Stock Rear Spoiler = -8%MPG

MikeKanterakis

SCCoA Member
The Numbers:

My '90 5-spd came to me with a stock rear spoiler. Best Freeway mileage recently was 21.xx MPG.

Last month I removed my rear spoiler to see if it was creating more drag than downforce.

Now, I'm getting 23.4 MPG.

There's no doubt in my mind b/c i can easily see the increased mileage on my fuel gauge. It's that much better.

I've only had the car up to about 100 - 120 since the spoiler came off, but the car felt just as stable at that speed. (to me)

Because my car has it's own characteristics that could have an influence on my particular increase in mileage, I am asking anyone else to please also conduct this experiment and report back your findings.

I got the idea for this experiment from reading a few posts about spoilers and also looking at a previous month's cover picture here at sccoa.com. It was the salt flats car that went up to 190mph and had this piddly little nub of a spoiler on the back. So much for the needed downforce at higher speeds.

P.S. I also found some rust around the rear passenger side bolt hole where the spoiler attached to the trunk lid. So you might want to have some sand paper and touch-up paint with you if you attempt this.

Too bad the darn thing makes the car LOOK so much more sporty. :mad:
 
Mike,

Glad you are getting better gas mileage. With today's gas prices I'm sure every little bit helps.

To clarify one point, the spoiler you took off your car was not stock. No SC's were ever offered with a rear spoiler. Someone added it, previous owner or maybe the dealership that sold it new.

The only MN-12 T-Birds that came with "stock" rear spoilers were the 96/97 LX's which I think was part of the Sport option.
 
It's about two bucks for the super. It's gonna get a lot worse this summer. My SC won't be an everyday driver. just a garage ornament waiting for that day when it will actually be worth something.
 
MikeKanterakis said:

My '90 5-spd came to me with a stock rear spoiler.

Actually, it didn't, Mike. The only MN-12 Birds that had a rear spoiler from the factory were some of the Sport pkg. 96 - 97 4.6L cars. Yours may have a Ford dealer-installed or accessory rear spoiler, so being the nit-picker that I am, I'll have to argue the point that you have a stock rear spoiler.

And yes, it's there for appearance, not performance. I can personally attest to my SC being quite stable at 151 mph with a bare trunk lid. ;)

cheers,
Ed Nicholson
SCCoO
 
OK, OK, OK, OK!

:)

But, I really wanted to get some feedback on the mileage increase after the removal of the spoiler. My comment about the Stock Rear Spoiler was nothing more than a reflection of my ignorance.

I can now understand why there was some rust under the spoiler. If Ford had an assembly line procedure for installing a spoiler, I would assume that it would have taken the time to paint over the hole after drilling it into my trunk. :)

I agree with Randy N Connie that anything that doesn't enhance performance is extra weight, and at 25lbs (or less) it's significant extra weight; however, I do think that if I took the wing off the car and threw in into the trunk, that I'd still get the increase in mileage regardless of the weight still being on the car.

I got interested in trying to understand the dynamics/engineering that went into the idea/design of a rear spoiler. So the easiest experiment I could come up with was the removal of the spoiler itself. I guess that I just don't understand anymore why the spoiler would be of any benifit ever! I mean, at VERY fast speeds, the amount of extra down-force gained would probably be pointless when you take into consideration that at 140+, the SC has practically no PUSH at the rear wheels that would break it free (even in the 5-spd).

NEXT IDEA:

Ok, so there's also this sucking force between the trunk and the rear window, right? And that's part of what the spoiler is supposed to compensate for, right? So, instead of having a spoiler there that compensates for the upward suck of the wind flowing over the car by creating a heck of a lot of extra drag, why not direct some vents to the section of the trunk that's closest to the rear window?

I got the idea for this from my first car, 1971 Lincoln Mark III. there was a vent that went from the interior of the car's rear (deck lid thing) by the window, and went to the outside of the car. On that car there was a lot of body space between the windshield and the trunk lid, not like our 1/2 inch strip of metal separating the two.

so, I was thinking, if there's this great sucking force at the back part of the car, that necesitates the use of a spoiler, why not give this sucking force all it can handle by directing some ducts either from the side of the car, or from the bottom, that would release that sucking preassure. Thereby, removing the necessity of the spoiler???????????????????????????????????????????????????
 
Mike, I'm not qualified to give you a full proper technical explanation, the science of aerodynamics is a pretty involved one.

But I can tell you this ... about 95% of production car spoilers do nothing for performance. They would have to be much larger, and farther up in the airstream, to be of any benefit for downforce. That why the rear spoilers on NASCAR racers are so large and at such an angle. The old Dodge Daytona of 1969 and Plymouth Superbird of 1970, plus the 2000 Cobra R Mustang for that matter, are good examples of what a spoiler has to look like to be effective on a production car body ... way up in the air, and even then they're not doing anything until 100+ mph.

I'm sure if you try a Google search you can get a better explanation than what I can give you.

cheers,
Ed N.
 
