Rear spoiler on 996 , why do the vents point forward whereas on the 997 that point backwards. It seems as though the 996 is trying to draw air into the engine bay, but on the 997 drawing air out. Noticed this when my 996 Targa (2004) was parked next to a 997 Carrera S (2007).
Spoiler vents 996 vs 997
- Thread starter MacOlaf
- Start date
Very interesting observation, and no doubt there is an explanation, but I haven't a clue what it might be!
Any aerodynamicists out there?
Curiosity killed the cat. This is what the 997 Technik says:
The redesigned rear spoiler has a carefully optimised edge that produces a defined air flow breakaway when the spoiler is extended. In combination with the optimised extension height of the rear spoiler, this ensures that the rear spoiler functions at the optimum aerodynamic operating point and that the desired rear axle lift with the optimum resistance advantage is achieved. On top of this, slotted openings have been integrated in the upper shell of the rear spoiler and, in combination with the underlying engine compartment scavenging blower, optimised to ensure adequate cooling and ventilation of the engine compartment at all times.
Optimisation of the cooling-air guide: The main objective when designing the cooling-air guide is to ensure the necessary cooling air requirement for the engine and brakes in all operating states of the engine. The general idea is to achieve a flow with as little resistance as possible to minimise the effect of the cooling-air flow on the resistance coefficient of the vehicle as a whole. The effect of the flow on the lifting forces must also be minimised or used as cleverly as possible to achieve the objectives for lifting forces and lift balance.
Hmmmmm.
The redesigned rear spoiler has a carefully optimised edge that produces a defined air flow breakaway when the spoiler is extended. In combination with the optimised extension height of the rear spoiler, this ensures that the rear spoiler functions at the optimum aerodynamic operating point and that the desired rear axle lift with the optimum resistance advantage is achieved. On top of this, slotted openings have been integrated in the upper shell of the rear spoiler and, in combination with the underlying engine compartment scavenging blower, optimised to ensure adequate cooling and ventilation of the engine compartment at all times.
Optimisation of the cooling-air guide: The main objective when designing the cooling-air guide is to ensure the necessary cooling air requirement for the engine and brakes in all operating states of the engine. The general idea is to achieve a flow with as little resistance as possible to minimise the effect of the cooling-air flow on the resistance coefficient of the vehicle as a whole. The effect of the flow on the lifting forces must also be minimised or used as cleverly as possible to achieve the objectives for lifting forces and lift balance.
Hmmmmm.
chriscoates81
New member
I understand most of that (i think). I suppose its like anything, with new models comes better and more efficent ways of doing things.
From what I remember in one of the many 996/Porsche books that I have (I think it was actually Karl Ludvigsen's revised Porsche:Excellence Was Expected book), the Carrera M96 engine had cooling issues hence the vents facing the airflow to help keep down engine compartment temperature. The turbo did not have that problem so they faced the vents to draw air out instead like the 997.
In the 997, they probably thought they had the cooling sussed hence they changed the vent direction round to a more aerodynamic profile but from Baz's (Hartech) posts, it is obvious engine temperatures are now a significant problem in the lifespan of some engines although that is more related to the water cooling passages within the block and coolant flow.
Fascinating stuff though.
In the 997, they probably thought they had the cooling sussed hence they changed the vent direction round to a more aerodynamic profile but from Baz's (Hartech) posts, it is obvious engine temperatures are now a significant problem in the lifespan of some engines although that is more related to the water cooling passages within the block and coolant flow.
Fascinating stuff though.
]
pmwanderer
New member
It also appears the number of vents is decreasing too. My 996 has 7, the 997 has 4 I think and the new 991 appears to have just 3...
Interesting thoughts, so lets see how many and what direction they come out on the 991.
With all those optimisations in the 997 it is a wonder Porsche have managed to make any improvements with the 991.
In the 18 months or so I have owned my 996 I have not noticed the engine bay cooling fan coming on, even during a track day, so hopefully my version does not have cooling problems.
With all those optimisations in the 997 it is a wonder Porsche have managed to make any improvements with the 991.
In the 18 months or so I have owned my 996 I have not noticed the engine bay cooling fan coming on, even during a track day, so hopefully my version does not have cooling problems.
Paul James
New member
Perhaps your engine fan isn't functioning properly? Mine always comes on after a spirited run.
Regarding engine bay fan, I have checked the fuse - OK - and no warning lights have come on so far. Does anyone know where the temperature sensor is in the engine bay, and can one check the fan operation.
As for the vents, the 996 Essential Companion says the spoiler when raised increases the air pressure at the front of the spoiler. This "reduces drag and rear axle lift" but also provides a bit of forced air to the engine intake. That would seem to be consistent with the direction of the vents. However, although I have never seen the engine bay cooling fan work, it would seem to be designed to push air upwards out of the engine bay (and hot air rises). So there seems to be a conflict between pushing air in and out.
Don
996 Targa Tiptronic
As for the vents, the 996 Essential Companion says the spoiler when raised increases the air pressure at the front of the spoiler. This "reduces drag and rear axle lift" but also provides a bit of forced air to the engine intake. That would seem to be consistent with the direction of the vents. However, although I have never seen the engine bay cooling fan work, it would seem to be designed to push air upwards out of the engine bay (and hot air rises). So there seems to be a conflict between pushing air in and out.
Don
996 Targa Tiptronic
The engine compartment temperature sendor is mounted on the top of the engine at the right hand side, between cylinders 5 and 6. It is clipped into a plastic bracket on the top, and has a pointy bit (technical term) pointing downwards.
The fan can be activated with a Porsche tester. Maybe next time it is in for work, you could ask them to check it.
Having said that, it seldom came on on my C2.
The fan can be activated with a Porsche tester. Maybe next time it is in for work, you could ask them to check it.
Having said that, it seldom came on on my C2.
chriscoates81
New member
Looking at the duct (on my c2 if you have a turbo it could be different) it goes into the filter so I would have thought thats where the air goes into the engine. As for spoilers,I was under the impression that they increased drag and provided more downforce at higher speeds to prevent the backend from taking off. I have a figure of 70 odd kilos of force being generated but i could be wrong.
In case anyone remembers.
I just bought "the Complete Book of Porsche 911", a bit American but good.
Regarding the 996 it says that "budget restrictions were extremely tight and there was no money to incorporate a retractable rear wing. They had a very tough bean counter who said they could only design a body that will meet the aerodynamic target" However in the wind tunnel they trimmed off one of the rear grille louver (sic) panels and remounted it backwards which changed the readings immediately. "We came up with the arguemant that it wasn't a moving spoiler, it was a moving grille"
Doesn't explain the difference between 996 and 997 - maybe they used the same arguement in reverse.
I just bought "the Complete Book of Porsche 911", a bit American but good.
Regarding the 996 it says that "budget restrictions were extremely tight and there was no money to incorporate a retractable rear wing. They had a very tough bean counter who said they could only design a body that will meet the aerodynamic target" However in the wind tunnel they trimmed off one of the rear grille louver (sic) panels and remounted it backwards which changed the readings immediately. "We came up with the arguemant that it wasn't a moving spoiler, it was a moving grille"
Doesn't explain the difference between 996 and 997 - maybe they used the same arguement in reverse.
Posts made and opinions expressed are those of the individual forum members
Use of the Forum is subject to the Terms and Conditions
