6L90 Upgrade List
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TECH Regular
Joined: Jun 2021
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From: Shlumpt, TX
6L90 Upgrade List Looking at putting a 6L90 in my '99 Silverado using the TCM-2650. Just trying to get a grasp on what pieces need to be upgraded and who is the best 6 speed tuner. This is a daily driver and NOT a racer. I would like it to be able to hold good torque in the future as I do plan on a supercharger at some point but this truck never sees the track. Don't want a 4L80. It seems everyone here does 4L80 and I cannot find any great information on the 90
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Joined: Dec 2012
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From: Iowa
will you be using a true 6l90 or will you be using a 6l80
They are different...it's not like 4l60/4l65/4l70 where they're all virtually the same
the 6l80 and 6l90 have case differences, drum differences, valve body differences, etc that make them pretty non-compatible
They are different...it's not like 4l60/4l65/4l70 where they're all virtually the same
the 6l80 and 6l90 have case differences, drum differences, valve body differences, etc that make them pretty non-compatible
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From: Iowa
the 6l90, with a clean bill of health, will handle any naturally aspirated LS just fine and most mild supercharged combos.
There are some common issues like drums cracking around the laser weld, lots of valve body/pump wear issues, cracked pistons, etc
but...fixing all those is just part of a clean bill of health.
As for upgrades, the best upgrade you can do is find someone who's good with the laptop.
These are synchronous shift transmissions...all controlled by the computer...so if you have a moron on the laptop, they can take a world class trans and turn it into garbage in about 10 minutes
Meanwhile someone good on the laptop can take a 60k mile trans and make it live a long healthy life.
Do not underestimate the tune and the effects it can have on the performance of a 6 speed automatic
There are some common issues like drums cracking around the laser weld, lots of valve body/pump wear issues, cracked pistons, etc
but...fixing all those is just part of a clean bill of health.
As for upgrades, the best upgrade you can do is find someone who's good with the laptop.
These are synchronous shift transmissions...all controlled by the computer...so if you have a moron on the laptop, they can take a world class trans and turn it into garbage in about 10 minutes
Meanwhile someone good on the laptop can take a 60k mile trans and make it live a long healthy life.
Do not underestimate the tune and the effects it can have on the performance of a 6 speed automatic
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Joined: Jun 2021
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From: Shlumpt, TX
@2BFAST What is the reason other than cheap? I'm not running a max effort 8 second truck so that is not a response either.
I believe that the 4L80e is a tried a true piece and has it's place for certain. My '96 Impala SS will get a 4L80e, there is no room for anything else and it will make more power than my truck most likely. So I am not bashing on it.
However, I believe that the 6L80/90 can be a great piece of equipment especially in a truck. It should allow me to get a little bit better gas mileage as well as better performance. The 6 speeds have a lot of stigma surrounding them originating from the early days of tuning which now I think has been rectified.
Just my opinion though.
I believe that the 4L80e is a tried a true piece and has it's place for certain. My '96 Impala SS will get a 4L80e, there is no room for anything else and it will make more power than my truck most likely. So I am not bashing on it.
However, I believe that the 6L80/90 can be a great piece of equipment especially in a truck. It should allow me to get a little bit better gas mileage as well as better performance. The 6 speeds have a lot of stigma surrounding them originating from the early days of tuning which now I think has been rectified.
Just my opinion though.
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From: Nitro Alley
The 6L Units can be good performing and power handling Transmissions.
The Tune is extremely critical with these two units.
Also, do not ever use a Stock Converter.
Between the Pump/ Bell-Housing and Rear Planet being regularly destroyed by debris from the Converter and the Trans itself...
Not to mention Drum failures and Valve-Bodies being worn-out.
I do not like to Build these unless someone really wants to pay the expense that these Units incur.
I much prefer the Original ZF Design, over what GM did to change these Units.
I would much rather chop up the ZF version for a Chevrolet Bell-Housing...
Than use a GM 6L Unit.
(Work in Progress).
The Tune is extremely critical with these two units.
Also, do not ever use a Stock Converter.
Between the Pump/ Bell-Housing and Rear Planet being regularly destroyed by debris from the Converter and the Trans itself...
Not to mention Drum failures and Valve-Bodies being worn-out.
I do not like to Build these unless someone really wants to pay the expense that these Units incur.
I much prefer the Original ZF Design, over what GM did to change these Units.
I would much rather chop up the ZF version for a Chevrolet Bell-Housing...
Than use a GM 6L Unit.
(Work in Progress).
Last edited by vorteciroc; Jul 6, 2022 at 06:21 PM.