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  1. #81
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    Hi James,

    Quote Originally Posted by James OLC View Post
    I have a couple of styles (of vortex generators) sitting on the shelf waiting for some track time I do some testing. One set are the "larger" shark fin style by agent 47 which are supposed to be fairly effective on mustangs (effective enough to be banned from AI and CMC competition). They do have to installed in the right pattern (both spacing and angle)... We'll see.
    I have seen those, but I don't have a photo. Can you post a photo of them for the others to see ?


    The other set I picked up were a cheap set off eBay - smaller, still shark fin style and, honestly, probably of limited effectiveness. My results (with the dynamic wing) may not be entirely representative but when I do get some testing in I will report back.
    That will be great.


    Which itself leads to an interesting question wrt quantifying the performance of something like VGs... What constitutes success?
    As usual , that depends on each person's goals.

    If someone is looking to make a spoiler, or low mounted rear wing, more effective ... then the goal of installing VG's on the trailing edge of the roof is to keep the boundary layer of airflow "attached" ... improve the airflow over the back glass & deck ... and end with more airflow on the rear deck. This will increase downforce. It may decrease drag, or it may even increase drag, but that is ultimately dependent on the size & angle of the rear spoiler or low mounted wing.

    If someone is looking to decrease the huge vacuum & horrible drag at the rear of the car, mounting VGs at the trailing edge of the body will help achieve a cleaner, less turbulent airflow detachment ... which will reduce drag.



    Better airflow as seen by tuff or oil testing?
    Frankly, for me, that's just a test the method to figure out where the car has detached airflow ... and needs work. Or, after work is performed, to confirm the airflow is now staying attached & going the right direction.


    Higher "ultimate" speed in the straight? Single car? Multiple cars?

    This goes back to what each guy's goal is.

    The Bonneville (and some drag) guys are looking for aero stability at speed. The front of the car is going to make tremendous downforce at 200+ mph, so they need rear downforce to achieve aero balance. Otherwise the car gets light and spins out when a cross wind comes up. Downforce can be calculated beforehand, but the real test for this is typically feel based. Was the car more stable on a run, or is it still unstable and light in the rear?

    Some guys (road course, PT, Bonneville, Silver State, drag, big oval, etc) have too much drag from turbulent flow detachment at the rear of the car creating a huge vacuum behind the car. So their goal is to smooth out the airflow detaching at the rear of the car to reduce the huge vacuum & decrease the drag coming from the rear of the car. The test here is were you able to see an increase in speed (with no other changes) on straights?

    Most of the time, I'm working on either increasing total downforce for more overall grip & cornering speed for road courses or oval racing. Or I'm working on increasing downforce at one end of the car to achieve aero balance for a balanced, neutral handing track car. My focus here is in the corners, where we need the car to have aero balance & neutral handing at the highest speed in the fastest corner on the track. I think you have been on many road courses. So you know the "fast sweepers" I'm referring to here that can give you a little butt pucker.

    Of course, we can always take away downforce at the end with more ... to achieve "aero balance" ... but we end up with less over grip. My philosophy here is to increase downforce on the end that is weak & therefore "light". The test here is also on track & typically driver feel based. If the car was light in the rear & loose (or on the edge) before ... does it now have more grip in the rear and handle neutral? If the car was light in the front & tight or pushy before ... does it now have more grip in the front and handle neutral? Can we now carry more corner speed?

    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

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


  2. #82
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    Quote Originally Posted by Ron Sutton View Post
    If anyone wants to ask questions or start a discussion on the topics outlined in the forum, simply post it up & we'll discuss it.
    Hey Ron, I have a few application specific questions that hopefully you could help me out with, given your experiences. Hopefully you can provide some incite. :D

    I have a 1971 Chevelle that I finally changed the suspension last year with with the help of Mark from SC&C. I have SPC Uppers and Lowers, tall howe balljoints, SPC springs, single adjustable Varishocks, Hellwig protouring antiswaybars (rear is adjustable), outback I have UMI double adjustable uppers and tubular lowers with roto-joints. I also had rebuilt the front end using PST parts, and did the jeep cherokee steering box conversion. From the original suspension to what I have now to say it's night and day is an understatement. Hell, I've been pulled over not for speeding, but because cops can't believe my car corners flat, then talk to me about my car and ask to see it.

