Spoilers: front and or rear

[Canada Kev]

OK, so I have read about instances of a negative reaction with both rear wing only or front spoiler only and am curious as to what might actually be the truth.

Here is my suppositions and what-i've-heard stuff as it now stands"

Long, long ago (in a land far, far away), the 911 was susceptible to high speed instability, likely due to its shape similar to an air foil. This prompted engineers and others of knowledge to install a rear deck lid spoiler to disrupt the airflow over the rear end, reducing the lift at higher speeds.

These duck tails seemed to work rather well, and as speeds rose the tails became larger and produced more stabilizing down force.

As I understand it, the air flowing UNDER the car is also detrimental to the stability of the vehicle. Enter the front spoiler. By reducing the allowable volume of airflow entering past the spoiler into a relatively larger space under the car, it creates sort of a vacuum affect further adding stability.

My inquiry is as follows: I have seen a number of cars with either the rear or front spoiler only. Is this a recipe for disaster at speed? The factory seems to have not included a front spoiler when not equipped with the rear. Is this one of those "if you have one, you need the other, as well" type situations?

-kevin

[the]

most feel you can run the front without the back, but not vice versa.

[Ole Petter]

The US 1975? Carrera had a duck-tail. But came without the front spoiler. They ran a test (Road and Track?) where they fount the rear spoiler reduced lift and gave more stability at high speed. There was no mention of a front spoiler in that test.

But I guess a "whale tail" would require a front spoiler as well.
I have asked around for adwice on using a front spoiler only, and has been told to use both front and rear if I should want spoilers. And so I do without.

[RoninLB]

I installed a front Carrera chin spoiler and a rear C2/964 electric spoiler.

for my local routine around here at a max of 70 mph I don't even bother to raise the rear spoiler.

otherwise without spoilers the car becomes "light" at 80+ mph.

another issue with me is that when on cross country roads when a big rig would pass, going in the opposite direction on a 2 or 4 lane road, my car would almost lift and be pushed away to the side. When directly following a Carrera with a front and rear Carrera spoilers it didn't budge when the rigs passed. Add 30+ mph winds and it would be more fun.

If the rear C2/964 spoiler doesn't help me I'll install the Carrera spoiler. It's the cat's ass.

[Noah930]

For a more detailed discussion, you can read through Paul Frere's book The Porsche 911 Story. He tells of how the factory developed the front and rear spoilers for true aerodynamic downforce/drag reasons (as opposed to just for aesthetics). Ideally, if you have one, you should have the other.

But as Ronin mentioned, unless you're doing high speed driving (and the number I've heard tossed about is 80 mph, though I would assume that that figure's going to vary a bit, depending on the shape of the car) it's unlikely that there is much effect from the spoilers. So for most streetcars, spoilers are more cosmetic than functional. I'd be willing to bet that far more crashes occur due to poor driving technique/inattention/etc, than due to loss of control from aerodynamic imbalance at speed.

[Bill Verburg]

The front spoiler was the first to appear on '72S w/ no rear spoiler.

Then the 2.7RS spoilers appeared as a matched set in '73(mit central oil cooler space/duck)

followed by
the '74 Carrera 2.7/3.0 f/r matched set of spoilers(p/u chin/whale)

eventually
the 930 chin/tea tray came to be in '78

all the dealers were issued a TSB that said not to mount a rear spoiler w/o a front

[gtc]

I have a friend with a '75 targa, equipped with a tea tray and no front spoiler. I've had the car up to ~130, and it really wasn't scary at all. My '84 targa with front and rear spoilers feels a bit more planted at those speeds, but it's also heavier, has wider, lower profile tires, and sits lower.

I don't doubt that the front spoiler helps, but I rarely find myself in serious corners at 100+ mph, which it seems to me is where you'd notice it the most.

Would I put a spoiler on his '75 if it were mine? Yes, but more for looks and to appease the Porsche masses than for performance.

[4sd911]

Putting a front spoiler on my '74 made a big difference with stability in the wind and from turbulence from big trucks. The factory will not use one without one on the other end, so I did use a 964 electric on the rear but I can not feel the difference with it up or down but I don't see high speeds. The early 'S' front spoiler isn't very effective, it is similar to the front valence on the '74-'89 cars without the rubber chin. Absolutely do not use a rear spoiler without a front one, If you have a early car with the 'S' spoiler up front a whale tail is to aggressive to be matched with the 'S" front. PCA has some good info on these matters in the upfixin books.

[Bill Verburg]

The faster you go, the slipperier the road is and the more of a cross wind there is the more you will appreciate front and rear spoilers.

yes, Frere in his 911 Story series and Bob White's articles in Upfixen are excellent reads.

[tshih]

Theoretically with more downforce in the rear and not enough in the front would result (ultimately if speed is high enough) in doing a wheelie where the front steering wheels are off the ground. Hence having no front spoiler (or 935 turbo flatnose front) is a step in that direction. This would seem to put reason to why Porsche posted those service bulletins. Both matched as they came from the factory is best followed by only the front or none at all.

