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  1. #21
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    I love reading Ron's posts when he gets on a roll, he certainly has a way to make something that seems so difficult to understand...easy to understand. Couldn't help but notice all of the swipes he took at mid 80s Monte Carlos as examples though...

    Just kidding... ;) It's not the first time I've been told I should have bought an aerocoupe.

    Good aero is one thing, but ungodly ugly aero coupe back windows is a whole 'nother animal.

    I will add this also, I was a big fan of the looks of the NASCAR COT when they brought it out over the Twisted Sister bodies they ran previously. I know they all had challenges getting the new COT body to react aero-wise like the well developed previous car, but purely from an aesthetics view point, it was not even close. The COT rocked, mainly because it looked like a real production car.

    How does that apply to most of our PT cars, I'm not sure. I'm sure there are some that will use the knowledge above to get every last little bit of aero advantage out of their cars especially if they track them. Probably more likely there will be more of us that use a few of the hints and tricks here and there to make our cars aero better, without making wholesale changes to the overall look of our body styles. Air dams and splitters on the front to keep air from going under the car for sure, and maybe some side and back changes as well. I autocross with a guy that runs a 10" tall clear lexan spoiler on the back of his CP Cobra...that ain't happening on my car though, I don't care how much it helps.

    It's real nice to have access to the knowledge Ron posted above though, just so that there is a road map in place for any changes one might make...so they don't go the wrong way with something.

    Lance
    1985 Monte Carlo SS Street Car


  2. #22
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    Quote Originally Posted by Damn True View Post
    If I understand Ron's post above and I think I do, vortex generators and spill plates can mitigate the flow detachment over the back of the greenhouse. Fix it entirely? Likely not but it should improve it a bit.
    Yeah, I had only skimmed that section before asking. The airtabs look....lets say, feminine. Sticking a bunch of those on the roof doesn't appeal to me at this point.

    Ron, any thoughts on the "shark fin" style VG that show up on factory cars like the Mitsu EVO? Past the VGs, given a choice between a wing or spoiler on a street car/track day car is the obvious winner?
    Donny

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  3. #23
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    Hey Guys ! Thanks for all the great interaction.

    I slammed with some stuff today & early tomorrow. I'll get back on here Friday afternoon or Saturday & start answering questions.

    Until then, take care !

    .
    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
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  4. #24
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    Hey Guys ! Thanks for all the great interaction.

    I slammed with some stuff today & early tomorrow. I'll get back on here Friday afternoon or Saturday & start answering questions.

    Until then, take care !

    .
    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

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  5. #25
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    Quote Originally Posted by parsonsj View Post
    Nice. Lots to read.

    Just a quick question: are there sensors available to measure lift/downforce? My first thought (which is 1/1000 as well-formed as your posts) is that without data, much of this is based on lap-times, which brings a lot of other variables into play.
    You mean like a linear transducer? Racepack has an example under the sensor tab on their site. There are some more ghetto ways of doing it, but I don't want to muck up Ron's thread with that kind of thing.
    True T.

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  6. #26
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    Default

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Size:  219.3 KB On Areo on a on a race car it would depends on the rules for the class you are racing in. From fairly stock to IMSA Camaros of the mid to early eighties. I used a little of both on my 79 Z-28 . The nose if for 1978-81 Fibermotive IMSA Race car kit. with 1980-1 Z-28 Camaro /TranAm Factory fender flairs. I would of bought the IMSA fender flairs and wing. But by the time I could afford to buy them .They were no longer in production. Since I can no longer do that .I plan on fabricating a rear diffuser and a wing like you see on the Continental Tire Road Racing Series. Since this for mainly the street.

  7. #27
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    Ron: You haven't talked about stability. If you add a bunch of drag at the front of a car, but don't add any or much to the rear (like adding a large splitter to the front and removing a rear spoiler), then you may move the center of pressure in front of the center of gravity. This would be unstable and want to swap front to back. Not a good thing at speed. This has unfortunately happened too many times at Bonneville.

    Do you have any low tech ways to prevent or check this?

