Porsche 718 Forum banner
1 - 20 of 34 Posts

·
Registered
Joined
·
1,709 Posts
Discussion Starter · #1 ·
What is the fastest way to launch a PDK-equipped 718 if there is no specified Launch Control or sport package other than the usual Sport Mode? In the old days car testers just held the brake, mashed the accelerator, then released the brake. (I'm sure the tranny loved it.) What would a "smart" car like a 718 w/PDK do? Simply not rev the engine? Rev just a little? Do it anyway? Or to phrase the question another way, what does Launch Control do for you that manipulating the pedals yourself doesn't do?

I'm just curious. I have few opportunities to even think about it. I wouldn't drive like that, now would I?
 

·
Super Moderator
Joined
·
2,100 Posts
I have read (I think it was here somewhere) that the proper launch procedure (without LC) is:
Hold the brake hard.
Floor the throttle.
When the revs rise let the brake go and hang on.
LC does basically this but (at least) manages the rpm to the ideal.

I tried it as the revs passed 4000 and it worked well. I did assume it would be hard on the clutch but not fatal. It's not something I'm likely to do more that once or twice more. (Car is now 2.5 years old.) Try a search for more specifics.

Car & Driver must have done something like this on their Boxster test. They turned off the traction control and got a 0-60 time of 4.0 seconds. I left the controls on--I've seen too many videos of cars going 90° off course and crashing to want to risk that.
 

·
Registered
Joined
·
113 Posts
What is the fastest way to launch a PDK-equipped 718 if there is no specified Launch Control or sport package other than the usual Sport Mode? In the old days car testers just held the brake, mashed the accelerator, then released the brake. (I'm sure the tranny loved it.) What would a "smart" car like a 718 w/PDK do? Simply not rev the engine? Rev just a little? Do it anyway? Or to phrase the question another way, what does Launch Control do for you that manipulating the pedals yourself doesn't do?

I'm just curious. I have few opportunities to even think about it. I wouldn't drive like that, now would I?
I asked about launch control on 718 PDK “non-sports chrono” vehicles (ie cars that only have normal and sport mode) when I did the Atlanta Delivery Experience.

The Delivery Specialist told me that all the 718 PDK cars are designed to launch. We did launches with the Experience Center vehicle in all 3 modes (normal, sport, & sport plus).

The difference is that sports chrono cars (when in sport plus mode) will hold the RPM at a higher value when the vehicle is launched. There’s a difference of about 500-1,000 rpm between each mode. I believe this is one of the reasons Porsche publishes faster 0-60 mph times for sports chrono equipped vehicles.

Also, the “launch control” text will not show up on the gauge cluster unless you have the sports chrono package.

I suspect this this could be a bit of a marketing/promotional decision to encourage customers to pay extra for sports chrono. My assumption is that the text is triggered to illuminate when the ECU recognizes that the RPMs are held constant and the boost pressure is fully built up.

You follow the same procedure when you launch in any of the 3 modes. Per the Experience Center, they are as follows:
  • Put the car in the desired mode (normal, sport, or sport plus)
  • Turn off traction control
  • Firmly hold down the brake pedal with your left foot
  • While holding down the brake, push and hold the gas pedal to the floor with your right foot
  • Look at the tachometer and make sure it is holding at a constant value
  • Check that the turbo boost pressure has built up
  • Release the brake (and hold on tight o_O)
 

·
Registered
Joined
·
538 Posts
The Delivery Specialist told me that all the 718 PDK cars are designed to launch.
This makes perfect sense. It would be cost-prohibitive to build cars with different transmission components for SC and non-SC, while different software for the CUs is a piece of cake.
 

·
Registered
Joined
·
1,709 Posts
Discussion Starter · #7 ·
I have read (I think it was here somewhere) that the proper launch procedure (without LC) is:
...
I tried it as the revs passed 4000 and it worked well. I did assume it would be hard on the clutch but not fatal.
Thanks. That's exactly what I would have expected. I imagine it isn't any harder on the clutch(es) than launching with L.C. It does seem like something you wouldn't want, let alone need, to do very often! (What's need got to do with it? you ask.;))
I asked about launch control on 718 PDK “non-sports chrono” vehicles (ie cars that only have normal and sport mode) when I did the Atlanta Delivery Experience.

The Delivery Specialist told me that all the 718 PDK cars are designed to launch...

The difference is that sports chrono cars (when in sport plus mode) will hold the RPM at a higher value when the vehicle is launched.
...
  • Put the car in the desired mode (normal, sport, or sport plus)
  • Turn off traction control
  • Firmly hold down the brake pedal with your left foot
  • While holding down the brake, push and hold the gas pedal to the floor with your right foot
  • Look at the tachometer and make sure it is holding at a constant value
  • Check that the turbo boost pressure has built up
  • Release the brake (and hold on tight o_O)
Thanks. That seem an authoritative answer. It is what I expected, that a non-Sport Chrono car would work the same way but some engine-control software elements would behave differently resulting is slightly quicker starts with L.C. than without. The Launch Control graphic in the display may be nothing more than the car letting you know when it was at max power.

