6l90e or 4l80e?

[67chevysupercharged]

Hey all,

I'm getting to close to finally installing an ls engine into my 67 short bed but I'm having a dilemma on trying to figure out which route I want to take. I have both a complete gen 3 6.0/4l80e and a complete gen 4 6.0/6l90e combo that I got together in a package deal. The plan for the truck is to be a fun driver that will see the track a few times a year. I originally planned on running the gen 4 due to it having the better flowing l92 cylinder heads, but am concerned about the lack of aftermarket support for the 6l90e and wonder if it will survive behind a higher horsepower application. Any and all help is greatly appreciated.

Thanks,
Zak

[scottybaccus]

Tuning support for the 6L90 is just now starting to materialize. Unless you are prepared to cope with the headaches, I'd go 4L80.

[BR3W CITY]

Take the GenIV and run the 80e behind it if you want the "Best of both worlds" in the simplest manner.

The 6 speed trannies require a different approach. If your interested in the 6's, take a look at Hart Rod's build, iirc he had to go through the 6spd ordeals.

[67chevysupercharged]

First off thank you to you both for the help. Kind of bums me out that the 6L seems to be a bunch of headaches, it would have been nice to have the double overdrive. What all would be required to bolt the 4l80e to the gen 4 6.0? And I apologize if the original post rambled a bit too much, it was a little late last night 😄.

Thanks,
Zak

[clinebarger]

Originally Posted by 67chevysupercharged

First off thank you to you both for the help. Kind of bums me out that the 6L seems to be a bunch of headaches, it would have been nice to have the double overdrive. What all would be required to bolt the 4l80e to the gen 4 6.0? And I apologize if the original post rambled a bit too much, it was a little late last night ��.

Thanks,
Zak

You will need a T42 TCM. I'm guessing you have a E38 ECM? Both will need a compatible OS flash into them.

You will need the flexplate, Spacer & bolts off the genIII engine.

It will be easier to sell the 6L90E with the matching ECM. The T43 TCM & E38 ECM are (for lack of a better term) Married to each other.

Then start over with a different E38 ECM & T42 TCM, Then either modify the harness to work with a T42 TCM or buy a harness.


T42 TCM.....Gen IV controller for 4L60E & 4L80E transmissions.

T43 TCM.....Gen IV controller for 6L80E/6L90E transmissions (Mounted inside the trans).

[68GMCCustom]

It was a couple of years ago but it seems the same holds true...from a racing prospective....my tuner told me to go with the 4L80e (got a 4L85e in my case) over the 6L90e, for the same "support" type reasons others have mentioned.

[Houston Ben]

I have the 6L80 in my 86' and is running good. I had the tuner change the shift points and it is a little to firm for me but that can be changed back. I run about 2200 rpm's at 80 mph.

[68c10airstream]

clinebarger can chime in on this one also but the 80 in 4l80 as well as the 90 in the 6l90 is the load rating. The higher number the more load it can handle. Consider what you will be doing with everything else, a/c, cruise, speedometer, etc. The gen4 i believe uses can bus to communicate were as gen3 doesn't. A/c can get a little dicey trying to integrate it with the pcm, but i'm doing this from memory. Hartrod will again be your go to guy. I've dealt with him in the past and has been helpful as this forum is really helpful also. Welcome aboard!!!!

[clinebarger]

Originally Posted by 68c10airstream

clinebarger can chime in on this one also but the 80 in 4l80 as well as the 90 in the 6l90 is the load rating. The higher number the more load it can handle.

That is correct.

There are 3 different versions of the 4L80E..
4L80E, All Planet carriers have 4 helical cut pinions.
4L80E-HD, 4 Straight cut pinions in the front & rear Planet carriers, O/D planet uses helical cut pinions.
4L85E, 5 Helical cut pinions in the front & rear Planet carriers, O/D planet...Same as the others.

Any of these unit will work good in high HP applications with minimal modifications, Most already have a 32 element Intermediate sprag from the factory (I have seen some with the weaker Roller Clutch). The Direct Clutches are really the only weakness. Double Feeding them fixes that.

These unit's shift "Straight Through"....Meaning one clutch doesn't have to disengage for another to apply for a oncoming shift.

1st gear, Forward clutch applied
2nd gear, Forward clutch, Intermediate clutch applied
3rd gear, Forward clutch, Intermediate clutch, Direct clutch applied
4th gear, Forward clutch, Intermediate clutch, Direct clutch, O/D clutch applied

A 4L60E for example has to knock the 2-4 Band off & simultaneously apply the 3-4 clutch pack for a 2-3 shift. The presents several problems when performance is concerned. You will almost ALWAYS end up with a "Flare" or a "Tie-up". You may not feel it...But it's there
"Flare" meaning during the 2-3 shift the band was released but the 3-4's have not fully applied, This would put the trans in 1st gear for a split second.
"Tie-up" meaning the band didn't fully knock-off before the 3-4's applied. This would put the trans in O/D for a split second.
Both these events are very hard on the 3-4 clutch pack.

The 6L90E Planet Pinions, Carriers, Sungears are longer/taller than the 6L80E, Other than this & the actual case being longer, Not many differences between the 2.

Every Up-shift & Down-shift requires "oncoming" & "offgoing" Clutch in these units. It's called "Clutch to Clutch". Again...Not really good for performance applications where torque & horsepower are uprated. I still don't like the Stamped drums but they seem to be holding. Bad tuning seems to be their biggest enemy...(Burnt Clutches).

For now, the 4L80E is still the best choice for high power applications.

[l92powered77]

I have a 2008 L92 and 6l80e in my 77 its not running yet.But i did have to take the tcm out and send it to PSIconversion.com so they could flash them e38 ecm and tcm together.Im in california and not in texas right now and dont know anybody who tunes good out here so thats route i took.I couldnt pass up the opportunity to have a 6l80e in a old school chevy;not too many people have a 6 speed auto ls swap in a old school.