    Thank you for sharing your experience with us.
    Larry
    67 Camaro, 350 SB, Custom A-Arms & 3-Link
    My Build http://www.pro-touring.com/showthrea...LOVE-67-Camaro

  8. #28
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    Great tech. Suscribed.

  9. #29
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    Really nice write up, thanks a lot! I look forward to your other topics
    Steve Calabro
    2015 Chrysler 300S
    2006 Lotus Exige
    1996 Dodge Dakota 4x4 5.7 Hemi on 35's
    1968 Dodge Charger All Wheel Drive project Ratón

  10. #30
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    Quote Originally Posted by parsonsj View Post
    Nice. Lots to read.

    Just a quick question: are there sensors available to measure lift/downforce? My first thought (which is 1/1000 as well-formed as your posts) is that without data, much of this is based on lap-times, which brings a lot of other variables into play.

    Hi John,

    At the level we raced at, it was easy to be confident in changes, because we had engineers on staff, data acquisition on the race cars & amazing drivers.

    As far as accurately measuring the downforce gained or lift reduced (same difference) , we would take a baseline shock travel graph (showing all 4) & compare that to travel graphs as we tuned, or changed, aero features. We had our own data acquisition system (see photo) and utilized Penny & Giles linear potentiometers ... which is a fancy way of saying we used very high quality travel sensors on the shocks. They were very consistent & accurate.

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    If we made a change in the front to increase downforce, or decrease lift, we could see how much it compressed the front end more. Of course you know this amount of downforce varied with speed.

    So in a slower corner we may have seen:
    .150" more compression, of 350# front springs (x2) x .70 MR and know we gained 63# of net front downforce.

    While in a faster corner, the front compression was:

    .250" more ... so we knew we gained 122.5# of net front downforce there.

    This is enough gain that it made the car turn so much better the car actually got loose. So we would increase the rear downforce to balance the car out. We may change wing angle, spoiler angle or wicker bill height to achieve aero balance.

    In the same slower corner we would see:

    .050" more compression, of 600# rear springs (x2) x 1.0 MR ... and know we gained 60# of net rear downforce.

    While in a faster corner, the rear compression was:

    .100" more ... so we knew we gained 120# of net front downforce there.
    * You'll notice the gains are not always linear when comparing downforce gains front to back ... just close.

    ----------------------------------------------------------------------------------------------------------------------

    BUT ... I need to make this clear. We did NOT tune the car based on data numbers. We tuned the car based on driver feedback.

    Realize we had VERY good drivers with amazing feedback skills. Drivers that can tell the difference in 1/16" of suspension travel, tell you if one corner is touching the bump stop before the other, notice if a tire is 1/2 pound low and/or tell you if you have excessive lash in the ring & pinion. No exaggeration. None. Not even a little bit.

    So we had complete confidence in the driver's feedback & tuned accordingly. We just used the data to learn & recreate that set-up at a later date.

    But I don't feel it's necessary
    for rookie drivers without data acquisition systems to avoid aero. Just the opposite. Aero is a great learning tool. When you can make some track runs ... then bolt on your new splitter & go run it ... learn to feel the difference ... and see what the stop watch says ... that's a win-win. If, as a rookie driver, you are not sure if it improved or not after a run ... do A-B-A testing of things as outlined above ... then not only will you learn as a driver, but the car will gain grip & go faster too.

    My strategy is do things to improve front tire grip with front aero ... then tune on rear aero to balance the handling. If you run out of rear aero adjustment, you can use mechanical adjustment to balance the car ... but only to a small degree. This is NOT ideal, as mechanical adjustments to increase rear grip gain in reverse of aero adjustments.

    What I mean is ...
    If we put a taller wicker bill on the rear spoiler to add more rear grip (to balance the car from the added front grip) ... both ends of the car will have more grip as speed increases.

    If we have to use a mechanical grip adjustment in the rear, we can increase rear grip on higher speed corners, while reducing rear grip on lower speed corners ... or ... increase rear grip on lower speed corners, while reducing rear grip on higher speed corners. But with most adjustments we can't increase rear grip in both low & high speed corners "mechanically".

