How the C8 Corvette’s Dual-Clutch Has Changed Since We Drove the Car
The new Corvette has an eight-speed Tremec DCT. We weren’t crazy about it in the pre-production C8 we drove, but engineers tell us the final version will be better.
For the C8 Corvette, Chevrolet abandoned the traditional manual and torque-converter automatic for a new, eight-speed Tremec dual-clutch. And in our Performance Car of the Year testing, the gearbox was the weakest component in the pre-production C8 Stingray we had on hand. It’s part of why the Corvette didn’t win.
In automatic mode, the DCT dolled out nice, snappy shifts, but when using the paddles, it could be clumsy. Too often we found ourselves running into the rev limiter, or having downshifts denied after a paddle pull. But, the C8 we drove wasn’t a finished product. There’s been development work since we drove the car, and that work will continue for the foreseeable future. At a powertrain engineering seminar held by Chevy last week, we asked Glen Hoeflinn, controls program manager for the DCT, what will change from the car we drove.
“Maybe you get some humpy-bumpy shifts here, you get a little bit of that there. That all gets refined out,” Hoeflinn said. “It’s in final refinement, and then it’s in final checks and looking what we’re doing and making sure that it’s behaving exactly [how] we want.”
“That’s what we’ve done since the car that you had. Doing all that refinement and making sure it’s ready to go for everybody across the all the cars.”
A dual-clutch presents unique challenges, no matter what sort of car it’s in. “There’s a lot of pre-selection interaction that goes on in the background,” Hoeflinn said. “It’s the same choreography” between the engine and transmission, he added, but without the “luxury” of a torque converter, there’s a lot more programming work involved.
As you’d expect, the transmission has different automatic shift strategies for the various drive modes, which adapt in real time. The more aggressive, the more spirited you drive, the more aggressive the car’s going to respond,” Hoeflinn said. “As you start to relax, the car’s going to start to relax.”
The DCT uses latitudinal and longitudinal accelerometers, and looks at information like throttle position and steering angle to gauge how the car is being driven, and react accordingly. For example, in Track mode with the transmission set to automatic, the car will downshift aggressively when the driver is braking hard into a corner, and hold upshifts until corner exit.
The C8 has two manual modes. If you pull a paddle while in Drive, you get a temporary manual mode, which automatically times out, or can be exited sooner by holding the upshift paddle. In this mode, the car will automatically upshift at redline. If you press the M button in the center console, you get full manual mode. There’s no time out, and the car won’t upshift at redline.
There are two other neat tricks available for drivers to exploit. First, if you hold the downshift paddle, the DCT will serve up the lowest possible gear. Do that while braking, and the transmission will keep downshifting as engine speed allows. And second, pulling both paddles at the same time is equivalent to pushing in the clutch pedal on a manual car, which allows you to rev the C8’s new V-8 as much as you want.
In the C8, the paddles are directly wired to the transmission control module (TCM) for quicker response times. “In other applications, from the paddle, the wire will go to the body control module and then from the body control module back over to the transmission. You have obvious latency there,” Hoeflinn said.
“It could be 25, 30, 40 milliseconds from the time you pull, to the time that transmission actually got the message. When you wire them directly from the paddle straight to the TCM, we’re getting the message instantaneously.” This doesn’t mean the paddles will give you a downshift that over-revs the engine—the TCM prevents that—it just helps reduce delay.
One of the headline figures of the C8 Corvette is its incredible acceleration. We timed a pre-production Z51 Stingray as hitting 60 mph in 2.8 seconds and running the quarter-mile in 11.2 seconds at 122 mph. With the C8’s Performance Launch mode, the car will actually use the inertia of the engine coming down between revs to propel the car forward. Chevy calls these “Boosted Shifts,” and they’re only used with a Performance Launch. In any other mode, they make the car feel unsettled.
From a mechanical standpoint, this new Tremec transaxle isn’t a radical departure from other DCTs. There are concentric clutches and input shafts for the odd and even gears. The even gears and reverse live near the front of the transmission, while the odds are at the back. A limited slip-differential is integrated within the unit. Base Stingrays get a mechanical diff with a 4.89:1 final drive ratio while Z51-pack cars get an electronic LSD with a 5.17:1 ratio. The overall gear ratio spread of 8.8:1 is the same regardless of differential.
