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    Thread: MkIV Aero Modifications Thread

    1. Member aircooled56's Avatar
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      06-21-2012 10:55 AM #1
      I've been on these forums for years now and I've seen very little in the way of functional aero modifications. Looking to see what others have done to there late model platforms, especially those pertaining to the Golf/GTI/R32 body style. Especially:

      Splitters
      Canards
      Underbody trays
      Rear diffusers
      Vortex generators
      Hatch spoilers/wings

      Post up what you have seen or done, or even if you just have input on the subject
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      06-24-2012 07:15 AM #2
      I think at this level of racing the effect of such parts would be minimal.
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    3. Member chois's Avatar
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      06-24-2012 09:26 AM #3
      I disagree. They would be very effective, but a lot of common rule sets don't allow much of it.

      We have definitely seen downforce benefits from a good splitter on the front of an A1, and wish we could do something in the back as well. I doubt there is much specific to the mk4 in terms of Parts or functionality. We ended up making the stuff we use, and would buy a universal wing if we could use one.
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    4. Member aircooled56's Avatar
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      06-25-2012 10:30 AM #4
      I'm not talking just for club series either. The open track days and time attack style events are growing in popularity where just about anything goes.

      Has anyone ever seen a wind tunnel flow picture of a hatchback. I'm curious to see how air reacts to the hatchback body. I understand that traditionally the nose of the car and the base of the windshield are high pressure zones. Also, that the air behind the hatch glass typically stalls out.
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    5. Member aircooled56's Avatar
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      06-28-2012 09:26 PM #5
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    6. Member aircooled56's Avatar
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      06-29-2012 10:38 AM #6
      That link brings out a lot of good points. It's interesting to note that just about all of the hatchback bodies produce a measurable amount of lift over the rear tires at speeds over 100mph. It's also interesting to note that according to that study 40% of a cars drag is due to the underbody (mainly the wheel wells) and another 20% is due to the surface area of the tires while the remaining 40% is mainly the frontal area of the car. The thread drops off after a few pages, but there is some really good information there!

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    7. Member unplugged92's Avatar
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      02-28-2013 11:28 PM #7
      common, no one here did any aero mods to their mk4?!?!?! I have a friend whoose making a custom carbon fiber splitter.

      I'm in the process of making a vented hood for my gti, in effort to get underhood temps down on the track. also i'm gonna make a front belly pan. I would love to make a rear diffuser if i get the chance.

    8. Member aircooled56's Avatar
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      03-01-2013 10:32 AM #8
      I actually have done the vented hood, working on dive planes, a new splitter design, and rear wing for the R32 track day in May.

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    9. Member unplugged92's Avatar
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      03-01-2013 11:15 AM #9
      that looks awesome! mine is a little different. I cut part of the hood and bent it down closer to the windshield. I'll post pics when i'm done, or almost done. I won't be painting until spring.

    10. Member aircooled56's Avatar
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      03-03-2013 12:34 PM #10
      Be careful where you place your opening on your hood. Too close to the windshield and it will actually suck air into the engine compartment. This pressurizes the engine compartment which causes you to lose cooling efficiency. You really don't want to go any further then about 18 inches from the leading edge of the car if you are looking to suck the hot air out. If you look directly down through my vent you see the space between the cooling fans and the intake manifold
      Last edited by aircooled56; 03-03-2013 at 12:37 PM.
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    11. Member unplugged92's Avatar
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      03-03-2013 12:52 PM #11
      Quote Originally Posted by aircooled56 View Post
      Be careful where you place your opening on your hood. Too close to the windshield and it will actually suck air into the engine compartment. This pressurizes the engine compartment which causes you to lose cooling efficiency. You really don't want to go any further then about 18 inches from the leading edge of the car if you are looking to suck the hot air out. If you look directly down through my vent you see the space between the cooling fans and the intake manifold
      Hmmm that is interesting. Well i already cut it and i'm in the process of smoothing it all out. I will see how it goes.

    12. Member lil_kano's Avatar
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      03-12-2013 10:57 AM #12
      In for info.

      Awesome thread!


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    13. Member aircooled56's Avatar
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      03-12-2013 09:44 PM #13
      Modified the rear bumper in preparation for a rear diffuser. Just by itself it allows trapped air at the rear to move more freely.


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    14. Member lil_kano's Avatar
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      03-12-2013 10:13 PM #14
      Any thoughts on making a full underbody cover out of ABS? Obviously with provisions for exhaust sections...may be use aluminum sheet for that piece and rivet together?