    This is why it's important to achieve aero balance. And this makes another case for why aero downforce is so valuable. It increases the grip in both low & high speed corners ... and in the correct direction ... meaning more downforce on the faster corners, where you need it more.

    I do not feel that engineers, data acquisition or professional drivers are required to gain from aerodynamics. Sure, that is the better method to more accurately quantify it, but it's not necessary. If you make changes and feel the car is better stuck, that is all that is required.

    I suggest your game plan be:
    • Work on gaining front downforce to turn better
    • balance it with rear downforce.


    Thanks for the great question !


    Last edited by Ron Sutton; 08-31-2013 at 05:30 PM.
    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
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  11. #31
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    Quote Originally Posted by NOT A TA View Post
    Thank you for taking the time to write the posts above Ron. I learned a few things and the ideas of B pillar mods and fender lips are things I hadn't considered for my aero project upgrades but will now.
    Cool.

    I have a 70 Firebird that I use for road tracks, Land Speed Racing, drags, and street.
    As a Trans Am fan, I love your car.

    I do not Auto-X the car. I've got a plan of installing many of the aero devices you mentioned in your posts and have the car apart now for these and other upgrades. Your comments on brake duct opening placement have me wondering if I placed mine where they will work well without fans in the tubing. I'm planning on a couple different aero "packages" that I would use depending on the use of the car. So I have 2-3 front dam, spoiler, splitter variations, and couple different rear spoiler setups as well as belly pans, side skirts, diffuser, etc. in mind so I don't want to hijack this thread. Your #7 from above leads me to believe a discussion of all the things I have planned might be better suited to a separate thread. I'll post the duct opening below for discussion here but if you want I'll just start a thread dedicated to my car.

    7. If I think your questions … and the answers to them will be valuable to others … I want to leave it on this thread for all of us to learn from. If your questions get too specific to your car & I think it won’t be of value to others … I may ask you to start a separate thread where you & I can discuss your car more in-depth.

    I planned on using the original park/turn signal openings for brake duct openings. I used headlights with park/turn incorporated to free up the opening. These will only be used for road track and will be blocked off the rest of the time. Do you think with a spoiler extension and splitter similar (but prettier) to the cardboard one shown the vents would have enough high pressure to function without fans?
    The spoiler extension (basically an air dam) and splitter will help keep a ton of air from underneath the car. This will force more of the airflow up & over the hood for increased downforce ... and more air around the nose for less lift.

    The challenge is the turn signal spots are so far away from the middle, I can't be confident in saying one way or another. I don't have a confident feel that it will work or won't work. If your car was track ready, I'd say put some tufts of yarn all the way across the front with a GoPro camera or two & see what the air is doing at different speeds.

    I think it may get a good volume of air at 60mph. But depending on the bow wave, it's hard to tell what it's doing at 80-100-120mph without testing it. Do you have any buddies that run a 70-73 Firebird on road course track days? If so, it may behoove you go do some testing with them.

    If they get good air there with no air dam & splitter, you may. If they don't, you for sure won't, as the air dam & splitter will force a higher volume of airflow "around" the side.



    To make your splitter work optimumally, you want it right on the track surface in the corners where you have the most front suspension compression. Some grassroots racers estimate this by knowing their suspension travel first, then sneak up on it with wear strips. Others test on track with a GoPro camera and lower it until it's almost scraping ... or is scraping.

    Last edited by Ron Sutton; 08-31-2013 at 05:31 PM.
    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
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  12. #32
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    Quote Originally Posted by NOT A TA View Post
    I learned a few things and the ideas of B pillar mods and fender lips are things I hadn't considered for my aero project upgrades but will now.

    John,

    Another thought. If you run track days with the windows down, you could make radiused B-pillar extensions that attach temporarily & get removed for street driving where you can roll the windows up.