Of course it is quite possible that the programming without L.C. could be quite different. For example without L.C. it could have cut back the power considerably to protect the PDK instead of just optimizing the power the way L.C. does. It could have limited the engine to, say, 2000rpm when the brake is on.

Those steps for launching seem to be to obtain the absolute quickest launch. If you didn't do all those things? I'm guessing that if you didn't wait for stable max rpms or full boost pressure you'd just get a slightly slower start. I wonder what effect traction control has. If it's on it probably detects wheel spin and cuts back the power, which may or may not result in a slower start (but saves the tires). Whether it makes the car more stable or more likely to launch sideways, I wouldn't guess.

Some day when I find a wide open, empty, deserted square mile of smooth asphalt I may experiment. I'll hold my breath looking, but, um, not today.
 

·
Registered
Joined
·
36 Posts
Maybe the cars are built well enough for it, but LC isn’t something I would ever do in a car I care about.

My friend used to show off LC in his M5. Now his transmission is shot and the car is essentially not worth fixing.
 

·
Registered
Joined
·
2,229 Posts
Road & Track launched a 911 Turbo 50 consecutive times with (apparently) no ill effects. I wouldn't do such a stunt, but Porsches are pretty good at rough handling. That is my main reason for choosing the CPO route. You can't over-rev the Cayman with a PDK, so it is kind of hard to damage. I know that the previous owner could have been doing launches at 2 mi on the clock, but somehow, the guy spent a fortune to PPF the car... I don't think he would be the type...

The 50 launches of Porsche video:

 

·
Registered
Joined
·
238 Posts
I'm still having issues trying to get away quickly at the lights. Maybe it's because I'm now used to Tesla's but it feelings like there's something missing compared to my previous cars.
It's a car with PDK but without LC. I don't see myself using LC anyway in traffic.

When I try to launch, the first second always feels sluggish and hesitant.
What's the best way to get away quickly at the lights without putting it under weird stresses like described above? (holding brakes and applying throttle)
 

·
Registered
718 Boxster S
Joined
·
67 Posts
This is coming from someone with limited mechanical knowledge, so please excuse me if I am asking a stupid question.
The 718 turbo torque peak is approx 1900-4500rpm. Power peak approx 6500rpm.
If you follow the launch control guide, it says rev to 6000rpm and release the brake.
At 6000rpm, the engine is close to the power peak, but not the torque peak - although it is still more than adequate
I thought acceleration was more related to torque than power?
Perhaps the launch control is optimized for the NA engines whose torque peak is between approx. 4500-6500rpm? (or 5000-7000rpm, I don't know the exact figures)
 

·
Registered
Joined
·
1,709 Posts
Discussion Starter · #13 ·
...Maybe it's because I'm now used to Tesla's but it feelings like there's something missing compared to my previous cars.
It's a car with PDK but without LC. I don't see myself using LC anyway in traffic.

When I try to launch, the first second always feels sluggish and hesitant.
...
I thought acceleration was more related to torque than power?
These two questions are related so I'm responding to both. (Two for the price of one!)

Erik, you will never feel in your 718 the same thing you feel in a Tesla for several reasons. First, electric motors have peak torque at zero rpm, so off-the-line acceleration is much easier to obtain. But the real answer is in the question Todd asked.

Torque at the road wheels does indeed produce (most of) the car's acceleration for any given gear, but with a lower gear you can get any torque and hence any acceleration you want. A lower gear comes at the expense of speed so a high-power engine can accelerate better at higher speed than a low-power engine because the high-power engine lets you get the same torque in a higher gear. Also the inertial load of the flywheel and all the gearbox internals upstream of the active reduction gears will be higher in a lower gear. That load is not insignificant so the need to use a lower gear costs you something even from a standstill when speed is not an issue.

However that isn't the only contributor to off-the-line acceleration. With a manual gearbox you typically rev the engine then drop the clutch. (Some people do it more smoothly than others.) That initial rev'ing creates angular momentum in the engine, mostly in the flywheel. The act of engaging the clutch transfers that extra momentum from the engine to the car above what the pure engine torque is producing. That's why some people prefer the extra-kick feel of the MT. The engine's torque curve isn't substantially different between a MT and a PDK (well, it is tuned a bit differently) but that isn't what people feel. Once the clutch is fully engaged to where disk and pressure plate are spinning at the same speed, there is no more momentum to transfer and the "extra" boost is all used up.

That extra momentum at startup can make the car a bit faster off the line. A PDK doesn't pre-rev the engine in normal use so you feel the build-up of torque in the engine's natural torque vs. rpm curve. Launch Control is essentially the same as dropping the MT's clutch after you've built up momentum in the engine. Whether the MT is faster to any given point down the road or to any given speed depends on how much in advance of releasing the clutch the driver can start rev'ing the engine and thus how much angular momentum it has. If you started both a MT and a PDK from idle at the same time, the PDK car would start moving sooner until the MT engine was rev'ed up for clutch drop. The MT's later start would be followed by a bigger punch. Which is faster? Physics says the PDK but in real life at a stoplight a MT driver is maybe more likely to anticipate the exact split-second launch time than is a PDK driver using Launch Control. Personally, I can't see using LC on any public street! Anyway, they are exactly the same, only different. They will always feel different.
 
  • Like
Reactions: Treemagnet

·
Registered
Joined
·
238 Posts
Of course I know I can't compare an electric car with the 718.
You can't match those launches. They are freakishly fun. Just floor it and look at the other cars disappear in your rearview mirror :ROFLMAO:

My previous ICE car had a naturally aspirated inline-6 and it launched quicker off the line.
I guess not having control of the clutch to pre-rev and the turbo adds up to the feeling that I'm missing something off the line.

What do you do to launch quickly without LC? Just floor it and let the traction control sort things out?
It feel like it's impossible to control the loss of traction with your right foot once the turbo kicks in.

I'm going to get a Cobb tune when the 718 comes out of winter storage. Would the PDK tune add anything off the line?
 

·
Super Moderator
Joined
·
2,100 Posts
I have found (base Boxster PDK 2017, no performance extras) that the best way off the line, for up to 60 mph anyway, is to NOT floor the pedal immediately but start off with somewhere around ½ throttle and then once it's moving give it the rest. This way the 'hesitation' at take-off is nil. A bit of experimenting should show you how to get the best.

One of my frequent fun drives has me cross a two lane highway from a stop sign a couple of times . When I need the quick take-off and use this method I occasionally get wheel spin.
 

·
Registered
2021 Boxster
Joined
·
1,108 Posts
I think Bumblebee would go on strike if I tried to launch her. It's so dang responsive without any tricks. And I'm not even broken in yet. Obviously "launch control" was adapeted by the auto industry to fill a particular need. I'm assuming it's mostly for drag strip operation?
 

·
Registered
2017 Cayman S
Joined
·
17 Posts
Launch control is great…on someone else’s car! It is one of the reasons I still go to the Atlanta PEC after getting my 718 S. In my brain, I could not abuse my baby without remorse that would spoil the fun. I did consider getting a Mustang GT for stop light drags but my wife held a mirror in front of my 65 year old face.
 

·
Registered
Joined
·
238 Posts
Honestly, after you've gone electric, nothing can come close.
So I might as well accept that and enjoy it. I'll try playing around with throttle positions when I get to drive her again in the spring.
 

·
Premium Member
Joined
·
636 Posts
This is coming from someone with limited mechanical knowledge, so please excuse me if I am asking a stupid question.
The 718 turbo torque peak is approx 1900-4500rpm. Power peak approx 6500rpm.
If you follow the launch control guide, it says rev to 6000rpm and release the brake.
At 6000rpm, the engine is close to the power peak, but not the torque peak - although it is still more than adequate
I thought acceleration was more related to torque than power?
Perhaps the launch control is optimized for the NA engines whose torque peak is between approx. 4500-6500rpm? (or 5000-7000rpm, I don't know the exact figures)
To me this is more of a physics question than a mechanical one. Peak acceleration is going to be at max power. Because our transmissions have discrete ratios, we have to shift such that we keep the engine running around peak HP. If we had a perfect CVT, we'd just keep it right at max HP. So in practice, since we don't have perfect CVTs, this is why we shift past the peak HP number a lot of times, because right after that shift we'll be right below the peak HP. So we're basically staying in that neighborhood, and bracketing the peak HP mark such that our average rpm is at peak HP.

From a standing still it's a little more efficient to start a bit below that peak HP depending on surface, tires, so on. That's because you have moving thing meeting stationary thing.

But think about it this way, if you were at 30kmh and wanted to accelerate 150kmh, you would definitely not shift gears to keep your engine near its peak torque, right? You would intuitively do that run keeping the engine around it's peak HP. Because that's the fastest way. If you were to short-shift to find extra torque from the engine, you would be losing way more by giving up mechanical advantage in the gearing too quickly during the run.
 

·
Premium Member
Joined
·
636 Posts
Honestly, after you've gone electric, nothing can come close.
So I might as well accept that and enjoy it. I'll try playing around with throttle positions when I get to drive her again in the spring.
I don't know that I completely agree with that. I have an Apple Watch, but I still enjoy my mechanical watches also. So every single weekend I "go back" to those. but to your point, as a DD, the Apple Watch wins.

Purely as a motor, electric motors are far superior in every objective sense to ICE. No doubt about that. And I'm sure I will be buying many electric cars in the future because of this. The one caveat, though, is that the battery adds a lot of weight right now. So my long term ICE cars will be a small collection of light ICE cars, because honestly the only real advantage of any ICE-based car today is weight. So Miata, mid-engine Ferraris, Porsches under ~1,500kg is where I am buying.

And for weekend/recreational use, I appreciate the mechanical nostalgia and art of a mechanical watch or a great sports car motor.

Otherwise in other uses electric makes way more sense for me, and I'm quite sure my next luxury car will definitely be electric. I don't understand ICE-based luxury cars anymore. I believe they are obsolete now, unless you happen to be one of the people who use it as substitute for planes in going from city to city over large distances. I use planes for that.
 
1 - 20 of 34 Posts
Top