The story isn’t changing, we’re just arguing over semantics. Your trying to present using launch control as some gentle event that’s easy on the transmission that can be done at any time after 500 miles (I bet launch control would work just fine at 5 miles you probably just wouldn’t get a record time). I don’t know why 500 miles is any better than 1500 miles if that were the case.

You’re trying to claim a “launch” and full throttle start are the same thing with the same impact to the drivetrain (not clearly defined in the manual). When I “launch” a conventional automatic, I hold the gas and brake, then drop the brake and work the throttle for the sole purpose of beating some lap time (described in the manual as a “competitive event”). You can do this with or without launch control.
Wide open start is just squeezing the throttle like you’re coming up an entrance ramp without spinning up the engine first. Huge difference to the powertrain as nothing is “dumped” into anything else. No spinning wheels, no slipping clutches, just acceleration but I’m not trying to beat my best time.

The manual describes launch control as a competitive event that you don’t do on public roads which they claim should be done after 1500 miles. In other threads we’ve argued the semantics “competitive” but it seems pretty straight forward to me.

 

To prevent wheel spin people attempt to get the tires sticky and dump everything they have at it to get the best times but if the wheels don’t spin all that load has to go somewhere and looks for the weakest link. My coworker broke his transfer case on his Subaru because his AWD was “so good at holding traction”.

Drag racing in general is hard on cars. People act like it’s easier on the car than running a road course but I’ve seen so many cars go sideways and hit the wall, break driveshafts, blown motors and transmissions, etc.

 

You just continue to prove you don't understand. Now that you've written War and Peace version of not understanding, tell me the difference for the drivetrain in a 2.7 with or a 2.7 without LC. BTW, a WOT START is not rolling along up a ramp. While rolling along is NOT a START. This would be a good place for you to say "you're right Phil, I'm wrong".

You need to stop spinning yarns too, where did I imply "Your trying to present using launch control as some gentle event that’s easy on the transmission"????? I didn't say that at all. What I said was, and I stick to, is GM clearly states no WOT starts until 500 miles. At 500 miles I can do a WOT start that yields the exact same load on the drivetrain as LC starts because I have done the same 0-60 times either way.

 

There is a reason that there is an ignore button and that it has been used on that particular poster.

 

whoever you are.

 

No Phil, it’s you making this too complicated. Squeezing the gas peddle to get up the entrance ramp at full throttle is easier on the transmission than launching the car. What you did to get 2.7 was launching your C8 you just didn’t use launch control.

 

Can you listen to yourself????? YOU said rolling up a ramp and THEN standing on it was a WOT START, and it's NOT. I asked you to tell me the difference to the drivetrain in a 2.7 to 60 with LC and a 2.7 to 60 without using LC.

 

Ok. Where are you getting the definition of a WOT start?

I told you. Launching the car with or without launch control is detrimental to the drivetrain. That’s why cars blow transmissions at the drag strip.

 

OMG, you are spiraling out of control. OK, read this slowly, a START is a take off from a stand still. WOT means wide open throttle or full throttle. GM says you shouldn't do that until 500 miles, which means you CAN after 500 miles. If you can equal a time to 60 with or without LC, there is no difference to the drivetrain as far as stress is concerned.

 

I’m not spiraling out of control Phil.
Bear with me as I’m trying to figure out where you’re getting hung up.

Do you agree starting from idle and squeezing the throttle to floor with no concern for your 60 foot time is a WOT start, not launching the car and gentler on the drivetrain?
I’ll use my “setting the anvil on the table” analogy.

Do you agree that launching a car with or without launch control is imparting the same stress on the drivetrain? I’ll use my “dropping the anvil on the table” analogy.

I sure do. I watched cars blow up at the drag strip long before launch control came out. In fact the first time I heard of launch control was on the Nissan GTR. Then people were blowing transmissions with it and they refused to cover it under warranty saying “it’s for getting out of the mud”. They eventually dropped the feature, then added it back later and it was a big controversy with that crowd.
https://jalopnik.com/gt-r-owner-bust...cl-5061221/amp

Launch control is just an aid. It helps you get consistent good 0-60 times. You managed to match it with your own skill so good for you, but you did impart the same stress on the drivetrain to do it.