[911boost]

I read every one of these threads when they come up. My 86 Carrera had a tea tray, and no front spoiler, I added the factory chin spoiler, and it did make a difference.

Fast forward to my 964 turbo, it has the tea tray as well, but no noticable front spoiler. Why is this? I am guessing that the air vents in the front valance, help direct the air to keep the car planted. This thing is a rock at 100+.

Just curious.

[burgermeister]

You need both spoilers to keep the amount of lift balanced front to rear.
Courtesey of UpFixin' Volume V:




Note that rear lift is about double the front lift, or around 66% of the total - not too far off from the weight distribution of the car. So, with no spoilers, the car gets light, overall lateral capability is reduced (significantly - looks like 15% at 150MPH), but the basic understeer / oversteer characteristics stay the same. Sort of like driving on wet pavement.

With both spoilers, lift is a lot less at both axles - again, no change in handling characteristics.

With one or the other spoiler, only 1 axle gets light. The lateral load / slip angle relationship of the tire changes on just 1 axle - this affects stability. And the lateral capability of just 1 axle is reduced - making the car behave differently at the limit depending on speed.

[Bill Verburg]

Originally Posted by BSiple

I read every one of these threads when they come up. My 86 Carrera had a tea tray, and no front spoiler, I added the factory chin spoiler, and it did make a difference.

Fast forward to my 964 turbo, it has the tea tray as well, but no noticable front spoiler. Why is this? I am guessing that the air vents in the front valance, help direct the air to keep the car planted. This thing is a rock at 100+.

Just curious.

964 superficially looks like a 911 but the air management is way more sophisticated.

even w/ the base front and motorized rear spoiler, lift is very close to zero at both ends.

[911boost]

Thanks Bill, I figured so with all of the air vents, etc.

Bill

[tshih]

Porsche is famous for form follows function rather than the reverse. All modern porsches stock have been refined in the windtunnel and actual testing of the mules around the world. If you look at the bottom of the 993 you'd see panels covering the bottom of the control arms that are there for lift and air management. When you buy a Porsche versus another marque, you are getting a highly tested and developed car for the money, that's why they are such great values and hold their values relative to others which are status symbols without substance and engineering to back up their visual impacts.

The 964's and others as Bill Verburg mentioned are passed the crude slapped-on protrusions of the early 70's-80's race car adapted to street designs.

[Ole Petter]

BURGERMEISTER, many thanks for posting the detailing on lift!
It really makes it all easier to understand. I have never seen the chart on front end lift before. Interesting to note that the lift kind of "follows or matches" the weight distribution! Of course I was aware that the 911 shape gives most lift at the back end.

[tshih]

If you look at the photo of the red 964 turbo, you can see that the whole front piece with the grill opening and the bumper incorporates all the air flow management that use to be handled by the front bumper, side bellows, front valence, and a lip spoiler (optional) in the 1974-1989 911.

As an aside the GT3 and GT3RS of today have a detachable front lip spoiler which is meant to be easily removed and replaced due to the understanding that those cars are meant to be driven on real streets and will suffer early and frequent damage to a vital part of the safety designed into the shape of the car. Again, a well thought out practical Porsche solution which integrates their form follows function philosophy of design.

[Bill Verburg]

Originally Posted by tshih

.....
As an aside the GT3 and GT3RS of today have a detachable front lip spoiler which is meant to be easily removed and replaced due to the understanding that those cars are meant to be driven on real streets and will suffer early and frequent damage to a vital part of the safety designed into the shape of the car. Again, a well thought out practical Porsche solution which integrates their form follows function philosophy of design.

That's the truth, part of the design that increases aero efficiency in front is projecting the lower snout out further to the front, each iteration from 964 up through 997 has placed the leading lip in increasingly vulnerable spots.

My 993 is a nightmare compared to my C3 in so far as hitting stuff on road transitions w/ the front end

People I know that own 997 GT3/ GT3RS buy their lip spoilers in bulk as they don't llast long in street useage

[rfloz]

I have a 1984 Factory Turbo Look with the stock 3.3 Turbo rear spoiler and the largish Turbo front spoiler. The car is very stable with the stock spoilers.

As part of my weight reduction plan I am thinking of getting a fiberglass duck tail and engine cover.

The car is primarily for auto-cross (maximum speed about 70 mph) and limited street use (85 mph) so the change should produce a only small amount of additional oversteer, yes?

I also will be doing the occasional DE at the lower speed local venues, Streets of Willow and Cal Speedway infield where the maximum in my car is about 110 mph. Is the added lift from the duck tail enough at that speed to cause instability? Should I plan to switch rear spoilers for DE?

I suppose a fiberglass IROC spoiler would solve all these issues, but the look of the duck is also an attraction.

Has anyone actually run this setup (Turbo front and duck rear spoilers)? If so, how was it out there?

[tshih]

Not to hijack your (OP) post but anyone can recommend the best value product that they own and installed for adding a duck tail spoiler for the 1984-89 3.2 Carrera with only the OEM front spoiler? Does a good company offer the tail and rear lid as one piece and anyone knows how expensive is it in both FG and CF versions?