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The comparisons I did above we using actual dyno numbers. Raw data (all from Sport Auto’s Supertest dynos):
Would it be possible for you to do the earlier .2gt3 acceleration/speed chart against the old 4.0? it's giving up 500rpm as well but it's got a bit more torque and 19" tyres so might balance out a tad.
Location: The way to hell is paved by good intentions “Wenn ich Purist höre...entsichere ich meinen Browning” "Myths are fuel for marketing (and nowadays for flippers too,,,)" time to time is not sufficient to be a saint, you must be also an Hero
The comparisons I did above we using actual dyno numbers. Raw data (all from Sport Auto’s Supertest dynos):
is indeed watered down, i wonder where are the +20/30HP from hydraulic valvetrain and steering removal, 13.3 compression ratio, less friction, direct injection
and the other 10HP from better ram air at high speed
the 7RS 12.6 to .2GT3 13.3 compression with the same 4.0 l capacity alone means more power
as soon as i get my own I 'll
change air filters at first and the ecu later to get it where I think is (530HP)
is indeed watered down, i wonder where are the +20/30HP from hydraulic valvetrain and steering removal, 13.3 compression ratio, less friction, direct injection
and the other 10HP from better ram air at high speed
The motors are sitting on an engine dyno, so no chance to measure the ram air achieved at 320kph
I've got a feeling Cobb will show us the way soon...
I suspect Porsche will. My bet is that the biggest gains will come from a cam swap, possibly combined with an intake, etc. If I were them I’d shoot for 535 hp from 4.0 liters in the new RS. 133.8 hp per liter would beat Ferrari’s 132.7 hp/liter in the 458 Speciale to take the production car normally aspirated record. Possibly for all time...
Facinating. What is the inference from the lumps in the torque curve of the 991.2 GT3?
I believe the lack of low end torque vs the 997 is largely intentional, and that accounts for the jump at ~5k. The smaller lumps are simply par for the course.
The 997 used a more complex 2 flap resonant intake design that was better suited to create low end torque. That said, those that have stroked the 3.6 or 3.8 to 4 liters plus know that it’s very hard to get mid-range torque as low as in the 997 RS 4.0. It naturally wants to be a good 40 ft/lbs higher, the downside being that it’s impossible to maintain at that level so torque then falls towards redline. That’s a very unnatural (and in my eyes unwelcome) feeling in a 911, so Porsche used massive intake runners and some cam tricks to bring mid-range torque down in the 997 RS 4.0 and leave the torque plateau flat.
In the 991.1 GT3 and RS they dropped back to a less complex single flap resonant intake which also limits low end torque. In the 991.2 they’ve added the second flap back, broadening the powerband slightly and also improving low rpm throttle response. However it’s my belief (backed up by little sold evidence) that they continue to intentionally cut low end torque because they are chasing a particular feel. The “oh, you thought you were going fast” surge at 5k rpm is dramatic and addicting behind the wheel, and plenty of tuners have proven they can easly dial in more low end torque with headers. What’s more likely- that they know something Porsche doesn’t, or that Porsche wants it that way? We already know they’re limiting the engine, remember...
Would it be possible for you to do the earlier .2gt3 acceleration/speed chart against the old 4.0? it's giving up 500rpm as well but it's got a bit more torque and 19" tyres so might balance out a tad.
Here. Given the lighter weight of the 997 I thought it would do better, but the extra rpm at peak power still give the 991.2 a clear advantage. That said I'd prefer the 997's lower gearing.
BTW I forgot to correctly account for the extra drop gear in the previous R vs GT3 Touring results. It changes the absolute acceleration numbers but not the relative answer, I'll go back and fix it...
Why does the 3.8 litre 991.1 have so much more low end torque than the 4.0 litre 991.1 and virtually as much midrange?
This is from Sport Auto's data, so I don't know for sure. For the low end perhaps they didn't go to full throttle early enough, or more likely Porsche got conservative after the 991.1 GTS and limited torque below 3k rpm in engine software (you can see the 991.2 is clipped as well, though less so). You really shouldn't be flooring it below that in any case, the resulting cylinder pressures stress the engine.
As for the mid-range torque it's quite possible Sport Auto got a relatively weak example, though Porsche only advertises +15 ft lbs so we shouldn't expect huge gains.