 

And FINALLY you have seen the light that it is OK to use LC after 500 miles. You yourself said it's the same drivetrain stress and GM says it's OK after 500 miles to do full throttle starts.

 

I was so close….
Ok so, you got the “launching with or without launch control is the same stress” Great.

But it looks like you missed the full throttle start does not equal launch control.

 

OMG, how does it not? If the times are identical, I CAN ASSURE YOU, I am not slowly rolling into it. If you perceive even the slightest wheel spin the times go into 3+ seconds. For everyone's sanity, I am officially done trying to get you to understand. I am right and you're wrong and I'm good with that. No matter what you reply with, I will not post again on this thread to you.

 

I know you’re not slowly rolling into it. That’s what I’ve been telling you. You’re launching the car without launch control. That’s the “competitive event” that the manual says to do after 1500 miles.
That is not the same as a WOT start that the manual says you can do at 500 miles. This isn’t that difficult.

 

From an engineering / calculus standpoint, this is a related rates problem.
You can arrive at the end result (2.7s) two different paths, one path with a very high delta in the torque impulse, and the other with less, so long as you can make up for it somehow.

Anyway, I would think that if you were sitting still, and engine idling (DCT clutch 99% engaged), and then you went WOT (100% throttle position), this would produce LESS torque impulse than launch control would. The reason is that the LT2 doesn't produce near as much HP and torque until it gets into the higher RPM range.
Launch control gets the RPM up to the 3K mark so you are already getting towards that power band region.

However, does releasing the brake under launch control cause the DCT clutch to be "partially" released to limit torque, but since the engine is already above 3k RPM it is better able to stay in the power band? It can just manage the clutch to avoid wheel spin?
Does going WOT from a standstill and idle RPM also do the same clutch manipulation, or does it pretty much dump the clutch once you are saying GO! ? (I think it dumps it if you are in burnout mode or if you have traction control and PTM engaged right?)

Since you are going WOT from a low RPM, even if it did dump the clutch, the torque impulse / delta might not be much different than managing the clutch from 3k RPM. Hence, it's a related rates problem and you still arrive at 2.7s, but one method may have a higher torque load. or they may vary in the amount of abuse the clutch pack absorbs.

I think it might be a little more complex a comparison than people may realize, and without knowing exactly the algorithms that GM and TREMEC incorporated into the TCM, I wouldn't be prepared to speak authoritatively on the topic.
My understanding is that the TCM actually drives the car and tells the engine what to do.

 

I don’t know if launch control controls clutch slip. A much less destructive way to manage wheel slip would be to back off on the throttle. If clutches and wheels are slipping then there’s too much torque going to the drivetrain.

 

Also controls the timing, direct fuel injection, and throttle body position, so maybe other ways besides slipping the clutch.

I think it would be interesting to test this out on a Dyno...
Test 1: Launch control, step on the brake, floor it, release brake, graph the torque curve.
Test 2: Light press on the brake, no throttle, release brake, WOT.

Now compare the torque and RWHP that was produced over time. Which one creates the biggest change in torque in a delta?.

I would be willing to bet the graphs are not the same. I don't think I have ever seen someone dyno like either of these test scenarios though.
Usually the engine speed is brought up gradually first. I think the issue is tire hop and wheel spin, etc. Those tests might not be easy to accomplish.

 

If only someone like, oh, maybe GM, actually tuned their launch control to work with the engine performing a variety of tests to get the best results before shipping the product to consumers.

 

How do you know that you have the throttle 100% engaged? Isn't it computer controlled?

 

Obviously GM / TREMEC did this testing before. If you would be so kind, please post the results that are known to the public from other sources.

It's a drive by wire car. Best you can do is tell it 100% throttle (or launch) and the TCM will take that info and tell the engine what it needs to do.

It would be interesting to see the difference on a dyno.