    But now here's the problem, at normal low speeds the steering is nice and heavy, but once I get up to around 55+ it gets light. Hell when on the highway I notice that when I try to stay straight and do a small correction its more of a major change, if that makes sense. I think it's because the steering is tight, rather then all loosey goosey like the original. With the original steering box it would still feel light at high speeds, but at low speeds it felt light too, and it was super sloppy. This has got me thinking its an aero issue, not a suspension issue. Hell the Chevelle is like a brick in the front.

    Now, I've been reading a lot about areo, and I figure this is happening because there is a ton of front end lift. I figure the best solution would be a front air dam/spoiler to stop as much air going under the car, and increase downforce. Now how does the design affect the efficiency and effectiveness of the part? IE: Flat vs Angled. What about height? I checked the measurements from the bumper to the ground and the chassis to the ground, I got 12in and 7.5in respectively. I've read in Race Car Aerodynamics: Designing for Speed by Joseph Katz that after 100mm (~4in) drag increase, reducing the effectiveness of the air dam. Now does that mean it would be 100mm from the ground? bottom of the front end? bottom of the lowest point of the vehicle? I also plan of putting a plate like the undercover innovations show panel above to direct air through the radiator, instead of being able to push upwards on the hood generating lift.

    After all the reading I've been doing about aero for our cars I'm worried about making things worse. Not to mention I don't want to make it so there's more downforce in the front then the rear so that I lose traction and create rear lift. Which I didn't even think about till i read this from Hot Rod magazine. Is this a good plan, or is there something else I should look into? Could it be a problem with my suspension.

    Some Pictures to see my ride height
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  3. #83
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    My first concern is partly covered in another thread here on hood heat extraction. I believe properly placed/size hood vents have additional aero advantages pertinent here. In order to shade tree test my potential vent locations, I bought a differential pressure gauge. My first question is, to facilitate easy testing, will a 70 mph street legal test speed be indicative and accurate enough to indicate a trend? And more importantly, what location do I want to use for my base reference pressure, IE inside the car with windows up or down, directly under the hood testing point, or somewhere else. Seems like the interior location would be a good reference for other future tests, but using a point under the hood might indicate a harmful back flow scenario. Suggestions?
    Last edited by j-c-c; 11-03-2013 at 06:10 PM. Reason: word ommission

  4. #84
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    71 beast, the first and pretty easy thing that I would do if i were you is have the front end realigned to get some more caster angle (the line drawn thru the ball joints when viewed from the side). If you have a lot of adjustment available in your front control arms, you should be able to get 2-3 degrees of negative caster which should help out with what you are feeling. Also your car looks like it has a really nice stance but if you can, lowering the rear more or raise the front end a little bit will also add some more caster angle. Start with those things before the heavy fabrication begins.

    Your (all) muscle cars sit really high off the ground for legitimately functioning ground effects. Your front air dam would have to be quite substantial. An alternative or perhaps something to augment a front air dam would be hood venting and also fender vents along with holes in the inner fenders to allow air to get to those fender vents
    Steve Calabro
    2015 Chrysler 300S
    2006 Lotus Exige
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  5. #85
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    Thanks guys for the ideas, and thanks for the compliments on my car. Interesting that you'd mention the alignment. I forgot that I had to add a small spacer in the front to raise it, and I don't remember getting an alignment again, so it probably is off from what it was/should be. II'm pretty sure that's what is causing my issue of "instability" at high speeds. Sad how that's the simplest thing and the easiest to over look/forget.

    From all I've been reading stopping air from going under the car can make the biggest difference in aero of our cars, which is why I'm looking at making one. Here's a link to the book I've been reading about automotive aero.

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    I'm not too keen on hood vents or fender vents, as I'm not quite sure how to make them look right besides functional. Also, in the aero book the talk about louvers and their placement. It's stated they should be places at the max curvature to allow for pressure to escape from around the wheels and increase downforce, similarly to GTP cars. Looking at venting the hood, if the placement is wrong its going to cause major problems by increasing the pressure in a low pressure area, rather the accomplishing the goal of decreasing high pressure areas, which is not something I really want to risk doing through test and tune.

