ohlang

Can anyone provide reasons why you shouldn't launch the S550 with automatic transmission? If it hurts the transmission and or other components of the car, can you explain why or if you hold the opposite opinion, can you explain why you think that?

I've never launched my car because I've always read that it harms the car with very vague explanations. I've read with GTR's, designed with launch control, that if you use it, it voids the warranty, is this myth? I know most of Chevy's and Dodge's high performance cars/SUV's today all come equipped with launch control in their automatics which give them an advantage when drag racing, but is it safe to do it even when the manufacturer says you can? In a lot of the supercharged/turbo charged S550 videos doing 8's & 9's with automatic transmissions, you can hear the engine rev'ing before the car launches so you know they're launching their cars.

I'd love to get better times in my 0-60 and 1/4 runs, but not at the expense of my car if it's undeniably harmful.

Joeywhat

"Safe" is a vague term. Every hard launch reduces the life of the effected components. Torque converter, transmission, rear end, rear suspension, etc. How much depends entirely on the specific circumstances and how well made the parts are. Any defects in the parts will reduce life even quicker (of course they could break easily under normal use as well, but more so when pushed hard).

You've gotta pay to play, and going faster means more wear on the car. Only you can decide just how much is acceptable. Tougher drivetrain parts will help, and not using slicks and launching at lower RPMs will also help longevity. Nothing will guarantee the parts will last forever, and even taking it super easy can result in broken parts.

5.M0NSTER

Launching an auto is as straight forward and as "safe" as it gets. Sure, there is always risk of braking parts, but unless you're brake standing and revving out high before you let the brake pedal go I wouldn't expect more than a slim % chance of breaking something on street tires with stock engine/trans cals. These cars are built to take the abuse. Nice thing about American Muscle.

If you have a tune, and your shift points have been firmed up, that means your drivetrain is shifting faster, which is good for acceleration and causes less slippage, which is also good. The price you pay is in how harsh the shift feels.

Now for the engine tune, if you have an aftermarket tune depending on how they set the cals your engine may be mimicking a power shift, or "no lift upshift". Meaning engine may not be reducing the torque (in some cases even increasing it still) while the tranny is shifting. This definitely causes more wear and increases chances of breaking components. If this is something you're worried about, or you think your tq converter or gear teeth are at risk you could contact the tuner and ask about the behavior of torque output while shifting (it could depend on % throttle apply for example).

Also the S550 stock rear end is prone to breaking half shafts while launching hard with slicks.

Just a few things to keep in mind

ohlang

Are you making a distinction between these two? The launch I have in mind is what I'm imaging you mean by brake standing, hard breaking while rev'ing to 3000rpm for example and releasing the brakes while flooring it. This is what I'm wanting to do in my car but fear damaging it more than normal wear and tear. Why is it bad on the transmission if it is? What specific material wear does it cause? Gear teeth? other things? Or is the wear of metal parts (& what parts) caused by heat and friction? I'm sure many people do this in their rear wheel drive cars even if the manual doesn't expressly say you can, but it does in the Chevy manuals for the Corvette, new Camaro, and I'm sure Dodge Challenger & SRT Jeeps. Am I at more risk of breaking something in mine than in these cars?

The manual S550 has launch control and I don't believe there are any warnings to avoid excessive usage, but nothing for the A6.

5.M0NSTER

I see what you mean. I wasn't sure if Autos has launch control. But yeah, your launch and my brake stand are the same thing.

The number 1 thing I'd worry about is the stall/tq converter, and the stator and impeller/turbine blades. Since unlike a clutch the tq converter never really disconnects from the engine, it has to absorb all the power the engine is making. This can lead to fluid overheating, high fluid pressures, and damage to the bearings, blades, or stator.

Here is a good video which helps illustrate the operation better. Immagine one side spinning fast with high engine RPM, and the other side static since you're standing on the brakes. Once you get into TQ multiplication the stator has to work extra hard to overcome tire friction, and brake friction of the rear brakes. This can lead to a lot of extra heat and high fluid forces on the blades and stator.


