TB993tt

This is the point, not sure how we got onto contemplating a turbo engine having characteristics of a N/A engine such that Walter doesn't need the extra 2 feet tolerance.
The 991.2 Turbo S has for a turbo engine zero lag, they've nailed it but it still isn't the same as prodding the throttle on a big torque N/A engine, never will be but "turbo lag" is not in the vocabulary of a big torque N/A engine.

If the new 2RS has lower CR and bigger blowers then it must have more lag but still it won't be much (if the ttS is the benchmark) and I don't think new owners will find it an issue.

Bardman

Fwiw EVO note the following differences over the turbo s motor:

"The extra power is produced from bigger, higher output turbochargers, a reshaped carbonfibre air inlet, an improved filter and free-flowing exhaust. Further power gains have been garnered thanks to a water spray system that dowses the intercooler with water to help reduce the temperature of the charge air."

http://www.evo.co.uk/porsche/911/192...che-911-gt2-rs

randr

Pete,

At the end of the day isn't that the point.

Particularly given the fact modern designs couple higher static compression ratios with systems that allow boost to be maintained during deceleration into, and importantly, through a corner.

Basically you don't have to have full boost to have the benefits of a "high compression" NA engine. Thats in part, how the circle has been squared.



The above data is from a single sighting lap (not full pace) the X-axis represents lateral g and the Y-axis represents boost in PSI (991.2S - static CR 10:1)).

The purpose of which is to show boost variability relative to corner position (max negative or positive lateral G).

You can see from this that the effective compression ratio ranges from ~ 13.4 to just beyond 21 (calculated from measured boost e.g. ~ 5 to ~ 16 PSI) e.g. at all times, in the above test, the engine response in this particular vehicle is well ahead of most NA engines at all times. For reference the minimum speed was 82kmh and maximum around 210kmh (gears 3 and 4, min rpm 3632, max rpm 7446).

As you correctly pointed out the move to higher static compression ratios makes a significant difference . The result is, you have great engine and throttle response at all times (at least on track even when one isn't going ***** out).

In many respects, the ability to hold boost is probably more important than the ability to create boost . I'm sure the GT2RS will have this type of technology in order to maintain boost and thus capability

Jean

Pete,

What you are describing in terms of handling difficulty for the 991 turbo is simply a result of high torque, not lag. You have on tap 700NM of torque from 2,500RPM (who exits a turn at lower RPMS?), and that's 0.8G of acceleration in 2nd gear, not much left in a R compound tire for lateral grip.

I use the 991TT as a DD, autocross, hillclimb and time attack very competitively, and I have done the same with every 911 turbo and GT iteration for the past 20 years including the GT2RS, I can vouch that there is no such thing as lag in these new VTG engines in normal load and usage conditions, meaning not off/on throttle from 1500 RPMs in 5th gear.

Petevb

Yep. Just realize that for the way some use the car, including me (sometimes), there's still a big difference.
Sorry Jean, it really isn't. I'm very familiar with high torque in both forms. My friend's supercharged (positive displacement) Viper will pull similar numbers to what you're describing. Another friend lets me play on the autocross with his modified, competition prepped GT2. My own competition prepped early car (normally aspirated GT3 Cup motor) has a better than 5:1 pound per hp power to weight ratio, and while it won't do jack at 2500 it puts enough torque to the ground to rip your face off at normal corner exit speeds. There is a huge functional difference between what I can do with these cars on the throttle. The normally aspirated cars take a far more delicate right foot, because if you snap rather than role in you're guaranteed to upset the car. Of course sometimes you want to upset the car, or balance it to play with a line, etc, and those options simply don't exist to the same extent in the turbo. It sounds like you have lots of experience in turbos, but do you have similar closed corse seat time in equal power and torque to weight non-turbo cars for comparison?

Lets face it- if lag wasn't still a functional issue why would WRC have gone to such extreem lengths to eliminate it with ever more sophisticated anti-lag systems?

hf1

Just wanted to support Pete again on this. It may be a very small minority that understands what he is talking about but he is far from being alone.

randr

I think you'll find that many understand what is being said but can equally point out a reality - look at the graph above and think about it.

Think what it means in terms of compression ratio. This is real data generated from a car with a current generation engine.

I can equally generate a different type of graph that will show some lag e.g. at low RPM - the question is, is it relevant given in the real world case I presented above you are already beyond the compression ratio of a NA engine as found in the Italia and indeed new GT3.

