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      07-30-2013, 04:07 PM   #1
BMWZ4RIDER
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Turbo Lag- Scared myself

09-35i, 7 Speed DCT
Car was in Normal Mode and full automatic.
I have known since I initially investigated the Z4 and definitely since owing it for 10 months, that there was severe Turbo Lag with the intital throttle response, but I just scared myself to near death today.
I was at a stop sign and based upon the performance of the Z had what I felt was a reasonable distance to cross 2 way traffic, with the car to my left much closer. I made the move, hit the throttle and what seemed like seconds passed, as the car beared down on me, before the Z kicked forward with speed. I made it across without incident BUT "did I ever scare myself beyond what the human heart can bear". This issue, I feel, is fully related to the Turbo lag in throttle response. The situation was a close, but not too close at the time I initially hit the gas to the time the car reacted.
Who has experienced this and agree's that the Turbo lag/throttle response is an issue, at Least in Normal mode with full automatic.
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      07-30-2013, 04:42 PM   #2
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I drive my 35is almost exclusively in Comfort/Auto and, while there are times that I can't believe how fast it gets off the line, there are others when I wonder if my foot somehow missed the gas pedal altogether.
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      07-30-2013, 05:09 PM   #3
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When I had the DCT I would always drive it in manual , partly because of what you're describing. Any BMW is going to drive like a completely different car when you drive your automatic on manual mode. But of course now I drive a 6MT but that's another story.
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      07-30-2013, 05:09 PM   #4
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It's not the turbo lag. Sure there is some but what you experienced is BMWs attempt to soften the throttle for normal driving (people that are crap at throttle control). Hence why the car is more responsive in sport mode because BMW expect people will know it will take off quicker.

If I am driving and I want to set off quickly I hit the paddle to take it into M1 and use the DCT manually or indeed switch to sport mode and get the car to do the work.

Normal mode is very soft on throttle response.
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      07-30-2013, 05:20 PM   #5
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I think that the computer should adjust itself to respond faster because this only happened to me when I first got my car. Now there is no lag in throttle response at all (I usu drive in Normal/automatic in the city).
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      07-30-2013, 05:28 PM   #6
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My throttle became less linear after the a Cobb ECU tune, meaning the turbo kick in can be felt a lot more noticeable, as well as the lag/bog effect. I have had the car respond in a lazy manner in lower revs before like you described, but I drive a manual, so it's a bit different. If I need to move quickly, I will keep the rev range in powerband, just so I have enough boost through the turbos should I decide to fuck the road in an instant. Have I not done that, and just drove normally in "normal mode" without downshifting, the turbos will need a moment to build boost, the harder you press that throttle the more you'd notice the lag.
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      07-30-2013, 05:29 PM   #7
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It has happened to me twice... and like yours, damn near caused an accident.

I believe that the warmth of the car / how aggressively it has been driven directly prior to any given point in time has a lot to do with it.

The only times that I've ever seen it have been on a cold engine a couple hundred yards from my house when entering roundabouts or crossing intersections. Each time the car had only been on for a minute or so, driven through very residential streets (i.e. no real speeds / rpms to speak of).
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      07-30-2013, 06:44 PM   #8
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Don't we have adaptive throttle response? If one drives like a bat out of hell then the car's throttle should behave differently even in Normal mode. I had a sluggish throttle and had the dealer perform a reset which helped a bit.
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      07-30-2013, 08:02 PM   #9
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I have not experienced this. No issue here. Excessive wheel spin in 1st and 2nd Is an issue.
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      07-30-2013, 08:19 PM   #10
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In four years, I have never experienced any turbo lag.
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      07-30-2013, 08:34 PM   #11
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Quote:
Originally Posted by army_men View Post
I have enough boost through the turbos should I decide to fuck the road in an instant.
Just what exactly are you doing with your car? LOL
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      07-30-2013, 09:10 PM   #12
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It has become a habit for me to put it into sport everytime I start the car.
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      07-30-2013, 09:13 PM   #13
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Many replies are on mark with the car response. The car was just minutes into the drive from a stone cold start. No question driving in manual in sport/plus has aggressive throttle response over automatic and normal mode. That will teach me to not drive this Z hard. I won't make this mistake again.
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      07-30-2013, 10:59 PM   #14
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Code it to drive in Sport all the time.
I dislike normal, especially with a stick shift.
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      07-31-2013, 02:10 AM   #15
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Quote:
Originally Posted by army_men View Post
My throttle became less linear after the a Cobb ECU tune,
You can use the "linear throttle" (LT) throttle response map if you don't like that behavior

OP I think this is pretty reasonable if you are driving below the "boost threshold" (minimum engine RPM needed to build boost), such as when the engine is around idle.

