Engine and gearbox swap from four speed to six or eight speed on 2008 Z71 ?

[Robert T]

I have a 2008 Tahoe Z71 in need of a new engine ! 338thousand kilometers from new and could rebuild, just wonder if anyone has done an engine and gearbox swap for a newer motor with either the six speed or 8 speed box, or possibly a Denali swap with an eight speed box, just wondering which one one be the eisiest swop ( 6 speed i've been told) or how much work to go with a newer denali or eight speed ? is there a conversion kit ? i'd be greatful for any info ? thanks

 

[Joseph Garcia]

I recently researched a potential high performance option for me that kind of parallels your question. I wanted to put an LT4 and its matching 10 speed high performance transmission in my 07 Yukon XL Denali, and I spoke with knowledgeable folks at GM Performance, GM crate engines, Summit Racing, and Summit's engine builder. They all told me that there are too many core and electrical interface differences between the LT4/10 speed trans combo generation and my 07 electrical and CANBus system generation to make the conversion a reality. If I just wanted to race my Denali (which I do not) and did not care about any loss of functionality in the interior of the truck, the swap 'could' be possible, but still not easy. All of their recommendations to me was to find a knowledgeable LS engine builder and have them totally rebuild my existing L92 engine with the appropriate high performance internal parts and put a supercharger on it.

 

[Miami-Dade]

@Robert T Moved you here from 2021+section.
Welcome from Miami&NYC!

 

[Marky Dissod]

I have a 2008 Tahoe Z71 in need of a new engine. 338,000km from new and could rebuild.
just wonder, if anyone has done an engine and gearbox swap for a newer motor with either the 6L80 or 8L90E, or possibly a Denali swap with an 8L90?
just wondering which one one be the easiest swap (6L80E I've been told),
or how much work to go with a newer denali or 8L90E? is there a conversion kit?

To paraphrase Joseph Garcia:
6L80E MIGHT BE POSSIBLE. MAYBE.
8L90E or 10L90E, you'd be in uncharted waters.

'kilometers' instead of 'miles' ...
does your local gov't let you upgrade to a 6.0L engine from 2008-2014?
That would be MUCH easier and cheaper than trying to use a newer engine.
Again, you'd be in uncharted waters.

 

[petethepug]

I’ve seen one YouTube clip of an 8SP 8L90 going into an 07-14 Gen truck but didn’t save a link. I’ll post it up when I find it again.

So yes, you can also go 6.2 w/ a 6SP 6L80 as that architecture is already in our Gen truck as well as the uncommon 08/09 Tahoe w/ the 6.2L.

The second option is the way I’d go as it would essentially be a part swap from a known (totaled) 6.2 w/ a 6SP trans like a Denali. That would also give you the option to plunk in it’s AWD to deal with rain & snow.

Sorry to hear about its demise but congrats on the journey.

So don’t forget 07/08 6.2L Denali is L92 385hp No AFM, 09 Denali is 403hp L9H e85 No AFM and 10-14 is L94 403 hp e85 with AFM.

Oh yea, then there’s L96 drop in, iron block/alum head L96 6.0 Reg fuel 365 hp No AFM from the 3/4 & 1 ton gasser trucks. Later models also run e85.

Subscribed!

 

[petethepug]

I’ll paste this here

8L90 to 10L80 Swap

I have a 2015 GMC Yukon Denali 4WD with the 8L90 tranny. I'm swapping in a 10L80 and would like to know whether or not my current TCM will support it or if I will need to get a different TCM. This is being matched up to a built LT-1 from a C7 w/ LT-2 Intake. Any input is greatly appreciated.

forum.hptuners.com

 

[Foggy]

Just my 2 cents... the 8 speed is a POS... some of it due to design, some
due to programming etc...
Too many problems to waste your time and money on

 

[Charlie207]

Just my 2 cents... the 8 speed is a POS... some of it due to design, some
due to programming etc...
Too many problems to waste your time and money on

They crammed 8 forward ratios into the same size case as the 6L80.

 

[Robert T]

I recently researched a potential high performance option for me that kind of parallels your question. I wanted to put an LT4 and its matching 10 speed high performance transmission in my 07 Yukon XL Denali, and I spoke with knowledgeable folks at GM Performance, GM crate engines, Summit Racing, and Summit's engine builder. They all told me that there are too many core and electrical interface differences between the LT4/10 speed trans combo generation and my 07 electrical and CANBus system generation to make the conversion a reality. If I just wanted to race my Denali (which I do not) and did not care about any loss of functionality in the interior of the truck, the swap 'could' be possible, but still not easy. All of their recommendations to me was to find a knowledgeable LS engine builder and have them totally rebuild my existing L92 engine with the appropriate high performance internal parts and put a supercharger on it.

Thanks for sharing this information

 

[petethepug]

Oh well, high hopes. At least I don’t feel bad about potentially missing the boat on a 10SP swap since I just replaced the 6SP.

