L31/6L80e

[618 Syndicate]

It'll only drop about 200 RPM if I had to guess. You got from a .75 to what, a .67 OD?

Yeah, I guess so.

 

[618 Syndicate]

Not to hijack your thread, but what are thoughts on running a 6L80e behind an L29 using a 0411 computer to run things? Can it even be done?

I don't think a 0411 can run the 6L transmissions. Not sure 100% though.

 

[Supercharged111]

I don't think a 0411 can run the 6L transmissions. Not sure 100% though.

It can't. 6L was a GenIV thing i.e. separate ECM and TCM and 58X. I'm unaware of a magical Mexican combination that would be factory plug and play for a 350.

 

[Grimpala]

Yeah, after some research on LS1Tech and LS1.com it would take a truck bed full of money to accomplish this. Guess I'll still with my 4L80. Maybe I need a 2 spd rear end.

 

[JeremyNH]

Yeah, after some research on LS1Tech and LS1.com it would take a truck bed full of money to accomplish this. Guess I'll still with my 4L80. Maybe I need a 2 spd rear end.

If you have a 4L60e (like both the OP and I do) and are looking to upgrade to a more stout transmission it may be worth considering a 6L80e over a 4L80e. It depends on how much the extra two gears are worth to you but it isn't small money either way. If you already have a 4L80e though I would agree that it likely isn't worth the money and time (unless you have too much of both). I've been thinking about it though and am happy to see someone actually do it on a platform same as mine without it becoming a fuster cluck pita. He mentions still needing to tune some of the shifts so I'll wait for the final verdict but definitely am interested in trying it myself if the outcome stays positive.

 

[618 Syndicate]

I've seen a 6L80 and a 6L90 both in crewcab squares, but neither in a 400.

 

[Supercharged111]

I've seen a 6L80 and a 6L90 both in crewcab squares, but neither in a 400.

You can put them behind a carb'd motor, I think with the TCM the OP used it only needs TPS and RPM.

 

[618 Syndicate]

You can put them behind a carb'd motor, I think with the TCM the OP used it only needs TPS and RPM.

In both cases they were behind the motors they left GM with, 5.3 and a Duramax respectively.
That TCM the op mentioned is a great option though.

 

[Supercharged111]

In both cases they were behind the motors they left GM with, 5.3 and a Duramax respectively.
That TCM the op mentioned is a great option though.

I know they put the 4L85 behind the Dmaxes in the vans, what about the 6L90?

 

[stutaeng]

I know they put the 4L85 behind the Dmaxes in the vans, what about the 6L90?

No.

On the 2021 express vans they are running the 8L90e with the 4.3 Gen 5 and the "baby" 2.8 TD Duramax, LOL.

The new 6.6 Gas version still comes with the 6L90e....if that tells you anything about what GM's confidence is on the 8 speed.