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Pete, did you drive the new Turbo S ? I could barely discern any lag in this latest engine/PDK set up, even the transition from off boost to on boost is amazing just a very linear curve with no real step up..... The RS I'm sure will be different with its CR and bigger turbos but I suspect it will be relatively lagless if the latest ttS is anything to go by.
Yes, the new Turbo S. I a) autocross and b) like to steer with the back end, both of which magnify any lag. If you're never attempting o control the cornering attitude it becomes far less noticeable, but if you are... A post I wrote a couple years ago on the new TS specifically:
Its interesting to note the 488GTB runs a static ratio of 9.4:1
It's correct that both the static compression ratio and the amount of boost run on top of it directly impact response time. Interestingly Ferrari brags about the 488 GTB as follows: "only .8 second response time to the accelerator at 2000 rpm in 3rd gear". More in higher gears, less at higher rpm of course, but it's that variability which effects most precision- if it was always the same your muscle memory is very good at adapting and anticipating.
To improve response manufactures build Turbo engines with more normally aspirated power. This both spools the turbos faster and allows them to run less boost, and a ratio of boosted vs non-boosted effective compression is a good indicator of response. If lower is "better" or not depends on your goals, but it does split the difference between the response of a normally aspirated engine and the torque hit traditionally associated with boost.
I know that lag between pressing the throttle and the car building boost can be an issue however I image you can learn to drive with this (open throttle a bit earlier) just like you have to adapt to different clutches. It would be hard to be used to driving an NA car and just jump in a turbo car and expect to be just as efficient. You would need time to learn the car. It's a different way to drive both have plus and minus just like mid-engine/rear engine, FWD/AWD, manual/pdk.
I can't get over that fact that the 2RS has more torque at 1600rpm than the 3RS has at it's peak.
I can't get over that fact that the 2RS has more torque at 1600rpm than the 3RS has at it's peak.[/QUOTE]
This is exactly what makes the car and creates the difference from the GT3 RS.
I am really disappointed by my GT3 RS lack of torque at anything below 5000 in any gear, coming from a stable of turbos.
On the track it does not make a big difference, but on the road is frustrating, at least for me.
This is the reason why I want the 2RS: turbo torque in a sort-of light body!
I can't get over that fact that the 2RS has more torque at 1600rpm than the 3RS has at it's peak.
So does a Carrera S (and a base Carrera has nearly as much as the 4.0L GT3/RS). It's a bit misleading though, since the GT3 has such better gearing (allowed by the 9k redline) that the torque multiplication through the gearbox delivers much more torque to the road than the flywheel comparison would suggest. Of course with the GT3, choosing the optimal gear is way more important to get some thrust...
like to steer with the back end, both of which magnify any lag.
^this, which is why I will never buy a turbo sports (back-roads, track, race) car, much less pay $300k for one. I'll take a base Boxster with sport suspension at 1/10 the price instead, thx. Point-and-shoot is boring and gets old fast for me, regardless of how strong the push is.
Turbos in my bmw 5-series appliance? All day, every day, and twice on Sundays.
I know that lag between pressing the throttle and the car building boost can be an issue however I image you can learn to drive with this (open throttle a bit earlier) just like you have to adapt to different clutches. It would be hard to be used to driving an NA car and just jump in a turbo car and expect to be just as efficient. You would need time to learn the car.
Unfortunately it's not that simple, both because of the variability of the lag and because of the delay simply reduces options.
Walter Rohrl was winning world rally championships during the early turbo days, and it was interesting chatting with him about that time. He'd apply full throttle over two seconds before he wanted the power, so it was all about anticipation and making allowances.
Today with even turbo responses in the fractions of a second it's a completely different game, but it's still about anticipation. A car that breaks loose at the rear can yaw a lot in the human reaction time of ~.2 seconds. The key is not reacting, but rather staying ahead of it by knowing what the car's going to do. Done correctly you're dialing in counter-steer as the car begins moving, but to do this you want to know exactly how far and fast it's going to go. As you can see from the link above even Walter Rohrl can't do that, and I'd go so far as to call it impossible to do perfectly with current street turbos. My current turbo car has 9.4:1 compression, and I've done 70k miles with traction control off in one with 10.4:1- both the street and competition. I enjoyed every mile, but I can safely say there is no way to fully anticipate exactly how the car was going to react every time when on throttle. And that's actually part of the widowmaker charm...
