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Old 06-26-2007, 03:45 PM   #21
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Whuuups !
Well... now that I am sure that the images - can actually be viewed - I'll have to add some notes.
About the test : This test was done some time ago.
At the time, I did not have any sort of belly pan in place ( sorry to mislead )
I installed an underbody covering a few months ago which extends to just behind the engine compartment. This should get rid of any 'parachute' effects happening back there.
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Old 06-26-2007, 03:50 PM   #22
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How can I link to one of those images folks ?


( Thanks for posting Bill - I guess I wasn't selecting the corect url thingee ! )
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Old 06-26-2007, 04:09 PM   #23
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Bill - it worked . Thanks ! I'd post some images and make some observations ( and ask some questions too ) but I don't want to hijack this thread.
I'll have to create my own thread.
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Old 06-26-2007, 04:46 PM   #24
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Let's see what happens when you expand an image, right click on it, click "properties" and copy the url and paste it into the image dialog box that you get when you click the little mountain and sun button...
Yep, that worked.
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Old 06-26-2007, 05:01 PM   #25
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]Very, very, very interesting..... partly because I hav a Civic, but still.....

Glad you could get some use out of it. It was really embarrasing, and I felt like an idiot when people were laughing ( including my parents who were my drivers for the test ) Now you guys have all the hard work done for you.

" - Kammbacl works on the side, but not the bottom (the bottom needs to be.... on the bottom. Where it is just introduces an additional voids and turbulence area"

Are you talking about the cardboard junk that I have taped to the side of the car ?
Nevermind that.
I originally had a cone shaped extention sticking out that I intended to test ( I have an image of the idea with the rest of the images )
I wanted to have one side with the extention and one without, but it all started to fall with gravity and rain was on the way, so I just took it all off except for the side piece.
I plan to do a better test next time I visit my parents.

" Look at the back bumper.... flow down, under, and forward? Makes no sense if you think wind tunnel. Does make sense if you think about the car travelling down the road over stationary air, pulling some with it, leaving a vacuum to fill in from the sides, back, front, etc."

It should be interesting to see what effects that my underbody cover has on the airflow of the car in comparison to these images. ( The only aero mods at the time of the test were the mirror pull back and the partial grill block using my liscense plate ....and that cardboard junk on the back )

Any special areas that you would like to see tufted on the car the next time that I run a test ?

" Rear wheel well sicking in.... see previous

- Front wheel well not sucking in.... maybe that really is brake dust on the front rims :-)"

I never noticedthat - I'll have to check that out better !

" Serious cowling into hood flow... bet the vent works well "

Actually, just the opposite ! It is horrible ! Do any of you other Civic owners have this problem too ? It just barely blows ..and the air is warm. The vent isn't clogged either )

" Texan eh? Not an Aggie I hope." Nope but I'm surrounded by them ...I live in Austin now !

" Something you have good that I did not... no flow into the front hood seams. I had to beef up the weather stripping there."

I would think that the hood seam would not be a problem at all. I'll have to create a post on a Hot Rod article that I read that completely changed my thinking about aerodynamics.
They got an basically stock looking '81 Camaro with big rear tires and a brick flat cow-catching front end to a .20 drag coefficient . No side skirts, tires hanging out in the breeze, a big honkin hood scoop and they didn't even make the door handles and window trim flush. I was shocked !
Small stuff doesn't really matter all that much apparently.


" Yeah, my mirror sux too"

Actually I did that on purpose - it decreases the cars frontal area by a small amount . So nice of Honda to let us be able to pull the mirrors back ...and if you notice , it almost looks intentional - the mirrors profile is streamlined when pulled back



Wow... thx for the shots.... very enlightening. Gives me some clear ideas on changes.

No problem !
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Old 06-26-2007, 06:33 PM   #26
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I started a new thread here : http://www.gassavers.org/showthread....0864#post60864

I posted the pictures that I have from a Hot Rod article that blew my mind. Seeing stuff like that just makes me want to throw up my hands and say forget it .
Air moves in strange ways and you would think that it would flow a certain direction only to find out that it goes completely opposite.
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Old 06-26-2007, 07:13 PM   #27
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Yeah my vent is no good either. i am studying it now and have concluded that the air pressure cushion at the cowling is not all that high. For example, opening the window helps a lot (very low pressure outside the window) but opening up the hatch actually hurts.... how the heck the air pressure at the back of the car could be higher than the cowling amazes me but that is what i am seeing.

I was suspect of the camaro claim of .2 until I looked at the pictures.... if you want a low Cd you want to get all the air moving around the object in a streamlined fashion and avoid separation in the back by a shallow long slope. it may look like a brick from one perspective, but i see something that will really slip through the air in those pictures

I am a former Austinite.... great great town. Every time I come back I go straight to Taco Cabana for the fajita's..... sounds crazy, but that is what I miss most.

Oh, and yeah on the Kammbach cardboard rear.... i was pointing out that the lower extension being half way up the rear of the car really does nothing, as the problem is the air turning the sharp corners (which is why the sides do work).
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Old 06-27-2007, 06:10 PM   #28
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Quote:
Originally Posted by lca13 View Post
This is one of those counter intuitive things. I think it helps to not think wind tunnel and think staionary air with car moving through it. The air under the car for example, on one hand gets battered around with a net forward momentum add. Contrasting this is the air up front which is rushing below and under the bumper picking up speed towards the rear. Messing it all up even further is the stuff exiting the engine compartment. So you likely end up with a pressure increase under the car up front, and a decrease near the rear. Note that the data in these pictures has me thinking of this explanation, not independently, but this explanation would describe the observed behavior.

If all this is correct, the following should help (let's see if the recommendations are consistent with other observations):

- Less air into the engine compartment means less backward velocity increase and turbulence underneath..... grill block.

- Smoothing out the underbody imparts less forward momentum into the stationary air..... underbelly pan.

- Deflectors underneath diverting air around remaining appenditures, like lower control arms would help in addition (but should be teardrop shaped completely.... just a parabolic front is not enough.

- