De-Automate Rear Spoiler

I would like to de-automate the rear spoiler on my 99 c2 coupe, i.e., make it so that I control the deployment of my rear spoiler instead of the car. I looked though the posts here and it appears that I can simply swap out the stock deck lid wiring harness with an alternate (part # 996.612.070.51) My question is: 1. Will installing this wiring harness prevent my stock spoiler from deploying at 75 mph AND prevent any warning lights? 2. Would I still be able to deploy the spoiler manually using the button under the dash? My apologies if this has already been discussed, but I could find anything that addressed this specific issue. Thanks in advance for any advice you can offer. -Jason

Ok, I have to ask... why do you want to do this? There is a reason the spoiler deploys. Also, I am pretty sure that wire harness is for the Aero kit rear deck like on my car and will remove power from the spoiler so it will not work, you also will not get a warning light.

One idea I have would be to manually disconnect the speed signal wire to the spoiler control module. This way the control module always think you are stuck in traffic.

Yeah I know it sounds weird. I think the car looks so much better with the spoiler down.

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I could see wanting to deactivate the automatic deployment at speed. It just points out to everyone that you are speeding. I will say that when I was driving my Targa well in excess of the posted speed limits, I would often push the button to raise the spoiler manually even though it was already raised (like I said, i was exceeding the legal limit) so that an officer couldn't use the fact that the spoiler was raised to demonstrate that I was speeding. I know it never made a difference, but I did it anyway.

so vain.

Just recall that when the rear air spoiler is up it produces additional drag on the aerodynamics of the car. If you don't need it for its downforce, you will pay a mileage price to keep it up.

all the rear spoiler on the C2s will do is negate lift at the rear axle. The 996 Turbo produces something like 20 lbs of positive downforce. Don't know if my numbers are actually accurate though.

The spoiler, in the open position, also increases airflow into the engine compartment. It also reduces rear lift which aids in handling. Is the spolier visable when up on a 996? My only ref point was my boxster where I couldn't tell if it was up or down when inside the car.

Without wind tunnel data I think the rear spoiler is a total gimmick and does nothing to improve aerodynamics. Ever see a race car with a chump 12" spoiler (or whatever it is) like we have? No way. Either a huge spoiler that dominates the rear end or no spoiler at all. Somebody with data jump in here and get you some. Tell me I'm wrong 'cause I'm with they guys here who think "whatever".

Quotes source post: 7084130

You're confusing a spoiler with a wing. They do different things. A wing generates downforce. A spoiler just prevents lift by disrupting airflow (the 911's profile is decidedly wing-like, which is why every fast 911 since the 70s has had a spoiler). They aren't meant to be "aerodynamic". Quite the opposite.

It definitely makes a significant difference. As a 911 driver from the pre-tail days I can tell you how incredibly unstable these cars are at speed without them. They did a study (Porsche) some time back measuring the downforce of the various tails (duck tail, early turbo tail (Carrera RSR) and then the whale tail with the integrated heatexchanger) and the numbers are significant. Without the added downforce the cars handle very differently and are substantially less safe.

I've run mine manually down at real speed, it is not a fun feeling. I do have a center radiator and last year added the gt3rs front spoiler (thank you Bruce!), and have 315 rubber out back, all of which would impact airflow in one way or another, but even on the 17 inch lightweights without the front lip it didn't feel right without the spoiler up past 90-100 Also, don't ask me to go into details on why I spent a week hypermiling this thing over a bet with a tree hugging crazy ex girlfriend, but I've actually gotten marginally better fuel economy with the wing in its deployed position (vs. manually lowered), again likely attributable to a host of factors beyond an implied effect on Cd or our preconceived notions of the spoiler's effect on the fluid dynamics or the lift vectors. One thing I'm sure everyone's noticed, the coolant temp and intake air temps drop fast when that thing goes up. And is it just me or does yours have a mind of its own? I'll notice that it's raised after extended WOT even if I pulled back well short of 75, and when it's hot out, well then I've seen it in my mirror at 50mph. And for those who think it's vestigial, I will present the following logic: If it were as useless as some newer members have purported, the same value engineering that gave us the much bemoaned integrated headlight assembly would have rapidly eliminated the need for something with such a huge financial impact on wind tunnel time, fuel economy testing, and structural integrity, and with as many electronic, electrical and mechanical considerations as an active spoiler engine lid, which the driver practically never sees. Best, Hans

I'll have to check my Porsche library in the AM but in a book I have it clearly states it does change rear lift and that the engineers/designers couldn't meet design goals without the spoiler. They proved it to the bean counters and were begrudgingly allowed to proceed with the spoiler as part of the design. I have had several older Carerras with and without spoilers. The '84 without was a handful at speed. The '85 with front and rear was majorly planted at trip digits. More so than my '99. It feels floatly in comparison.