  6. #86
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    Greetings,

    A few quick questions:
    1) What is the convention for designating spoiler rake? Angle WRT vertical or WRT horizontal?
    2) Can underhood air pressure above atmospheric be effectively vented through the rear portion of the wheel well housings? It seems this is a very easy means of ducting that wouldn't disturb hood or fender lines. If the effective point of airflow exit from the body can be made rearward enough, I'd imagine it wouldn't much upset the car's bow wave. Plus, by having underhood air follow a longer and more circuitous path before exiting the engine bay, it can better help reduce underhood temperature. Is this correct?

    Edit on 11/8/13: pondering point (2) a bit further, it occurs to me that exiting underhood air in the fenderwell, has no choice but to collide head-on with the centrifugal flow of air thrown-off by the spinning tire. The strength of the latter probably overwhelms that of the former, so that the final flow exiting the wheel well might be a swirling vortex of air which next collides with, and probably then broadens, the car's bow wave. If true, moral of this story: the airflow exiting the engine bay should be isolated from airflow around the spinning tire. Is this right?

    Also, being unfamiliar with the (amazingly infrequent given the topic) use of jargon here (kudos to Mr. Sutton for keeping the topic so accessible,) but what is a wicker bill? I'm not getting a clear answer from browsing the web.

    Many thanks,
    MAP

  7. #87
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    Sorry for the delay in responding. I have been at SEMA & Optima all week.

    I have some requests to handle first, then I'll be back on here mid-week to answer questions.

    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!

  8. #88
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    Hi Ron,

    Looking for some thoughts for my 68 Chevelle Pro touring car that will be used for auto cross and track days. First a little of what I have planned and have already done to the car. I have shaved the drip rails and plan on flush mounting all the glass with no chrome trim. I am planning on a front air dam with splitter, narrowing and moving the front bumper as far in as possible, adding about 2-3 inches to the front fenders, rocker panels and quarter panels, rear air foils under the rear of the car and some sort of Nascar type spoiler. My question is what height and angle should I make the rear spoiler? Also how bad is the aero on the car if I can keep a lot of the air from going under the car. It does not look to bad as far as aero goes because of the long hood, roof and fastback style rear. Any help would be great and I would still like to have it look like a Chevelle as much as possible.


    Thanks
    scott

  9. #89
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    Hey, sorry for the long delay. I have some answers for you ...

    Quote Originally Posted by 71beast View Post
    Hey Ron, I have a few application specific questions that hopefully you could help me out with, given your experiences. Hopefully you can provide some incite. :D

    I have a 1971 Chevelle that I finally changed the suspension last year with with the help of Mark from SC&C. I have SPC Uppers and Lowers, tall howe balljoints, SPC springs, single adjustable Varishocks, Hellwig protouring antiswaybars (rear is adjustable), outback I have UMI double adjustable uppers and tubular lowers with roto-joints. I also had rebuilt the front end using PST parts, and did the jeep cherokee steering box conversion. From the original suspension to what I have now to say it's night and day is an understatement. Hell, I've been pulled over not for speeding, but because cops can't believe my car corners flat, then talk to me about my car and ask to see it.
    Sounds cool.


    But now here's the problem, at normal low speeds the steering is nice and heavy, but once I get up to around 55+ it gets light. Hell when on the highway I notice that when I try to stay straight and do a small correction its more of a major change, if that makes sense. I think it's because the steering is tight, rather then all loosey goosey like the original. With the original steering box it would still feel light at high speeds, but at low speeds it felt light too, and it was super sloppy. This has got me thinking its an aero issue, not a suspension issue. Hell the Chevelle is like a brick in the front.
    You "probably" have front end aero lift issues. You should confirm you don't have any steering or geometry issues just to be safe. But aero issues on 60's-70's muscle cars are as common as boobs in a strip club. You most likely are experiencing lift or negative down-force in the front end. Very common.


    Now, I've been reading a lot about areo, and I figure this is happening because there is a ton of front end lift.
    Yup, yup!