The packaging of the transaxle is such that there’s a common oil sump—filled with 11 liters of Pentosin FFL-4 fluid—for all components. A cooler mounted to the top of the transaxle assembly means there’s no need for additional hydraulic lines, while two filters keep things clean. An externally mounted pressure-side filter requires replacement every 20,000 miles, while the internal suction filter mounted to the sump is a lifetime part.
We asked about why the C8 team didn’t try to do a manual. Hoeflinn and the other engineers present gave us a similar answer to Corvette chief engineer Tadge Juechter, when we interviewed him before the car debuted. They’d need to develop a new manual just for the C8, and considering the stick-shift market is shrinking, it would be an expensive endeavor seemingly without much reward. There are packaging constraints with the Corvette’s central backbone tunnel, too, which would require a hole to accommodate the shifter and gear linkage, hurting structural rigidity. Juechter also said the pedalbox would be cramped with a clutch.
Our first experience with this DCT was less than positive, but this is a gearbox that shows a lot of promise. We look forward to driving the finished product.
Originally written by Chris Perkins; Road&Track
Highlights of the 2019 SEMA Show in Las Vegas
SEMA is the United Nations conference of all things aftermarket, and here’s some of the best stuff we spotted there.
1.Quintin Brothers Dodge Challenger
This 1000-hp Dodge Challenger went on a wild adventure after it arrived in Las Vegas. Vermont-based Quintin Brothers Auto & Performance had their truck and trailer stolen days before the show. Their custom Challenger was inside. Video surveillance helped track down the perp, but when Nevada state trooper Adam Whitmarsh tried to block the stolen Challenger into a parking space, the suspect rammed the Trooper’s Ford Explorer and escaped. After exiting the parking structure, the suspect smashed through a fence and drove the stolen Challenger across a nearby karting track—during a karting event. He eventually ditched the car and was later arrested. The Quintin Brothers and their Dodge Challenger arrived at the SEMA show wearing battle wounds from the wild chase.
2. Chevrolet E-10 Concept
It’s not an engine, it’s a motor. The Chevrolet E-10 concept is a 450-hp electrified C-10 pickup. Typically the only time a 1970s Chevy pickup is plugged into anything, it’s connected to a trickle charger. The E-10 has its batteries in the bed. The two electric motors seen here are called eCrate motors, a nod to the popular Chevy crate engines that can be found swapped into just about anything. GM claims the E-10 can complete a zero-to-60-mph run in about five seconds with a quarter-mile time in the high 13s. A Tesla P100D might be quicker, but it doesn’t look as cool.
3. Vibrant Performance Titanium Chair
Had Game of Thrones producers used Nissan Skylines or Toyota Supras instead of dragons as source material, this might be the Iron Throne. Vibrant Performance didn’t have to vanquish their enemies to build the thing, but they did use more than 50 pieces from their lineup of titanium exhaust products to construct what’s likely the most uncomfortable Adirondack chair on the porch. But it’s fun. Feeling exhausted? Have a seat.
4. Hyundai Veloster Grappler Concept
You’re unlikely to see a Hyundai Veloster on an off-road trail, let alone a dirt road, but this overland concept is out to change that. The Veloster Grappler concept is equipped with typical in-car camping accessories like a rear-hatch tent, solar panels, LED light bars, big all-terrain tires, and a roof basket to carry a spare. It’s still pretty low to the ground, and the tire clearance isn’t ideal for crawling, but it’s a concept. We’d pitch a tent with this thing.
5. Toyota Supra Wasabi Concept
Toyota’s Genuine Accessory Team cooked up a color for this concept that we hope will soon find its way onto a Camry. This Supra’s paint mimics wasabi paste and features white accents on the brake calipers, mirrors, stripes, and spoiler. The forged-aluminum wheels were designed at Toyota and have center caps with the original Toyota emblem. Ohlins coil-overs drop the Supra concept two inches. This was one of many Toyota Supras at the show.
6. AEV Jeep Gladiator
This Jeep Gladiator is equipped with all the proper get-dirty-quick gear. It has tough Bilstein dampers, a lifted suspension, and 37-inch tires. American Expedition Vehicles (AEV) is known for swapping big engines into off-road vehicles and then adding lift kits and other off-road accessories. They’re also responsible for the coolest parts of the Chevy Colorado ZR2 Bison. This year AEV brought three green machines to show off their latest accessories.