It is important to understand this

hf1

Your graph and argument show that you don't understand. It's as if we're talking two completely different languages. Your meaning and understanding of 'response' is completely different from Pete's.

Petevb

randr, I'm sure you can come up with a graph to convince yourself of anything. But ask yourself- every form of top Motorsports that uses turbos currently uses anti-lag technology not found on street cars (assuming it isn't banned as it is in super GT, etc). WRC, F1, LMP1, etc.

Why would they bother (or bother banning them) if there was no advantage?

randr

Nope, compression generates torque, torque generates power (in conjunction with rpm). If your effective compression ratio is "high" the engine response to relatively small or variable fuel inputs (throttle) is large due to high amounts of torque generated due to the compression ratio and.......on it goes as the revs increase...

actual measurements ------>data------>graph------>fact

hf1

Except with a turbo it's all over the place and with varying lags for small throttle adjustments at varying rpms. 1/10sec lags (and not even consistently so) mean feet of distance while positioning a car driven by throttle at limits of grip. For a 700HP car it probably means more -- the difference between making the turn and crashing. Granted, not many of us here would ever throttle-dance a 700hp car on sticky tires mid-turn, but IF they did they would definitely know the difference.

Personally, I would far prefer to 'throttle-dance' a 190hp car at its grip limit mid-turn than point-and-shoot a 700hp turbo well below its grip limit, but that's me -- I understand that many others prefer the latter and for them the turbo-lag will be just fine, if noticeable at all.

randr

Pete, I completely understand what you're saying - I'm just a mere mortal, I'm not Walter Rohrl - the examples you are giving are at the extremes of motorsport - in the WRC a whole event (multi leg - multi stage), conducted over a full week can come down to a few seconds. A F1 GP can come down to a few hundredths of a second - to the vast majority of people its lost on them as a real exercise (and given that both WRC and F1 use turbo charged cars its somewhat moot - more so in regard to the WRC).

So, in a well meaning way - I'll throw it back to you . I'm pretty sure you know exactly how to read the graph above and you know exactly what it means.

In these newer generation engines, when you have a small amount of boost, you have the compression and torque to move around on throttle at will. If I miss an apex by a foot is going to worry me, no (and I say this a someone who has and still does give it a pretty good go - on the clock).

I am comfortable enough with my position that I happily moved my deposit from a .2GT3 RS to a McLaren 720S. Peace.

Jean

Pete yes I own a 996RSR and decent seat time in several other street and race N/A Porsche cars.

WRC cars have to use 33 mm restrictors and have large sized Garrett turbo for high end power in extreme conditions and controlled temperatures. The restrictors make an already laggy turbo even 'laggier" hence the use of Anti-lag during off throttle. There is no doubt that anti-lag systems give you full boost "now", but turbo sizes are different and without them the cars would behave the same as the 1980s Renault 5 turbo 2 that threw me off a cliff when boost showed up at 4,500RPMs.


Would love to drive that car
Pete, the peak longitudinal force exerted to the tire on a car like yours with the Cup engine torque, is around 0.55G in second gear. The turbos long G forces are 30% more in general terms, so the threshold of total tire grip between longitudinal and lateral acceleration is very easily reached, causing loss of traction, but not the boost onset or lag, you are at full boost and torque already as you exit the corner.

No to extend anymore on this topic of N/A vs Turbo, I do acknowledge your broad experience, and that throttle response is different and faster in N/A cars, but the facts are that the new gen turbos are lag free from a driver/user perspective. The new GT2RS might have larger turbos than the 991.2TTS, and that could mean more lag but I really doubt it will be felt on the race track or going through the gears at full throttle.

Petevb

And I fully understand that choice- sacrificing a little throttle response you don't really notice for more torque and power that you know you will makes sense in your case.

I largely divorce the turbo vs NA debate from the cars themselves. In isolation, do street turbos still have lag? Yes. Enough to matter? Depends on the driver and the usage. Is that lag the most important factor when deciding on a car? For nearly everyone probably not- I'm one of the normally aspirated zelots and I've owned seven Turbo cars over the last two decades, so clearly in many cases not for me... But in other cases for cars with different uses lag's still enough to tip the scale, which is part of the reason I've owned the same number of normally aspirated cars in the same time period.

Will I rise to the bait when someone says "my xx has zero lag"? Yep. I'm an engineer, one of my many faults.

Kobalt

I don't know much but like this thread.