I was actually wondering the same thing as the OP... Running this car in the winter, with a build up of ice and snow on the rear of the car ... I can only imagine this will lead to issues with the spoiler deploying? (I know... I know... Clean it off)

This topic doesn't warrrant any other post than: Whether you think it looks good up or down(and both questions have been asked here) the simple fact remains that you should not inhibit the spoiler from doing the job it was designed to do or you pretty car could end up in a bunch of little pieces scattered all over the highway do to your vanity. It is true that the beancounters at Porsche fought this spoile tootha and nail but the car would not function properly at speed without it.

I vote for leaving the engineering to Porsche engineers! The spoiler breaks up the airflow at speed - why would you want to mess with that? Try going 70, and stick your hand out the window in spoiler position, and you'll see how much air even your hand deflects! Don't mess with science in favor of looks!

The previous 911... 993 and 964 spoilers were more for engine cooling. The impact of downforce was very minimal. 996 was the first 911 that actually produced downforce.... Ill post my source later, when I find it.

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Never once in over 226K miles of driving my Boxster, and over 20K miles driving my Cayman or Turbo been pulled over cause spoiler's up. Have not even been issued a ticket for having a radar detector and in fact used its presence to help convince a Texas LEO he made a mistake pulling me over for speeding (he did, only had eyes for the Porsche and not the car next to mind in the fast lane that passed me and triggered the excessive speed warning a the radar gun). Lots of things to worry about while driving but that the spoiler being up is going to bring down the law on you for speeding is not one of them. Sincerely, Macster.

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A "right on" to your "It is true...." comment. Let the OP ask early Audi TT owners how they liked it when their cars were flying off the road cause the Audi beancounters won out and prevented a proper spoiler from being fitted to the car from the outset. Sincerely, Macster.

Quotes source post: 7085259

Again, not to be pedantic, but none of those spoilers, old or new, were meant for creating downforce. That's what a wing is for. A spoiler is meant to keep the whole car from becoming a wing. They superficially look alike, but they're really two different things. I'd hazard a guess that the 'downforce' created by our spoilers is close to zero, especially given that it's louvered. There's very little surface area to pressurize. The idea is simply to create controlled turbulence at the back of the car in order to counteract lift. Given that there is so little mass in the front of a 911, you can imagine that high speed lift at the rear could have pretty scary consequences. IIRC, there are one or two pilots on this board. They could probably do a better job of differentiating the physics than I can.

Quotes source post: 7085309

The perfect illustration. And they didn't fix it with a wing. They fixed it with a little strip of plastic meant not to create downforce, but to deliberately mess up airflow.

Technically the spoiler isn't even needed until somewhere around 90mph. Porsche had to lower the threshold on the US cars or else they would never come up. (can't remember the source).

As a long time flier, let me enlighten you. The shape of the 911 is essentially that of a wing--the chord of a wing. By that shape, it naturally will want to move up because the air pressure on the top of the wing (car) is lower than the pressure beneath the wing (car). As such, the natural tendency is for it to want to fly. In the case of the 911, for it to raise up upon its suspension. The tails are there to essentially SPOIL that flow over the top rear of the car and keep it from raising up on its suspension. When you alter the shape of the wing chord you are altering the flight properties of that wing (car). I started off my 911 days with a new 911S many years ago and it had no tail. When on the autobahns it truly wanted to fly. If I was alongside a black truck I could look out to the side and see that the rear end of the car was way up. It was literally trying to fly. Later, when I had a turbo-charged 911, it came with the Carrera RSR tail (first seen on the 1976 Turbo Carrera street cars). It made a pronounced difference when driving that car. I used to run it up to 5th gear redline routinely (162 mph) and I couldn't have done that safely without the tail. With my current car, the tail deploys at an honest 75 mph (77-78 indicated) and it absolutely keeps the rear rend down--enough to inspire confidence in the car's stability. I had it over 180 mph on the autobahns and felt quite secure. Several years ago in Porsche Panorama, they had an article about tails and air dams and such, striving to clarify the entire issue. The article discussed the downforces achieved from each type of tail. So the story goes, one day a long time ago (early 1970s) a Porsche mechanic took a car out for a test drive and had neglected to close the rear deck lid. He discovered how much more stable the car handled at speed. The 911RS wound up with a Duck tail soon, and the rest is history.

Thanks for all the input, but nobody has answered my question. Is there a way for me to de-automate the rear spoiler while keeping the option for manual deployment?

Quotes source posts: 7085964, 7083337

Yes it was. Robin answered it in post #3.