Good news is there are aftermarket tq converters specifically for drag racing. Some go as high as 4000 or 5000 rpm.

5.M0NSTER

Oh, and to answer your other question Ford, GM or Chrysler Autos all have the same limitation, and similar performance.

If you plan on doing this at high RPM on regular basis the convertor will eventually fail. But you can look into a racing type.

Also, once the rear wheels start spinning the stresses are then applied to tranny gears, and the rear diff as well. But the converter is first in line.

5.M0NSTER

And the more I think about it the more sense it makes that Auto doesn't have launch control. Since there is no way for the converter to disconnect, it would be taking a beating if it was allowed to rotate as the rear wheels are stationary.

In a manual car the clutch is disconnected, so the gears, the dif and the clutch are sitting idly by as the engine revs. Then the clutch takes the brunt of the abuse when the driver releases the clutch pedal.

5.M0NSTER

So I'm thinking the TQ converter would also be an issue for burn out mode.

Can any auto owners confirm or bust my theory that Autos don't have burn out mode?

Joeywhat

I'm sure they do. Doing a brakestand a few times doesn't hurt anything, especially at short intervals. Heat kills torque converters, and some slipping is OK and won't heat things up too much.

It should also be noted that higher stall racing converters aren't just better made to stand up to racing use, they have a considerable effect on how the transmission operates. Not to be installed unless the user is OK with said changes as they are not always street friendly.

5.M0NSTER

Well, if it is, that just speaks to the robustness of TQ converters, and intended use. Ford wouldn't allow a feature which knowingly reduces component life under the 3/36 barrier.

So this may be a better answer OP. If Ford allows burnout mode on Autos, your brake stands are also OK. At least for the first 3 years or so.

EDIT: It is also possible that Ford has some intelligence in the TQ converted to lock the clutch when burn out mode is entered (like GM's electronic Limited slip differential on the corvettes and camaros). In that case the TQ converted would lock the clutch when the car enters burnout mode which would alleviate the concerns above. This I do not know, just speculation on my side.

Joeywhat

Remember, doing a brake stand doesn't do anything different to the converter than being at a stoplight in drive. Just faster.

5.M0NSTER

As long as the rear wheels aren't spinning, then technically yes. But at the same time the stock tq converter is designed to be in stall mode at less than a 1000rpm. So above that it tries to enters tq multiplication mode and sends more tq to the wheels. Now you need more brake pressure to keep the vehicle still, fluid temp goes up, fluid pressure goes up and seals, bearings, blades etc take more abuse.

OPs question was what components can fail during a brake stand and why. Hope thi info above is helpful.

ohlang

Thanks for all the info. I've seen other videos now that speak to the increased fluid temp. From what I'm reading from your posts, the torque converter takes the brunt of the abuse. Is it the case that if there is component failure, it's limited to the torque converter or are we talking about components outside the TC also. The seals, bearings, blades I take are inside the TC housing? Is it "easily" repaired by replacing the TC?

Joeywhat

Replacing the converter is not terribly difficult.

The entire drivetrain takes abuse when you launch. The includes the diff, axles, driveshaft and gearbox. Again, how much depends on how you launch. Just taking off from a stop induces wear, the more aggressive you are the more aggressive the wear.

5.M0NSTER

Yes, the components I was talking about are all in the housing of the TC. I think that would be where highest stress is, but Joey also has a good point. Once the TC is in torque multiplication mode it passes good part of the engine's energy into the trans gears, driveshaft and dif gears. Where exactly the first failure will occur is not too clear. If there are any imperfections in the teeth of the dif or the trans it's possible that would go first too.

Joeywhat

In regards to the transmission, the real killer is the heat. It's what will cause failures the most. If you don't heat up the fluid (and the gearbox) then you really won't have many problems. The converter is intended to allow a difference in rotation between the engine and transmission. Too great a difference means lots of heat. An oil cooler can help, so can better fluid.

Just realize that once the fluid gets good and hot it's pretty much toast and it's not doing anything good for your transmission. I imagine if you swapped fluids immediately after doing a lengthy brake stand you really wouldn't see a ton of damage to the gearbox.