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

petethepug said:

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.

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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.

Charlie207 said:

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.

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

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.

petethepug said:

The more the gears, the more the performance.

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

petethepug said:

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.

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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.

petethepug said:

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.

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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.

mikeyss said:

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

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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.

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

Dustin Jackson said:

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

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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.

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.

Dustin Jackson said:

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

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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.