    I figure the best solution would be a front air dam/spoiler to stop as much air going under the car, and increase downforce.
    Correct.

    Now how does the design affect the efficiency and effectiveness of the part? IE: Flat vs Angled.
    When you say flat, do you mean vertical? Vertical air dams work best ... especially if you can bow out the front into a curve or point ... to help the airflow change direction and go "around" to the sides. But frankly, the angled "chin spoiler" type look better and would still work. They're just less effective than a vertical air dam.

    What about height? I checked the measurements from the bumper to the ground and the chassis to the ground, I got 12in and 7.5in respectively.
    This is a risk versus reward situation. The longer you make the air dam ... going down from the bumper ... the more airflow you will redirect from going under the car and causing lift ... to going around the car.

    I'm not sure you could tell the difference if you only added an inch or so, but a 3" air dam would redirect a small amount of airflow from going under the car. 6-8" would redirect it a lot more and a 12" air dam ... where it is literally scrapping the ground ... would redirect it all. Of course, that's impractical.

    If you desire to add an air dam to your PT car, I think you should outline your goals. If all you want to do is eliminate the lift and achieve a small amount of downforce for freeway stability ... you don't need to do much. A 3"-5" air dam or spoiler should achieve that if properly shaped & installed.


    Of course, this forum thread is about designing aerodynamics for track performance. So if you were building a serious road course track car ... and wanted maximum front end downforce ... you would want to design the air dam with adjustable wear skirts ... and get it down on the track surface under braking & cornering.


    I've read in Race Car Aerodynamics: Designing for Speed by Joseph Katz that after 100mm (~4in) drag increase, reducing the effectiveness of the air dam. Now does that mean it would be 100mm from the ground? bottom of the front end? bottom of the lowest point of the vehicle?
    Reading this out of context from the book, I do not know what Joe is trying to say. Ultimately, maximum downforce is achieved by getting the air dam on the track surface during braking & cornering.

    I also plan of putting a plate like the undercover innovations show panel above to direct air through the radiator, instead of being able to push upwards on the hood generating lift.
    Sounds good.

    After all the reading I've been doing about aero for our cars I'm worried about making things worse.
    I doubt it. It's hard to mess up an airdam or front spoiler. You may not be as effective as you want, but you're not going to make it worse.

    Not to mention I don't want to make it so there's more downforce in the front then the rear so that I lose traction and create rear lift.
    You'd need to get aggressive ... like putting the airdam on the ground ... to make this happen.

    Which I didn't even think about till i read this from Hot Rod magazine. Is this a good plan, or is there something else I should look into? Could it be a problem with my suspension.
    Sorry, but I did not take the time to read the Hot Rod article. If you have a specific question from the article, post that up.

    Yes, it could be steering or suspension geometry, so like I said above ... check it. But you probably have some areo lift & a air dam or spoiler is the right direction to correct this issue.

    Best wishes & ask more questions if you have them.

    Last edited by Ron Sutton; 12-06-2013 at 08:45 AM.
    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!

  10. #90
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    Quote Originally Posted by j-c-c View Post
    My first concern is partly covered in another thread here on hood heat extraction. I believe properly placed/size hood vents have additional aero advantages pertinent here.
    As I think I mentioned in my original posts or in response to someone's questions in a post, The airflow coming out of hood openings typically creates chaos with the airflow over the hood. So it's usually a gain & loss situation.

    What we really care about is the net downforce number. My goals are usually to increase downforce on the top side of the body & reduce lift from underneath. Remember we're dealing with 2 sides of the coin ... downforce & lift. If you have good attached boundary layer of airflow all across the width & length of the hood, combined with a high pressure base at the bottom of the windshield, you already have a certain amount of downforce on the hood.

    Just for sake of discussion, let's say you have 300# of front downforce at a given speed. And, due to airflow under the car, you also have 300# of frontal lift ... so your net front downforce is 0. If you vent the hood and achieve and effectively vent out 200# of lift ... but disrupt the boundary layer of airflow across the hood ... and lose 150# of the downforce, you only gained 50# of net downforce.

