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Thread: Very old bird gets updated aero

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    Default Very old bird gets updated aero

    I found this site looking for info on aero stuff a while back and joined. I know most of the discussions here involve more modern cars but I thought some of you guys might be interested in this and perhaps have suggestions and/or answers to questions.

    Back in the late 60's when the General Motors 2nd gen F bodies were being designed the engineers at Chevrolet supposedly did some wind tunnel testing. While they chose not to use the information collected for racing applications, legend has it that the engineers over at Pontiac (racers) got a copy of the test files and put the information to use when designing the 70 Trans Am which would be used for road racing with the number of the original 70 production run of Trans Am's being enough to fulfill homologation requirements of the sanctioning body.

    So while the 70 Camaro only received a small rear spoiler the 70 Trans Am got a tall rear spoiler, functional fender vents, low front air dam, and flares in front of all the wheel openings. My car's a 70 TA clone I built from an Esprit and I've owned it about about 25 years. Although the car is street driven I've run it at several drag strips, 1 mile LSR's at Maxton and Dade/Collier, and HPDE's at Lime Rock, Road Atlanta, the old Moroso & new PBIR, as well as Sebring. Road courses are my favorite place to run the car and I'd like to try open road racing eventually.

    What I'm trying to do is incorporate some of the air flow management techniques for racing that have been used since the car was built as though the Pontiac engineers who were racing had them available to them back in the early 70's. I don't have to stay within any "rules" since I don't race in any particular class so things like rear diffuser tunnels that start forward of the rear axle are fair game. Hopefully the aero mods will improve the performance of the car. I know once I get the car back on track there'll be a lot of testing and tuning to get things right. I fully expect things like spring rate changes to be necessary.


    Here's the car before being stripped to the unibody for the current rebuild.



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    What started as a project to do a few upgrades went right down the slippery slope to a complete restoration stripping the car to a bare metal shell and putting it on the rotisseri. I figured as long as I'm in this deep I should do a lot of the little things I'd dreamed of and talked about.

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif emilio700's Avatar
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    Subbed!

    Welcome to our little corner of the net. Interested to see how this turns out. Are you thinking about keeping all the aero mods stealth/invisible or letting it hang out time attack style? I think it would be cool to keep the aero low key, sleeper style. The diffuser could certainly be that way.

    What do you have for a powertrain?
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    But obviously I just dont get it. -fatbillybob

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    Yes yes please god yes.
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    Quote Originally Posted by emilio700 View Post
    Subbed!

    Welcome to our little corner of the net. Interested to see how this turns out. Are you thinking about keeping all the aero mods stealth/invisible or letting it hang out time attack style? I think it would be cool to keep the aero low key, sleeper style. The diffuser could certainly be that way.

    What do you have for a powertrain?
    Thanks! While I appreciate the stealth approach for some cars you can probably guess that a guy running 5" side pipes and bright red paint probably isn't going to go for the stealth approach. Probably end up looking like a slightly subdued version of what a 70 Trans Am WTAC car might have looked like. I am trying to keep everything removable as well as adjustable so I can run different versions on the street, drags, LSR's , and on road tracks.

    Current powertrain is a mildly built Pontiac 400 with Canton RR pan and other goodies, T-400 with shift kit etc., and an 8.5" 10 bolt 2.41 posi with Moser tapered axles etc. I figured better to learn track skills by not having a lot of power so it's kinda like a big momentum car. After I get the aero and suspension set up I'm going to build a serious engine and swap to a 5 speed manual. Hopefully the driver will progress at the same time.

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    Quote Originally Posted by SDSUsnowboards View Post
    Yes yes please god yes.
    I've read your home brewed aero thread a couple times and figured you'd like this! I've been making everything myself so far.

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    Man that is awsome. I hope you post up more. Please consider a redesign on your doorbar. That doorbar setup is useless but the Full containment seat is about as safe as you can get.
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    http://www.trackhq.com/Banners/yellowsitesponsor.gif Blackbird's Avatar
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    I was going to say the same thing about the door bar, not doing much as it is and should be revised.
    Otherwise I like this idea quite a bit and look forward to see what you're coming up with

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    I'm curious why you guys would change the door bar. As with most things there's always compromises to be made. This car is not used in any wheel to wheel racing and I don't want to hollow the doors and climb over NASCAR door bars every time I go to the store. When the cage was designed we used the regulations from the SSCC, SCTA, NHRA. After discussing material options with tech guys from the various sanctioning bodies we decided on 1 3/4" 1020 DOM main tubes. Here's a thread on the safety upgrade project with the cage, fire systems, etc. I did back in 2008. The 14 Car safety thread, Roll Cage, Kirkey seats,Fire systems.

    Here's the basic list of things on my aero adgenda.

