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991 turbo - turbo lag

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Old 11-29-2015, 08:52 AM
  #31  
FBA
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All that is true, but it you're not standing on it most of the time, the engine longevity shouldn't be compromised.

The added power really only kicks in when you're in it for somewhat more than part throttle.

If you're tracking the car, that's a whole different story though...
Old 11-29-2015, 09:52 AM
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turbo8765
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Originally Posted by ipse dixit
The 991 TT/TTS is about as turbo lag free as you will find. Perhaps the 991.2 Carrera will be better, but we won't know for sure until March 2016.

Honestly, most modern turbo setups are so advanced that to complain of turbo lag you're either Walter Röhrl, and just showing off, or you're one of those super creatures that can hear facial hair grow.


A 3.8 making 20# of boost with turbos sized to make 650hp or more is going to have lag. Technologies such as VTG help, but there simply isn't sufficient engine exhaust energy to fully spool the turbos at low revs. Look at a graph of boost vs RPM, it's unavoidable.

In general, increasing engine displacement and decreasing peak boost pressure will decrease lag (increased energy in exhaust gas flow vs decreased energy required to fully spool the turbos).

The only way to SIGNIFICANTLY alter lag with a 3.8tt making 500-600hp is to use electric motors i.e. Maclaren style "torque fill".
Old 11-29-2015, 11:30 AM
  #33  
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Originally Posted by kkabba
The most pronounced turbo lag I feel is when I accelerate off the line from a dead stop. Is it simply a split second or less of lag? Perhaps, but I still feel it and I don't like it. And no, I don't go around drag racing at lights or anything but I'm just trying to see if there's a solution to 2 annoyances I have with what easily is the best city driving car I've ever owned 😀
If you want to experience the quick takeoff, use launch control, it is very easy to use, otherwise even in sport you don't get that great acceleration from a dead stop unless you hold the brake and run up the RPMs which is similar to launch control but which only works in sport plus. As to the better sound, either decat or get some high flow cats like the 200 cell HJS or one of the really good 100 cell solutions out there. AWE probably has them. If you do that you can put anyone's stage 2 tune on your car and there are a lot to choose from.
Old 11-29-2015, 04:50 PM
  #34  
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Originally Posted by FBA
All that is true, but it you're not standing on it most of the time, the engine longevity shouldn't be compromised.

The added power really only kicks in when you're in it for somewhat more than part throttle.

If you're tracking the car, that's a whole different story though...
Agree here. The car is just so fast as it is - to be able to run the engine at high loads for any length of time that would even create problems is virtually impossible during street driving, even fast country runs for that matter. Track would produce the worse case type scenarios in terms of sustained high loads which could bring about increased engine wear as in that environment gears tend to be held for longer,and often using full power for longer. Other thing is most of us don't hold our cars long enough anyway so even if anything was wearing out too soon from the AM tune it will become the next owners issue. I think it comes down to how you drive and where you use your car as well. I recall my 997tt ownership where I would run that car with the stock tune file at the track mainly to preserve the engine knowing the stock file had more than enough power for that environment. It was mainly during street use that I found real benefits of the AM tune as the engine was more torquey at lower rpm. With the the TTS i find it more than torquey enough stock.. Problem is finding a place where you can stretch the engine out in the first 3 gears without getting busted.

Last edited by speed21; 11-29-2015 at 08:29 PM.
Old 11-29-2015, 06:03 PM
  #35  
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Originally Posted by kkabba
I drove a 991S (PDK if it matters) for 3 days straight a few months ago on backroads and on track so I am familial the 991 NA engine. Off the line, although slower than the TT in acceleration, it seemed to have a more gradual and predictive increase in torque along the curve. And perhaps, as pointed out by some on this post, I am either imagining things or am going out of my way to say that I can pick up incredible subtle levels of turbo lag. But in the event that I am not imagining things or making things up, and someone else experienced the "lag" and have found something that helped with this deficiency, any input would be helpful and most appreciated
Right, that's what I mean. The torque curve of the TT is a steep climb to ~2K rpm and then a plateau (approximately), while the curve of the NA is a more gradual curve that gets steeper around 4K rpm. So it might feel like "lag" in either case (albeit different). When you step on the gas at, say, 4K rpm on the TT, if you feel a lag and then a hit of torque (kind of like a downshift that isn't a downshift), that's turbo lag; if you are talking about how things build from 0rpm when floored, that's the torque curve. I don't feel any turbo lag but I may not be as sensitive as you.
Old 11-30-2015, 08:21 PM
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I am very sensitive to turbo lag. The 991 TTS has noticeable turbo lag (I've driven several, and every one I've driven has displayed this trait); strictly my opinion and no offense intended to anyone. It's the only car I've ever driven that has actually made me appreciate non-linear acceleration. I still can't stand Turbos in any other cars, but the TTS is just a damn special car and for whatever reason, it doesn't bother me in the least that I feel turbo lag every time I step on it between 2500 and 3k, for about .7 seconds.
Old 11-30-2015, 09:45 PM
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You can't change the laws of physics. Turbo only engines will always suffer from turbo lag. Blowers do a much better job when it comes to FI, but are nowhere near as efficient. N/A cars are nowhere near as efficient either; hence, turbocharging.