    I'm not saying you can't reduce most of the lift & keep most of the downforce. There are great race car designs (BMW & Mitsu I think) that achieve this with precisely designed aerodynamic tunnels from the front of the car that exit out the hood and onto the trailing edge of the hood & base of the windshield.

    But it's no walk in the park to vent the underhood airflow without creating chaos with the airflow over the hood. The aerodynamicists that successfully developed these cars did so with the benefit of a wind tunnel. The challenge for guys like you & me trying to do this without a wind tunnel is guesswork and trial & error. I am clear I do not have the knowledge & experience to pull it off.

    With my experience & aero knowledge, if it were my car, I would ...
    a. Keep the hood clean & keep the 300# of downforce
    b. Vent the hot engine compartment air out the side of the fenders behind the wheelwells
    c. Run an airdam & splitter that closes the airgap to almost nil under braking & cornering.

    From my experience, this decreases the lift by 250# to only 50# ... forces some of the airflow around the front end ... while forcing some additional airflow over the hood ... increasing the hoods downforce by 50# ... creating a net downforce around 600# on the front end.


    In order to shade tree test my potential vent locations, I bought a differential pressure gauge. My first question is, to facilitate easy testing, will a 70 mph street legal test speed be indicative and accurate enough to indicate a trend?
    It can show somewhat accurate trends, but occasionally you'll be thrown a curve ball. if the goal is race track speeds of 120-150, ultimately you need to test at those speeds.

    And more importantly, what location do I want to use for my base reference pressure, IE inside the car with windows up or down, directly under the hood testing point, or somewhere else. Seems like the interior location would be a good reference for other future tests, but using a point under the hood might indicate a harmful back flow scenario. Suggestions?
    This is not my expertise, but if you're working on reducing undercar lift (pressure) then you need to have the sensors in that general area.
    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!

  11. #91
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    Hi Steve, Thanks for chiming in.

    Quote Originally Posted by Motorcitydak View Post
    71 beast, the first and pretty easy thing that I would do if i were you is have the front end realigned to get some more caster angle (the line drawn thru the ball joints when viewed from the side). If you have a lot of adjustment available in your front control arms, you should be able to get 2-3 degrees of negative caster which should help out with what you are feeling. Also your car looks like it has a really nice stance but if you can, lowering the rear more or raise the front end a little bit will also add some more caster angle. Start with those things before the heavy fabrication begins.
    I would not raise the front of the car nor lower the rear of the car. Both of those changes will increase aero lift in the front end. Just to be clear, this thread is about designing aerodynamics for track performance. If you're running 120mph+ on road courses, you don't want to adjust the car rake to add caster. Do that mechanically with the control arms.

    For improved aero on track ... lower the front of the car and reduce the gap allowing airflow in & under the car. Also, raising the rear, allows the faster exit of airflow, which also decreases lift. I am not suggesting you put your car at some extreme rake. But rake (down in the front) does decrease lift, therefore increases net downforce.


    Your (all) muscle cars sit really high off the ground for legitimately functioning ground effects. Your front air dam would have to be quite substantial.
    I concur. I'm not sure you could tell the difference if you only added an inch or so, but a 3" air dam would redirect a small amount of airflow from going under the car. 6-8" would redirect it a lot more and a 12" air dam ... where it is literally scrapping the ground ... would redirect it all. Of course, that's impractical.

    This forum thread is about designing aerodynamics for track performance. So if you were building a serious road course track car ... and wanted maximum front end downforce ... you would want to design the air dam with adjustable wear skirts ... and get it down on ... or close to ... the track surface under braking & cornering.


    An alternative or perhaps something to augment a front air dam would be hood venting and also fender vents along with holes in the inner fenders to allow air to get to those fender vents
    Hood venting is tricky, because it's real easy to cause chaos with the attached boundary layer of airflow across the the hood & with the desired high pressure base at the bottom of the windshield. For that reason, I recommend side vents in the fenders, behind the wheel openings.

    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!

  12. #92
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    Hi "MAP" ...
    What is your real name?