Another thing to consider is that there is a momentary delay from when you press the throttle to when the DCT clutch engages when the car is stopped.

Glad you are ok, and agreed it takes a bit of getting used to, but I think there are legitimate technical reasons why the car behaves the way it does and it isn't a flaw.

As an aside, I think this is delay between throttle and clutch engagement and lack of "creep" forward are the reasons why dual clutch gear boxes are having a very hard time replacing torque converter automatics for mainstream cars like Dodge Dart or Ford Focus
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      07-31-2013, 02:36 AM   #16
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Quote:
Originally Posted by BMWZ4RIDER View Post
Many replies are on mark with the car response. The car was just minutes into the drive from a stone cold start. No question driving in manual in sport/plus has aggressive throttle response over automatic and normal mode. ...
Yeah I think this "turbo lag" issue you're describing is actually a result of the setting DCT is in as mentioned.

My 6spd has plenty of punch from a stop - when it's kept in 1st the whole time. Of course one of the advantages of the 6spd (or sport setting with a DCT) is being able to keep the car higher up in the hp curve whenever you want... or a higher RPM for more boost. The 35i has a pretty flat torque curve but it starts just below 2kRPM, not from dead idle.
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      07-31-2013, 03:19 AM   #17
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I agree with what Nicknaz said, if the problem was that the car wasn't moving after you pressed the throttle it is not simply turbo-lag. The engine produces plenty of torque to move the car even without the turbos spooled up. I think I have experienced something similar when pulling out from my compound in normal mode and with a cold engine.

The clutch-engagement delay can also be felt when going from D into R and back. Some of this is eliminated with tunes such as ESS, but our DCT will never match a torque converter in these matters.

The unlinear throttle response that army_men mentioned also might be because there is simply more boost, so we can better feel when the turbos kick in.

That being said, when I switch back and forth between ESS and OEM I realize that the OEM responsiveness is tuned for more comfort. And it makes sense, because not everyone driving this car is wearing racing shoes, and not everyone would appreciate that the engine responded just because the car passed a bump and ones foot vibrated a little. So the car is easier to drive smoothly with OEM settings, especially in stop and go traffic. But there are times that it also makes the car more dangerous to drive, because it simply does not react to throttle inputs instantly. That is, if you are used to ESS and go back...

As others have said, try the sport or manual modes next time. There is a reason we have different modes to choose from. And since we didn't always have these options in our cars, we need to learn to use them at the right times. Like flipping the gear lever from D into S just before an over-take. It only takes a split second if you remember it, and makes a world of difference.
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      07-31-2013, 03:22 AM   #18
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I think you're right there . There's a reason there are modes. We can't expect the car to know what we want every time without making some input to the scenario (modes). IMHO manual mode is where the best control is at.
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      07-31-2013, 05:28 AM   #19
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I agree with what has been said.

With DCT in comfort mode, everytime I need to do a quick move on the road (insertion, start after a STOP sign, overtake, etc), I flip the gear lever to the left (D to S mode).
I have made the "mistake" few times to push hard the pedal to overtake and the result was not what I expected: You push the pedal and then wait for 2 seconds to get the power you need (DCT is shifting down twice or more).
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      07-31-2013, 09:54 AM   #20
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Everyone must be too young or just not "blessed" to have experienced the turbo lag of the Chrysler cars of the 80's. Once you experience the throttle delay and the extreme torque steer from those cars, you will never complain about what we are now working with
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      07-31-2013, 12:16 PM   #21
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Quote:
Originally Posted by Asbjorn View Post
The unlinear throttle response that army_men mentioned also might be because there is simply more boost, so we can better feel when the turbos kick in.
I believe army_men was posting about his Cobb tune...

In the Accessport logs there is "accelerator pedal position" and "throttle opening".

My understanding it the "stock throttle" (ST) Cobb maps and the factory map the "throttle opening" is not proportionate/linear to the "accelerator pedal position" (i.e. the change in throttle opening is much larger than the change in accelerator pedal position, to give the feeling of more responsiveness/power)

Cobb has an option for "linear throttle" (LT) maps which in my opinion makes it easier to modulate the power but the result of this is the you really have to go wide open throttle to get pushed back in the seat

As an interesting aside, I was at the 1/8 mile recently and was having a hard time getting a good reaction time because of the elapsed time from pressing the throttle and DCT clutch engaging.

It is an interesting tradeoff, because the DCT has very consistent (and super fast) shifting but the launch is sometimes a challenge (both on the track, and on the street as we have been posting about)

EDIT: my vote for turbo lag champ is 2.0L WRX, and answer then, as it is now, is just to maintain RPM in the 3000+ range to always be ready to accelerate
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      07-31-2013, 02:55 PM   #22
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