    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
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  13. #33
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    Hey Donny,

    Quote Originally Posted by Ron Sutton View Post
    Smooth body work & gentle radius curves help air flow smoothly over a car body. Excessive turbulence is often caused by the opposite of smooth & gentle. When you can accurately describe parts of the body as abrupt, sharp, severe … those things will most likely create turbulence. The notchback style roofline of an 80’s Monte Carlo, Cutlass, Grand Prix & Regal all had a sharp trailing edge to the roof. This caused the air to “break away”… churn & crash … therefore create excessive turbulence … over the deck lid.

    If the air isn’t flowing over the deck lid smoothly … therefore it is not “attached” … you will have less downforce in the rear. It was so bad the NASCAR teams running these cars convinced GM to make some with the “aero rear window” to help the problem. It didn’t solve the problem. It just made it less horrible.

    Quote Originally Posted by dontlifttoshift View Post
    This area is where I feel most 60s cars are lacking. Your 57 is better here than a Mustang coupe. With out redesigning the entire backglass area, what can be done to fix it?
    [COLOR="#0000FF"]
    This is where personal preferences of style & taste come into play ... as well as a decision of how hardcore are you and how important is this to you. I'll list the things that "can" be done. And each of you can think about this and decide what you want to do, if anything.

    Donny, I'm focusing on two things you said in your post:
    • "coupe" meaning notchback style.
    • "entire" meaning you're open to some changes, but not changing it to a fastback style, as some have done.


    Body Options:
    • Rounding/radiusing the trailing edge of the roof
    • Adding Vortex Generators near the trailing edge of the roof
    • Installing a long, flat, low angle (or zero angle) drag racing style rear spoiler with wicker bill
    • Making the door glass flush with the body, so more side air flows onto the deck lid


    These would reduce rear turbulence & drag, while adding downforce. Of course there are things you can do for the airflow under the car that would also reduce rear turbulence & drag, while reducing lift, resulting in a net downforce increase.

    Under car airflow options:
    Splitter
    Side splitters
    Flat bottom belly pan
    Diffuser

    Again, I think how far a person goes with these fixes & improvements, depends on each person's preferences of style & taste ... as well as a decision of how hardcore they are and how important this is to them.

    Last edited by Ron Sutton; 08-31-2013 at 05:33 PM.
    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
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  14. #34
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    Quote Originally Posted by Damn True View Post
    If I understand Ron's post above and I think I do, vortex generators and spill plates can mitigate the flow detachment over the back of the greenhouse. Fix it entirely? Likely not but it should improve it a bit.

    You're spot on with the vortex generators. I know from first hand experience how big a difference they can make. The challenge for many PT guys is how they look.

    Spill plates on the roof would add downforce, but not necessarily help the turbulence & drag problem created by the notchback style. Of course spill plates on the notchback itself are useless, because there is practically no airflow there to spill over.

    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

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  15. #35
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    Quote Originally Posted by Ron Sutton View Post
    • "coupe" meaning notchback style.
    • "entire" meaning you're open to some changes, but not changing it to a fastback style, as some have done.
    Yes, coupe/notchback, a 66 to be more precise. Yes open to changes, VGs have come up in past conversations with other people smarter than me.

    Body Options:
    • Rounding/radiusing the trailing edge of the roof
    • Adding Vortex Generators near the trailing edge of the roof
    • Installing a long, flat, low angle (or zero angle) drag racing style rear spoiler with wicker bill
    • Making the door glass flush with the body, so more side air flows onto the deck lid
    The early coupes have a strange concave reveal around the backglass that makes it interesting back there.

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    Sharkfins?

    When comparing a low angle spoiler to something closer to 70*, if length were adjusted per design could I expect similar downforce results with less drag on the low angle spoiler? Roughly, how much length are we looking at? Is 6" worth the time?

    We must run with the windows down so nothing to gain there. If the backglass stayed in the stock location but the sail panels stretched back (ala 69 charger) does that help. Theory being that air off the roof can start to settle on to the decklid before having to mix with air from side of the greenhouse.

