This is for my new buggy. Its going to have the mog 404 axles at 7.56:1, an NP205 transfer at 2:1 and ether a C6 auto (2.5:1 ??)or an NP435 (6.67:1) behind a 302 windsor.

Ive already got the NP435 but I really like the idea of the C6 auto. A good thing about this is that both gearboxes are interchangable in terms of pattern/length/splines so I can always change later.

Now I know 100:1 with a manual will be good but how will 38:1 (??) go with an auto. I know alot of the comp guys are running these sort of numbers with the autos so how do they crawl, I guess they never get stalled up or anything??

Any thoughts??

Sam

Sam,
How did you come up with 38:1?

I am missing something?

(I do suck at math)

j

2.5*2*7.56=37.8

sam you have to take into account the torque converter's reduction, so technically it would "feel" like 76:1 which is great for having a good V8, the squirrel motor'd guys want more gear cause their wimpy motors cant make any power :D

That's what I was talking about. I always include the torque converter in my figuring.

j

sorry this is long, but i want avoid math, and help y'all understand something (or maybe divulge enough of my dillusion so someone can tell me where i'm wrong)

the fact: with an automatic transmission and stock(ish) gearing, one revolution of the wheel in reference to engine RPM is numerically equivalent to having lower gears with a standard transmission while engaged in 4WD low, and having RPM's somewhere (usually) under 3500 rpm.

the assumption: given that the angular velocity ratio to engine RPM is equivalent to having lower gears, the torque multiplication also must also be equivalent.

This assumption, I argue, is false. velocity and force are two different things.

The effect, I agree is true to an extent. With most drivers, even though the torque multiplication isn't the same, the benefit from the auto often outweighs the deficiency.

explanation:

The torque converter really is just an automatic clutch. Without it your vehicle would stall out on those tough climbs that give the manual transmission folks fits of fury, and yearn for a "slush box".

In order to make the same climb, the manual transmission driver must "slip" the clutch to achieve the same effect, or risk stalling out. The other option is to hail-mary with the throttle and side-step the clutch in hopes that enough momentum is created to stay in the power band while the clutch is fully engaged while traversing an obstacle.

"this is all bunk of the worst kind!" you might be saying! well, I offer you this small puzzle:

if the manual transmission with lower mechanical gears and the "magic"-automatic with higher mechanical gears were mechanically equivalent (meaning they produce the same mechanical work), then the automatic transmission would not generate more heat than a similarly geared manual transmission at equivalent velocities.

"ahhh" but we know this is false. Autos are notorious for over-heating on the trail. Why? Conservation of energy is why. While the torque converter is slipping it is creating heat, and that heat has to go somewhere. Unfortunately, much to everyone's dismay, it is assuredly NOT helping in the torque department.

_IF_ the auto were creating an equivalent torque multiplication as a manual, the heat would not exist, and the energy would be headed for your wheels instead of heartache.

Manuals offer the clutch in sacrifice of the transmission, whereas the auto slowly implodes from the heat soak transmitted from the torque converter.

to really prep an automatic transmission for the trail, I think you DO need the lower gears in the transfer case, and you also need to install a manually operated torque converter lockup device to lock the torque converter while on the trail. Don't fool yourself when adding another transmission cooler - it is needed to help the longevity of your transmission off-road, but I say still, spend the money on the gears and the manual lockout as you can afford them.

again - just because you're moving at the same speed doesn't mean you're producing the same torque on the ground as that guy with the "squirrel" motor and 5-speed manual transmission.

more variables:

more torque to the ground does not mean more traction! I think this is universally accepted, as anyone who's witnessed chebbies powering up climbs can attest to. If you're not an especially skilled driver, you might want to forgo the manual TC lockout until your driving gets a bit better.

What you are not producing in torque you're getting back in increased control. Why? Because the lockup in the torque converter is _progressive_, and instead of your wheels spinning at crawl speed, which is a break in the static coefficient of friction between the tire and ground, it spins in the converter producing more total _work_ when observing the system as a whole.

hope this helps - end of lesson!

cheers,

isaac

The max temp my auto has reached on the trial is 195 degrees. thats with 34's and 4.11 gears. Of course, I have a bigger tranny cooler. I think Doug M. will attest to the fact that with the right cooler, the ZF tranny will run well under 200 degrees all the time. Right Doug or did you ever break 200. My tranny almost runs to cool!! Not to dispute your heat increase in the T/c but what you posted does not apply in all situations. My tranny runs cooler than a manual. And now I am running 36" tires and 4.11 gears. I can crawl pretty well. Although, your right, the tourqe is not there like a manual would be, but a small tap of the throttle, and its there. Oh, and I never stall out!! thats the best part. Oh, and as for the tourqe manaul lock up, its not going to help you.

I have to say it, Auto's are much better on the trail in most situations. I have convinced several of this, and they have not gone back to mauals since. I would not run a manual unless I had at least 100:1 ratio. then it might be ok. I am pretty sure Bills 110 would climb a sheer wall in first Low Low at idle if it could get the traction. Cant imagine if he ran an Auto!! talk about creepy crawly.

Never broke 180!

I've been contemplating going with a smaller cooler to keep normal op. temps up a little (above 150).

Suck in a hot canyon, it's nice to see the gauge under 200 though!

I'm curious to see how long the ZF lasts under it's new found loads...However with 5:89's and 42" TSL's, I'm about 5-6% lower than I was with 35's and 4:70's....Of course that 5% is eaten up with the heavier tires and rims. We'll see...Hmmmmm. 7:17's ? :)

--D

Like I said I really do like the way and auto works in the rocks. The control at very slow speeds is great and you can still get the speed whan you want it all in the same gear.

What worries me is will 38:1 with the auto be low enough with the 42s?? KC you would be at 34:1 with 34s and you say it works well and never stalls out. And Doug you will be at 50:1 with the 5.89s, that sounds more like where I want to be. (Im guessing everyones 1st gear is 2.5:1)

The only thing I can go on is the comp guys generally run 35:1 to 45:1 with the autos. So i guess it should work well and not stall out.

Sam

i should delete the utter bullshit i posted earlier, but to let it live on in infamy would be far better punishment than any flaming could ever provide :rolleyes: :rolleyes:

torque converters DO increase torque when not locked up - around 1.8:1 as is commonly thought -

http://www.victrans.com/multiplication.html

- gives a decent example with a visual. now, back to my corner of shame . . .

cheers,

isaac

wow. you even served up your own humble pie.

j