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  #211  
Old November 4th 2011, 08:41
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Got a few speedholes punched in the fenders. I drove it this morning and it does seem to help already, the car felt more planted to the road on the highway. Gonna try to get the fender flares mounted before tomorrow's autocross race.



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  #212  
Old November 4th 2011, 10:19
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Porsche did introduce their 2012 model 911 GT3 RSR today. With the 48mm increased width compared to last year, they relocated the engine intake and did some 'drastic' modifications to the shape of the rear fender.

2012




2011
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  #213  
Old November 4th 2011, 12:33
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Thanks AJ!

I like the ducktail of the 2011 model better BTW :-)
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  #214  
Old November 6th 2011, 16:57
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Quote:
Originally Posted by Jadewombat View Post
Where did you get those!?!?!?!
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  #215  
Old November 6th 2011, 18:08
proughj proughj is offline
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Where did you get those!?!?!?!
I asked the same thing he said datsun 260z
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  #216  
Old November 6th 2011, 23:04
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Yep, made for a Datsun Z 240/260/280 car. I just guessed as those cars came with 15" rims and the curve of the fenders looked roughly the same as a bug. I got them off eBay. Various sets are about $110-150 new. These cover 2 3/4" width, actually mounted on the bug I'd say closer to 2" or less extension. Read the shipping time before you bid on a set, I didn't look closely but the auction I won could ship in 11-14 days--meaning I think he waits until gets enough orders then lays the fiberglass.

Anyhoo, I didn't have enough time to mount them before the autocross. I did one this afternoon and it does fit pretty well.





Just trying to think how I can taper out the transition of the lower edges smoother with the fenders, especially the front. I don't plan to run this car on the track regularly (maybe once, if that), I autocross it mostly and don't plan on putting a front air dam on either as my driveway is pretty steep. I do drive it to work about once or twice a week. I'd like to fab something to at least cover more area where the tire is exposed under the fender here, just send the air down and out to the side of the wheel. Thoughts of something I could use already made to adapt to the car again?



Next thing, related to the above about not running a front air dam. I do have a lower carbon fiber shield I made for the underside to close up that gap between where the underside of the front apron and the sway bar exists, or where the stock air-conditioning would be normally.



I've done some testing with a generic manometer to see what the readings were (a tube of water mounted at 30 deg. on a board). The slotted vents on the front apron are open. So my results are:

At 65mph:

Underside of the front of the car, tube outlet mounted just behind the front sway bar
--With the CF shield pulled -.25" of water
--Without " " " pulled -.1875" of water

which stands to reason. The shield installed guides more air under the car as it smoothes out the underside. But...

Underside of the front of the car, tube outlet mounted below the spare tire wheel well (or in other words, mounted on the top side of the front sway bar)
--With the CF shield pulled +.1875" of water
--Without " " " pulled -0.125" of water

which I was not expecting at all. That whole area on the underside of the wheel well, but above the sway bar with the shield becomes positively charged. The only way I can justify this would be it helps keep my front brakes cool, but is this creating a significant amount of drag? Would I be better of blocking those vents? I think if I block off the vents though this would send more air under the car and create more lift though, correct? Whew.
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  #217  
Old November 7th 2011, 12:42
proughj proughj is offline
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when you mounted the fender flares how much of the original fender did you need to cut? could you take a pic with the flare removed or a pic of the underneath wheel well
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  #218  
Old November 7th 2011, 14:08
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@Jadewombat: Maybe you results can be explained by a smaller boundary layer under you car (that would be a good thing).
See the picture and text in this link: An overview of vehicle aerodynamics (start reading at the previous page).
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  #219  
Old November 7th 2011, 22:10
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Thanks for the link, that helps to visualize it a bit better. Maybe I need to block off the vents and try retesting?? I took another couple of photos, in this photo the area just behind the vents I was getting a positive pressure reading with the shield installed meaning it was a positively charged (high pressure) area.



Here where I'm pointing on the underside of the sway bar I was getting more negative draw meaning more air was being directed on the underside with the shield in place.



As for the fender, I didn't cut anything. I just lined up the front and rear edges as best as I could while matching the curve of the fender lip. I could still cut it if I get ambitious but this is also a dual-purpose car. I plan to rallycross with it at the next event here. My off-road and snow tires match the fenders just fine so there's not really a need to cut it. What I'm getting at is autocross--flares installed/wide tires, rallycross--pull the flares off and change the rims/tires. In case you can't tell, this ain't a show car. Gonna paint the flares silver to match the underside of the car:



With off-road tires:


The bug is my play car, just trying to have fun with it on a limited budget and power (and time to invest) constraints. My bus is a different story though, just came home from the paint shop today:



That link said a lot of drag created from the spinning wheels, what about something like this? Not this exact overpriced piece, just something like it on my front end of the bug:

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Last edited by Jadewombat; November 8th 2011 at 08:48.
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  #220  
Old November 9th 2011, 00:11
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Hi everyone, im back and about to leave again.. (I'll just be honest, i like it on the countryside with a new engine in my bug...)

Did a tiny bit of research thought...
most importantly

the air cooling the brakes is the air flowing under the car.

