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Trans swap from a 4L80E to a 6L90E

Mac1947

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I have a 99 Chevy 3500 van with a 7.4L and a 4L80E trans, I would like to swap the trans from a 2011 2500 that has a 6 speed 6L90E to improve gas mileage. Has anyone done this before and what do I look out for? I am looking at this 2011 to purchase, (totaled in an accident), so I will have everything I will need to make the swap. Thanks
 

Mac1947

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Thanks for your reply, it's not a question of the engine, it's the electronics, (wiring, computer, trans mount, driveshaft, and yoke), if they can be exchanged or not. Besides, the 2011 has a 4.8L engine, my 1999 has a 7.4L engine with only 63,298 miles, the 6 speed trans will give a boost to gas mileage while towing!

Thanks again
 

red

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Thanks for your reply, it's not a question of the engine, it's the electronics, (wiring, computer, trans mount, driveshaft, and yoke), if they can be exchanged or not. Besides, the 2011 has a 4.8L engine, my 1999 has a 7.4L engine with only 63,298 miles, the 6 speed trans will give a boost to gas mileage while towing!

Thanks again
The electronics is the reason I was saying swapping them together would be easier. The physical bolting them together is easy since it's the standard GM bellhousing pattern, and moving the transmission crossmember with driveshaft mods.
 

FellowTraveler

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I think it was TCI that as marketed a 6 speed 4L80e some years ago not sure it is still available. Its programming made use of overdrive for the extra gear ratios.

The 4L80e can be made more a wide box with a low 1st gear ratio allowing you to use taller ring and pinion limited by whatever is available for the differentials used in your application this works well with a diesel like the Cummins which has its peak torque output between 1.5 & 1.8k rpm or even a gas motor that is built for torque down low I suspect the 7.4 has planty of torque and its more of an educated guess with other applications.
 

Mac1947

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Thank you, well put Sir, this is by far the most info I have received. I will follow up on your suggestion and let you know the out come!

Thanks again Fellow Traveler
 

red

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Might want to clarify the weight you are towing, axle gears/tire size as well as engine upgrades done and terrain. The .67 6th gear will help a little on fuel economy when empty, but if you're towing more than a few thousand pounds in hilly or mountainous terrain the trans will be in 5th which is higher than your current .75 od and result in worse fuel economy. 454's torque band is usually in the mid 2000's-low 3000's rpm range, make that your target operating range when doing the math. Figuring 4.10's with 265/75/16"s and a cruising speed of 70mph (for example) puts the engine at 2040rpm in 6th gear which it can't maintain and will downshift to 5th.

Stand alone computers for the 6L90e are available around $900. Also going to need a different computer for your 454 that's calibrated for a manual trans because the programming between the 2 different model years won't work together. 6L90e computer will need a few inputs from the engine, TPS and RPM.
 

FellowTraveler

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Might want to clarify the weight you are towing, axle gears/tire size as well as engine upgrades done and terrain. The .67 6th gear will help a little on fuel economy when empty, but if you're towing more than a few thousand pounds in hilly or mountainous terrain the trans will be in 5th which is higher than your current .75 od and result in worse fuel economy. 454's torque band is usually in the mid 2000's-low 3000's rpm range, make that your target operating range when doing the math. Figuring 4.10's with 265/75/16"s and a cruising speed of 70mph (for example) puts the engine at 2040rpm in 6th gear which it can't maintain and will downshift to 5th.

Stand alone computers for the 6L90e are available around $900. Also going to need a different computer for your 454 that's calibrated for a manual trans because the programming between the 2 different model years won't work together. 6L90e computer will need a few inputs from the engine, TPS and RPM.
Great info.
 

THEFERMANATOR

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And double check the 11 has a 6 speed. As far as I have seen, the 4.8l was coupled up to the 4l60e most of the time right on up past 2011. And if it had a 6 speed, it would most likely be a 6l80. As to making it work, you'll have to get a custom tune to turn off all the trans controls, but maintain a p/n input so you get proper idle control(hptuners and tunercat are best suited for this). Then you'll need the pcs-2650 gateway module to talk to the t43 tcm inside the 6 speed. There is no way to install a stand alone tcm on the 6 speeds as it's tcm is part of the valve body. All you can do is buy the pcs-2650 gateway module that can read your engines sensors, and translate them into GM high speed lan. It can also be used to manipulate/alter the outputs to make it shift how you want, but you will most likely end up needing custom trans tuning. The pcs-2650 cannot be purchased direct, only through select authorized dealers, and the price varies from around $750 up to $1700 for just the gateway and harness depending on who you buy it through. Otherwise you have to fab up a 58x crank reluctor, 4x cam reluctor, and some other inputs to make a late model ecm think it's running the engine, and let it talk to the tcm(this method has less functionality than the pcs box). So as you can see, it is not a cheap, nor easy endeavor. And this is all assuming you have a 2 wheel drive as a 4x4 adds even more complexity.
 

FellowTraveler

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And double check the 11 has a 6 speed. As far as I have seen, the 4.8l was coupled up to the 4l60e most of the time right on up past 2011. And if it had a 6 speed, it would most likely be a 6l80. As to making it work, you'll have to get a custom tune to turn off all the trans controls, but maintain a p/n input so you get proper idle control(hptuners and tunercat are best suited for this). Then you'll need the pcs-2650 gateway module to talk to the t43 tcm inside the 6 speed. There is no way to install a stand alone tcm on the 6 speeds as it's tcm is part of the valve body. All you can do is buy the pcs-2650 gateway module that can read your engines sensors, and translate them into GM high speed lan. It can also be used to manipulate/alter the outputs to make it shift how you want, but you will most likely end up needing custom trans tuning. The pcs-2650 cannot be purchased direct, only through select authorized dealers, and the price varies from around $750 up to $1700 for just the gateway and harness depending on who you buy it through. Otherwise you have to fab up a 58x crank reluctor, 4x cam reluctor, and some other inputs to make a late model ecm think it's running the engine, and let it talk to the tcm(this method has less functionality than the pcs box). So as you can see, it is not a cheap, nor easy endeavor. And this is all assuming you have a 2 wheel drive as a 4x4 adds even more complexity.
Yep FERM "you are the wizard of tech for sure" great post!
 
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