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Holy high mpg Batman. I can’t get above 23 mpg. Maybe 25 if I’m really holding back, steady at 60-65mph. More like 18 mpg combined city/highway. C2S 997.2 here.
mpg?? What? Never heard of the word in the same context as the word porsche.
The 997.2 motor has proven to be much better and there are some high mileage guys here with them, like Wayne & Bruce. There have been some reports of engine failures by both Raby and Hartech and they seem to be bore scoring related. For a DFI motor, it also does not seem prone to carbon buildup like most other DFI motors are, probably because they're using the injected fuel stream to clean the valves. This graphic is on the Cayenne 957, but is also in the 997 9A1 literature.
So based on that picture, fuel would spray on the valve, but that depends on the injectors location in the cylinder, which you consistently leave out
So based on that picture, fuel would spray on the valve, but that depends on the injectors location in the cylinder, which you consistently leave out
True, there are a ton of assumptions we are making about that graphic..... but we do know something ..... I never read a post on these forums of any DFI engine needing valve blasting. I know that does not imply the graphic shows why, but the takeaway appears true... our DFI engines don't have that problem.
So based on that picture, fuel would spray on the valve, but that depends on the injectors location in the cylinder, which you consistently leave out
The whole reason Porsche created that graphic is to show how on their DFI motor, the intake valve is being cleaned by the directly injected fuel washing the valve during the intake stroke when it's open. The other benefit to this is that is that the valve interference scatters the fuel within the combustion chamber for more even combustion and also helps to prevent cylinder wall washing of the oil film. It's a really well thought out design that mitigates well-known common problems with the technology and provides for additional benefits.
The whole reason Porsche created that graphic is to show how on their DFI motor, the intake valve is being cleaned by the directly injected fuel washing the valve during the intake stroke when it's open. The other benefit to this is that is that the valve interference scatters the fuel within the combustion chamber for more even combustion and also helps to prevent cylinder wall washing of the oil film. It's a really well thought out design that mitigates well-known common problems with the technology and provides for additional benefits.
Im not doubting you but I'm curious where they may have documented that? They dont list that under the picture as one of the development objectives nor the achievements. Again, not doubting you but just curious. I only say that because Porsche choose a bad angle to prove their point. The placement or orientation of the injector to intake valve in that 180 cutaway photo could be anywhere.
Here is an example of an angle that can give perspective on a diff motor...
Again, was just curious since it seem a brilliant idea. Its probably moot anways since I assume people like Bruce who have a ton of miles have looked at their valves before and everything was good?
Yes, that would be a better view for that purpose, but shows less of everything else (angle of valves, etc). Maybe someone like Hartech or Raby who has had one of these motors apart can chime in with how the alignment of the injector stream is oriented to the intake valve to confirm what's suggested by the Porsche graphic is actually what's happening.
Again, was just curious since it seem a brilliant idea. Its probably moot anways since I assume people like Bruce who have a ton of miles have looked at their valves before and everything was good?
Mike
Mike, I never looked at my valves...... I have no idea if they are clean or dirty enough to be robbing me of power. Who knows, with 122K miles on my engine... maybe be at 130K all hell will break loose and I will need a complete tear down! My only "evidence" of no problems is what see is virtually no posting of valve problems on these forums.
Mike, I never looked at my valves...... I have no idea if they are clean or dirty enough to be robbing me of power. Who knows, with 122K miles on my engine... maybe be at 130K all hell will break loose and I will need a complete tear down! My only "evidence" of no problems is what see is virtually no posting of valve problems on these forums.
Peace
Bruce in Philly
fair enough, in that case I shall tip a beer for you tonight in wishing you clean valves
hehe, but seriously yes I agree if people were having serious valve deposits you'd get misfires, CEL, or noticeable power loss eventually. So at least theyre not that bad for folks hopefully.
The whole reason Porsche created that graphic is to show how on their DFI motor, the intake valve is being cleaned by the directly injected fuel washing the valve during the intake stroke when it's open. The other benefit to this is that is that the valve interference scatters the fuel within the combustion chamber for more even combustion and also helps to prevent cylinder wall washing of the oil film. It's a really well thought out design that mitigates well-known common problems with the technology and provides for additional benefits.
From this picture, you can see that unless this injector has an insanely wide spray angle, not much of the valves are being washed by the fuel and I can't imagine a lot of the valve stem closer to the guide is seeing any cleaning.
Maybe it works and maybe it doesn't, but porsche's picture is misleading.
Ok, something is not right. The head you show, Mr Quadcammer, has the fuel injection between the exhaust valves (larger discs) and the famous diagram Mr Petza presented shows the spray spritzing on the intake valves (per the flow arrow)..... do I have this wrong?
Dumb question: on which valves does the infamous carbon buildup occur? Ithought it was the intake as the port injection would wash these valves with gas/air mixture and keep them clean (in the older systems).
Ok, something is not right. The head you show, Mr Quadcammer, has the fuel injection between the exhaust valves (larger discs) and the famous diagram Mr Petza presented shows the spray spritzing on the intake valves (per the flow arrow)..... do I have this wrong?
Dumb question: on which valves does the infamous carbon buildup occur? Ithought it was the intake as the port injection would wash these valves with gas/air mixture and keep them clean (in the older systems).
Peace
Bruce in Philly
EDIT: LOL, sorry i get dizzy looking at the boxer engine setup. yes you are right they are spraying between the intake valves
Ok, something is not right. The head you show, Mr Quadcammer, has the fuel injection between the exhaust valves (larger discs) and the famous diagram Mr Petza presented shows the spray spritzing on the intake valves (per the flow arrow)..... do I have this wrong?
Dumb question: on which valves does the infamous carbon buildup occur? Ithought it was the intake as the port injection would wash these valves with gas/air mixture and keep them clean (in the older systems).
Peace
Bruce in Philly
The intake valves are almost always larger than the exhaust valves, so yes, the injector is aimed between the two intake valves
OK, then I had something backwards in my knowledge (!) of how the system works. The volume of air/gas in, is less than the amount of air/gas/emissions to be expelled because of the release of energy. So I thought the exhaust ports were always larger because they need to remove more stuff.
MPG in these cars is ridiculous to worry about, but I feel it does reflect on the design quality and says something about the PDK.
As far as valves ... push out > suck in. Bigger valves (specifically total circumference which is why two is better than one) allows more potential energy in. Intake velocities are smaller allowing a difference in turbulence and mix.
The picture makes it look like the injectors are near parallel to the head surface and thus pointing to the back of the valves when they open. The high fuel pressure should insure wide dispersal of the fuel. I believe the Porsche engineers were pretty brilliant with the 9A1. The proof is in the result. We have enough cumulative miles on these beasts to draw some conclusions, directly or indirectly.
03-02-2018, 06:06 AM