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    15. 03-13-2013 11:09 PM #15
      Quote Originally Posted by aircooled56 View Post
      Just by itself it allows trapped air at the rear to move more freely.

      Please tell me there isn't holes replacing the bumper.

      Plus I doubt it helps.

    16. Member aircooled56's Avatar
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      03-14-2013 08:43 AM #16
      Quote Originally Posted by soeuroithurts View Post
      Please tell me there isn't holes replacing the bumper.

      Plus I doubt it helps.
      I don't understand what you mean by holes. I just removed the lower center fencing on the stock bumper. With the factory exhaust removed the rear floor is nearly even with the bumper. This modification is only one part of whole, other paneling as well as a functional adjustable wing are planned. It's pretty extreme, but then again you don't see too many mkiv's doing time attack style events.
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    17. Member aircooled56's Avatar
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      03-14-2013 08:49 AM #17
      Quote Originally Posted by lil_kano View Post
      Any thoughts on making a full underbody cover out of ABS? Obviously with provisions for exhaust sections...may be use aluminum sheet for that piece and rivet together?


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      With the factory rear exhaust removed and single outlet in place I can now start to seriously looking into a full under tray. I'm looking at corrugated alumilite versus plastic to cope with high thermal areas.
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    18. 03-14-2013 11:37 AM #18
      Quote Originally Posted by aircooled56 View Post
      I don't understand what you mean by holes. I just removed the lower center fencing on the stock bumper. With the factory exhaust removed the rear floor is nearly even with the bumper. This modification is only one part of whole, other paneling as well as a functional adjustable wing are planned. It's pretty extreme, but then again you don't see too many mkiv's doing time attack style events.
      http://i41.tinypic.com/v5ljl3.jpg

      But honestly, i doubt theres going to be a grand difference. It barely help's in the 1/4 mile yet along racing. But i'm curious to see you see a difference.

    19. Member aircooled56's Avatar
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      03-14-2013 01:05 PM #19
      Quote Originally Posted by soeuroithurts View Post
      http://i41.tinypic.com/v5ljl3.jpg

      But honestly, i doubt theres going to be a grand difference. It barely help's in the 1/4 mile yet along racing. But i'm curious to see you see a difference.
      No, holes in the bumper for me. It would make sense if there was a large cavity behind the bumper skin but there is not. Besides, if I were to do something like that I'd make it look a whole lot cleaner then that! Alone, no it won't make much of a difference, but as a whole package it should make a noticeable difference.
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      03-14-2013 02:51 PM #20
      Quote Originally Posted by lil_kano View Post
      Any thoughts on making a full underbody cover out of ABS? Obviously with provisions for exhaust sections...may be use aluminum sheet for that piece and rivet together?


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      AC56 thanks for the link from the MKIV.:R32 forum!!!

      Hopefully someone in this forum can help. About 4 years ago I was farting around on Vortex and found a thread that had a link to a YouTube video. The video was of some dudes with a shop in Burbank, CA who were doing aero testing on a MKIV Wookiee. They mounted yarn all over the car with cameras taking video of the yarn movements. The footage was epic! Then they were testing a CF Undertray. The conclusion they came to was any undertray for the MKIV.:R32 would have to have a cut out to channel air to cool the rear diff/clutch packs. When they tested the undertray the temps of the diff got critical and were in danger of boiling the Haldex fluid and oil in the diff. That was the last video and I have not a) found that original video, b) I have not found any updates on there research.

      I'm in for any areo mods! Especially a rear diffuser and an underbody tray. A rear diffuser would look cool, and when combined with a good rear spoiler it could smooth out the air flow at the rear and keep the air at the rear from stalling out.

      Edit: A rear diffusers effectiveness is reduced with out a flat bottom. The air is very turbulent from the front wheels and underbody components. That makes the rear diffusers job that much harder. Smooth out the flow underneath and the diffuser can put in mad work! With smooth air exiting the rear it will help the air from the top. Keeping the LAMINAR FLOW at the back is what we are after. If this is achieved the car will be transformed!!!
      Last edited by GOT R32?; 03-14-2013 at 03:05 PM.
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    21. Member lil_kano's Avatar
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      03-14-2013 05:29 PM #21
      Quote Originally Posted by GOT R32? View Post
      AC56 thanks for the link from the MKIV.:R32 forum!!!

