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Discussion Starter #1
So my car has been sitting since 2008 when it decided it only wanted to do 2nd gear. Was in process of getting some body work done so it is still a work in progress. I am trying to plan out my next steps and have some things I will be working on.

Going to bring over to my house from storage and looking at what I need to do with it.

I will be installing a 24x LS coil type conversion to it. Likely the Torqhead setup.

I also have an Eaton M112 Lightning blower I plan to install on this car.

This means I will have the 411 style PCM on the car and go from there. I saw a video where a guy did his own conversion for much less using GM parts from different year cars. I could go that route too. Just not sure.

Anyhow, since my 4l60e transmission is not operating properly I am considering my options since I expect to be putting a lot more power to the ground with this blower. I also have 3.73 gears in it now. Is a 4l80E easy to do? Since I have the interior out of the car and this will be something I want to be able to drive long distances when done I am considering a different transmission such as a 6l80E if possible?

One other consideration is that if I do blow this engine up I will have to decide if I want to keep this motor or go to an LS swap. Does this LT1 and the LSx engines have the same bolt patterns so I can just swap the engine at that time? I will do what I can to keep this car alive but just curious what the options are. This engine is a stock Caprice engine with less than 80k miles on it.

I am sure I will have other questions as I move through this process but for now I am considering installing a bigger transmission to be able to handle more power. The rear end is already a 10bolt rear end internally and setup to handle 700+ hp. Along with an aluminum driveshaft.
 

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With the 411 PCM conversion, I would definitely consider a 6-speed like the 6L80 or 6L90. They are not without their problems though so you may want to contact a trustworthy local trans shop and ask their opinion. There are at least a few guys who have done that swap here, and if I was going LS, I would definitely do a whole engine/trans package, that would enable me to keep a 2.93 or 3.08 rear axle drastically lowers driveshaft RPM.

Personally I would do the math first before committing to any approach. I am in the midst of a built LT1/Trans combo and even getting a very good deal on the engine and building the trans myself, I'm at over $6200 just in engine/trans/headers/torqueconverter, and still stuck with a 4-speed automatic.
 

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Discussion Starter #3
Thanks, I am aware of the cost. I will have about $7000 tied up into an LS build for my truck. That too will be supercharged but likely will end up with 4l80E. I figure that truck will have somewhere around $12k into it if not $15k by the time I am done with the drivetrain on it. I have plenty of time to consider my options.
 

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6L90Es (NOT mere 6L80Es) have proven themselves behind supercharged 6.2L LSA V8s & turbodiesel 6.6L LGH V8s, for whatever that's worth.
Depending on tire size, 2.93, 3.08, or 3.231 axle gear would make the 4L80E's gearing look … anachronistic at best.
 

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8L90's 1st & 8th gear are 4.56 & 0.652. (Not sure the 12200411pcm can operate a 8L90.)
6L90's 1st & 6th gear are 4.03 & 0.667.
4L60's 1st & 4th gear are 3.06 & 0.696.
4L80's 1st & 4th gear are 2.48 & 0.750.

If money truly is no object with a 12200411pcm, why not the 6L90?
 

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How's the floor fit with a 6L90E?
'Fix Until Broke' can answer that question from experience, seeing as his Buick Roadmaster wagon already has an LGH-6L90E powertrain.
 

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If the body lift is adamantly out of the question, TCI will change the ratios in the 4L80 to a slightly less unimpressive
2.97 … 1.57 … 1.00 … 0.75

As for the vibes, that's probably just a matter of time which Rodney has.
 

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Discussion Starter #11
At this point I am looking at my options.. As I mentioned, my rear has 3.73 gears in it already (If I didn't I am now.)

My only issue with the 4l80e is the powertrain loss. How do the 6l90 and 8L90 do in those departments? Not really concerned with the tunnel as this is a 9c1 and as long as the seats fit I have to build a custom center console anyhow. Would be nice to have a street driveable car that doesn't stop at every gas station but can still smoke em at the dragstrip.
 

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Can the T43 TCM talk to a 0411 PCM?
I wasn't aware that was even a thing.
Wouldn't he have to move up a generation?
6L80 / 6L90 is a Gen4 transmission, it uses a tcm that converses with an ecm.
12200411 is a Gen3 pcm.

It would seem like they are incompatible, but that has not been the case for almost ten years now.
SpearTech has it figured out, and they are not the only ones.
 

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.....How's the floor fit with a 6L90E?
'Fix Until Broke' can answer that question from experience, seeing as his Buick Roadmaster wagon already has an LGH-6L90E powertrain.
He has a body lift doesnt he ?
Edit, I think ??
And a vibration
Yep, ~1.75" body lift (depending on how much you tighten the bolts :)). The vibration was from tightening the body mount bolts down which pulled the floor down into the transmission where I didn't clearance it. A little prybar action took care of it for now, but if/when the transmission is out again I'll do a bit more clearance on the floor.

Local shop services a fleet of FexEx trucks from the 2010's with 6L90's and he makes them sound like 4L60's - Haven't had one make it past ~150k, Certified rebuilds have lasted past 200k though. All kinds of failures, one split the case in half radially by the tailshaft, another got so hot it melted the filter into a pile of goo in the bottom of the pan (stinky!), etc. Now these are fleet trucks so not the most loving care, but also stock with 5.3's and 6.0's in front of them.
 

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Hi All, Not much to contribute except that youtube algorithm started suggestion 4L60E transmission rebuilds videos to me. There seems to be a father and son shop called Precision Transmissions out of Texas that seems to know our tranny's well. I have no personal experience just sharing info.
Vinny in PA
96 SS
 

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Precision Transmissions is good; not all of their info is correct, but they are good. Performabuilt has some great videos out there too. 6L80s and 6L90s are fairly well known in the aftermarket now so there's good support for them. Sonnax has a lot of parts available. The 6L80 torque converters have problems, but that's easily replaceable while you're swapping it in.
 

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Did you try replacing the shift solenoids? There are two (1/2 and 3/4) and are both the same, can easily be replaced once the trans pan is dropped. Run about $20/ea.
 
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