7. 1999 Honda Civic Si Super Street Build
Was this the car that sparked the movie The Fast and the Furious in 2001? It sure looks like it. Honda brought a handful of concepts to the show in celebration of its 60th year in North America, and what better way to do it by showcasing the Civic Si Super Street magazine modified for the Civic Si Challenge in 2000. If you collected buckets of Mattel die-cast cars as a kid (or shamelessly as adults, like us), this car might look familiar.
8. Nissan Frontier Desert Runner
The current-gen Nissan Frontier might be 16 years old, but this concept proves that Nissan knows what people at SEMA want in a truck: tons of suspension, awesome off-road tires, some type of light bar, and a 600-hp 5.8-liter V-8. In the meantime, we can only hope one of these ingredients get put to use on the upcoming Frontier refresh.
9. RTR Rambler Ford Ranger Concept
The RTR Rambler Ford Ranger does everything right without going too far. Ford chose 33-inch Nitto Ridge Grappler tires with custom RTR Tech 6 wheels, because they know anything bigger than that will be unnecessary in most cases. Three LED light bars are tastefully tucked into a custom front grille to complete an almost Ranger Raptor–like appearance. A two-inch suspension lift is installed as well as heavy-duty rock sliders, which act as both a step and as extra protection against rocky terrain. It’s a simple package done well, saving the flashy stuff like wild paint for the Insta-campers.
10. 1972 Honda N600
If it looks like this 1972 Honda N600 has a motorcycle engine under the hood, it’s because it does. This oddball is powered by a Honda VFR 800-cc V-4 motorcycle engine that puts power to the rear wheels. Although the car itself predates the era of high-revving VTECs, with the bike motor installed, this is likely the only N600 with a 12,000-rpm redline. This was one of several cars Honda showcased at the SEMA show.
11. Honda Civic Si Drift Car
This is a peek under the hood of a 926-hp Honda Civic Si. The engine is turned longitudinally and transforms a front-wheel-drive coupe into a rear-wheel-drive drift-spec machine. The work was done with help from Jeanneret Racing and Olson Kustom Works.
12. Chevrolet Silverado ZR2 Prototype
We saw this Chevrolet Silverado Desert race truck back in early October, when it competed in the Laughlin Desert Classic, a 17-mile race event in Nevada near the Arizona border. It was there for “engineering development,” but we still think it’s a preview of an upcoming Silverado Z
13. Honda Rally Passport
Honda R&D in Ohio built this rally-ready Honda Passport in their spare time. It has already survived a handful of rally competitions, finishing second in its class at the Southern Ohio Forest Rally. It has had typical safety additions like a roll cage, but other than that it’s unchanged except for tires, brake pads, wheels, and skid plates. Oh, there’s also the addition of a hand-operated hydraulic brake, for epic drift action.
14. 1968 Ford Bronco
There’s been plenty of buzz lately about the upcoming Ford Bronco, which is expected to debut in early 2020. A collaboration between Jay Leno and Ford, this Bronco has a supercharged 5.2-liter V-8 from the Ford Mustang Shelby GT500 and a five-speed manual transmission. The restoration maintained the simple beauty of original Bronco. The 18-inch steel wheels by Detroit Steel Wheels are a great combination of old style and modern needs. The Bronco’s Tonight Blue color would look great on a Mustang or F-150 Raptor.
15. Hyundai Veloster N Performance Concept
The Veloster N is quick, but this Veloster N Performance concept is quicker. Hyundai modified its hot hatch with carbon fiber for the front splitter, side skirts, rear diffuser, and spoiler while adding carbon fiber to each wheel’s center caps. The suspension is made up of Extreme Racing coil-overs and H&R coil springs with aluminum chassis bracing to add rigidity. Orange-accented interior bits stand out among more carbon-fiber pieces and an Alcantara dashboard.
16. SpeedKore Dodge Charger
Routed through the front fender of a 2019 Dodge Charger Pursuit is the exhaust from a 1525-hp Dodge Demon V-8. This project, put together by SpeedKore Performance Group and MagnaFlow, began as a police car. After fitting a carbon-fiber widebody kit, they turned it into something that would outrun police cars. The stock supercharged 6.2-liter V-8 was transformed into a twin-turbo engine and received an upgraded upper intake manifold designed to withstand the 26 psi of boost.
Written by: Austin Irwin, Car&Driver