    These would reduce rear turbulence & drag, while adding downforce. Of course there are things you can do for the airflow under the car that would also reduce rear turbulence & drag, while reducing lift, resulting in a net downforce increase.

    Under car airflow options:
    Splitter
    Side splitters
    Flat bottom belly pan
    Diffuser
    Yes
    Likely
    I don't think I can go full length, but I plan on running the splitter to at least the front crossmember. I am sure I can "pan" from the rocker to at least the SFCs and
    Yes on the diffuser.


    Everyone has their own idea styling wise, here is the plan. Hood vents will be as far forward as I can get them, other than that I was trying to keep all the aero work to the bottom of the car.

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    Donny

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  16. #36
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    Quote Originally Posted by sccacuda View Post
    Ron, you never cease to amaze me. I've got questions!
    After reading your post, I think I've got answers.

    You've seen my build. It is a PT car, but more road course, with standing mile and Bonneville thrown in.
    This thing is going to be mean!

    I will be taking it to A2's wind tunnel before any land speed runs. I've calculated my CD at .38.
    In my experience, that number is low, unless you're doing things to improve it.

    The stock body has 440 lbs. of lift, 125 lbs. of rear down force and 325 lbs of drag.
    That's a great stat & somewhat typical of cars from that era. The lift is the killer that needs to be eliminated, then add downforce from there ... especially in the front.

    I have modified the body slightly, trying to keep a stock look. I lowered and flattened the rockers 3/4".
    I am very visual & would like to see photos to understand this.

    I can now attach rocker extensions/side splitters depending on the data I get from A2.
    This era of car has majorly rounded sides. That "curve under" from the mid body down is a killer. The air wants to roll under on half the body. Adding "mean" side splitters would be a good move. I'd make them 2"-3"+ out of .100"-.125" thick aluminum ... have them dzus mount under the car to the Flat Bottom Belly Pan ... so they can be removed for street driving.

    Just an FYI, the top racing aerodynamicists tell me the proximity of the car body to the wind tunnel walls plays a role in how the airflow looks on the side of the body. The closer the walls are, the easier the air reattaches ... giving a false sense of confidence everything is ok. A2's wind tunnel has closer walls than most, so detached airflow on the side of the bodywork reattaches to the body easier.

    All wind tunnels do this, and it not a huge deal ... unless you're doing weird stuff on the side of the body that causes serious detachment. But in the real world, where you not running next to walls, this air may not reattach. If you're doing anything tricky, see if you can talk to Gary Eaker, the owner of A2. From reputation, he is one of the sharpest minds in race car aerodynamics.


    I actually widened the front fenders in front of the tire 1-1/2" to "hide" the tire from the air.
    Awesome!

    The rear spoiler is a factory 'Cuda trunk mount spoiler that I cut apart and slid an aluminum structure inside of for attachment, prevent deformation, and the ability to run different wicker bills. Again, depending on A2 data.
    Great move.

    On the bottom, I build the frame connectors flat to run a belly pan. It can start as far forward as the front air dam/splitter.
    Good. Your photo showed starting it at the rad mount. But the Flat Bottom Belly Pan ideally needs to start at the splitter & go all the way back.

    This is where I have a question. Should the pan be dead flat or slightly concave for downforce?
    The Flat Bottom Belly Pan should be flat or convex, never concave. Concave will slow the airflow down, creating more pressure & lift. The only exception to this rule is where you have shaped a panel convex to get over some object & need to transition the panel back into the next flat panel.

    My watt's link bracket will pick up the belly pan about 1" higher the main pan and is level to rear valance. Do I terminate the pan in front of the rear axle and then just pick it back up behind the axle to the rear valance?
    Not if you can avoid it. As you know, it's a jungle back there at the rear suspension. If you can make a panel that connects the cockpit belly pan to the trunk belly pan ... by all means do it. I suggest you make the panels removable with Dzus quarter turn fasteners, or something like that, for easy access.

    The pan will have to be almost level and flat to keep the rear valance from becoming a parachute. Do you have any better ideas? I will throw in a bottom pic for reference.
    Your photos showing the underneath are great at showing how cluttered the underside of street cars are. Think about it. The air flow at 100mph, 150mph, 200 mph has to flow under this jungle. That's why they have so much lift.