    Quote Originally Posted by MAP View Post
    Greetings,

    A few quick questions:
    1) What is the convention for designating spoiler rake? Angle WRT vertical or WRT horizontal?
    Your question is not quite clear for me. Are you talking front or rear spoilers. Vertical front spoilers or airdams work best to charne the direction of the airflow around the car. But for the rear ... there are a lot of variables and different strategies. Just look at Pro/Stock drag cars versus NASCAR stock cars, which are both going 200mph, but have different goals & strategies.


    2) Can underhood air pressure above atmospheric be effectively vented through the rear portion of the wheel well housings? It seems this is a very easy means of ducting that wouldn't disturb hood or fender lines.
    It's too trubulent in the actual fenderwell. It works best to vent the underhood air out through fender vents behind the wheel well opening.

    If the effective point of airflow exit from the body can be made rearward enough, I'd imagine it wouldn't much upset the car's bow wave.
    This is correct.

    Plus, by having underhood air follow a longer and more circuitous path before exiting the engine bay, it can better help reduce underhood temperature. Is this correct?
    I'm not sure why you would want the path to be longer and more circuitous. The goal is simply to provide the hot air & underhood pressure (lift) a fast & easy exit.

    Edit on 11/8/13: pondering point (2) a bit further, it occurs to me that exiting underhood air in the fenderwell, has no choice but to collide head-on with the centrifugal flow of air thrown-off by the spinning tire.
    Correct.

    The strength of the latter probably overwhelms that of the former, so that the final flow exiting the wheel well might be a swirling vortex of air which next collides with
    Typically, when you try to create a new airflow exit into a stream of turbulent, rolling & boiling airflow, you simply add to the turbulence without achieving your goal of getting the airflow to exit.

    , and probably then broadens, the car's bow wave.
    It does not.

    If true, moral of this story: the airflow exiting the engine bay should be isolated from airflow around the spinning tire. Is this right?
    Yes. But having it exit behind the fender opening works quite well if designed properly.

    Also, being unfamiliar with the (amazingly infrequent given the topic) use of jargon here (kudos to Mr. Sutton for keeping the topic so accessible,) but what is a wicker bill? I'm not getting a clear answer from browsing the web.

    Many thanks,
    MAP
    I was surprised there is not more info on wicker bills, since it is such a common tuning tool. Quite simply, it is a short strip placed at the trailing edge on the upper surface of a deck, spoiler or wing ... it slows the boundary layer airflow speed down ... increasing the pressure & downforce on the deck, spoiler or wing.

    A secondary benefit, is small wicker bills help the airflow break cleanly away from flat or rounded surfaces such as deck lids or flat spoilers. This helps reduce the degree & amount of airflow crashing into the air coming out from under the car. This is not needed on properly designed wings, so increasing the pressure & downforce is the key benefit.

    Wicker bills can be at an angle or up to 90° to the surface. Taller wicker bills slow down more airflow & increase the downforce more, but add to turbulence. There as as many versions of angles & heights as their are guys tuning them. I have used them made out of plexiglass & aluminum. From my experience, I choose 90° versions only when they are very short, like 3/8" or less. Anything taller & I find cleaner airflow, less turbulence & less drag behind the car with wickers at a 40-50° angle.

    Just to put this in perspective, an angled spoiler mounted on the trailing edge of a decklid ... is simply a tall wicker bill ... meant to slow the airflow speed down over the decklid ... to increase the pressure & downforce on the decklid.

    Here are several photos showing many variations in action.

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    Below is an example of the wicker bill concept used to break the airflow cleanly up & away from the body surface over a cockpit opening. This wicker bill tool is also used on the leading edge of fenderwell openings to get the airflow to go around the fenderwell opening & rotating tire which has very turbulent airflow.



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    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!

  13. #93
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    Hey Guys, 71beast (which is Zach) PM'd me with this message & said it was ok to post it.


    Quote Originally Posted by 71beast
    Thanks Ron. I really appreciate that you took the time to help. What you said makes more sense and puts some of this aero into context instead of just written black and white. Everyone seems to have an opinion, but it's good to hear it from someone with first hand experience. After much thought I actual think the issue is mostly because the alignment needs to be corrected. I had to add a spacer in the front suspension and completely forgot to get a new alignment. Before I added the spacers the car felt like it was glued to the road. I feel like an idiot for forgetting

    But I still want to add an air dam, hopefully to make her less of a brick moving through the air. Is it still worthwhile?
    Yes. I'm positive you have some lift.