For comparison, Porsche's own published curves do look different, with less of an advantage for the 991.2:
Here. Given the lighter weight of the 997 I thought it would do better, but the extra rpm at peak power still give the 991.2 a clear advantage. That said I'd prefer the 997's lower gearing.
BTW I forgot to correctly account for the extra drop gear in the previous R vs GT3 Touring results. It changes the absolute acceleration numbers but not the relative answer, I'll go back and fix it...
Ah ok that's why the .2 has different g numbers vs the earlier one with the R.
much appreciated for the graph, really interesting to see those. cheers.
This is from Sport Auto's data, so I don't know for sure. For the low end perhaps they didn't go to full throttle early enough, or more likely Porsche got conservative after the 991.1 GTS and limited torque below 3k rpm in engine software (you can see the 991.2 is clipped as well, though less so). You really shouldn't be flooring it below that in any case, the resulting cylinder pressures stress the engine.
As for the mid-range torque it's quite possible Sport Auto got a relatively weak example, though Porsche only advertises +15 ft lbs so we shouldn't expect huge gains.
For comparison, Porsche's own published curves do look different, with less of an advantage for the 991.2:
To clarify, for anyone who got confused like me:
Top graph: 991.2 GT3 is black torque curve and red power curve; 991.1 GT3 RS is blue torque curve and black power curve.
Bottom graph: 991.1 GT3.
As well as the low rev differences between Porsche and Sport Auto and the two 991 4 litres being much closer in the Porsche graphs, there are other differences such as Porsche showing the 991.1 GT3 kicking up at 4,000 and Sport Auto at (in the 4 car overlay) at 5,000 and Porsche showing the 991.2 GT3 having a smooth peak of 500 hp rather than the potentially higher peak capped at 500 hp by Sport Auto. The plot thickens.
Last edited by turbofreeFLAT6; 12-27-2017 at 02:23 AM.
To clarify, for anyone who got confused like me:
Top graph: 991.2 GT3 is black torque curve and red power curve; 991.1 GT3 RS is blue torque curve and black power curve.
Bottom graph: 991.1 GT3.
As well as the low rev differences between Porsche and Sport Auto and the two 991 4 litres being much closer in the Porsche graphs, there are other differences such as Porsche showing the 991.1 GT3 kicking up at 4,000 and Sport Auto at (in the 4 car overlay) at 5,000 and Porsche showing the 991.2 GT3 having a smooth peak of 500 hp rather than the potentially higher peak capped at 500 hp by Sport Auto. The plot thickens.
Yep. I've learned not to trust Porsche's own graphs too much over the years, especially where torque is concerned. They tend to show what they want you too see, and often leave out both major lumps and dips in the torque curve.
I suspect Porsche will. My bet is that the biggest gains will come from a cam swap, possibly combined with an intake, etc. If I were them I’d shoot for 535 hp from 4.0 liters in the new RS. 133.8 hp per liter would beat Ferrari’s 132.7 hp/liter in the 458 Speciale to take the production car normally aspirated record. Possibly for all time...
The Speciale HP ratings are overrated. Only the journalist cars put out that much power. Most of the owner's Speciale's and 458's put out less.
Real life data:
R is slightly faster than GT3RS, and as fast as Speciale (in a straight line). 997 4.0 is fastest of all, but not by much. .2GT3 is very similar to RS and R.
if anyone is choosing or ranking their roadcars, based on the slight differences in Bhp and the torque curve, they are making a big mistake.
SWap any of their engines around, and they'll still be just as different, or similar, in the way they drive as they were before.
Real life data:
R is slightly faster than GT3RS, and as fast as Speciale (in a straight line). 997 4.0 is fastest of all, but not by much. .2GT3 is very similar to RS and R.
Interesting. For reference, Auto & Motor Sport clocked them as follows between 100 and 200 kph:
997 RS 4.0: 8.1 seconds
991.1 RS (pdk): 8.0
911 R: 8.3
991.2 GT3 (pdk): 7.7
991.2 GTS: 8.3
Goes to show that at this level small variations in spec, engine tolerance, driver, engine break-in, even how much fuel is in the tank and how heavy the drivers are will trump. Buy cars on feel...
12-26-2017, 02:51 PM
