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    1. #21
      Join Date
      Jun 2009
      Posts
      91
      The belly pan does not have to be continuous or complete. Although for the best aerodynamic affect it should be as smooth as possible. The goal is to keep the air under the car moving as fast as possible over the underbody.

      That said, the exhaust(at least mufflers and cats) don't have to be covered.

      Here's what we did for the One Lap Odyssey I built at work(Honda).

      Using a single roof/floor manometer reading and assuming the same pressure difference over the main roof area, we measured an improvement of 230lbs(191lbs of lift --> 40lbs of downforce) at 100mph.

      FYI the van is 532whp twin turbo 3.5 V6 Honda Odyssey. 6-speed manual. H&R coilovers, Enkei 19x10, 275/35/19's. Turbo system built and tuned by yours truly with Autronic ECU. Built for the '06-'08 One Lap of America.

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    2. #22
      Join Date
      Mar 2006
      Posts
      27
      maybe if you can do a few louvers at the back of the car, and than hook up a couple of small fans up front on a toggle switch. i think might work..

    3. #23
      Join Date
      Oct 2009
      Location
      New Derry, PA
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      1,265
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      Quote Originally Posted by dr.gonzo View Post
      maybe if you can do a few louvers at the back of the car, and than hook up a couple of small fans up front on a toggle switch. i think might work..


      ?????????

      Ray Kaufman - Wyotech Chassis Fab and High Performance Instructor. Words of Wisdom from an old master... at Asylum Custom Interiors website

    4. #24
      Join Date
      Jan 2008
      Location
      Long Beach, Ca
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      1,564
      Country Flag: United States
      Chaparral 2j! Pure Awesome.
      Jon Rasmussen
      Ex Team OLJ.
      '72 Nova

    5. #25
      Join Date
      May 2002
      Location
      Northern California
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      10,715
      Country Flag: Bosnia Herzegovina
      I remember that, it sucked all the chrome off itself. Multiple fans provide the proper amount of suction.
      MrQuick ΜΟΛ'ΩΝ ΛΑΒ'Ε

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    6. #26
      Join Date
      Aug 2006
      Location
      Easton, PA
      Posts
      989
      Country Flag: United States
      I wouldn't enclose the exhaust; make some real pretty bends in SS, then bring the pan right up to it.
      OR, you could cover the floor of the car w/ space shuttle ceramic tiles.
      Keith C.

    7. #27
      Join Date
      Oct 2004
      Posts
      2,544
      Country Flag: United States
      Quote Originally Posted by Wicked View Post
      Here's what we did for the One Lap Odyssey I built at work(Honda).

      Using a single roof/floor manometer reading and assuming the same pressure difference over the main roof area, we measured an improvement of 230lbs(191lbs of lift --> 40lbs of downforce) at 100mph.

      FYI the van is 532whp twin turbo 3.5 V6 Honda Odyssey. 6-speed manual. H&R coilovers, Enkei 19x10, 275/35/19's. Turbo system built and tuned by yours truly with Autronic ECU. Built for the '06-'08 One Lap of America.
      HHhhmmmm, wife could use a minivan, is this thing for sale? LOL!
      Red Forman: "The Mustang's front end is problematic; get yourself a Firebird."

    8. #28
      Join Date
      Nov 2008
      Location
      TN
      Posts
      938
      Quote Originally Posted by exwestracer View Post

      ?????????
      or with a corvette?

      http://grassrootsmotorsports.com/articles/plan-attack/
      Benjamin

      Twin Dusters
      '72 Plymouth Duster "Aero Duster" project
      '72 Plymouth Duster "Daily Duster" project
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    9. #29
      Join Date
      Oct 2010
      Location
      SLC
      Posts
      590
      Perhaps a compromise is in order. belly pan as much as you can within reason but leave the trans tunnel open. combine that a good front splitter and rear diffuser and you should have a noticeable increase in down force provided you have effectivly expanded the air passing under the car. you could always have a removable piece for the trans tunnel just for track use. obviously this won't be as good as a race car, but i hear race cars aren't the most comfortable.
      Zach

      1970 Mach 1 build - Half-Breed (pro-touring.com)

    10. #30
      Join Date
      Jul 2001
      Location
      Calgary, AB
      Posts
      1,826
      Country Flag: Canada
      Th agent 47 mustang incorporates a naca duct in the rear window with an air tube down to an opening over the exhaust system to aid in cooling... I'm thinking of something similar for the '69...
      James
      1967 Camaro RS - The OLC
      1984 Camaro GT1
      1989 Camaro 1LE - The BOC

    11. #31
      Join Date
      Sep 2006
      Location
      Southern Indiana
      Posts
      4,699
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      OK if you use a high grade stainless like 321, and have it thermal barrier coated inside and out,using the same stuff they coat jet engine "tail feathers" with and as for a "belly pan" from what I read from ol' Smokey Unicks (sp) ideas and testing a pan between the bumper and the crossmember and behind the rearend to the rear bumper.
      I wouldnt get too radical near floor and driveshaft area. dont do as complete enclosure, keep it real and clean. like from pinch welds to tunnel. leave exhaust exposed so you dont enclose the heat, and I dont care what metal you use wrapping is a no no. The thermal stress it will have cracks and fractures in no time.
      This came from 3 different stainless header manufacturers, no wrapping UNLESS your protecting a hose or critical part. The shorter the better.
      Cleaner air under car is good as long as your work helps it build a suction at speed nad also let the engine compartment bleed air properly.
      Good Luck.
      Lee Abel
      AFTERMARKET PERFORMANCE

      1977 Chevy Monza 2+2:Project "Cheap Trick"
      1978 C10 Long bed , On air and trailer puller
      2006 Buell Blast ,Just a bike to ride and for mileage
      1966 Caprice 4dr Sports Roof fact.327/now 350/SOON 454???? Project "II Old,,,ZERO BUDGET OR LESS CAPRICE!"

