How fast before you need a wing?
 

So how fast can a 911 go before it should have spoilers to keep it nailed to the ground? I can't remember the exact speed that the C2/C4 spoiler automatically extends, but I think that it wasn't anything blindingly fast, like around 50 or 60 mph. Also, the extended wing aided in engine cooling, I hear. Likewise, the Turbo's wing served to house the intercooler, although I'm sure they can go plenty fast enough to need a bit of help staying rubber side down.

Reading the 911ST thread a week or so back has me thinking about the big flares/no wings look. It looks way cool, but is it practical?

It's my understanding you can feel a difference at speeds as slow as 80- mph and that the wing and matching front spoiler make the car MUCH, MUCH more stable at triple-digit speeds.

Maybe it is all in my head, but my car felt more stable at normal freeway speeds, particularly in a gusty crosswind.

I went from no spoilers to a Carrera tail and chin spoiler.

Tom

I wouldn't know because my Porsche has never gone over the speed limit. ;)

I'm currently in the process of installing a front spoiler and Carrera rear wing on my 85 Carrera. In DE at Road America you can nearly hit top speed in 5th gear on the main straight, that is if you do everything right coming out of turn 14. I have noticed that when going really fast at the end of the straight, my car was being blown around by the wind. I suspect that the airfoil shape of the 911 causes some lift at high speeds and a wind coming from the side or the quarter pushes you around slightly. The last time this happened I glanced at my tach and I was doing the equivalent of about 120 mph. It is controllable but you have to be careful. I'm hoping the spoiler and wing make a difference and counteract some of the high speed lift inherent in the 911 shape. I'm sure it will work, thats why they put the spoiler and wing on the 911!

Positive effect at high speeds
 

I would also say about 80mph. I can also say at about 125mph, without spoilers, my 911SC would drift. Steering felt disconnected in that I constantly had to make corrections to keep it straight. With spoilers, the car is rock steady over 140mph. However, I must admit, I haven't driven at these speeds since the 80's.

My SC has only the chin spoiler and is rock solid up to 135mph. The only time the steering got light was when I went over a rise at 120mph then it came right in about 10 seconds :)

i wouldn't because mine doesn't run:(

I hope my dad doesn't read this! He is out of town for the week so hopefully this thread will be over by the time he gets back!:D The '84 Carrera has both chin and tail spoilers and it is soooo steady and smooth up to and beyond the 125 mark. The '69 S, on the other hand, gets a little twitchy when I put it up past about 95. We are in the process of doing the alignment, its all screwed up, so I imagine thats is a major reason for the unstability at such a "low speed":D http://members.rennlist.com/911andson/

I heard you can't feel it at speeds lower than triple digits, but I thought I felt a difference in the mid 60s after I installed front and rear spoilers. (keep in mind I'm at sea level)

However, I assumed I was misinterpreting all of that until I removed the wing a few weeks ago and drove with just the decklid.
Same roads. Same speeds. The car was much more glued to the freeways in the mid 70s and low 80s with the tail than it is now. Definitely makes a difference that you can feel with and without it.

At this point, I spend much more time at low speeds than I do high speeds, so I'm going without the wing to save weight, since they are quite heavy.

I didn't have spoilers on my Carrera until a year ago. I only installed them to stabilize the car for the high speed banked turns at Pocono. Even at speeds over 100 mph, the car is quite stable w/o spoilers - especially in a straight line.

Paul
87 Carrera

The 'before the braking zone' speeds at Summit Point and VIR are around 120 - 125 mph for my 85 coupe, given I didn't screw up the launch out onto the straight.
It has a chin spoiler and no tail - I know, supposed to have both or none, but I prefer the clean lines without the tail, and the car did not have one when I bought it.
Maybe it would be stuck down like a rock with the tail, which at 120MPH reduces over 300 pounds of lift to something less than 100 pounds, but the car never feels twitchy or unstable when lining up for braking or at full initial braking effort.