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    At the rear of the car I recommend a removable panel (see blue lines on photo) that keeps the air flowing along a smooth flat surface from the cockpit belly pan to the trunk belly pan. It should start off level with the cockpit belly pan ... roll up gently, then roll back gently ... to keep the air flowing smoothly onto the higher trunk belly pan.

    Also, for the front belly pan, If you can make it follow something like the blue lines, the belly pan will be more effective. Otherwise the wheel well acts as a parachute. BUT, you need to build a smooth, gentle radius inner fender ... behind the tire ... that initially follows the same curvature as the tire, then curves back to blend into the belly pan.

    Final tip for this photo: The black outlined areas are trouble spots. Stuff has to go in these areas, but do your best to reduce the openings that allow airflow to get in here & cause drag & lift.

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    In this photo, where I've drawn the black lines, can you build diffusers?
    Also, where I've drawn the blue lines, is there enough room to build an effective diffuser? ... or if not, can you at least curve the panel up to build a mini-diffuser?

    My tip is, you have a good flat bottom belly plan design already. Now you need to help the air get out faster ... and flow upward a bit to to better merge with the air coming off the deck lid.

    Make sense?

    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

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  17. #37
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    Quote Originally Posted by SSLance View Post
    I love reading Ron's posts when he gets on a roll, he certainly has a way to make something that seems so difficult to understand...easy to understand. Couldn't help but notice all of the swipes he took at mid 80s Monte Carlos as examples though...
    I love the look of the cars from that era. I had an '84 Hurst/Olds Cutlass drag car. Loved it. The notchback hurt it, but the loooong deck lid helped. Of course another 12" of flat spoiler helped too.

    I thought really hard about building my PT Track car with a late 80's Monte SS body. But California is so strict on the smog laws, it would limnit what I did with the engine.


    Just kidding... ;) It's not the first time I've been told I should have bought an aerocoupe.

    Good aero is one thing, but ungodly ugly aero coupe back windows is a whole 'nother animal.
    This is just my personal opinion, but I do not like the look of the aero coupes either.

    I will add this also, I was a big fan of the looks of the NASCAR COT when they brought it out over the Twisted Sister bodies they ran previously. I know they all had challenges getting the new COT body to react aero-wise like the well developed previous car, but purely from an aesthetics view point, it was not even close. The COT rocked, mainly because it looked like a real production car.

    How does that apply to most of our PT cars, I'm not sure. I'm sure there are some that will use the knowledge above to get every last little bit of aero advantage out of their cars especially if they track them. Probably more likely there will be more of us that use a few of the hints and tricks here and there to make our cars aero better, without making wholesale changes to the overall look of our body styles. Air dams and splitters on the front to keep air from going under the car for sure, and maybe some side and back changes as well. I autocross with a guy that runs a 10" tall clear lexan spoiler on the back of his CP Cobra...that ain't happening on my car though, I don't care how much it helps.
    I know aero starts having an effect beginning around 50 mph, but I don't think it does below 50. So I don't see aero adding much for AutoX. I'm sure there are guys that think differently or have different experience. I'd love to have guys chime in on this ... but only if you have personally experienced gains from aero aids on AutoX cars.

    It's real nice to have access to the knowledge Ron posted above though, just so that there is a road map in place for any changes one might make...so they don't go the wrong way with something.
    Thanks for the kind words. Take care !

    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

    Features: Suspension, Chassis, Cages, Brakes, Rear Ends, Engines, Transmisssions, Aero & Much, Much More!

  18. #38
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    Quote Originally Posted by dontlifttoshift View Post
    Yeah, I had only skimmed that section before asking. The airtabs look....lets say, feminine. Sticking a bunch of those on the roof doesn't appeal to me at this point.
    I don't know if I agree about the "feminine" part ... but that's personal to each of us. Regardless, I don't desire to put Airtabs on the roof of my 57 either ... if I don't need them. But if I find it hard to get enough aero downforce in the rear, I'll paint them to match & be running them.