    12. #32
      Join Date
      Nov 2008
      Location
      TN
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      938
      Quote Originally Posted by James OLC View Post
      Th agent 47 mustang incorporates a naca duct in the rear window with an air tube down to an opening over the exhaust system to aid in cooling... I'm thinking of something similar for the '69...
      I looked that up... and they have it in backwards... Which makes it do absolutely nothing.
      Benjamin

      Twin Dusters
      '72 Plymouth Duster "Aero Duster" project
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    13. #33
      Join Date
      Apr 2009
      Location
      san diego
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      Quote Originally Posted by Bjkadron View Post
      I looked that up... and they have it in backwards... Which makes it do absolutely nothing.
      Actually they are correct.

      Once you consider boundary layers it makes sence. The air closest to the car " boundary layer" move at the same speed as the car. The NACA duct creates vortices that deflect the boundary layer away from the intake, but draws in the faster-moving air above it.

    14. #34
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      san diego
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      Reversing the NACA duct will actually draw air out of the car, rather than drawing it into the car.

    15. #35
      Join Date
      Nov 2008
      Location
      TN
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      938
      Quote Originally Posted by Bryce View Post
      Actually they are correct.

      Once you consider boundary layers it makes sence. The air closest to the car " boundary layer" move at the same speed as the car. The NACA duct creates vortices that deflect the boundary layer away from the intake, but draws in the faster-moving air above it.

      Reversing the NACA duct will actually draw air out of the car, rather than drawing it into the car.
      I know how they work in the one direction. But I'm pretty sure they were only designed to work one way. I don't know a whole lot about fluid dynamics but I'm pretty sure it wouldn't draw much, especially where they have it mounted. They have nothing to reduce flow separation along the back window and the spoiler is creating a high pressure zone.



      Do you by any chance have a CFD picture or something of a NACA Duct that I could look at?
      Benjamin

      Twin Dusters
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    16. #36
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      Apr 2009
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      san diego
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      Benjamin, I though we were talking about the quarter window ducts. Hmm. I have to give those some thought. I dont think those would work very much. They would have to do some windtunnel testing to verify flow over the back window. Usually the flow has not come back down to the window at that point. But the interior of the car is usually high pressure and the back window is lower pressure. So you would have a outward flow at that point but not due to the NACA duct specifically. If you had a laminar flow over that duct it would work.

      Let me look through my areo books and see if I can find the calculations for the NACA ducts.

    17. #37
      Join Date
      Dec 2008
      Location
      Lehigh Valley Pa
      Posts
      1,269
      The reversed NACA duct would be easy enough to test. Say make a temp side window out of something with the duct mounted to it. Heck even cardboard would work. Then go for a drive and see if it pulls air, draws it in, or does nothing.
      1996 Federal Cadillac hearse
      1988 Eureka Chevy hearse

    18. #38
      Join Date
      Nov 2008
      Location
      TN
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      938
      Quote Originally Posted by Bryce View Post
      Benjamin, I though we were talking about the quarter window ducts. Hmm. I have to give those some thought. I dont think those would work very much. They would have to do some windtunnel testing to verify flow over the back window. Usually the flow has not come back down to the window at that point. But the interior of the car is usually high pressure and the back window is lower pressure. So you would have a outward flow at that point but not due to the NACA duct specifically. If you had a laminar flow over that duct it would work.

      Let me look through my areo books and see if I can find the calculations for the NACA ducts.
      Nope, the side ones are correct. I was talking about the one in the picture. Every fastback I have seen has flow separation or at least increased boundary layer thickness or turbulent flow. With the spoiler there creating a high pressure area, and with the tubing going somewhere the inside/outside pressure difference would be negated I wold think.
      Benjamin

      Twin Dusters
      '72 Plymouth Duster "Aero Duster" project
      '72 Plymouth Duster "Daily Duster" project
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    19. #39
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      Apr 2009
      Location
      san diego
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      Quote Originally Posted by Bjkadron View Post
      Nope, the side ones are correct. I was talking about the one in the picture. Every fastback I have seen has flow separation or at least increased boundary layer thickness or turbulent flow. With the spoiler there creating a high pressure area, and with the tubing going somewhere the inside/outside pressure difference would be negated I wold think.
      I dont think that spoiler does much unless the car has vortex generators on the trailing edge of the roof.

      It would need testing to verify. I would just put some pitot tubes (monometer) in that area to test for pressure. If you have a lower pressure on the outside versus the inside of the back window you could make those vents work.

      I saw a studebaker streamliner that had a huge duct from under the car to right behind the rear window. I will try to find the picture.

    20. #40
      Join Date
      Apr 2009
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      san diego
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