rear end ratio

I have 4.10s with my slow spinning CTD and I've run all day at 80+ and ~2600 rpm and got 18.3 mpg. Mr. Cummins didn't mind it a bit! 4.10 or even maybe 4.30s would be fine for a SB gasser. Craig

g4sbrg wrote:
OK so I feel I am stressing the truck to much in hilly conditions pulling my 5th wheel camper, seems fine out on open road but needs help near the lakes and camp grounds going up those sometimes large hills, currently planning on changing from the 373 rear end to a 456 one would think I would loose a lot of mpg but in reality in general wont I be lowering the needed rpm and reducing the extreme rpm needed to go upwards, thus it will be a wash while towing, and at this point is it not more about performance towing. the truck is a tow truck for me not transportation to and from work or every day driving.
2000 f150, 5.4L 373 rear end

your comments would be appreciated

You feel like you are trashing your truck because you feel like your gear ratio is too high. I think you will feel like your gear ratio is too low with 4.56 and you will also feel like you are trashing your truck. I went from 3.54 to 4.11 and I don't like to drive faster than 55 on the highway because I feel like I am over-reving my engine.

I think you will like 4.11 with your setup better than 4.56.

4L80E Gear ratios:
1 2 3 4 R
2.48 1.48 1.00 0.75 2.07

Here is how power is transmitted to the pavement

2.48 x 410 ft/lbs of torque = 1,016 ft/lbs of torque delivered to my transfer case

If it is in 'high', it is a 1:1

1,016 ft/lbs of torque to the diff x 4.1 = 4,168 ft/lbs of torque to the rear
drive axles

If I go with a gear spliter and a 0.7 ratio and 4.5's in the diff...that would
mean

1,016 x 0.7 x 4.5 = 3,200 ft/lbs in first and plenty of power for me

Or can go with a 0.8 ratio for the gear splitter, or whatever other ratios they
have

Here is what 4th gear of the 4L80E would look like:

0.75 x 410 = 307.5 to the diff x 4.1 1,260 ft/lbs of torque to the rear axles
now in OD

1,260 x .7 = 882 ft/lbs to the rear axles in 4th gear (OD) and plenty to cruise
and get better MPG...but am not after or willing toss performance for MPG

What with the price of new these days...the cost of rebuilding my Suburban with
a bullet proof 4L80E, forced 7.4L and a gear splitter with a 0.7 ratio will beget
me an 8 speed +2 spd reverse automatic with a final ~0.5 ratio to the
diff (4.1's...which I might go to 4.5's) would save me tens of
thousands of bucks that will then buy fuel for a loooooong time...and
yes...have received both posted and PM's asking how could I stand to
drive a 19 year old TV...not a problem for 'me'...I also drive a 1980
Silverado which is 35.5 years old... :B

Toss in my 2 speed transfer case and the above number of gears are doubled

All these high numbers of geared automatics is just close ratios to keep the ICE
closer to their peak power...along with a double OD

Issue is that the gear splitters are not up to my spec's yet...more noodling
time required

Glacier D wrote:
How about a gear splitter? I have heard that these things are awesome, but a little expensive.

The new six speed transmissions is what we all need.
I would love to swap in a six speed when my 4R70W gives up.
Unfortunately the best option is probably a new truck.

How about a gear splitter? I have heard that these things are awesome, but a little expensive.

theres a difference in a big block and a small, small block when it comes to gearing, towing and HP.

Changed my 01 Superduty with a V-10 to 4:30's from 3:73's....huge difference. And no drastic change in mileage when towing or empty.

g4sbrg wrote:
so you want to know.
2000 F150, 5.4 L V8 (this is a 2 valve) 373 rear end it is rated for 8800 towing and has greatly expanded payload, tranny cooling and oil cooling tow package. I think the auto tranny is 3 speed with OD
motoring down the interstate at 65 it runs about 2800 to 3200 rpm (no OD) pulling that 8000 pound brick, (6900 dry plus cargo) getting up the hills she may downshift and 4000 rpm, not really an issue so much (haven't been to any mountains) getting into the two lane roads curvy and hilly I find myself progressing upwards at 40 to 45 mph at 5000 rpm. just seems to me I should not worry about mpg and change the ratio to getter up those hills with less stress. (maybe it just me, first large trailer you know, have gotten the advice before to find the sweet spot on the rpm and let sit there weather its 3200 or 5000)
I would hate to get to some real elevations and need more torque which changing the ratio does ???

Thanks

Yes gearing will make a huge difference. it`s like using a longer pipe as leverage. as far as mileage goes, most people see an increase when towing because the engine doesn`t have to work as hard and it will make O/D usable while towing.

It`s not all about rpm at a certain speed either. a different gear ratio will effectively change the ratio of each gear in the trans, like I said the engine will not work as hard. there is a reason auto manuf. have increased towing capacity with a lower ratio. no where in an owners manual does it tell you to just run in 3rd with higher gears as it is the same as O/D with the lower gears!

so you want to know.
2000 F150, 5.4 L V8 (this is a 2 valve) 373 rear end it is rated for 8800 towing and has greatly expanded payload, tranny cooling and oil cooling tow package. I think the auto tranny is 3 speed with OD
motoring down the interstate at 65 it runs about 2800 to 3200 rpm (no OD) pulling that 8000 pound brick, (6900 dry plus cargo) getting up the hills she may downshift and 4000 rpm, not really an issue so much (haven't been to any mountains) getting into the two lane roads curvy and hilly I find myself progressing upwards at 40 to 45 mph at 5000 rpm. just seems to me I should not worry about mpg and change the ratio to getter up those hills with less stress. (maybe it just me, first large trailer you know, have gotten the advice before to find the sweet spot on the rpm and let sit there weather its 3200 or 5000)
I would hate to get to some real elevations and need more torque which changing the ratio does ???

Thanks