I recall where C&D tested a Porsche Carrera (I believe) and they have this spoiler that automatically deploys at a certain speed. Well, they ran the car on a test track to 150 with the spoiler up and down and could percieve no difference. Point is that even factory designed spoilers may have arguable effect in the real world.

I also recall a study in aerodynamics were the conclusion was that if you were to add small venturi type contours to the roof of the car so that air was directed down against the trunk, that the "vacuum" could be all but eliminated. Problem is they didn't think anyone would buy the look of them (they look "different").

Mike Puckett claims that removing his spoiler from the trunk of his car was worth .2 in the 1/4. Something to think about.
 
Thanks for the input guys.

XR7 Dave, if you have any pictures of what this Venturi style vent looks like, please send me a link.

Any other ideas on the vacuuum created behind the rear window? I'm partial to the vent that comes in from the passenger compartment like on the Mark III. It's a great option. you can drive with the windows down at 75 miles per hour, and have virtually NO air turbulence in the cabin of the car. It's really cool. imho
 
For what it's worth, I always thought the area behind the rear window had positive pressure. I used to have a second generation Corvair and the engine cooling air was drawn into the engine compartment from this area. A friend swapped a Torinado powertrain into another Corvair and mounted the radiator in this location.

Joe
 
hmmm

so u guys mean those rice burners with those big aluminum wings serve a purpose other than looking like sht too bad most of them are on front wheel drive cars haha i always thought the saleen wings for the fox body mustangs were pretty sweet they look like they produce downforce i seen one on a thunderbird here in conroe and i didnt know what to think about it whats your guys oppinions
 
When is a Wing, NOT a Wing?

Have you ever looked at the cross sectional area of an airplane wing? A wing creats lift. If you Invert the wing, it still creats lift, just in the opposite direction (ie: downforce). The "wing" (actually an Air Foil, or as Ford called it, a "Foiler") on the '69 Mach 1 is a true inverted wing. Years ago I remember reading a wind tunnel report, done by Ford. They said that the '69 Mach 1 foiler added 150 lbs of downforce, @ 150 mph. However the aerodynamic drag associated with the foiler took 1 mph off the top speed of the car. Ford used the same "basic" spoiler on other models too. Cougar Eliminators, Torinos, Talledegas, Mercury Spoilers, & maybe a few others. I say "basic" spoiler, because the pedistal mounts on some are different widths, to accomodate different under trunk layouts.

Now back to that 25 lb. chunk of fiberglass on your trunk. If you look at the cross sectional of just about any "wing" (including yours!) made after the mid 70's, you'll see that it Isn't a "wing" at all. Since it isn't a true air foil, it creats NO downforce. However it still creates a lot of aerodynamic drag. Getting rid of that aero drag, is why your car gets better mpg with the "wing" Off the car. I've said (sarcastically) for years that you can improve the high speed handling of your SC more, by throwing a few cement blocks in the trunk, than you can by bolting 25 lbs of air turbulence on the back of the trunk! The current crop of glass wings are for sombody who wants the "look" of a race car, but without the "function" of a race car. Hmmmmmmmmmm!!!!!!!

68COUGAR
 
Not to nit-pick but Ed I disagree with some of your examples. Rear wings do not have to be huge to work. A lot depends on the design of the rest of the car. The wing and vehicle must be designed together for proper effect. You are correct that it is a very complicated science. Some are huge, as in the Cosworth Escorts, some aren't.

I am sure you all remember when the Audi TT came out. Remember they had no rear spoiler? They were becoming unstable and flying off the roads at 140 MPH or so. Audi added a spoiler that is only about 2 inches high to cure the trouble. The chassis group had asked for that spoiler to begin with, but marketing didn't want it to clutter up the design. The marketing guys won the first battle, but the Chassis guys were right.

The thing that popped right out at me was the example of the Dodge Daytona and Plymouth Superbirds. While the wing was a result of high speed development for NASCAR, they did not have to be that big. If I recall correctly the wing that was tested to have the desireable result was only 3 or 4 inches off the surface of the decklid.

However with their design of attaching the wing to the edges of the quarter panels would prevent the trunk from opening. Not a problem for NASCARS, but a problem for the general public. So on the production cars the wing was raised high enough that the trunk would open and clear the wing and adjusted to have the least amount of drag.
 
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Production vs Race Cars

Surely you're not saying that the race cars Didn't have the 24" high spoiler. There are plenty of pictures of "Winged Wonders" at speed, & they ALL have the huge air foils. It IS true that they could make the required amount of downforce with a shorter wing.

As a side note. Have you ever looked at the differences in the nose cones between the Daytona Charger & the Daytona Superbee? The Chargers nose cone was designed first & is much higher. It was catching air & causing lift, so on the Superbees, they lowered it & cured the lift.

I think it's still debatable if the reverse air scoops over the front tires were to releave a high pressure area in the wheel wells, or to allow the suspension more travel. Some say it was a way to "bend" the rules.

68COUGAR
 
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The Dodge rear wing placement had nothing to do with the truck lid raiseing.

The sides of the wing were to keep the car stable.T he top of
the wing was raised to get it in clean air for more down force
and less air turbulence.
 
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