Gear ratios

[PaulW]

The quick answer is YES, stick needs a lower gear (bigger number like 5.13 vs 4.56) compared to an automatic. Lots lower. (Bigger number so the engine revs higher in the power band. Same comment applies with a modified high reving engine with poor low end power).

Ford says one should expect a stall multiplier of 2:1 from their various torque converters. (Others quote values like 1.8 or 1.9:1).
So the 2.71 becomes 5.42, but that is only at TC stall.
Anyway now you see why the manual trannys always have a lower 1st gear. Remember the granny gear trannys of old. This was done when autos were crappy and the trucks had to have a super low 1st to get going.

I don't believe the 2:1, but for sure the TC will give you a much lower starting ratio than the manual. To compensate we all just slip the clutch and specify a lower final drive ratio. Works fine for a while.

My story:
I have always had manual trannys until I deciced to have a offroad truck and then I chose the auto. The reason is when one needs to creep in low gear & shift fast, and it is just what the auto was made for. Sacrifice a small amount of MPG and enjoy the ease of driving. Point - have you ever had to downshift in a panic on a really steep trail or when you bog in unexpected deep silt? Good luck and even if you are succesful you will take some metal off the gears. With a auto it is seamless and can be done for an unlimited number of times. That is what we do on the trail and in the deep sand.

Bottom line an automatic best for desert use and I would still chooe auto for the trail. The trail guys always challange this statement and a lot of them are true believers in the stick shift. I challange their judgement.
Just my opinion based on my engineering evaluation. I will let the GFB guys challange my take.
Paul
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Sticks are going to need more gear too without the torque multiplication of the convertor.

Can you clarify this and explain "torgue multiplication"? So does a 5 spd m5od need a lower gear (488) or higher gear (456) versus and auto?

If I understand it correctly based on the gear ratio a manual should be turning higher rpms on 456 than a auto on 488s in 1st and overdrive....

M5OD-R2 3.91 2.24 1.49 1.00 0.80

E4OD 2.71 1.54 1.00 0.71

[johncharlesb]

The convertor slips and allows the engine to spin faster than the input shaft into the transmission. This happens at all speeds, but greatest at higher loads (when you first take off). A stock convertor will stall around 1800 rpm, but still slip until electronic lock up. The ratio is around 2.5:1, but there are a lot of variables and the ratio changes with the load as the convertor couples.
http://en.wikipedia.org/wiki/Torque_converter

I prefer a slightly lower rear gear in a stick because it prevents me from having my foot on the clutch all the time at low speeds, and generally cuts down on the clutch slip. My first gear is 6:1, too deep for typical driving, so I start out with a 3:1 ratio in second. With a m50d I would still look at the lower gear, but you need to be careful of getting too deep and making first gear worthless. If you have 35s and a 302/m50d, you may need deeper gears to help the engine along. I would ask someone with a similar setup.

[Dust]

Curious what the E4OD and 35" tire ratio of choice is for y'all that actually run the desert?

[Nick]

I'd think 4:88's with that combo would work rather well. I'm running 4:56's with 33's and really like it.

[Polarcub]

I run 4.88s with 35s and the e4od and would not want anything less! I can cruise freeway comfortably at 70 and about 2500 rpms and have plenty of grunt which helps make up for the anemic motor of mine. Mileage is still respectable on the street too about 14mpg on the highway if I keep the rpms 2500 and below

[philofab]

I don't like dealing with installing 4.88 gears. You really can't tell the difference between 4.56 and 4.88. I have 4.56 in mine.

[damon1272]

4.56 for me. Like the engine not to rev too high when on long trips. If I were just going to use off road i would go with 4.88

[BajaBronco13]

I'm running 35" BFG All Terrains and just ordered 4:56 gears.

Chris

[Dust]

I don't like dealing with installing 4.88 gears. You really can't tell the difference between 4.56 and 4.88. I have 4.56 in mine.

I don't like doing gears at all; to the point where I usually farm it out!!
Them and Automatic Transmissions... I can do it but I'd rather not.

[BajaF250]

Running 4.56 with 35's... detroit in the rear and trac loc in the front. The Lightning motor seems to turn the 35's just fine... the point being, you need to design around the motor and use.

[Dust]

Running 4.56 with 35's... detroit in the rear and trac loc in the front. The Lightning motor seems to turn the 35's just fine... the point being, you need to design around the motor and use.

Completely agree however I was unsure how the Auto would play into the mix.
When I ran the numbers I was surprised at the OD calculation.
Y'all have confirmed my numbers.

[tcm glx]

4.56 on 35s with the 351 and e4od. I really like it, good power off road, and can cruis 70-75mph on the HWY all day long

[Dust]

I've been toying with going to 37's; when I run the numbers with that tire it is looking like I can run a C6 and forgo the OD completely, doing that would be a rather significant saving in the total cost of the transmission. At about 65-MPH it would be just under peak Torque adding in the low gear set would give the same low end performance. Might be the way to go and decomplicates the computer issues as the computer need only interface with the engine...
Just thinking out-loud.

[philofab]

I've been toying with going to 37's; when I run the numbers with that tire it is looking like I can run a C6 and forgo the OD completely, doing that would be a rather significant saving in the total cost of the transmission. At about 65-MPH it would be just under peak Torque adding in the low gear set would give the same low end performance. Might be the way to go and decomplicates the computer issues as the computer need only interface with the engine...
Just thinking out-loud.

You can run any size tire you want with a C6. Just gear the rear end accordingly. I ran 3.50 gears with 33" tires forever with a C6 and had no problems and plenty of power.

[RyanDS650X]

I run 4.88s with 35s and the e4od and would not want anything less! I can cruise freeway comfortably at 70 and about 2500 rpms and have plenty of grunt which helps make up for the anemic motor of mine. Mileage is still respectable on the street too about 14mpg on the highway if I keep the rpms 2500 and below

This is my set up also and i love it, especially in the sand washes and dunes.

[SteveG]

You can run any size tire you want with a C6. Just gear the rear end accordingly. I ran 3.50 gears with 33" tires forever with a C6 and had no problems and plenty of power.

I currently have 4.10 gears with 33" tires and a C6. Once I convert to EFI (resulting in more power) I'll likely switch back to 3.50 gears to drop the RPM on the highway.

[Dust]

Back when my 79 was only 8 years old I ran 3.54's and 33's for thousands of miles/years and even with maybe 150-BHP I was not wanting anything...
Other then to win a drag race against a little ol'lady pushing a shopping cart:lol:
Still wheeling, or getting there, the Bronco worked good enough to log tens of thousands of miles off road.
4.56 gears and 37's is only slightly lower overall gearing at 1:1

[Phoenix0783]

I use 4.56s with my 351, 35s, e4od and I like them.

[Mojo]

I am getting ready to order my parts from Summit: 4.88 gears Detroit Truetrac for rear & open diff front. I have a stock 351w with 149k & auto trans/od, I will be running 35" General's, mostly weekend toy for Ocotillo Well's with a few trips from the house.

[Polarcub]

I am getting ready to order my parts from Summit: 4.88 gears Detroit Truetrac for rear & open diff front. I have a stock 351w with 149k & auto trans/od, I will be running 35" General's, mostly weekend toy for Ocotillo Well's with a few trips from the house.

I think you will like that set up I really like the 4.88s...on a side note please let us know how you like the generals on the street I am thinking that they will be my next tire