Gearing Questions

[HornedFrogHooah]

Bought a 78 F250 4x4 from my girlfriends grandfather. It has D44-9F up front and a D60 in the rear. When he custom ordered the truck, he got 3.54 gears, 4 speed manual trans. For me, it's mainly a daily driver, but it is used out on a friends ranch maybe once a month and I also cant help but take it offroad for fun every once in a while (once or twice a month).

I'm considering in the future a 4" lift and 35" tires, however now I'm just concerned about restoring it to its former glory. Don't criticize me on this one please , I know it's a 78 F250 and gas millage will aways be GPM instead of MPG. However, I'm just curious about other peoples builds and perhaps going to 4.56 or 4.10 gears.

How will this affect gas mileage?
Will I be starting off in 4th gear to get rolling?
Will I regret it?
What's the optimal gear I should use instead if not 4.10 or 4.56?
What would yall do?

This is out of JBG and what I was using as a reference.

"The acceptable RPM range at cruise speed is 2000-3000, which is represented by the entire shaded area below. The optimal RPM range is 2300-2600 (represented by the lighter shaded area). When trying to improve mileage choose a ratio in the shaded area above the lighter shade, when trying to improve power choose a ration in the shaded area below the lighter shade."


I figured before I bought anything I should get other peoples input and advice. Yea forums!

 

[FordF-SuperDuty]

With a stock engine and 35"s, 4.10 would probably be the best choice.

 

[HornedFrogHooah]

if i'm keeping the 32's for awhile though, do you still suggest 4.10s?

 

[FordF-SuperDuty]

I'm no expert by any means. If you were going for a re-gear I'd go for 4.10s. Personally I'd save my money and do everything at once. Also, how much highway driving do you do? What engine do you have? Is there a limited slip unit in the rear currently?

 

[HornedFrogHooah]

Highway driving, not so much. About 1100 miles a month, 900 being backroads. Engine is a I6 4.9L, no limited slip.

 

[1985 Ford F-150]

35s with 4.10s are fine youll be sittin around 2500 at 65 with 33s youll be 27-2800.
Edit with that motor ya need low RPMs unless its got a differnt cam in it. I honestly would leave it be and dont lift it that motor dont really have the power to turn them big tires.

 

[FordF-SuperDuty]

I would not go higher than 4.10 with an I6, I'd also put in limited slip or a locker when you do the regear.

 

[HornedFrogHooah]

Thanks guys, I appreciate the help.

 

[Alvin in AZ]

I don't know if this will help or hinder ya but this is the way I went at it...
http://www.panix.com/~alvinj/file12/600rpm

It was what I came up with to help a "new guy" on FTE that turned out
wasn't worth spitting on, but the method I came up with, helped me out
a bunch! LOL

The original question was about the gearing needed to start from a dead
stop and wondering about tire and gear change effects, like you are asking
about.

So the section showing speeds in 2nd gear @ 600rpm are the originals
but just kept growing as I wanted more and more information -for me-.

The trick would be to continue on your own with 35" tires or whatever
if the format looks useful to you. Copy it into a simple text editor and
snip out the stupid crap I put in there you don't need/want? LOL

Which 4 speed you got?
T18 or NP435 or what?

Alvin in AZ

 

[HornedFrogHooah]

its got a NP435

 

[HornedFrogHooah]

Not gonna lie, I'm getting all confused by these number and have no clue what they all mean. Why would the above spread sheet say that the optimal gears I need would be 4.10/4.56, but everyone else says just dont touch it?

*scratch head*

 

[DNFXDLI]

The numbers don't lie...that would put you in an optimal rpm range for torque and hp. Issues start to come into play when you start driving at higher than 70-75mph for extended periods of time...mileage goes in the toilet further.
The NP435 has a 1:1 output ratio...the I6 does make good torque down lower in the rpm band, but 27-2800 rpm at highway speed isn't going to hurt things much.

 

[HornedFrogHooah]

... .... .... ............. so what youre saying is that .... ....

 

[DNFXDLI]

The numbers in the graph are valid. You could use the 3.54's with 35's but the rpm's might be a bit low for acceleration at highway speed...it might be doggish in 4th....for off road, you do have 4 LO which would help compensate for those higher gears.

 

[HornedFrogHooah]

and if I stay with 32's I'm perfectly fine where I'm at?
Sorry, as you can tell, im completely ignorant when it comes to gearing.

 

[DNFXDLI]

and if I stay with 32's I'm perfectly fine where I'm at?
QUOTE]

IMO, yes.

 

[HornedFrogHooah]

gracis scary priest looking avatar guy!

 

[DNFXDLI]

Anytime

 

[UNRULEE]

First of pull that 300-6 and put a 400 in there.......













Seriously though, I have a similar truck, a 1979 F250 with 6"s of lift, 35" tires, 3.54 gears, a C6, and a warmed over 400.

The 35"-3.54 combo is tolerable in my rig but, I know that I need lower gears. If I'm serious about getting offroad the (almost) 2:1 low range of the NP205 comes in handy for now. North Dakota is pretty flat and the rocks are few and far between. Once I finally swap out for deeper gears it will be for 4.56's or maybe even 4.88's.

If the big tire bug bites you hard enough (my next set will me 37"s......at least) you'll wish that you'd have went with the deeper gearsets.

If you don't plan on doing much highway travel with it, who cares about mileage anyway?

 

[Jolly Green]

I have 4.10 gears with 33" tires with a cammed 351M and a T-19. For that tire size I think my 4.10's are just right. I have all the low end I need, but the bigger tire size also helps to bring the rpms down a little on the highway.

If I went to 35's (and I might someday) I would probably go with 4.56 at that point. I don't think it would be a necessity, but I like a low gear since I use this truck largely for hauling/towing/pulling.