    1. Extend air dam
    2. Splitter
    3. Underbody pans from splitter to diffuser
    4. Side skirts & side splitters
    5. Wicker bills in front of wheel openings
    6. Rear diffuser, possibly two types
    7. 3 different rear spoilers
    8. Foilers behind wheel openings (these may actually be detrimental and not used on track)
    9. Seal radiator support so only air allowed past is through radiator and brake ducts
    10. Side window panels from cage to body to reduce chute effect on road courses
    11. Roof fences?
    12. Tire air dams
    13. Front splash pan opening block offs
    14. Modify fender vents
    15 Rear wing if needed

    I'm a grassroots racer type guy. No engineering degrees, no supercomputer with CFD programs, no full size wind tunnel, no friends named Katz, McBeath, or Brilliant and don't have the math background to use Bernoulli's equation. However, I'll do as much testing as possible while building and then do track testing with video to see what actually works and how well in the real world.

    The first modification is a taller rear spoiler. Lots of testing has been done on rear spoilers in general and for the shape of a 2nd gen the height after the first couple inches increases the downforce more so going from a 3" spoiler to a 4" spoiler doesn't increase the downforce as much as the change from say 4" to 5". The penalty is increased drag that will slow the car. Eventually I'll probably have 3 different rear spoilers and also full wing to test.

    Although increased drag will probably lower the top speed capability the cars lap times on a road course may actually be reduced if the cornering grip is increased enough with the tall spoiler with the combined effects of splitter and underbody tray. I'll be making other spoilers for straight line top speed (less drag)and some for road course use so there will be several versions of aerodynamic prep I can set the car up with depending on what kind of track activity I'll be doing. At the same time I'll have most of the aero stuff removable so the car can look like a sort of stock bodied TA clone.



    Last edited by NOT A TA; 11-17-2015 at 09:33 AM.

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    Shown above is my rudimentary aerodynamic setup with very high speed additional wind provided by a Stihl leaf blower. Testing worked out surprisingly well to determine what I wanted to test for modifying fender vents.




    The stock fender air extractor vent shown above (without screen) during base line yarn tuft testing at normal driving speeds shows the vent does work to help reduce air pressure underhood based on my crude testing. Even at normal driving speeds the vents pull air out of the engine compartment. As speed increases the vents pull more air. I have long strands of yarn inside the fender attached at various distances from the vent opening so I can see how much suction there is pulling air out.

    Now the stock vent opening is about 15 Sq. In. and the stock screen blocks off about 5 Sq. In. of that. The air coming out is subjected to turbulence slowing it down which is caused by the screen itself. So anyone wanting to increase the breathing a quick 50% plus over stock can just remove the screens.

    Theoretically the vents help reduce under hood air pressure that causes the "floating" feeling due to lift that a lot of cars (including base 2nd gens) get at high speed. Having spent quite a bit of time over 120 MPH in my car I'll say it's very steady and stable feeling at speeds up to 150 MPH in part due to the stock TA aero parts I believe. Since I'm going to try and go a lot faster at Land Speed Races I want to make a set of vents that will optimize under hood evacuation with the least amount of drag. I also want to make a set that will help maximize usable down force by reducing under hood pressure as much as possible and by design perhaps add some additional down force by the exterior design of the vents themselves.

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif Blackbird's Avatar
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    The three things that popped into my eye the moment I saw the door bar are -
    1. Your body is completely exposed at bumper height.
    2. There's no triangulation to keep the things from bending upwards.
    3. It's just one tube.

    I realize you built it to clear the factory door panel, but the safety aspect of it is compromised as a result.
    Hope you take this all as constructive criticism, as it was meant to be that way

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif emilio700's Avatar
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    In for DTM T/A
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    But obviously I just dont get it. -fatbillybob

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    Quote Originally Posted by Blackbird View Post
    The three things that popped into my eye the moment I saw the door bar are -
    1. Your body is completely exposed at bumper height.
    2. There's no triangulation to keep the things from bending upwards.
    3. It's just one tube.

    I realize you built it to clear the factory door panel, but the safety aspect of it is compromised as a result.
    Hope you take this all as constructive criticism, as it was meant to be that way
    Appreciate the criticism. When using a street car as a track car there's going to be compromises and a certain level of what one considers an acceptable risk. This goes both ways and I've heard the roll cage on the street side often as well. Anyone who asks I tell them "Build a track car for the track and keep your street car a street car". It's a lot easier that way.

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    Quote Originally Posted by emilio700 View Post
    In for DTM T/A
    AHAHAHA, now if I could shed 1300 lbs and get a carbon tub in the process that'd be awesome!

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    Quote Originally Posted by NOT A TA View Post
    Appreciate the criticism. When using a street car as a track car there's going to be compromises and a certain level of what one considers an acceptable risk. This goes both ways and I've heard the roll cage on the street side often as well. Anyone who asks I tell them "Build a track car for the track and keep your street car a street car". It's a lot easier that way.
    Would a bar going from the rear foot up to the diagonal to form a triangle fix most of the issues and still clear the door?