I'd really like to drive a similar car with a tail to see if it really feels more stuck down - might be a big wake up call!

Everyone is talking about the carrera and turbo tails but what about the duck?? How does it help, if it does? Also would you need the chin spoiler with the duck tail spoiler? The patient would be a 78 SC.

Plain Fan:

According to testing at Weissach by Porsche the duck tail reduces the lift at the rear wheels by:

about 150 lbs at 150 mph

about 100 lbs at 120 mph

about 45 lbs at 90 mph

overall, the duck tail reduces lift by 50-60% from 60mph and up...

the lift generated at the rear with no tail at 150 mph is nearly 300 lbs

For further reading refer to Up-Fixin Vol. V, pg. 313, Fig. 12

spoilers
 

My 85 came without spoilers. I put them on shortly after buying the car but I put the Carrera tail on first. I could feel a considerable difference in the rear at or above about 80 mph, but at about 100, the front began to feel very light...more so than without any. I gave this some thought and determined that the added downforce in the rear, which is behind the rear tires actually unloaded the front somewhat, allowing more air under the front which creates more lift in the front and so on. With the front chin spoiler added, you get some added down force but more importantly the air dam effect creates a vacuum under the car minimizing the lift and works beautifully to approx. 145 which is as fast as I've had it. They do definately need to work together but if you were only going to use one for functionality, it would have to be the front. Don't forget, they add drag so you will need a couple more ponies to reach the same top speed!
Rob

Chin spoiler and no tail may not be perfect, but is not dangerous.
Tail and no chin spoiler at high speeds is Baaaaaad Booogie.

I thought someone at sometime posted that since the SC's front bumper had the same form as the original Carrera's it didn't need the rubber chin spoiler, since the original Carrera had the ducktail and not chin spoiler. Am I wrong?

quote:"Don't forget, they add drag so you will need a couple more ponies to reach the same top speed! "

That's what I thought too.
Interestingly, the Duck and the early turbo tail reduce drag. I would believe the Large 3.3 turbo tail may increase drag. (don't know though)
It is a bit counter-intuitive, putting something that big on the car and having it reduce drag. But then, consider a golf ball. Dimples mean more surface area, more surface area means more drag. And yet they end up with less drag. (engineering type qualifier:. . . for a certain speed range.)

Which tail to use on the SC?
I was just checking the efficiencies of the tails per Paul Frere's book.
The short answer is the early turbo tail out performs the duck tail on the big bumpered cars.
A trusted source here had me thinking, and likely repeating, that the duck tail was the most aerodynamically efficient (meaning best lift-kill for the best drag cost) and now I'm seeing that for the SC's the early turbo tail is the winner.

Not sure about the drag issue.
 

In a different post, I recall it was mentioned that earlier Porsches did not have enough HP to red line in 5th. I distinctly recall on about a 10 mile straight stretch, my 79SC's tach was at the red line, the speed was just under 150 mph and the car was still pulling. This was with the front lip spoiler and turbo tail.

I'm probably not the best person to give advice but after hitting an animal (I think it was a coyote) in Oklahama in my Bimmer, I realize it doesn't matter how well your car handles or how good a driver you are, there are just too many intangibles (retreads, potholes, other drivers, etc.) on the street. At just 80mph, this animal completely disintegrated. The couple behind me said it looked like something out of Friday the 13th. Imagine what this would do to a 911.

So my unsolicited advice now is to save the high speed stuff for the track, where most variables are controlled. Don't mean to be hypocrital, but after I got older, I realized it's only by sheer luck and the grace of God that I made it this far without hurting myself or someone else.

Well you don't "need" a tail either then; just slow down :(
On one hand, the duck tail alone doesn't really change the lift on the front. On the other hand, that little strip of rubber does a whole lot. It takes the front lift coef, from .113 down to .010 when used with the tail. That's a lot of bang for the buck. . well maybe not the buck; thay are knda spendy.