I must confess that I loved challenge of the previous GT2. When it was on great tires and in the dry, anyway... If I ever picked up a GT2 RS I would get it precisely because it's turbo and challenging to drive. Given the lack of a stick I doubt that will ever happen, but IMHO the turbo significantly adds to the level of difficulty if you're driving on the edge, and at the end of the day there's something powerfully attractive and compelling about scary cars.
Just buy a Turbo S, throw a tune and a wing on it and magic- you will still have s car that will catapult you to all speeds and more car than one can manage
This whole GT2RS fixation I find hysterical. The car is over priced and Porsche must be laughing in the board room as they are stuffing their sox with money
Well, I'll say you would not want the gt2rs rear aero without the front aero. The turbo has a bit more weight in front due to awd, but that doesn't go up quadratic with speed.
I also suggest that the RWD car will feel quite a bit different.
I know that lag between pressing the throttle and the car building boost can be an issue however I image you can learn to drive with this (open throttle a bit earlier) just like you have to adapt to different clutches. It would be hard to be used to driving an NA car and just jump in a turbo car and expect to be just as efficient. You would need time to learn the car. It's a different way to drive both have plus and minus just like mid-engine/rear engine, FWD/AWD, manual/pdk.
I can't get over that fact that the 2RS has more torque at 1600rpm than the 3RS has at it's peak.
The lag is a bit more complicated, since it has several sources, and all the hacks against turbo lag only address one source:
You need pressure on the exhaust side of the turbo, which needs two components:
rpm (takes time to get to rpm)
a delay from having enough rpm to actual overpressure. Air is not a fluid, it is compressable. That means you will need more air in the pipes to the turbo. (a supercharged car doesn't have this delay)
overcoming the inertia of the turbo - 2 wheels and the shaft
building up pressure on the to-intake side of the turbo. Again, the fact that air is compressible means a delay here. If you used a fluid you wouldn't have the lag component
Torque and horsepower curves are the same. The torque curve expresses some low-rpm power buildup, however that is pretty meaningless if you are driving a car with short enough gears at always high rpm.
Lag could be addressed via electric turbo; VAG already has experience with the Audi SQ7. I suspect Porsche decided against due to added weight of hardware and 48V system required to power, especially as they aren't using regenerative braking. Wouldn't be surprised to see it in the future as hybrid creeps into the 911 platform.
I just hope they've programmed the power delivery to be somewhat linear unlike most turbo motors.
I certainly wouldn't suggest that it is easy to manage a turbo car's track performance but things have come a long way since since the 80's turbos. Not just the turbos but transmissions and general engine performance management. I think the Can-Am racing days with crazy horsepower turbo cars is just as historically relevant as more modern high rev'ing GT3 engines or 2L flat 6's.
I find it interesting that many people want the linear, even, predicable power application of an NA motor but hate those benefits you get with a pdk. It's hard not to love the sound of a 9000 rpm engine but its also hard not to love a huge torque build up/shove. Different people get excited about different things.
I think two of the biggest things that make cars exciting are sound and power/torque. That is my issue with the new 718's. Not a great sound and not great power/torque.
Only thing I hate about it is the Porsche allocation BS. I want the car but if they won't sell me one there are lots of other options.
With the GT2 they've said there is no limit to the amount they make, 918 owners get their allocation first but anyone else that wants one can put their name down.
I am not so sure about the increased "lag" or boost threshold of the new 991GT2 RS. We still haven't had the chance to check dyno curves for this engine or in-gear acceleration performance from 80-120/160 in 5th or 6th gear.. Is it an assumption or a fact that it has larger turbos than the Gen 2 Turbo S 580bhp?
Simplistically I would think that they have the same 991.2TT larger turbos and intercoolers (maybe IC with slightly increased size) from a production and R&D cost perspective, which can well take you into 720hp.
As we know, the Gen 1 68mm cold side only modified VTG go to 670-680 within reasonable compressor efficiency levels and 720hp with high octane fuel and stock intercoolers (Techart). For Porsche standards hp levels at the track, 700hp + water spray on the intercoolers would ensure temps are in check with 991.2 VTG turbos and IC, no need for large size.