The 991 is a beast, and although has some lag, is still very tolerable - to me.

My FGT was upgraded to a Whipple 4.5 liter blower, making over 1000 HP, but still can't take my 991 TTS off the line...or even at 80....

It has no lag, develops instant thundering power from the get go that can cause the tires to literally light up, but can't put it down to the ground. It gets 2-3 MPG under WOT and it's one of the coolest cars around...but my TTS will destroy it from a standing start, turbo lag and all.

I'll just have to "suffer" through the turbo lag I guess. LOL
Old 11-30-2015, 10:17 PM
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It's the most lag-less turbo charged car I've driven period.... which makes me a very happy sufferer too.
Old 11-30-2015, 10:58 PM
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Originally Posted by turbo8765
A 3.8 making 20# of boost with turbos sized to make 650hp or more is going to have lag. Technologies such as VTG help, but there simply isn't sufficient engine exhaust energy to fully spool the turbos at low revs. Look at a graph of boost vs RPM, it's unavoidable.

In general, increasing engine displacement and decreasing peak boost pressure will decrease lag (increased energy in exhaust gas flow vs decreased energy required to fully spool the turbos).

The only way to SIGNIFICANTLY alter lag with a 3.8tt making 500-600hp is to use electric motors i.e. Maclaren style "torque fill".
That's not really a fair point of comparison.

By that account, one could (or should?) also use an electric motor to torque fill a NA engine b/c anything short of instantaneous torque (through an electric drive train) would have lag.
Old 12-01-2015, 12:54 AM
  #40  
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Agree. Everything could be said as having some form of lag, depending upon gear and throttle command. This new car is as good as it gets...until Porsche brings us something even better...and even "less lag-ier" (if that is a fair or applicable comment).....like say the .2tts from what I'm reading today. I mean how much better can it possibly get now!

No doubt I will be standing corrected after I drive it...
Old 12-01-2015, 07:05 AM
  #41  
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Originally Posted by turbo8765
A 3.8 making 20# of boost with turbos sized to make 650hp or more is going to have lag. Technologies such as VTG help, but there simply isn't sufficient engine exhaust energy to fully spool the turbos at low revs. Look at a graph of boost vs RPM, it's unavoidable.

In general, increasing engine displacement and decreasing peak boost pressure will decrease lag (increased energy in exhaust gas flow vs decreased energy required to fully spool the turbos).

The only way to SIGNIFICANTLY alter lag with a 3.8tt making 500-600hp is to use electric motors i.e. Maclaren style "torque fill".
You can on some cars, add a supercharger to get to a blown, turbo-charged car. You get the best of both worlds that way...pretty much "negative" lag, a ton of TQ down low and up top! FGT is a perfect example. Comes with a factory blower, forged internals, and then just add a twin turbo kit. A cool 1200 RWHP instantly...on pump gas with a very mild tune.
Old 12-03-2015, 04:38 PM
  #42  
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Originally Posted by ipse dixit
That's not really a fair point of comparison.

By that account, one could (or should?) also use an electric motor to torque fill a NA engine b/c anything short of instantaneous torque (through an electric drive train) would have lag.
It's neither fair nor not fair. It's factual.

Turbo lag is the delay form throttle application until full boost. In general, the smaller the engine and the greater the peak boost the greater the lag.

A car that does not make boost, by definition, cannot have turbo lag.

I am not an advocate of torque fill via electric motors in any application. I'd rather deal with turbo lag than the weight and complexity of batteries and electric motors.



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