General Motors faced tough challenge when searching for the proper transmission to pair with its all-new 625 horsepower supercharged LT4 engine in the 2015 Corvette Z06. The General wanted to match the lightning-fast shifts offered by Porsche’s PDK transmission, but no dual gearbox existed that met both of GM’s requirements — compact size and the ability to handle the LT4’s 635 lb.-ft. of torque.
The answer? Build one that could. The 8L90 eight-speed automatic transmission found in the new Z06 was developed entirely within GM. It’s a traditional automatic gearbox in its design, but GM says it shifts not only faster than any dual-clutch, but smoother as well.
Lead Corvette engineer Tadge Juechter highlighted the stringent packaging requirements the team had to meet for the 8L90.
“It’s engineered by GM, internally, and many of the parameters were focused on this car,” Juechter told Motor Authority. “So it’s almost a custom transmission.”
Juechter explains that the transmission, which offers 5 percent better fuel economy than the equivalent six-speed automatic, was designed to work seamlessly with the Corvette’s cylinder deactivation system.
“We wanted a transmission that provided everyday drivability and compatibility with cylinder deactivation,” he said. “When you run in four-cylinder mode, a torque converter is really your friend.”
Juechter confirmed the transmission will find its way into other applications, even though it’s design was influenced solely by the Z06 project.
A key piece of the design in the 8L90 is what GM is calling a “smart pump”. Under heavy acceleration, the transmission uses two inlet discharge ports, providing more flow to the clutch packs. When cruising, the system automatically calms down a bit and resorts to a single inlet port, reducing drag.
What’s more, the 8L90 is designed to be compatible with the standard Corvette Stingray’s torque tube, suggesting that it could eventually find its way into the standard car as a rolling update or mid-cycle refresh. The gearbox is the same physical size as the existing six-speed automatic, but thanks to a lightweight aluminium and magnesium construction, its eight pounds lighter. Despite its light weight, the 8L90 can handle up to 738 lb.-ft. of torque.
The transmission features a tall overdrive ratio for seventh and eighth gears (0.86 and 0.65, respectively), while the sixth gear is a direct drive. The new setup also allows GM to lower the final drive to 2.41 from 2.73, though the taller base axle is still available as an option. GM is still honing in shift patterns, shift points, and the map for cylinder deactivation, so we’ll have to wait a bit for official fuel economy figures for the Z06.
But between the efficient eight speed transmission, lightweight construction and cylinder deactivation system, the Z06 is shaping up to be one of the fastest and most fuel-efficient supercars on the market.
Comments
I’m so glad GM decided to go this route and not a dct! Well done GM!
This sounds awesome. Great job, GM! I sure hope once this application is finished, they set right to work on other applications that it can work in.
Now put it across the GM lineup; Silverado, Tahoe, Suburban, ATS, CTS, Escalade, Yukon, Sierra
Its possible, they said it will work with all rear-wheel drive set ups.
Taste said a while ago that this set up would be faster and better in more ways ,
This need to be on every vehicle except for spark
Would you rather have a 8 speed or the future 9 or 10 speeds
I can definitely see this being used in the next coming of V-series cars.
The Spark EV has a simple planetary transmission with only one gear, because the electric motor can vary its torque from zero to over 400 foot-pounds electronically. So in a way it is better! Now, if GM made a larger electric motor with the same type of transmission, it will out-accelerate the Z06 even with this 8-speed!
Well this sounds like a great trans. The bolt patterns at the front and rear look like they need some sort of adapter to get to the engine/driveshaft. What I’d like to know is if this will bolt up to an LS 6.2L motor and be able to connect to a standard type rear end. Love to have one for my ’35 Chevy!
Don’t suppose there is any idea of what this might cost yet, is there?
with the torque handling capabilities, this tranny would be a shoe-in for a diesel suburban.
First cars that need to get this are the ATS and CTS, it’s embarrassing to sell the ATS with a six speed given the competition and the 8speed on the V-Sport is pretty annoying based on reviews
The 8L90 can handle 738 LB FT. of torque. This is more than the ATS cts v sport camaro SS or LT1 corvette needs. This is for supercharged V8. Look for a lower cost 8L80 for these vehicles. And an 8L50 for the LFX and LTG.
I own a 2003 ZO6. Had it since it was new. I am now running on a club track with some minor modifications. I LOVE MY VETTE! I was recently at the track when a couple of ne Cayman S models got on the track and began to tear the track up. They both had the PDK tranny’s. They were very impressive… I plan on purchasing a 2015 ZO7 as soon as they become available. This put’s me on the horns of a dilemma, do I go with the manual tranny or the new 8L90 transmission? Will it truly work on par with the Porsche PDK, not over heat, and most importantly, will I be faster around the track with the 8L90 automatic? Any answers from a GM engineer will be welcome. Semper Fi !
When you DO get this new Z06 let us know if it causes any side affects…you know, like having to get a pacemaker installed because it almost gives you a heart attack with how fast it is.
Don, I’m on Criswell’s list for the 2015 Z06. Too old to race anymore so I’m passing on the Z07 package. This new 8L90 8-speed automatic with the paddle-shifter is what pushed me over the top in deciding on the new Z06. And if it’s true it’s going to out perform Porsche’s PDK, then that makes this old man very happy. To top it all off, if this transmission allows the new 625+ HP Z06 to reach 30+ miles per gallon on the Hwy then I’ll be beside myself.
The manual would probably be the funnest to drive at the track but in terms of track time the automatic just might do a better job of returning better lap numbers
This really comes down to ego, if you want look Kool then get the manual but if you want to go fast at a track then the automatic might be better off!