      Hopefully someone in this forum can help. About 4 years ago I was farting around on Vortex and found a thread that had a link to a YouTube video. The video was of some dudes with a shop in Burbank, CA who were doing aero testing on a MKIV Wookiee. They mounted yarn all over the car with cameras taking video of the yarn movements. The footage was epic! Then they were testing a CF Undertray. The conclusion they came to was any undertray for the MKIV.:R32 would have to have a cut out to channel air to cool the rear diff/clutch packs. When they tested the undertray the temps of the diff got critical and were in danger of boiling the Haldex fluid and oil in the diff. That was the last video and I have not a) found that original video, b) I have not found any updates on there research.

      I'm in for any areo mods! Especially a rear diffuser and an underbody tray. A rear diffuser would look cool, and when combined with a good rear spoiler it could smooth out the air flow at the rear and keep the air at the rear from stalling out.

      Edit: A rear diffusers effectiveness is reduced with out a flat bottom. The air is very turbulent from the front wheels and underbody components. That makes the rear diffusers job that much harder. Smooth out the flow underneath and the diffuser can put in mad work! With smooth air exiting the rear it will help the air from the top. Keeping the LAMINAR FLOW at the back is what we are after. If this is achieved the car will be transformed!!!
      That's interesting!! I was just having thought on heat effects on the transmission fluid - oem vs aftermarket. Didn't cross my mind on the rear diff.

      Makes me wonder now about high Hp applications (more frequent engagements) creating more heat.

      Sorry to go off topic but had anyone seen the mk5 and mk6 belly pan with louvers to push air to the trans and brake area (wheel well)?


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    22. 03-14-2013 06:42 PM #22
      I see. Yet us know the results.

    23. Member aircooled56's Avatar
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      03-14-2013 06:44 PM #23
      Quote Originally Posted by soeuroithurts View Post
      I see. Yet us know the results.
      Yet another productive response. Find another thread to browse troll.
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    24. 03-14-2013 07:08 PM #24
      Quote Originally Posted by aircooled56 View Post
      Yet another productive response. Find another thread to browse troll.
      What? Dude i'm being serious, I really want to know the results from doing your modifications.

    25. Member aircooled56's Avatar
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      03-14-2013 07:33 PM #25
      My bad, I thought I sensed some sarcasm in that message.
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    26. 03-14-2013 07:43 PM #26
      Quote Originally Posted by aircooled56 View Post
      My bad, I thought I sensed some sarcasm in that message.
      No worries. Out of curiosity, what kind of diffuser will you be running?

      Similar to this? http://www.nextcar.com.au/i.renault....user.06mar.jpg

    27. Member aircooled56's Avatar
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      03-14-2013 07:54 PM #27
      Probably a flat bottom style like Corvette and Porsche used in ALMS. A strake, or fin style, isn't practical for my current driveway and trailer.

      Last edited by aircooled56; 03-14-2013 at 08:59 PM.
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      03-17-2013 05:45 PM #28
      Bookmarking this!!

    29. 03-17-2013 10:24 PM #29
      Tested this today along with some trailing arm bracing. Netted a 3 second improvement. (Note last timed lap was on slicks, this was on street tires so actual improvement was greater) 5 mph drop on the straight, about 10+ mph improvement in the corners. Really planted the rear end comming off of curbing and into hard downhill braking. Trailing arm bracing was to address flex causing dynamic rear toe. I have video from under the car where the trailing arm was flexing in under load.

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    30. Member aircooled56's Avatar
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      03-18-2013 12:48 AM #30
      Very cool! Thanks for sharing!
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      03-18-2013 05:16 AM #31
      wow was it just that one piece of sheet metal that improved cornering speeds that much? or was it that combined with the spoiler?

      thumbs up for ground control sleeves! just put that on my street car

    32. 03-18-2013 11:06 AM #32
      I assume your referring to the picture of the underside of the car. The "sheet metal" piece is stock, the picture is to show the bracing from the trailing arm to the spring perches.
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    33. Member unplugged92's Avatar
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      03-18-2013 04:20 PM #33
      oh **** lol, i just realised that's the plastic under panel that keeps comming off my car...

    34. Member aircooled56's Avatar
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      04-01-2013 12:54 AM #34
      Just found out this week that any Audi TT quattro has two flat panels to smooth out the transition between body/gas tank/rear suspension; we happened to have one in the shop for service and never noticed them. Looked into getting them new (they also require new gas tank straps to mount) and it was nearly $400 haha. Time to call the scrappers While I'm at it I'm going to try to locate some mkv full floor undertrays and try to retrofit them to the mkiv.

      Last edited by aircooled56; 04-01-2013 at 01:02 AM.
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      04-01-2013 01:10 AM #35
      This thread is always evolving and applies to mkiv's as well as the mkv's in many cases...

      http://www.golfmkv.com/forums/showthread.php?t=163575
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