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Thread: Stock Rear Spoiler = -8%MPG

  1. #1
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    Stock Rear Spoiler = -8%MPG

    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.

  2. #2
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    Those wings weigh about 25 pounds to.

    RANDY

  3. #3
    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.

  4. #4
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    To me the look of a spoiler would outweigh the 2 mpg.

  5. #5
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    I just spend 44 bucks to fill up here in CA.

    How much is gas in Rhode Island?

  6. #6
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    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.

  7. #7
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    Re: Stock Rear Spoiler = -8%MPG

    Originally posted by MikeKanterakis

    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

  8. #8
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    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??????????????????????????????????????????? ????????

  9. #9
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    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.

  10. #10
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    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.
    Quote Originally Posted by Miller View Post
    Ya thats why i tape mine down. People think its bc i dont have a moonroof seal (which is true) but its really to keep my roof from ripping off .
    Email me here.

  11. #11
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    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

  12. #12
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    Feb 2004
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    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

  13. #13
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    Crap.

  14. #14
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    That wasn't directed at anyone in particular.

  15. #15
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    Oct 2003
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    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

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