..............and belive it or not, i can hook up the trailer and 4000lb mud drag truck and get 10-11mpg also........mods link in signiture

as it has been discussed on here before, a gear change rarely hurts milage, and in some cases it can increase stop light to stop light driving mpg.

here's a truck that got 12mpg hwy running 44's and 5.38's.........
http://www.team-mudd-racing.com/index/DSC02531.JPG

 

Well said.

With proper gearing you can still get good mpg. With 37s and 3:73 you will get worse mpg than 37s and 4:56.

 

Mr. Mudd - I think all Ford F250/350's need a 40-45 gal. tank whether they have a V10 or a Diesel engine.

 

fuel weighs 6.8lbs per gal, some people have added a second tank (under truck or in the bed), and have reported that their fill up days are about the same.

before they added the tank they would fill up every 4 days.........they add more tanks (more fuel weight, and more tank weight) and have to fill up on the 5th day anyway.

if you go from a 30 to a 45 gal tank your adding an average of 100lbs of fuel, and that's not counting the heavier tank........more weight = more power to move = fuel milage drop.........i can see where an added tank would come in handy if you were sitting idle for a while, or had a service type truck.

 

A 15 Gallon Aux tank would be on the small side. I would go with a 20 or better. You math makes scence on paper but in the real world it does not. In the real world the additional weight of fuel (20 gallon tank X 6.8= 136lbs plus a tank weight of 75 lbs or so) and tank at 206 lbs. is negligable on the HWY and the same as one "Average American" passanger. How much does hauling around your buddy cut down your mileage? BTW the average Aux tank is usually between 60 and 95 gallons.



I have a question for you 2V V10 guys though, I am contemplating a gear swap from 3.73 to 4.30 with 275/65-15 and would like some real world mileage numbers towing HYW speeds. My tt is 5K and I like to tow around 65 and do allot of hills. Any info would help.

 

Marty,

I keep records of all my towing and mpgs.

I have a 2V V10 Excursion.

In 2006 I HAD 3.73's in this Ex. I towed at 15,500# combined. I towed 7000 miles including the Black Hills, Big Horns and Rockies. My hand calculated TOWING average was 7.8mpg. I KNOW speed is my issue...I tow at 65-70...but for me time is LIMITED so I trade speed (time) for $$$ at the pump...my choice.

In 2007 I now have 4.30's (BEST DARN MOVE I've EVER made). I have a HEAVIER TT and roll down the road at 17,000# combined. I towed 5000 miles this year including the Appalachians. My hand calculated TOWING average is 8.2mpg. Again I tow 65-70.

With the 4.30's and HEAVIER load...I'm getting BETTER mpgs towing due to the fact that I can tow in OD much longer. And in fact on some serious grades (7% 5 mile long ones on I-64 in West Virginia and Virginia)...IF (big if) I can hit the grade at 3200RPMs (which for my tire size equates to 70mph)...I can pull the hill in 3rd gear at 70mph. Fall slightly BELOW that 3200...well and you are gonna downshift to 2nd. But you will still be able to pull that same hill...just at higher RPMs and 'only' at 60mph steady...

So the secret with the V10 and 4.30's is to keep that 3200rpms for REAL GRADES.

Most grades can easily be pulled in 3rd...so I 'believe' the higher mpg's is due to an overall 'reduced' average RPM over what I had with the 3.73's.

Hope this helps...

BTW...I'm planning the Rockies again this coming summer with Eisenhower pass on the route...so I've got ALL THE CONFIDENCE in the world in this 2V V10 4.30 combo...

Good luck and let me know if you have any other questions.

joe.

 

after reading mudd's post im leaning towards 37's with 4:56s. is this going to be a decent combo if i tow a boat 1/3 of the time?