    I did mean vertical not flat. You mentioned that angled air dams are not as effective as vertical ones. How come? I would have thought they would produce more down force due to the way the air would move, rather then just blocking it like a wall.
    Zach,
    the angled chin spoiler type does reduce the amount of air from getting underneath, but doesn't redirect the air around the car as effectively as a vertical airdam. The air just gets stalled there, increasing the length the bow wave is from the nose of the car. This disrupts the airflow over the hood surface to a degree.

    So yes less airflow is getting underneath, but the bow wave gets bigger, which is not optimum.

    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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  14. #94
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    Hi Ron,
    I am am building a 68 chevelle auto cross/ track day car. What type of rear spoiler would you suggest, I don't want to use a wing but would like to stay close to a NASCAR style spoiler. What height and angle would you suggest and should I put a wicker bill on it?

    Thanks
    scott

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    Quote Originally Posted by pro68chevelle View Post
    Hi Ron,
    I am am building a 68 chevelle auto cross/ track day car. What type of rear spoiler would you suggest, I don't want to use a wing but would like to stay close to a NASCAR style spoiler. What height and angle would you suggest and should I put a wicker bill on it?

    Thanks
    scott

    Hi Scott,

    You should put a red spoiler on your car.


    ...

    ...

    ...

    I'm just kidding. I can't tell you what to use
    ... especially without a ton of detailed info. I can only tell you what stuff does. It sounds like you have already chosen your spoiler style (like a NASCAR stock car). Now you need to figure out how tall and at what angle.

    I can provide some tips to send you down the right path ...
    a. Whatever you do will have little or no effect at the cornering speeds seen in AutoX.
    b. The road courses ... where cornering speeds can be 50-120mph ... will be where you want to achieve optimum aero downforce assistance.

    c. As others have mentioned on here, eliminating front end lift & getting front downforce is important.
    d. You want the rear downforce to work with the front downforce to have a aero balanced (neutral handling) car.
    e. You want to achieve this aero balance on the fastest sweeping corners on the track you run.

    So, after you work out what you're going to do on the front end, top of the body and possibly sides of the car to reduce lift & increase downforce ... on track ... I'd suggest you have a removable & adjustable rear spoiler ... so you can change the length & angle to achieve aero balance on the fastest sweeper.

    This next tip is "my preference" and very debatable amongst knowledgeable tuners. I am in a small group that prefers running longer spoilers (8-12") at very low angles (0-15°) with a medium to large wicker bill (1/2" to 2") at a 40-50° angle. A larger group of tuners prefer to run shorter spoilers (5-7") at high angles (45-65°) with no wicker bill. Races are won with both strategies and both groups have their reasons.

    Once you pick a route, the most important thing is make the spoiler adjustable or removable so you can "tune".

    Please feel free to ask more questions as you go along on your project. I can provide better answers when you provide more detailed info.


    Last edited by Ron Sutton; 12-07-2013 at 02:38 PM.
    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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  16. #96
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    Thanks Ron

    I am planning on running a front air dam and splitter that is height adjustable so I can have the splitter as close to the track as possible for track days. For the sides I was thinking abouout adding 2-3 inches to the rear portion on the front fenders next to the rockers, 2-3 inches to the bottom of the rockers and about the same to the QTRS. The only thing I have done to the roof is shave the drip rails and reshap that area and will be flush mounting the glass with no moldings. I do not plan on doing anything to the hood or roof.

    Scott

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    Quote Originally Posted by Ron Sutton View Post
    Hi Steve, Thanks for chiming in.



    Hood venting is tricky, because it's real easy to cause chaos with the attached boundary layer of airflow across the the hood & with the desired high pressure base at the bottom of the windshield. For that reason, I recommend side vents in the fenders, behind the wheel openings.

