Consolidated 991RS thread
06-17-2015, 12:44 PM
#8776
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What your saying is correct. The speed is the same. However we are suggesting the RS engine does not go beyond 8600 most of the time due to a soft limiter. This may have indeed been built into the re design to increase service life of the engine even though the crank has been upgraded and we are told the rods, fasteners etc are all "military grade".
My concern is the valve train. This is not to do with fasteners/rod bolts, cranks and rods etc. This is a pure function of revolutions. New rocker fingers, lifters, springs and cams, oil channels and windage, valves and valve guides are the items of importance here and their wear will accelerate exponentially with a lift from 8600 rpm to 9000 rpm regardless of the capacity of the engine.
This is not particularly exotic tech, 9000 rpm is done at Ferrari every day, however their engines are more stressed than Porsche GT engines typically and require more maintenance over similar intervals. maybe thats what 991 GT3 owners in 4-5 years time will have to learn to accept. Higher top end engine wear.
My personal belief is we wont see PAG revisit the 9000 rpm limit with another GT engine for at least a generation and by then Im sure force induction or Hybrid/Kers tech will be knocking on the door so engine speeds beyond this may not be needed.
The 991 GT3 3.8L was an ambitious project which ended up costing PAG significantly in money and reputation. The 4.0RS engine has a more conservative performance envelop as a result. The engines are now basically identical. The crank is quoted as a key difference. Id be curious once the PET comes out what teh detail changes are. Id be curious is there any additional oil galleries or channels in the head or rockers to aid lubrication etc
My concern is the valve train. This is not to do with fasteners/rod bolts, cranks and rods etc. This is a pure function of revolutions. New rocker fingers, lifters, springs and cams, oil channels and windage, valves and valve guides are the items of importance here and their wear will accelerate exponentially with a lift from 8600 rpm to 9000 rpm regardless of the capacity of the engine.
This is not particularly exotic tech, 9000 rpm is done at Ferrari every day, however their engines are more stressed than Porsche GT engines typically and require more maintenance over similar intervals. maybe thats what 991 GT3 owners in 4-5 years time will have to learn to accept. Higher top end engine wear.
My personal belief is we wont see PAG revisit the 9000 rpm limit with another GT engine for at least a generation and by then Im sure force induction or Hybrid/Kers tech will be knocking on the door so engine speeds beyond this may not be needed.
The 991 GT3 3.8L was an ambitious project which ended up costing PAG significantly in money and reputation. The 4.0RS engine has a more conservative performance envelop as a result. The engines are now basically identical. The crank is quoted as a key difference. Id be curious once the PET comes out what teh detail changes are. Id be curious is there any additional oil galleries or channels in the head or rockers to aid lubrication etc
06-17-2015, 12:58 PM
#8777
Not to fuel the fire but I had heard they had major issues with 9k on the RS test mules from very very reliable sources back in January. They then backed down to 8800 for production. Have they backed down the motor again? And for what reasons? We might not ever know.
06-17-2015, 02:41 PM
#8778
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So, if you double the piston's mass, you double the kinetic enery.
But, if you double the piston's speed, you quadruple the kinetic energy.
http://www.physicsclassroom.com/clas...Kinetic-Energy
06-17-2015, 05:56 PM
#8779
Rennlist Member
Not to fuel the fire but I had heard they had major issues with 9k on the RS test mules from very very reliable sources back in January. They then backed down to 8800 for production. Have they backed down the motor again? And for what reasons? We might not ever know.
I knew about the 9000-8800 but I believe the story is in the 8800-8600.
I spent more time trawling the net last night. Watched around 30 videos. Can't see the tacho needle go beyond 8600 on any of them. Still looking for the one where I did see it go to 8800 in manual mode...
06-17-2015, 05:58 PM
#8780
Rennlist Member
Agreed on all points. We might get one more clean N/A motor in the 991.2 GT3/RS, and if we do I expect the same soft limiter detune in the base GT3. After that all bets are off as increasing levels of complexity are introduced into drive systems - turbos, kers, electric motors, VCR (http://www.ferdinandmagazine.com/por...ine-technology) - as Porsche seeks to balance often contradictory performance, environmental, cost, and driver engagement targets.
06-17-2015, 06:59 PM
#8782
Rennlist Member
This is why I can't ever sell my SLS Black Series, and why I also have two C63 Black Series's (well, 3 at one point). The world is never going to see another production car with a 6.2L N/A V8.
06-17-2015, 07:01 PM
#8783
the key messsage from the last Porsche annual results presentation was all about how they're the only luxury car brand to offer hybrids in 3 segments - SUV, Sedan and Sports Car (918). I think this was the most telling evidence on future direction.