    I did use Wheeler Vortex Generators (which look different) 2" in front of the roof trailing edge on the C4 Vette drag car I ran with a partner in the 80's. They worked extremely well. I have used the Airtabs & they work well too.


    Ron, any thoughts on the "shark fin" style VG that show up on factory cars like the Mitsu EVO?
    I do not have any first hand experience with them. But Subaru & Mitsu both use them, so I tend to think they have an effective shape to generate vorticles.

    Past the VGs, given a choice between a wing or spoiler on a street car/track day car is the obvious winner?

    They each have pros & cons, so I think it comes down to your goals. For maximum downforce in the rear ... which I don't think is necessary in most PT cars ... the wing is the clear winner. The only question becomes how high to mount it & how big. But the wing doesn't help clean up the turbulence at the rear of the car, nor the drag created by it. In fact, the wing will add drag, not reduce it.

    It's funny, when you see a 8.90 / 150mph dragster with a wing on it. They're running it for looks ... to look like a Top Fuel car. Because the additional drag the wing adds takes another 60-80hp to go the same speed in the typical Super/Comp dragster. So most racers in this dragster class run without wings.

    The spoiler will add rear downforce. Running it tall & angled like a stock car spoiler will add downforce, but more drag too. Running it flat, or "low angle" like a drag car ... with a decent size wicker bill (1/2' to 1") will add "some" downforce ... and reduce drag ... because it will help reduce turbulence behind the car. Longer is more effective.

    This is what I'm running on my 57, along with a lot of other aero aids.

    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

    Features: Suspension, Chassis, Cages, Brakes, Rear Ends, Engines, Transmisssions, Aero & Much, Much More!

  19. #39
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    Quote Originally Posted by Damn True View Post
    You mean like a linear transducer? Racepack has an example under the sensor tab on their site. There are some more ghetto ways of doing it, but I don't want to muck up Ron's thread with that kind of thing.
    Yes, we use the Penny & Gilles linear potentiometers (fancy way of saying travel sensor). But I'd like to hear your "ghetto way" of doing it too. As car guys, we don't always have access to Data Acquisition, Engineers & such.

    I have some crude but effective ways of measuring things when I don't have the high tech stuff. I call them "car guy methods". I believe having crude info is better than having no info.

    Please share.

    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

    Features: Suspension, Chassis, Cages, Brakes, Rear Ends, Engines, Transmisssions, Aero & Much, Much More!

  20. #40
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    Quote Originally Posted by MIKE67 View Post
    Ron: You haven't talked about stability. If you add a bunch of drag at the front of a car, but don't add any or much to the rear (like adding a large splitter to the front and removing a rear spoiler), then you may move the center of pressure in front of the center of gravity. This would be unstable and want to swap front to back. Not a good thing at speed. This has unfortunately happened too many times at Bonneville.

    Do you have any low tech ways to prevent or check this?

    Thank you for sharing your experience with us.

    Hi Larry,

    I covered it briefly in post #3 ...


    Quote Originally Posted by Ron Sutton View Post
    A key component of aero downforce is “aero balance”. Before the COT & Gen 6 cars in NASCAR, teams had a pretty wide area to work in with body design & placement. Of course they did a ton of work to reduce undercar air & a lot of shaping to create downforce on the body. When you look at a car body, you may say “where is the downforce at on the body?” If it’s done right … it’s all over. There is downforce on the hood & front fenders, windshield, roof back glass & deck lid. After testing, the wind tunnel operators may say we have 1260# of net down force with this body shape.

    But the downforce is not exactly even. At that time, NASCAR allowed the teams up to 10” of fore & aft range in mounting the bodies. So for short tracks that were challenging to get & keep the car turning in the corners … the teams would mount the bodies farther forward on the chassis to place more downforce on the front tires. At 1.5-2 mile super speedways where turning is easier, and rear grip is important, the teams would mount the bodies farther back on the chassis to place more downforce on the rear tires.

