Porsche and it's 15% rule
11-17-2007, 11:35 AM
#31
I don't think that these developments are purely done for performance gains. The emission laws are getting more and more restrictive around the world and Porsche needs to make an effort to meet the new and tougher emission standards. The GT3 MK1 was drawn from the market because it didn't meet the required emission standard.
Next year Porsche will introduce DFI for the turbo models which shall improve efficiency by 10% and give more power.
Next year Porsche will introduce DFI for the turbo models which shall improve efficiency by 10% and give more power.
Last edited by Pingo; 11-17-2007 at 12:12 PM.
11-17-2007, 06:13 PM
#32
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11-17-2007, 06:21 PM
#33
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15% really isn't that much more efficient because like someone said earlier you're only getting 4-6mpg at full throttle anyway...but most of the improvements on mpg have to do with better either direct or indirect ECU stuff which, being computer hardware and software can evolve at an extremely high rate.
11-17-2007, 08:52 PM
#34
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Well, an exception to that would be if the car was running pig rich to begin with and the cooler air leaned the AFR back into a more efficient zone. I know my old E55k would run AFR's in the upper 10's stock, and picked up a bit of power just through air intake mods.
11-17-2007, 09:36 PM
#35
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if chip speed can double so quickly then in ECU's it stands to reason that they can figure out how to fuel map to bring all the components into both high hp and mpg. that's how the VTG is supposed to work also, dual-core pentium style.
11-18-2007, 05:45 AM
#36
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I don't think this is true. If the air is cooler, but at the same pressure, there is more air (in # of molecules) and you pump in more fuel and get lots more power. What I'm comparing is the SAME # of molecules so you use the same amount of fuel for the same AFR. One situation has hot air at a higher pressure and the other has cool air at a lower pressure but with still the same amount of air and fuel. I think the cool air will make more power.
11-18-2007, 06:12 AM
#37
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At or near combustion it's all hot air/fuel at high pressure! It's the amount of charge, period.
The advantage of Forced Induction is more charge (# of molecules of O2 and hydrocarbon) due to...well, force. Pre injection cooling just allows even more charge per cycle.
The advantage of Forced Induction is more charge (# of molecules of O2 and hydrocarbon) due to...well, force. Pre injection cooling just allows even more charge per cycle.
11-18-2007, 11:13 AM
#38
Exactly!
It is a case of the marketing department outdoing the engineering dept.
If you remove the drivetrain friction loss going from AWD to 2WD and reduce the wieght by a couple of hundred pounds you better be more effecient not only at WOT but across the board...
Why don't they compare the 996 GT2 to the current model for a more apples to apples comparison... I'll bet you that the new GT2 is more effecient than the Cayenne Turbo at WOT too!
DUH !
11-19-2007, 11:07 AM
#40
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no they're not direct injecting, what i meant in my post was that the ECU improvements in our technology-age society are what really make the increase in efficiency. cars have been able to put out 500 hp for decades, and gas has been pretty similar since the old auto union cars went 150mph + in 1930 or so- it's just that now they can do it in a hippie friendly manner.
if chip speed can double so quickly then in ECU's it stands to reason that they can figure out how to fuel map to bring all the components into both high hp and mpg. that's how the VTG is supposed to work also, dual-core pentium style.
if chip speed can double so quickly then in ECU's it stands to reason that they can figure out how to fuel map to bring all the components into both high hp and mpg. that's how the VTG is supposed to work also, dual-core pentium style.
11-19-2007, 11:10 AM
#41
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But why not 1.6 bar or 1.8 bar? Well, I'm guessing that the energy loss due to increased heat outweighs the benefits at that point.
11-19-2007, 11:21 AM
#42
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Interesting, I don't know the answer to this. I will ask my Chemist father for his opinion on it.
11-19-2007, 01:28 PM
#43
Nordschleife Master
I am a Chemist. That's why I said what I said.
While the whole thing may seem appealing, the truth is that regardless of temp of the charge at entry to the cylinder, during the compression phase of the cycle things will heat up real fast. Combustion is combustion and all that is in question here is how much of the charge is oxydized during the explosion.
%-age of oxidation is no doubt variable dependant on many design parameters of the chamber, timing, scavaging and so on. But entering temp of the charge is likely of little importance if the actual number of molecules of hydrocarbon and O2 are the same.
Actually this will pretty much follow the volumetric rules of the Ideal Gas Law. So the same mixture at lower temps will have less volume. This takes us back to where we began. The advantage of F.I. is more molecules per unit volume, intercooling...the same.
11-19-2007, 02:46 PM
#45
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I am a Chemist. That's why I said what I said.
While the whole thing may seem appealing, the truth is that regardless of temp of the charge at entry to the cylinder, during the compression phase of the cycle things will heat up real fast. Combustion is combustion and all that is in question here is how much of the charge is oxydized during the explosion.
%-age of oxidation is no doubt variable dependant on many design parameters of the chamber, timing, scavaging and so on. But entering temp of the charge is likely of little importance if the actual number of molecules of hydrocarbon and O2 are the same.
Actually this will pretty much follow the volumetric rules of the Ideal Gas Law. So the same mixture at lower temps will have less volume. This takes us back to where we began. The advantage of F.I. is more molecules per unit volume, intercooling...the same.
While the whole thing may seem appealing, the truth is that regardless of temp of the charge at entry to the cylinder, during the compression phase of the cycle things will heat up real fast. Combustion is combustion and all that is in question here is how much of the charge is oxydized during the explosion.
%-age of oxidation is no doubt variable dependant on many design parameters of the chamber, timing, scavaging and so on. But entering temp of the charge is likely of little importance if the actual number of molecules of hydrocarbon and O2 are the same.
Actually this will pretty much follow the volumetric rules of the Ideal Gas Law. So the same mixture at lower temps will have less volume. This takes us back to where we began. The advantage of F.I. is more molecules per unit volume, intercooling...the same.
997 GT2 compression ratio: 9.4:1
997 Turbo compress ratio: 9.0:1
This, finally, explains it. Of course, direct injection or a revised combustion chamber, or something like that could also explain it. But better turbos, intercooler, or a better intake definately does not!