This is true for every vehicle that has enough ground clearance ( us for example). the opposite is true for purposely built track cars (i.e lmp class, gt2/3, and road going versions such as the radical sr3 etc)
Imagine top view of the car and the front at the top. the air goes under the front valance/splitter, under the front section (along the front wheel wells) and then it gets sucked outwards each side, due to the vortices created by the rotating wheel. Going super low requires another means of providing the brake disks of cooling air ( naca ducts on the bottom of the front splitter/ air intakes on the front surface of the car). In plain words the wheel works as a "fan" and sucks air out through its self (weird wheel covers on 934/5 P cars etc)

Jadewombat: if I understand your testing correctly there is a possibility that the positive value that you get is due to the flow reduction caused by the louvres on the front valance. Sounds weird doesn't it?? The louvres actually by letting air flow through them act like a "see through" fabric...its there supposedly covering up something but actually you can see through...
but what you see is a differentiated image of the original. If you had the normal front valance maybe you could still gain negative values (due to high turbulence) in the same area...

Now as for the rear diffuser discussion, aartjan thank you very much for the pics, on the new cup car we get a very nice idea for a diffuser.
IMO that would be, fabricate a symmetrical 4-1 exhaust system that fits and has EQUAL primary tube lengths.
Chop the rear part of the rear fenders and enclose the exhaust manifold within the diffuser.ie place two vertical pieces (one each side) somewhere between the rear upper shock mount and the inside fender wheel well (where the Z bar attaches on swing axle beetles).

I strongly believe that much is to be achieved by splitting most of the air around the engine (still providing airflow to the sump) and then expanding the air flow in a sideway's manner since the engine sits in the middle


Sooooooooooorrrryyyyyy for the long post.
I hope it makes sense

Chris
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  #221  
Old November 9th 2011, 00:13
beetle1303 beetle1303 is offline
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have a look at this

http://www.youtube.com/watch?v=uMEYe...BDD1ACE&lf=BFp

Chris
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  #222  
Old November 9th 2011, 15:35
ace_bug ace_bug is offline
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Thats what i'm doing in the back of my front fenders.


Uploaded with ImageShack.us
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  #223  
Old November 29th 2011, 13:07
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Jadewombat Jadewombat is offline
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Quote:
Originally Posted by beetle1303 View Post
Did a tiny bit of research thought...
most importantly

the air cooling the brakes is the air flowing under the car.

This is true for every vehicle that has enough ground clearance ( us for example). the opposite is true for purposely built track cars (i.e lmp class, gt2/3, and road going versions such as the radical sr3 etc)
Imagine top view of the car and the front at the top. the air goes under the front valance/splitter, under the front section (along the front wheel wells) and then it gets sucked outwards each side, due to the vortices created by the rotating wheel. Going super low requires another means of providing the brake disks of cooling air ( naca ducts on the bottom of the front splitter/ air intakes on the front surface of the car). In plain words the wheel works as a "fan" and sucks air out through its self (weird wheel covers on 934/5 P cars etc)

Jadewombat: if I understand your testing correctly there is a possibility that the positive value that you get is due to the flow reduction caused by the louvres on the front valance. Sounds weird doesn't it?? The louvres actually by letting air flow through them act like a "see through" fabric...its there supposedly covering up something but actually you can see through...
but what you see is a differentiated image of the original. If you had the normal front valance maybe you could still gain negative values (due to high turbulence) in the same area...

Chris
Well, did some more testing. I put my off-road and snow tires on the car as I'm having the five spokes updated with semi-slicks for this weekend. Anyhoo, I decided to test with the louvers completely blocked off and see what happened. Mind you, this was different than with the 215/55 16 sticky street tires I had before and the rallycross tires put the car higher off the ground. Even so:

-Louvers blocked off pulled -1" of vacuum under the car just behind the front sway bar
-Open louvers was not even registering under the car " " " (I'm guessing this was because I'm higher off the ground than before when I tested)

So, what next I thought to improve the front area?? High positive pressure in that are behind the louvers or no pressure and send all the air down and below the car. My first thought is sending that air below the car will cause lift, but it may be smoothing out airflow though reducing drag? I've decided to split the difference and installed some screen material just behind the louvers to let some of the air pass through.



In case you're wondering why I don't just install an air dam, my driveway is way too steep. Will retest once I get the front end aligned. I also drilled the inner edge of the fenders, trying to shave as much weight as I can and hopefully vent more of that trapped air out from under the fenders.

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Last edited by Jadewombat; November 29th 2011 at 22:46.
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  #224  
Old December 4th 2011, 20:56
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I tested it once more:

-Screen material behind louvers yields 3/8" of negative vacuum under the car

Took it out to the autocross today, did pretty well. It was my first time on semi-slicks which made the car feel quite different. Just trying to forge ahead and do any more low-cost aero. tricks to go faster then look at modifying the engine and trans.




One thing I also noticed looking at the front of my Audi RS4 (mine's black, I borrowed this picture below), there's these short deflectors almost like mudflaps on the front to counter the drag of the front tires. Gives me an idea...

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  #225  
Old December 5th 2011, 14:04
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Gerrelt Gerrelt is offline
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Yes, those are called "wheel deflectors" or "wheel spats". I am planning to make a pair too.

These things can be found more and more on modern cars. Not only at the front wheels, but also at the rear.
I want to make a set for the rear wheels.
It can't be hard to make, it's just a piece of flat plastic/fibreglass that sits just in front of the wheels.
I only wonder how to determine the correct size and position in relation to the wheel..
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