    A tidbit of trivia for you NASCAR fans: When NASCAR would step in & change the rear spoiler rule … say from 6.5” to 5” … this messed up the aero balance so much, that teams had to cut off the bodies, throw them away & start over. Today, this is not the case, as the body rules have been tightened up a zillion miles compared to just 10 years ago.
    But your post tells me two things:
    1. I didn't cover it well, so I need to add to it & make the explanation more thorough.
    2. Bonneville & other straight liners call it "Aero Stability" ... where circle track & road racers call it "Aero Balance".
    I'll add the term "Aero Stability" to my writings.

    Thanks for bringing this up.

    ---------------------------------------------------------------------------

    For circle track & road racing, Aero Balance is huge. This is an edited copy of my response to John Parsons. (Edited for brevity)


    Quote Originally Posted by Ron Sutton View Post
    If we made a change in the front to increase downforce, or decrease lift, we could see how much it compressed the front end more. Of course you know this amount of downforce varied with speed.

    So in a slower corner we may have seen:
    .150" more compression, of 350# front springs (x2) x .70 MR and know we gained 63# of net front downforce.

    While in a faster corner, the front compression was:

    .250" more ... so we knew we gained 122.5# of net front downforce there.

    This is enough gain that it made the car turn so much better the car actually got loose. So we would increase the rear downforce to balance the car out. We may change wing angle, spoiler angle or wicker bill height to achieve aero balance.

    In the same slower corner we would see:

    .050" more compression, of 600# rear springs (x2) x 1.0 MR ... and know we gained 60# of net rear downforce.

    While in a faster corner, the rear compression was:

    .100" more ... so we knew we gained 120# of net front downforce there.
    * You'll notice the gains are not always linear when comparing downforce gains front to back ... just close.

    ----------------------------------------------------------------------------------------------------------------------

    My strategy is do things to improve front tire grip with front aero ... then tune on rear aero to balance the handling. If you run out of rear aero adjustment, you can use mechanical adjustment to balance the car ... but only to a small degree. This is NOT ideal, as mechanical adjustments to increase rear grip gain in reverse of aero adjustments.

    What I mean is ...
    If we put a taller wicker bill on the rear spoiler to add more rear grip (to balance the car from the added front grip) ... both ends of the car will have more grip as speed increases.

    If we have to use a mechanical grip adjustment in the rear, we can increase rear grip on higher speed corners, while reducing rear grip on lower speed corners ... or ... increase rear grip on lower speed corners, while reducing rear grip on higher speed corners. But with most adjustments we can't increase rear grip in both low & high speed corners "mechanically".

    This is why it's important to achieve aero balance. And this makes another case for why aero downforce is so valuable. It increases the grip in both low & high speed corners ... and in the correct direction ... meaning more downforce on the faster corners, where you need it more.

    I suggest your game plan be:
    • Work on gaining front downforce to turn better
    • balance it with rear downforce.

    That was a brief but accurate strategy for road course & short track oval aero tuning. But for Super Speedway ovals & straight line, I have a different approach. It is simple.

    Start with more rear downforce than you need. Then "trim" it out a step at a time. "Trim" means to take away down force to gain speed. Do this a step at a time. And as you get close, make tiny steps. The driver's feel for the car here is key. If you're doing this with a less experienced driver, I'd be working at lower speeds.

    If ... I misunderstood your request ... and you were asking either "do you" or "how do you" create rear downforce to add stability, the answer is going to be in the form or a wing or rear spoiler, along with aero work underneath the car to decrease lift in the whole car.

    Feel free to chime in or ask technical questions. I am here to help where I can.

    Ron Sutton

    Ron Sutton Race Technology
    Your One Stop, Turn & Go Fast, Car Building Resource Center for Autocross, Track, Road Racing & Triple Duty Pro-Touring Cars

    Check out our 400 Page Car Building Catalog HERE

    Features: Suspension, Chassis, Cages, Brakes, Rear Ends, Engines, Transmisssions, Aero & Much, Much More!

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