What's a good tranny?

[DnStClr]

Like Vile said- almost all the trannies have a 1.00:1 third gear. Here's a page from Bowtie overdrives- great tranny site!

http://700r4.com/faq/gearrat.shtml

[Stewart G Griffin]

What i meant was max mpg in cruise mode;  Yes, we could put the 700r/2004r in 3rd while we cruise at 55-65 and we'd be in direct drive, BUT, with the lower diff gear--say 3.73, 4.11 etc., we would be rpming rather high.   i still feel that a TH-350c with 2.56 gears will deliver slightly better mpg all other factors equal.

The 700/200R4 might(probably) give better mpg in city.

Yes, we are splitting hairs here, but maybe we should be splitting hairs.


Actually, i will get into deeper detail but cannot now due to being physically incapcitated---overworked.  Must rest.

[VileZambonie]

Stewerat, I'm not really following your logic here.

[Stewart G Griffin]

i'm basically as far as mpg goes talking about highway cruising where i feel most of us, myself at least, spend most of our driving.

When i personally do 65, i'm turning 2100 rpm with my setup.  i am in third gear and top gear when this is occuring because i have a TH-350C.  And, this of course, is direct drive (1:1) as we've established.

Now, if in another example we have the/a same truck except equipped with a 700R and say 3.73 gears AND depending on tire size we are able to ALSO turn 2100 rpm at 65 miles per hour i feel that the above setup will achieve better mpg.   This is due to the fact that in this second setup, we are in overdrive which takes a little bit more power to turn than direct drive-----.70 to 1 vs. 1 to 1. 



In both examples, we are traveling at 65 miles per hour with the engine turning at 2100 rpms.   But one is taking a little less energy to operate.

[Lt.Del]

it is true the less you have to press your accelerator to maintain a certain rpm or speed, you will save that much gas.

The question becomes, does overdrive require more "power" therefore accelerator action to maint 2100 rpms?  I wouldn't think so, or, your accelertor action will knock it out of OD

[Stewart G Griffin]

Actually, after this post i resign from the discussion----because explaining it itself is requiring more energy than nessesary.


i don't think it would kick out of OD if it takes more energy than direct drive;  i believe there is a predetermined setting at the TV cable (if the 700 uses one) or by some other means.


So, nevermind;  Let's not worry about it.  Since the difference is probably pretty small.

[VileZambonie]

You will not be in overdrive if the transmission is functioining correctly if you require torque multiplication as there is a torque decrease and speed increase. In 3rd gear the 700R4 is the same as the 350C except you have the addition of 4th giving you overdrive.

[Skunksmash]

Anyone happen to know what all cars came with the 6l80e? I know the 2006 Cadillac STS-V did, and the new vettes do. They are not really all that expensive, as tranny's go. $3000 newly rebuilt according to google. I had to give half that just for my 700R4. But i was thinking maybe some junkyard find might work. Hopefully it's getting common by now. Also, would it be hard to mate it up to an old TBI motor like mine? What all would be involved in that?

Here are the ratios of a 700R4, and a 6L80e.


Gear Ratios: for 6l80e
1st: 4.02
2nd: 2.36
3rd: 1.53
4th: 1.15
5th: 0.85
6th: 0.67

700R4 Ratios:

1st: 3.06:1
2nd: 1.63:1
3rd: 1.00:1
4th: .70:1


Maybe you could have the transmission guy change the 6th gear in the 6l80 to be something like .50 or something? That way, you could run 4.55's and have the best of both worlds? (maybe that's the wrong numbers on that last ratio, but you know)

[Lt.Del]

2 OD gears, wow.

[Skunksmash]

Yeah but look at 'em. They suck. At the end, they don't put you any better off than a 700R4. You would need to have the transmission man set the 5th gear to like .50, and the 6th to like .34 to have it be worthwhile.

[1976Scottsdale]

Well, with a 91 sub, 4x4 on a 3/4 ton chasis with a 4l80e, I have gotten 17 mpg on the interstate with a 5.7 that has 200k miles.  And, that is with the family on board.  Going to the outer banks of N.C. 4th of July weekend, about 5 hrs away to Cape Hatteras, gonna check my mileage again then.
I dont loose too much through the drivetrain i dont guess, because the 350 has little problem pulling my 30' camper trailer over the Blue Ridge Mountains.

And when might we be able to expect your second installment of the almighty 383 stroker into said suburban? Bet it pulls the camper just fine with one of those.

[Lt.Del]

And when might we be able to expect your second installment of the almighty 383 stroker into said suburban? Bet it pulls the camper just fine with one of those

with the 383 in my 79, I have no problem pulling the camper.  With the sub's 5.7, on the longest, steepest part going over the Blue Ridge, I have to put it in L2.  I have 200k on the 5.7, so, whenever she does go, which may be a while from now because it still doesnt use any oil and runs great, I will rebuild it with a 400 crank, no doubt.  I just hope it doesnt mess my computer up on the sub.

[Skunksmash]

you know, it's too bad we don't all live in the same state. We could all have some kind of get together where we bring our trucks and show em off.

[Captkaos]

You can't have a transmission shop "change" the final drive on the 6L80E, you also don't want to drop the OD ratio any lower. 

You could run 4.56's in the 700R4 and it would be like 3.23's in OD and you wouldn't need a $3000+ controller to operate it.

[timl1978]

I have an 85 K-10 with the same HP or slightly more.  My setup is a 700R4 with 3.73 rear and 31" tires.  I tow a 5000lb boat and the setup seems to work very good for me.  I don't use OD when towing though.  I just got the 700R4 working good (TV cable issues separate topic) and I really like it.  The 700R4 will give you the "fuel efficient flavor" for less money than a later model tranny IMO.