911 Rear wing deployed = better times?
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From: Mtl, Canada
911 Rear wing deployed = better times?
1st season in the 996, I was wondering if anyone tried to run with the rear wing manually deployed & if if affected their times favorably... or not.
Race Car
Joined: Sep 2006
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From: Jacksonville, FL Duval County
It's my equivalent of the cool runnings lucky egg. I always deploy it manually. When you cycle the ignition off with it manually raised, the wing will stay up until you start rolling, then it'll go down. You have to manually lower it and raise it again before each run to get it to stay up, unless you leave the car idling between runs.
No time improvement, but great photos.
No time improvement, but great photos.
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From: Mtl, Canada
Just found some more info:
I think I will also kiss that lucky egg ... I may not always hit the 75 mph trigger speed to have the spoiler deploy, but closing in on the rev limiter in 2nd gear (close to 70 mph), I think some of the effects of lifting the spoiler manually could be beneficial. I will surely try it out. If just for the cool factor! 
The full detail from the Tecknik Book:
"The spoiler stabilizes the air-flow at the rear-end of the vehicle by means of a defined burbling of the air-flow while simultaneously increasing the pressure around the front of the rear spoiler.
This reduces both drag and rear-axle lift.
An additional side-effect of this increase in pressure is an increase in the volume of air drawn in by the engine as well as in the flow of air through the engine compartment ventilation system whose inlets are located at the rear lid.
At low speeds, aerodynamics play only a minor role in the composition of road resistance values. For this reason, the spoiler is only extended at approx. 75 mph and is retracted again at approx. 37 mph. As a result of detailed and intensive work on the aerodynamics, it has been possible to reduce the size of the spoiler on the new 911 Carrera compared to that of the old 911 Carrera."
Also (as far as cooling and ventilation) ...
"The engine compartment is ventilated by an opening in the rear cover positioned beneath the spoiler. An additional opening beneath the spoiler grille is used to draw in the required combustion air.
The extended rear spoiler, by increasing the pressure around the spoiler, improves the air-flow in the engine compartment and thus the cooling process itself. The engine compartment scavenging air is blown into the engine compartment (assisted by the fan) if the switching temperature is exceeded."
"The spoiler stabilizes the air-flow at the rear-end of the vehicle by means of a defined burbling of the air-flow while simultaneously increasing the pressure around the front of the rear spoiler.
This reduces both drag and rear-axle lift.
An additional side-effect of this increase in pressure is an increase in the volume of air drawn in by the engine as well as in the flow of air through the engine compartment ventilation system whose inlets are located at the rear lid.
At low speeds, aerodynamics play only a minor role in the composition of road resistance values. For this reason, the spoiler is only extended at approx. 75 mph and is retracted again at approx. 37 mph. As a result of detailed and intensive work on the aerodynamics, it has been possible to reduce the size of the spoiler on the new 911 Carrera compared to that of the old 911 Carrera."
Also (as far as cooling and ventilation) ...
"The engine compartment is ventilated by an opening in the rear cover positioned beneath the spoiler. An additional opening beneath the spoiler grille is used to draw in the required combustion air.
The extended rear spoiler, by increasing the pressure around the spoiler, improves the air-flow in the engine compartment and thus the cooling process itself. The engine compartment scavenging air is blown into the engine compartment (assisted by the fan) if the switching temperature is exceeded."
Racer
Joined: Apr 2008
Posts: 499
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From: Rochester, NY
just realize it's a spoiler, not a wing. It's going to reduce lift by "spoiling" the air and creating a nice low pressure bubble between the rear window and the spoiler itself.
If anything, you're raising the center of gravity of the car . . . .
If anything, you're raising the center of gravity of the car . . . .
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From: Mtl, Canada
Most pics I've seen of 996s autocrossing didn't have the spoiler deployed... Thought it didn't make sense... Thanks for sharing your experience, as I'm trying to gather a general consensus...
Seat of the pants wise, any improvement? More rear grip? engine breathing better? More understeer?
Seat of the pants wise, any improvement? More rear grip? engine breathing better? More understeer?
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Three Wheelin'
Joined: Mar 2010
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From: McKinney, Texas
I always deploy the wing on my 964, because it aids cooling. Since the auto deployment is around 48mph it would be up when the car reaches speeds where the spoiler would have an effect.
Most all SCCA prepared and street prepared cars run some sort of spoiler.
Most all SCCA prepared and street prepared cars run some sort of spoiler.
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Racer
Joined: Apr 2008
Posts: 499
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From: Rochester, NY
They run 10" tall blade spoilers . . . . . . there's a difference between that and the factory spoiler that's designed to reduce rear end lift at 75+ mph (as a result of Porsche's slavish devotion to the slope back "Beetle on Steroids" shape).
Three Wheelin'
Joined: Mar 2010
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From: McKinney, Texas
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From: Mtl, Canada
The mathematical formula for lift (Negative lift is what we are looking for in our particular situation)
where
L is lift force,
ρ is air density,
v is true airspeed,
A is planform area, and
Cl is the lift coefficient at the desired angle of attack
The lift force increases exponentially in relation to airspeed. At low speeds the spoiler has very little effect, but in the fast swepers & slalom gates of a run where speed is generally higher, the spoiler should have a beneficial effect. In theory.
On the other hand, all the slots on the spoiler have a negative effect on the Cl (Lift coefficient). Was Porsche aiming to cool the engine better at speed, or generate negative lift (read reduce rear-axle lift & drag)? That remains to be seen.
where
L is lift force,
ρ is air density,
v is true airspeed,
A is planform area, and
Cl is the lift coefficient at the desired angle of attack
The lift force increases exponentially in relation to airspeed. At low speeds the spoiler has very little effect, but in the fast swepers & slalom gates of a run where speed is generally higher, the spoiler should have a beneficial effect. In theory.
On the other hand, all the slots on the spoiler have a negative effect on the Cl (Lift coefficient). Was Porsche aiming to cool the engine better at speed, or generate negative lift (read reduce rear-axle lift & drag)? That remains to be seen.
Last edited by SPEEDEM0N; Jan 23, 2015 at 03:19 PM.
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From: Mtl, Canada
