Why the interest in the 6L80/90? Gearing options!!! The 6L80/90's 1st gear is 4.027. This is the lowest GM automatic 1st gear available. Only manual trannies with granny gears are lower (SM420 is 7.05, SM465 is 6.55, NV4500 is 6.34 and 5.61, NV5600 is 5.63).
As a comparison, I calc'd the mechanical advantage in 1st gear over other popular GM slush boxes.
60% lower than a TH350
62% lower than a TH400 or 4L80
and still 32% lower than a 700R4, 4L60/65/70
I also calc'd the advantage in overdrive too.
n/a for a TH350 or TH400
12% higher than a 4L80
and still 4% higher than a 700R4, 4L60/65/70
For you drag guys, this means you should get the same launch (assuming no other mods) running 4.11 gears in your diff with a TH350, or highway friendly 2.50 gears in your diff with a 6L80.
For you 4WD guys, this means you should get the same crawlability running 5.13 gears in your diffs with a TH350 as you would 3.23 gears and a 6l80. However, if you ran 5.13 gears with a 6L80, to achieve the same 1st gear crawl you'd need 8.20 gears in your diffs, which I failed to find (7.17 seems to be the lowest gears you can get).
And besides the amazing 1st gear, you still have the best O.D. of any tranny too!
