Question about Launch Control
Thread Starter
Instructor
Joined: Nov 2022
Posts: 191
Likes: 142
From: Thornton, Colorado
Question about Launch Control
Wondering if anyone knows how it works.
With all the capabilities of the electronics I have no clue.
When doing a power brake on a standard automatic, you get an rpm increase due to the stall of the converter spinning.
With the DCT I just can't believe that they are letting the clutches slip.
Any idea how they are limiting the rpm and not wearing the clutch pack?
With all the capabilities of the electronics I have no clue.
When doing a power brake on a standard automatic, you get an rpm increase due to the stall of the converter spinning.
With the DCT I just can't believe that they are letting the clutches slip.
Any idea how they are limiting the rpm and not wearing the clutch pack?
Melting Slicks
Joined: May 2021
Posts: 2,562
Likes: 1,579
The RPM is limited to 3.5k by the ECU and TCM. (The TCM knows it is doing launch control and directs the ECU accordingly). I think the smaller inner clutch is fully open, so no wear and the larger / outer 1st gear clutch is only lightly engaged if not at all until you release the brake pedal when it fully locks up.
If you watch videos of C8's doing launch control, you don't see the rear squat or anything when you hit the 3.5k limiter, and I don't think I have ever seen a video of the rear tires turning or anything until the brake pedal is released.
If I had to guess, it is only dumping the clutch when the pedal is released. It does put a lot of stress on the car. People have snapped their half shafts doing launch control. I think JerryU has a nice table that shows the torque at the rear wheels for the Z51 version that includes the gear ratios and final drive ratio.
If you watch videos of C8's doing launch control, you don't see the rear squat or anything when you hit the 3.5k limiter, and I don't think I have ever seen a video of the rear tires turning or anything until the brake pedal is released.
If I had to guess, it is only dumping the clutch when the pedal is released. It does put a lot of stress on the car. People have snapped their half shafts doing launch control. I think JerryU has a nice table that shows the torque at the rear wheels for the Z51 version that includes the gear ratios and final drive ratio.
Race Director
Joined: Sep 2016
Posts: 13,180
Likes: 10,522
But you're right that launch control monitors for wheelspin and reduces throttle as necessary to prevent it after a brief bit of allowable wheelspin on launch. So on a low traction surface LC will reduce power more than on a high traction surface to control wheelspin. I don't know for a fact, but I wouldn't be surprised if it doesn't also modulate clutch engagement as part of the process.
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 34,932
Likes: 12,344
From: NE South Carolina
Wondering if anyone knows how it works.
With all the capabilities of the electronics I have no clue.
When doing a power brake on a standard automatic, you get an rpm increase due to the stall of the converter spinning.
With the DCT I just can't believe that they are letting the clutches slip.
Any idea how they are limiting the rpm and not wearing the clutch pack?
With all the capabilities of the electronics I have no clue.
When doing a power brake on a standard automatic, you get an rpm increase due to the stall of the converter spinning.
With the DCT I just can't believe that they are letting the clutches slip.
Any idea how they are limiting the rpm and not wearing the clutch pack?
GM never provided details but this very interesting statement was made by GM’s Chief Corvette Engineer, Ed Piatek: “We found that during very aggressive launches we can drive torque through both shafts/clutches simultaneously which improves the 0 to 60 times.”
Road and Track interpretation of that statement was: "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.
First, Ed Piatek was the Corvette Chief Engineer under Tadge Juechter the Executive Chief Corvette Engineer (higher pay grade!) But he and other Corvette engineers were moved to EV's :
GM Announcement August 2020: GM Shifts Corvette Engineering Team to its Electric Vehicle Programs
Ed Piatek will now be chief engineer of “future products." Under this new role, Piatek will work across the organization on future EV programs.
So the above comment was in the early C8 days. No further info on "Boosted Shifts" that I have found. Because of Piatek's words "we found" I thought what we would do in our LAB if asked how fast we could release one clutch and engage the other. (Our Lab was totally unrelated to cars, we developed welding shielding gas mixtures and filler materials for the very profitable, largest US Industrial Gas Company. We had a blank check on what we worked on as the company had ~60% of the North American Argon production and controlled the price! At the time over half used for welding.)
If we were asked to define how fast we could disengage the 1st gear clutch and how quickly we could engage 2nd, we'd keep decreasing times to a point of having both engaged until something broke. Then see what it was and could we beef it up!
So just how does it happen and only in Boost Shift (Launch Control?) Allow the gear shaft tortional displacement under max loads to deal with having both engaged for a few milliseconds??? 
Last edited by JerryU; Mar 3, 2023 at 06:49 PM.