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    I posted in the parts wanted section of a TA forum to get some extra expendable fender vents I wouldn't be worried about hacking up and then tossing if my plans didn't work. One set came from a guy named Barefoot and another from a guy named Jack. From here on the more radical vent design are called the Track Jack vents and a more streamlined set will be referred to as the Barefoot vents. Anyway, I stripped them of paint and this way I'd have my stockers along with two more sets to modify so I can see the difference changes make by just doing all my testing on one side of the car and not having to reshape one vent over and over to test different theories.

    The first thing I tried was changing the exterior of the vents to change the airflow and increase the suction of under hood air. I made two different designs and it appeared to me that both designs drew substantially more air through the stock openings with the larger more radical angle design pulling more air than the more streamlined one. I realize that using a blower to flow air over the vents without the normal under hood and other air flow that will affect vents during actual use limits the accuracy but I was just looking for trends.



    Pic below shows the yarn tufts with no air movement and the more radical "just for the track Jack" concept mocked up with cardboard.



    Pic below is the track Jack concept with high speed air moving over it. You can see how air close to the surface is actually drawn backward from the rear of the vent housing to join the air coming out the vent opening. Seems to me like this also shows increased drag.



    The streamline barefoot version shown below with the wind speed the same as the track Jack version pic shown above. You can see some of the long strands of yarn have been pulled out from inside the fender and how the boundary layer air moves over the Barefoot vent opening as opposed to above and below it as seen in the pic above.

    Last edited by NOT A TA; 11-17-2015 at 07:20 PM.

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    I added a small wicker bill (Gourney flap) to each of the cardboard mock up vents and tested. Adding the flap seemed to increase the suction of air out the vent while reducing turbulence and boundary layer reversion just aft of the vent. Notice in this pic the strands on the fender are all aimed rearward while in the pic above without the wicker the strand just behind the vent is pointing forward. both modified vents had similar changes with the track Jack vent appearing to pull a lot more air out of the engine compartment.



    My next change was increasing the size of the opening itself in the vent to allow more volume. It appeared that even with the stock vent exterior shape the volume exiting increased while the boundary layer airflow was smoother. This leads me to believe the stock shape was capable of pulling more air but stylists probably decided the opening size and use of a screen.



    In the pic below I added the Barefoot cardboard with wicker and it appeared that the vent could pull more air than even the larger opening could provide as the yarn tufts at the rear of the vent flipped to a forward direction. Seeing this I skipped testing the Track Jack version and decided to open the vents more.

    Last edited by NOT A TA; 11-17-2015 at 07:34 PM.

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    I opened up the rear of the stock opening to the metal upright in the inner metal structure. Still seemed to be able to pull more air as seen in the pic below.



    I decided to try cutting a slot in the fiberglass vent behind the metal support and was surprised to find yarn strands a few inches in from the slot were being sucked out the slot even with the stock exterior vent shape. Boundary layer flow seems good with very little drag. Perhaps something like this was what Pontiac's engineers wanted to make the vent look like before stylists got their hands on it?


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    With the more Barefoot cardboard installed (pic below without wicker) the drag increased apparently and the suctioning of yarn strands increased inside the fender.



    Then I set up the track Jack cardboard setup (with wicker)and found I could really pull a lot of air out of the engine compartment pulling long strands of yarn 10" away taped by the hood hinge out the opening! However there appeared to be a lot of turbulence so I decided to try adding strakes to help smooth the flow and reduce turbulence.





    The strakes seemed to straighten the flow coming out of the vent (pic below) so my thinking is that a little more air was being be drawn through with less turbulence. At this point my openings were limited in size by the metal inner structure and it appears the exterior vent shapes can still pull more air soooo the next step will be to start cutting the inner structure and open the vents up more!


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    I removed a lot of the unnecessary metal inner vent mounting structure. Looking at the design I decided the vertical metal section was probably incorporated to keep the inner structure from bending or twisting before and during installation (spot welding) to the fender skin. So I cut it out and opened up the leading edges as well so I could make the vent opening as large as possible. With a stock fender vent in place no one could tell from the outside. With a modified vent you can see some of the inner structure if you look and are close. From any distance more than a few feet no one would notice.





    I'd put a slot in the vents previously and decided that now that there is no support in the way I'd try opening up the vent even more. I won't bore you guys with a lot of different pics of the progression of tuft tests but the Track Jack design with wicker, strakes, and wide opening seems to pull the largest volume of air through the vent. I kinda like the looks of the stock vent with the big opening and it seems to have the least drag.





    The large opening of the Track Jack vent now has over 30 Sq. In. to draw air through which is more than 3 times the stock vent with screen. When combined with the increased angle, size, wicker, and strakes I'd imagine it can pull 4-5 times or more the volume of air that a stock vent with screens can pull. I'm going to see if I can find someone with a flow bench I can test my theory and designs on. Meanwhile I'm going to modify the vents to be ready for paint. I'll be making a flow straightening piece to fit inside the fender vents the next time I have the fenders back off the car (which will be pretty soon).

    Here's the difference between stock and modified size openings.


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