 

[Charlie207]

Oh well, high hopes. At least I don’t feel bad about potentially missing the boat on a 10SP swap since I just replaced the 6SP.

As time goes by, the 6L80/90 is getting lots of aftermarket support to handle grip-loads of power. Precision Transmission is doing a 4-digit HP 6L90 build for a twin-turbo CTS-V right now. He did a video the other day of all the upgraded parts for the build.

 

[Geotrash]

As time goes by, the 6L80/90 is getting lots of aftermarket support to handle grip-loads of power. Precision Transmission is doing a 4-digit HP 6L90 build for a twin-turbo CTS-V right now. He did a video the other day of all the upgraded parts for the build.

Really, really cool to see. Our transmissions are enjoying peak aftermarket support, which benefits us in numerous ways.

 

[petethepug]

The more the gears, the more the performance. Getting 4:10’s in an AWD and a 10SP with overdrive would feel like an extra 100 hp as well as put you in love with your milage.

 

[Marky Dissod]

The more the gears, the more the performance.

True, but only up to a point of diminishing returns, and an MpG tradeoff well before that point is reached.

4.10-to-1 in an AWD and a 10SP with overdrive would feel like an extra 100 hp as well as put you in love with your milage.

The 10L80's gear spread-range is so wide (7.33), that it ALMOST doesn't need an axle gear upgrade ... ALMOST.
For SUVs & pickup trucks, going up to 3.42 or 3.73 for taller tires may improve city MpG with little to no highway MpG penalty.
More gear than that will likely not improve city MpG, and may cost some MpG.

The 8L90 gear spread is pretty close to the 10L80 (6.99).
Same gears and advice as above.

 

[mikeyss]

The more the gears, the more the performance. Getting 4:10’s in an AWD and a 10SP with overdrive would feel like an extra 100 hp as well as put you in love with your milage.

I remember a TFL comparison on youtube when they compared a 5.3 8 speed against the 10 speed, and every test the 8 speed was quicker. They did mention one had bigger tires, but if you think about it, each time the trans shifts takes a milliseconds away from the acceleration.

 

[Marky Dissod]

... compared a 5.3L 8L90 against the 10L80, and every test the 8L90 was quicker. They did mention one had bigger tires ...

If both 'need' (read that as 'has been programmed') to go through EACH gear in sequence,
then yes, the 10L80 has too many gears to be quicker than the 8L90.

Lemme show ya somthin.
Since no 1/4 mile drag race with any of these gearboxes uses its final gear ...
6L80 1st gear divided by 5th gear: 4.03 / 0.8521 = 4.73
8L90 1st gear divided by 6th gear: 4.56 / 0.8455 = 5.39
10L80 1st gear divided by 7th gear: 4.6957 / 0.8536 = 5.50
In other words,
the 8L90 uses 1 less gear to cover very nearly the same gear spread as the 10L80
or
the 10L80 wastes a shift's worth of time vs the 8L90.

The major benefit of the 6L80, 8L90, & 10L80 is metro/urban stop'n'go MpGs -
and the 10L80 has already crossed the point of diminishing returns there as well.

 

[Dustin Jackson]

My opinion of this generation of Tahoe is that you are probably better off keeping the 4l60e. You got 300+k out of the 4l60e which is a more than most people get out of their 6l80e. Just my thoughts

 

[Marky Dissod]

My opinion of this generation of Tahoe is that you are probably better off keeping the 4L60E.
You got 300+k out of the 4L60E, which is more than most people get out of their 6L80E. Just my thoughts

Miles per Gallon? 6L80E.
Miles per Transmission? That depends on who last rebuilt them.

With a proper rebuild using updated materials, a decent pcm / tcm tune, & fresh ATF every 2 years,
I see no reason why either would not last 150k miles. On the other hand,
any OE geartrain lasting 150k miles is often an aberration.

 

[petethepug]

Most of my travel is local. The hills to get from point A to B are the equivalent of a 8-10 story building. The most desirable thing about the 07-14 trucks is they’re the last generation that’s not direct injection. That’s good for future tuning and motor swaps.

 

[j91z28d1]

My opinion of this generation of Tahoe is that you are probably better off keeping the 4l60e. You got 300+k out of the 4l60e which is a more than most people get out of their 6l80e. Just my thoughts

4L60 gets a bad rap but the one in my obs was solid. truck had 325k on it, I put a good 150k of that, I was told it wasn't rebuilt when I got it, but who knows forsure.

I know they don't hold big power well and don't like to tow in overdrive. but stock for stock, with just fluid changes by the book in a daily driver soccer mom suv. I bet it l
out lasts these newer 6, 8 and 10 speeds.


6 seems to be better for towing if your builder is good. I don't see the point of a 10speed. we have a new Ford truck at work with one, and honestly it's kinda annoying. it's always doing something.