Regardless, the days of lag are long gone.. If we consider the best measure of turbo response to be acceleration tests in 5th and 6th gears, here is the data:
80-120kph acceleration 5th gear (~1900 RPM-2800RPM) (ref same Autobild test for the 991TT)
991.1 Turbo S (560hp): 3.7 s
991.2 Turbo S (580hp): 3.5 s with larger VTGs
997GT2RS: 4.5s
991GT3: 5.5s (~2700RPM-4000RPM)
80-120kph acceleration 6th gear (~1600 RPM-2400RPM)
991.1 Turbo S (560hp) : 4.8 s
991.2 Turbo S (580hp) : 4.7 s with larger VTGs
997GT2RS: 6.5s
991GT3: 6.9s (~2300RPM-3500RPM)
Despite the much slower performance for the 997 GT2RS vs. 991TT, the lag on my 997 GT2RS is somewhat noticeable, but almost inexistent on the track (high RPMs consistently), and my 991 turbo (non S) has "zero" lag from a driver butt feel perspective.
I don't expect the new GT2RS to have any perceptible lag, and certainly not on the track.
Regardless, the days of lag are long gone.. If we consider the best measure of turbo response to be acceleration tests in 5th and 6th gears
Yea, that's not a measure of turbo response at all, instead it's a measure of area under the curve through that RPM band. Ferrari's definition of "response time to the accelerator" is the correct one: the delay between fully depressing the accelerator pedal and receiving full boost (.8 seconds at 2k rpm in 3rd gear for the 488, pretty good for a boosted engine).
I'll quote my previous post from another thread. As good as their new engines are you're not going to hear anyone (not in marketing) from Porsche or Ferrari tell you the days of lag are over I'm afraid, though I fully understand that the way many use their cars they may well see zero functional difference.
Originally Posted by Petevb
I was blessed to go out to Sweden last week with Porsche for a little ice driving. Walter Röhrl was there giving rides in his 991 Turbo S down a tight but flowing single track snow rally course. He's an absolute master, everything they claim and more. Perhaps predictably the question of Turbo vs NA came up while we were driving in a way I thought was relevant to this thread.
First the drive itself: Walter was miles ahead of the course and car. The steering wheel was relatively quiet- much of the time it was entirely still as he casually balanced it with one hand, relatively little input and few large corrections required. Most of the steering was done with the throttle.
The car was preset far before the corner, and he was clearly thinking 3 corners ahead. He'd use left foot brake and throttle to initiate a slide 50 meters or more before the corner, put it into a mild drift, control the line with the throttle, then smoothly link that drift to the next one in a way that was almost slow motion and never jerky or violent. The car never actually hooked up.
There was never any understeer- he said that if he didn't provoke the drift before the corner then every 5th corner the car might get understeer. By setting the car into a four wheel drift before the corner he insured oversteer which he could control as opposed to understeer he could not, and from there he simply managed how much.
He said he clearly prefers normally aspirated for this application. The turbo's lack of throttle precision makes the car harder to place, because when he goes for the throttle he's never sure how much drift he'll get. I asked him how much less accurately he could place the car due to this- six inches, or 1 foot?
"I would say...." Walter thought for a moment, pregnant pause as he considered an answer before turning to face me fully, still at speed: "Two Feet". Awesome moment:
Given that we were drifting edge to edge as it was, that two feet would have meant we'd be kissing the snowbanks on every single corner. It already seemed close to perfection to me, no sense of drama or chasing the car and needing to catch it. Velvet smooth.
When we talk about turbo "lag" or throttle delay with the upcoming turbo cars it's at this level. If you're using the throttle to initiate and dial a drift then the lag or lower response from the newest generation of turbos is still an issue. For the way most of us drive 99.9% of the time, however, it's completely transparent and nearly irrelevant other than feel. Many newer turbo owners will tell you with a straight face that their cars "have no lag". And they fully believe this, because it's subtle enough that they won't notice as they use the car.
Even Walter says that his 991 Turbo S is awesome and his first choice on the street, comfortable with easy passing grunt and poise that makes it a weapon in the real world. However at the limit, in some conditions, something is lost. That day it was two feet. Exactly.
One last thought. It's been said before, but I can confirm: Walter Röhrl is unequivocally the man.
07-10-2017, 10:59 AM