Anyone want to start a Singer timeshare?
Anyone want to start a Singer timeshare?
06-17-2015, 07:06 PM
#8784
The question is why is the car shifting short. It's fairly common to limit peak RPM in 1st gear to protect the engine, and Porsche has done this before. Excepting this, however, you'd expect redline shifts in 1st and 2nd. In higher gears, however, redline shifts won't be the fastest. If you look at the published power curve you can see power dropping off steeply by 8750 rpm (the last point on the curve below). In the higher gears the RS rpm drops get so small (~900 rpm) that running to redline will result in slower acceleration. Instead they shift short and land at ~7500 rpm where power is higher.
This explains at least some of the short shifting in the highest gears, but not all. Per the published curves I'd expect the car to shift almost 100 rpm later across most of the range to get maximum acceleration. However we've seen in the past that Porsche often publishes curves that differ from reality, sometimes substantially, and we know this car is making more than 500 hp so this curve can't be correct.
I suspect when we see a wheels dyno we'll see the car is making more torque than advertised and fall off faster up top, explaining half the difference, and I expect they are protecting the engine in at least first gear explaining the rest. But that's just an educated guess...
06-17-2015, 08:09 PM
#8786
Rennlist Member
You guys are being silly. Who cares if it doesn't show but 8600 or so on the tach. An analog tach cannot keep up with the revs in real time. I would bet if you could see a digital reading the car is shifting in the 8700-8800 RPM range. It is optimized to shift at the best points without hitting the rev limit. This shift showcase differently in the lower gears because of the tacos delay.
To nitpick this over a couple of online videos is crazy.
To nitpick this over a couple of online videos is crazy.
06-17-2015, 08:35 PM
#8787
Older tachs that's correct. good modern tachs, stepper motor driven, etc, can absolutely keep up with anything the engine can do. You're comparing turning a <1 gram needle slightly vs accelerating nearing 100 reciprocating or spinning lbs. If the tach can't keep up with the engine that's an issue with the tach... but that's also clearly not what we're seeing here.
06-17-2015, 08:51 PM
#8788
Rennlist Member
Nate thanks for the intel on Bosch coil packs. Its something I've been aware of but only have 3-4 examples to hand to date. I agree the German suppliers need to pick up their QC game. For example PAG need to fire whomever makes their thermostats - they've been failing in their production cars across the range for over 2 years now!
Pete. Agreed that need looks like its closer to 8700 than 8600. Could be the angle of the lens too. A GoPro there likely sits a bit higher than a straight on line of sight. Ive run up data using mu AIM Solo DL with OBD2 on the GT3 on the track in sport auto mode. Admittedly Ive never seen "9000" bang on but the ECU data shows within 25rpm of 9000 in at least two gears depending on situation on track. Visually (and Ive watched it many times) the needle appears to be calibrated, Ive seen it just touch the 9000 mark before bouncing back on a change.
My observations were not meant to upset awaiting 991 GT3RS owners. The drop from 9000 to 8800 was something I brought to the table months ago. The dashed red marks from 8400-8800 I have been contemplating since the car was launched at Geneva. It just occurred to me after watching a couple of dozen video reviews that I wasnt seeing anyone get to the redline. Thats not a bad thing for the longevity of the valve train and I dont see it as a negative....however at this stage I believe PAG are pulling the wool over our eyes - the car headlines with 8800 rpm but appears to have a soft limiter in place below that in all the gears Ive witnessed (2/3/4) so maybe 8600 is closer to the mark. Just an observation that is all....
Pete. Agreed that need looks like its closer to 8700 than 8600. Could be the angle of the lens too. A GoPro there likely sits a bit higher than a straight on line of sight. Ive run up data using mu AIM Solo DL with OBD2 on the GT3 on the track in sport auto mode. Admittedly Ive never seen "9000" bang on but the ECU data shows within 25rpm of 9000 in at least two gears depending on situation on track. Visually (and Ive watched it many times) the needle appears to be calibrated, Ive seen it just touch the 9000 mark before bouncing back on a change.
My observations were not meant to upset awaiting 991 GT3RS owners. The drop from 9000 to 8800 was something I brought to the table months ago. The dashed red marks from 8400-8800 I have been contemplating since the car was launched at Geneva. It just occurred to me after watching a couple of dozen video reviews that I wasnt seeing anyone get to the redline. Thats not a bad thing for the longevity of the valve train and I dont see it as a negative....however at this stage I believe PAG are pulling the wool over our eyes - the car headlines with 8800 rpm but appears to have a soft limiter in place below that in all the gears Ive witnessed (2/3/4) so maybe 8600 is closer to the mark. Just an observation that is all....
