1500 or 2500

redwngr · February 12, 2015

I'm sure the 3.73 option was for someone that does a lot of interstate driving. Not only will it get a little better mileage but it will lower the RPMs so maybe the wear and tear wouldn't be as much. I care more for lower RPMs than mileage because of that. I personally see no need in anything lower (higher #) than 3.73 unless it's lifted. Even if it was just a tow rig. For a diesel it might help the towing if the RPMs were a tad higher on the interstate, but a gasser I would prefer lower RPMs.

The LML develops max torque at 1600 rpm - about 60 mph in 6th gear.

It has 765 ft-ls of torque - more that 150% of the 6.2 (L86 is 460 ft lb @ 4100rpm). It does NOT need to run any faster.

Every Duramax pickup ever sold came with 3.73's. The older ones had a 5 speed, they are all now 6 speeds, which has REDUCED the highway rpm.

redwngr · February 12, 2015

Gear ratio comparison for 8 speed with 3.23 vs 6 speed with 3.42.

8 speed 6 speed

3.23 3.42

First: 14.73 13.78

Second: 9.59 8.07

Third: 6.72 5.23

Fourth: 5.46 3.93

Fifth: 4.10 2.91

Sixth: 3.23 2.29

Seventh: 2.75 N/A

Eighth 2.10 N/A

Reverse: 12.34 10.47

Cowpie · February 12, 2015

Ratios for the 6 spd 6L80 (and 6L90) are:

1 4.027

2 2.364

3 1.532

4 1.152

5 .852

6 .667

R 3.064

You want a great little spreadsheet based on the ratios for this transmission that you can plug in tire rotations and rear diff ratios in to find the actual road speed you would be traveling at various RPM's, PM me with an email and I will send it to you free. It won't let me post an Excel spreadsheet here for some reason.

SMiller · February 13, 2015

I am with you guys, keep the 4.10 gears and give us the 8-speed! A lower 1st gear with a close ratio perfect gear spread would be awesome, having said that it will never happen, GM will make us get 3.73 gears which will make that 8th gear useless and make it gear hunt and get worse mileage, let it rev!

Big Whiskey · February 13, 2015

I am with you guys, keep the 4.10 gears and give us the 8-speed! A lower 1st gear with a close ratio perfect gear spread would be awesome, having said that it will never happen, GM will make us get 3.73 gears which will make that 8th gear useless and make it gear hunt and get worse mileage, let it rev!

Yep, that's what I'm afraid of happening. Just like the 3:08's in the 1500's. Why can't GM engineers figure that out??? It seems so simple to all of us gear heads, haha.

SMiller · February 13, 2015

Yep, that's what I'm afraid of happening. Just like the 3:08's in the 1500's. Why can't GM engineers figure that out??? It seems so simple to all of us gear heads, haha.

Another big problem is a HD truck is pushing so much air that it takes keeping some rpm to overcome that, bogging the motor just makes for worse mileage.

Let's hope for the best.

Big Whiskey · February 13, 2015

Another big problem is a HD truck is pushing so much air that it takes keeping some rpm to overcome that, bogging the motor just makes for worse mileage.

Let's hope for the best.

Agreed.

Cowpie · February 14, 2015

There is a move all over the vehicle industry to down speed the engines. The heavy commercial truck engine makers are playing in this sand box also. It all seems reasonable when one is only on a flat 4 lane road with no serious load on. But break out of that, and it just doesn't play out well in the real world. At least, even though they try to shove it down a person's throat, the heavy truck folks still knuckle under and let you spec the ratio you want so you can run the engine in the optimum band for what you are doing. The pickup folks are bound and determined to make owners deal with what they think is best.