6 Speed FWD
Pay Attention - This is the Next Big Thing
According to Hydra-Matic specs,
there will be four distinct variants
(covering FWD, RWD, and AWD)
launched in 25 different models this model year.
When the Atomic Orange C6 convertible arrived,
we were more than anxious to flop the top and flail the pedals.
But what’s that? It’s an automatic!
All of a sudden the fun factor seemed to shrivel up
like a spider on a hot griddle.
But we put our chauvinism aside
and were in for a very pleasant surprise.
Tell you right now,
this thing was more fun to drive than any stick shift,
and we’re stick-shift junkies.
In short,
it’s nothing less than a bellwether transition
for the performance generation.
By ’08, GM plans to have put nearly a million of them on the road,
so it’s likely that one might eventually end up in your hot rod.
In the Corvette, the transmission is mounted at the rear of the car,
but in the supercharged ’06-‘07 Cadillac STS-V sedan
(the only GM car so-equipped at this writing) it mates directly to the engine.
It’s a Hydra-Matic unit called the 6L80.
Trucks powered by 6.2L L92 engine get the 6L80, too,
Heavy Duty models get the beefier 6L90 behind the6.0L
In this report, however, we’ll focus on the former.
The “old” 4L60, 4L65, and 4L70
offers 3.06, 1.63, 1.00, and 0.70:1 ratios;
already in its sophomore year,
the 6L80/90 has ratios of 4.02, 2.36, 1.53, 1.15, 0.85, and 0.67:1.
As example, when pared with the Corvette’s standard 2.56:1 axle ratio
it poses a very loooong-legged 1.72:1 final drive.
Jeff Baran, chief project engineer, remarked:
“We used knowledge and experience
from the entire GM Powertrain network
to engineer this transmission.
It is a modular design
to facilitate a broad application
and it enables an easy plug-and-play approach.
The transmission architecture was designed
to satisfy a large matrix of attributes
for current and future vehicle programs.
It’s the first GM transmission ever designed in this way.”
Obviously, most of this is in regards to avoiding a gas guzzler tax
and promoting excellent highway mileage.
If it is in anticipation of the ever-circling fuel gouge,
is it strong enough for high performance application?
According to Hydra-Matic specs,
there will be four distinct variants
(covering FWD, RWD, and AWD)
launched in 25 different models this model year.
Torque capacity ranges from 258lb-ft to a fat 520lb-ft.
Shift speeds are up to 7,000rpm, driven by a 32-bit controller.
Remember torque ratings are measured in 24-hour constant cycles at WOT,
so there’s plenty of capacity here for a high-performance engine.
Though the trucks use a button on the shifter,
the C6 employs paddle shifters,
located just above the center of the steering wheel
that can be up- or downshifted with a thumb or forefinger
at least as quickly as a full-on power shift with the T56.
Gear changes happen right now.
And your arm won’t get sore. Keep it mind.
So what’s the subtext?
While this configuration might be misconstrued as a fuel economy-only ploy,
it was also created to enable premium shift quality and drivability,
and therefore make the engine more flexible
and add to the performance factor.
It features new technologies as found in clutch-to-clutch operation,
automatic grade braking, driver shift control (DSC),
and enhanced performance algorithm shifting (PAS).
What the gobbledygook boils down to is
a tough transmission that fits the hot rod case so well that it’s scary.
Yes, it’s electronically controlled.
Yes, it will bolt to any Gen-III or Gen-IV LS engine.
A 4-pinion input carrier gearset (left) and a compound 3-pinion output gearset uses three sets of pinion gear pairs;
one set meshes with the sun gear and the other set with the ring gear.
Although it’s rosy on the surface,
in the short term there are some rather tall hurdles
that make this proposition impractical for the hot rod nation.
The 6L80, along with the rest of the car’s major functions
(HVAC, stability control, ABS, etc.) are integral to the whole.
When they “talk” to one another,
they must all be present for the conversation,
so if you installed a 6L80 in your LS-powered hot rod right now,
it flat wouldn’t work.
According to GM Powertrain Engineer Jim La Fontaine,
the transmission might be able to engage Low gear, but that’s all.
By SEMA ’07, there will be better news.
Facilitation for the swap might better come from the aftermarket.
To giant GM, it doesn’t even blip the radar screen—yet.
So for the immediate present, the carrot dangles,
but we suggest that you do not bite.
So why is this carrot so tempting?
That 4.02:1 Low gear ratio is very generous,
so launch acceleration is stout.
GM engineers estimate that the gear spread cuts 0-60 acceleration times
by as much as 7 percent compared to a four- or five-gear automatic.
Gearing is fairly wide,
but since there are six speeds instead only four,
engine rpm between upshifts does not dip appreciably.
Finally, the tall overdriven gears help fuel economy.
The 6L80 employs an internal controller that operates in a bath of fluid.
Although it isn’t uncommon to have a transmission control module
that adapts to the specific gearbox,
and to also have programming that optimizes transmission performance characteristics
according to a variety of input, 6L80 adds another level of “thinking.”
Components within its seven major subsystems learn from one another
via the controller software in a unique form of self-adaptation
that maximizes the interface of all the “networked” components.
6L90
This transmission was recently introduced in the HD 2500 series Silverado and Sierra trucks.
Think of it as the heavy-duty version of the 6L80,
featuring a strengthened input gearset
that has two additional pinion gears (6 total),
and a stronger output gearset that uses wider gears than 6L80
The 6L90 shares about 75 percent of its parts with the 80,
although the transmission case is slightly (35mm) longer.
The torque converter is an 11-inch unit.
Gear changes from Second to Sixth are by clutch-to-clutch control,
e.g., an oncoming clutch is engaged
and an “off going” clutch is released in a precise manner
to achieve the ratio change.
The first-to-second upshift, however, is a freewheeling action
where the second-gear clutch engages while the first-gear one-way clutch spins freely.
This was done to allow a greater degree of smoothness at lower speed.
This was also incorporated to lend more efficiency to an overall package
that’s not much larger than the 4L60.
The 6L90 has three gearsets,
a conventional input planetary gearset with four pinion gears,
as well as one compound output gearset
and one simple output gearset.
The compound output gearset uses three sets of pinion gear pairs,
with one set of pinions meshing with the sun gear
and the other set with the ring gear.
A 4-pinion input carrier gearset (left)
and a compound 3-pinion output gearset
uses three sets of pinion gear pairs;
one set meshes with the sun gear
and the other set with the ring gear.
Click here to See the Differences in Size
and go to the bottom of the page
What happens next?
We’ll have to wait a little while until the boneyards claim some victims.
Hopefully, the aftermarket will have aided and abetted by then.
Probably sooner than later,
GM Performance Parts will offer some version of the six-speed for hot rod use.
Undoubtedly it will entail some sort of pony electronics
to make it work with your LS-series engine.
MaxChevy will keep you up to date on the 6L80/90’s forward progress.
Currently their are three different bellhouse configurations,
the Corvette style,
the Chevy/GMC pick up style,
and the Cadillac STSV/XLRV.
These transmissions will not interchange
because the pump is attached to the bellhouse.
This transmission also has a lip seal located in the bearing,
so replacing bearings, is an important procedure.
The nuetral safety switch
is also located in the pan
so transmission entry is now required.
1st gear ratio is 4.027:1
2nd gear ratio is 2.363:1
3rd gear ratio is 1.532:1
4th gear ratio is 1.152:1
5th gear ratio is .852:1
6th gear ratio is .667:1
Dexron VI is required. 10-12 Qts depending on application.
weight: 222lbs
max gearbox torque: 664lb.-ft.
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Originally Posted by EarlT
