Porsche and it's 15% rule
11-16-2007, 04:07 PM
#1
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Porsche and it's 15% rule
Every time Porsche comes out with a new car, they claim 15% better this and 15% better that.
In this latest example, "Car & Driver" magazine tests the new GT2, which "...curns out 530 horsepower at 6500 RPM..." and "Despite the power hike, Porsche claims fuel consumption at full throttle is improved by 15 percent compared with the Turbo."
Now how can you save 15% fuel economy at full throttle while making 530 horsepower versus the lower horsepower 911 Turbo engine? If the compression ratio had changed, I could understand it, but it appears this GT2 engine makes power with larger turbos and a new intake manifold.
In this latest example, "Car & Driver" magazine tests the new GT2, which "...curns out 530 horsepower at 6500 RPM..." and "Despite the power hike, Porsche claims fuel consumption at full throttle is improved by 15 percent compared with the Turbo."
Now how can you save 15% fuel economy at full throttle while making 530 horsepower versus the lower horsepower 911 Turbo engine? If the compression ratio had changed, I could understand it, but it appears this GT2 engine makes power with larger turbos and a new intake manifold.
11-16-2007, 04:18 PM
#4
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11-16-2007, 04:21 PM
#5
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I get what are saying about 4 wheel drive and 2 wheel drive - that would make sense if the horsepower numbers were the same 480 HP engines as found in the Turbo. But to make more HP with larger Turbos and intake means more air and more air means more fuel.
11-16-2007, 04:22 PM
#6
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Oh, and I don't know how weight has anything to do with it at full throttle. Even if the car were 1,000 lbs heavier, it would still make the same 530 claimed HP would still consume the same amount of fuel at full throttle, wouldn't it?
11-16-2007, 04:46 PM
#7
giving you are accelerating while at full throttle (unless you are going off a cliff, floating in space, are up on blocks with your wheels being stolen, etc) you are in the case of a GT2 accelerating less mass and also with less drive train loss with 2 wheels so you will not require as much energy to do so = more full efficient
i would think it is possible given the wt and additional drive train loss that their 15% statement at WOT is correct but who is oging to test this anyways
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11-16-2007, 05:10 PM
#9
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No
giving you are accelerating while at full throttle (unless you are going off a cliff, floating in space, are up on blocks with your wheels being stolen, etc) you are in the case of a GT2 accelerating less mass and also with less drive train loss with 2 wheels so you will not require as much energy to do so = more full efficient
i would think it is possible given the wt and additional drive train loss that their 15% statement at WOT is correct but who is oging to test this anyways
giving you are accelerating while at full throttle (unless you are going off a cliff, floating in space, are up on blocks with your wheels being stolen, etc) you are in the case of a GT2 accelerating less mass and also with less drive train loss with 2 wheels so you will not require as much energy to do so = more full efficient
i would think it is possible given the wt and additional drive train loss that their 15% statement at WOT is correct but who is oging to test this anyways
11-16-2007, 05:27 PM
#10
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Are you sure they meant 15% fuel effeciency at WOT? Who calculates mpg ratings at full throttle? Usually its just CITY/HWY, not CITY/HWY/WOT! LOL!
They only thing I can think of is that the new turbos/intercoolers are more effecient and create less heat. If they create less heat, then they would not have to run as rich.
-Scott
They only thing I can think of is that the new turbos/intercoolers are more effecient and create less heat. If they create less heat, then they would not have to run as rich.
-Scott
11-16-2007, 05:31 PM
#11
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In the latest Panorama Mag they quote 15% as well. The compression is different according to them and some other stuff. Read Panorama if you have it, it's pretty detailed.
11-16-2007, 06:57 PM
#12
The GT2 is fitted (a first from Porsche) with a expansion-type intake manifold which they describes as a "genuine revolution". It keeps the fuel/air intake cooler which improve efficiency and reduces fuel consumption.
11-16-2007, 10:00 PM
#13
Cars don't live on a dyno, they must move their mass from point A to point B from lets say speed 0 to 100mph - it clearly requires more energy to move 3400#s than 3200#s - if Porsche wants to interpret this as efficiency (stretch) than the GT2 is more efficient as it has to accelerate less mass
11-16-2007, 10:17 PM
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As an engineer I dont know if I believe thier "genuine revolution" claim.
The air going into the turbo still gets compressed and PV=nrT says that as the
gas gets compress its temperature is still going up. Then it gets
compressed in the cylinder once again so that slight expansion
in the intake would be of minimal importance and certainly not
a genuine revolution.
The air going into the turbo still gets compressed and PV=nrT says that as the
gas gets compress its temperature is still going up. Then it gets
compressed in the cylinder once again so that slight expansion
in the intake would be of minimal importance and certainly not
a genuine revolution.