So I was contemplating buying new gears and possibly alim slipdiff for my all powerfull V6 ram . But I was not sure as to what advantage would I have if I went to say 3.92 or 4.10 or even 4.56. I came across a site that did some numbers to get actual torque at the wheels. I am not sure I did it right, but one of the variables I believe is the actual torque at the flywheel, which I think is the torque in the specs. In my Super V6 , torque is said to be an awesome 235 lb-ft @ 4000rpms. So here is the equation (I got the gear ratios from Dodge):

235lb-ft x 4.23(1st gear ratio) = 994.05lb-ft

994.05 x 3.21(stock differential gear ratio) = 3190.9lb-ft total torque at wheels

3190.90 / 2(if equipped with LSD) = 1595.45lb-ft of torque per wheel

Using the above, I plugged in different diff gear ratio:

3.92 = 1948.34 per wheel of torque
4.10 = 2037.80 per wheel of torque
4.56 = 2266.43 per wheel of torque

Now my question is, IS THIS RIGHT? if it is, going for a 4.10 will be nice enough for my truck byincreasing the torque at the wheels dramatically. Another thing will my truck be able to take that additional torque?

Thanks all of yous that know about this stuff. And for all of yous that say "I think", half a thanks.

 

Sorry bro, I have no idea.

 

am i reading this right? your thinking over 1000 ft/lbs of torque?

 

Torque shouldn't be related to velocity. Your torque should be same regardless of the gears. You get a performance boost from new gears because your engine is able to go through the gears faster; thus hitting the area of max power faster.

 

You are going about it basically right
but you need to consider two more things:

1. There is always friction.

Only about 85-95% of the engine shaft torque gets through the transmission. Gear and bearing friction eat this up.
Then, only about 92-97% of the transmission shaft torque gets through the differential. If the wheel begins to turn, more is lost in what is called 'rolling resistance' which goes up and down with tire pressure, concrete vs blacktop pavement, road wetness, etc.

2. Force, not torque, finally moves and accelerates the vehicle.
This force is applied where 'the rubber meets the road'.
The amount of the force is equal to the torque divided by the distance in feet from the centerline of the axle shaft to the pavement...this is why 'tall' tires reduce the force to accelerate the vehicle. If the vehicle begins to pick up speed, then there is a force acting backwards from the drag of the wind.

You are on the right track, you just need to put in the additional details.

About 200 years ago a self-educated Scottish machine shop operator named James Watt figured all this out. James Watt was a 'natural genius'.

http://en.wikipedia.org/wiki/James_Watt

James Watt also understood that as engine shaft speed increases in rpms, more gear ratio could be used to turn the shafts at whatever rpm you really needed, and that this ratio multiplied further the torque of the whole setup.

James Watt also realized that as engine speed got higher and higher, friction eventually began 'killing off' torque faster than additional gear ratio could be used for any additional advantage.

James Watt was the first to realize that the spot on the torque and rpm curve where this happened was 'SPECIAL' in that it was the spot where an engine could be operated so that AFTER the transmission applied its gear ratio to the axles....torque was as high as possible.

Watt named this relationship between torque and rpm 'horsepower' and called the spot on the curve where it 'tops out' the maximum horsepower.
It all began in Watt's brain.

Always keep in mind that you can apply maximum torque to an axle after the gears if the engine is turning at the rpm of maximum horsepower.

Do you understand why?
Do you understand that sentence is true 'in theory' but slightly wrong in the real world (hint: think of 'real' friction in a 'real' transmission instead of a perfect transmission)

 

Me thinks.

Depends on what you are trying to accomplish.
Drag racing - Probably not, Tranny and/or drive train componetsmight explode
Towing - Maybe, if you keep it light
Mudding / Off road- Should be ok (again keep it light)

 

Thanks HankL, half-thanks Pappy and Jimmy, your honesty is appreciated.
So Dodge used different components for drive-shafts, differential housing and axles for their engines? That sucks. So I better stay with what I have then. I was thinking of buying a small boat and towing it. But since I have no LSD and a small/high gear, I did not want to be in the water with the boat if you catch my drift.
HankL, will changing my gear ratio help me in any way achieve better towing? and do I have to keep it light as Pappy says, and also will it explode at extreme RPMs?
Thanks all, seriously.

 

Checked OEM Dodge parts catalog, diff housing and propeller drive shaft are the same for 3.7-5.7. Now theyhave a 1 piece and a 2 piece, whatever that means, but no difference in engine size. Axle shaft is the same unless you have an SRT.

 

Since I am assuming you have a manual trans
the numerically higher differential gear ratio will allow you
to start a heavy trailer load from a dead stop
a little easier.

At 'normal' highway speeds the higher diff ratio
will slightly hurt MPG on flat and downhill highway sections.

On some hills, the higher diff ratio will allow you not to make a downshift
but downshifting to climb hills with heavy loads
is what a transmission is all about.
Don't fall into thinking the truck should stay in one gear all the time.

Instead of talking about ratios
it is better to work out what each gear gives
in mph per 1000 rpm.

For example,
if your engine is at 2000 rpm at 70 mph
that is 35 mph per 1000 rpm

This way of looking at it takes everthing into account:
tire diameter, gear ratios, torque converter slip, etc.

Figure this out for each gear.

 

Alright Hank, I went here http://www.4lo.com/calc/gearratio.htmand did the calculations using the gear ratios for my truck (yes its a manual)
4.23 1st
2.53 2nd
1.67 3rd
1.23 4th
1.0 5th
.79 6th (OD)

At 70mph in the 6th gear with 3.92 my RPMs are 2349.6, which is a bit below the 2500 borderline. With 4.10s, I'm at 2457 RPMs. This just verifies what DJR was saying about getting through the gears faster. What I really want to know is about the pulling strength, power, what you want to call it. You say, it will make it easier to start from dead stop. That is what I am looking for and correct me if I am wrong, but with the 3.21s I have no get-go. My truck bounces when I step on the gas from a dead stop on 1st, and I mean, I am flooring it. Will the gear, say 3.92 or 4.10 help me with this, as well as towing a small boat. Thanks again.