    Ron, the pan I'm building runs the full length and width of the car, actually extending out on the sides and front for splitters. I'm using a rocker extension to bridge the gap under the stock rocker to the pan. I need to vent the engine compartment and had a couple of ideas. Two large NACA ducts in the bottom of the pan or vents in the rocker extensions with angled fins. Not sure which way to go. Recommendations?
    Craig Scholl
    CJD Automotive, LLC
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    "I own a Mopar, I already know it won't be in stock, won't ship tomorrow, and won't fit without modification."

  18. #98
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    Hi Scott,

    Quote Originally Posted by pro68chevelle View Post
    Thanks Ron

    I am planning on running a front air dam and splitter that is height adjustable so I can have the splitter as close to the track as possible for track days.
    This will be a BIG improvement. Reducing the majority of air coming in, creates a ton of downforce on the front end, in the corners, where you need it most. Plus prevents a lot of air from getting under the car on the straights. Good decision.

    For the sides I was thinking about adding 2-3 inches to the rear portion on the front fenders next to the rockers, 2-3 inches to the bottom of the rockers and about the same to the QTRS.
    Basically, a 2-3" skirt from the trailing edge of the front fenderwell openings to the rear bumper ... somewhat matching the splitter ... to reduce airflow rolling around the sides of the body & getting under the car. Another good car except one spot.

    Leave the rear quarters alone. You want that area open, as there is a high volume of airflow trying to get out from under the car back there. There is no airflow getting under the car in that spot. But if you skirt it back there behind the rear wheels, you're trapping air & creating lift.


    The only thing I have done to the roof is shave the drip rails
    Nice. Those create a lot of turbulence.


    and reshape that area and will be flush mounting the glass with no moldings.
    Very nice. Another good move to keep a higher degree of attached airflow at the boundary layer. This reduces drag, helps the airflow stay stuck to the greenhouse, which helps the airflow follow the curve back onto the deck lid ... which makes the spoiler be more effective.


    I do not plan on doing anything to the hood or roof.
    Do you plan to make the windshield and/or the back glass flush mounted?

    Scott

    Scott, that makes things WAY more clear.

    I stick with my suggestion to install a removable & adjustable rear spoiler ... so you can change the length & angle to achieve aero balance on the fastest sweeper of the track(s) you run.

    Frankly, the way you're doing your car ... especially if you flush mount the windshield & rear glass ... would work well with "my preference" of spoiler design that utilizes a longer spoiler (8-12") at very low angles (0-15°) with a medium to large wicker bill (1/2" to 2") at a 40-50° angle. This creates the necessary downforce for a balanced handling car WITHOUT creating airflow chaos & massive drag behind the car. So stability & good grip ... along with higher top end speeds.

    The tuners that prefer to run shorter spoilers (5-7") at high angles (45-65°) with no wicker bill are usually doing so because the rest of their bodywork creates "dirty airflow" with very little attached airflow. That 5-7" spoiler at the 45-65° angle creates the necessary downforce for a balanced handling car ... even though the rest of the body was neglected .... BUT THIS METHOD CREATES airflow chaos & massive drag behind the car. So stability & good grip ... but with slower top end speeds.

    Regardless of which route your pick, the most important thing is make the spoiler adjustable or changeable so you can "tune" and balance the handling for different weather, different track conditions and different tracks.

    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. #99
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    Quote Originally Posted by sccacuda View Post
    Ron, the pan I'm building runs the full length and width of the car, actually extending out on the sides and front for splitters.
    I like this design. Good call.


    I'm using a rocker extension to bridge the gap under the stock rocker to the pan.
    Makes sense.

    I need to vent the engine compartment and had a couple of ideas. Two large NACA ducts in the bottom of the pan or vents in the rocker extensions with angled fins. Not sure which way to go. Recommendations?
    You don't want it going under the car. You need the air to flow out the side of the car. So rocker vents & potentially fender vents are the optimum route.

    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. #100
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    My thoughts/plans on this issue are that I want essentially 2 floors with a channel in between them. I want it going all the way from the engine bay and out to the tail panel of the car, exiting between the tail lights with that whole area cut out and covered with mesh. It is worth noting that I will not have the fuel cell in the standard location. Instead it will be in the trunk area...don't worry, it works in my head, lol
    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

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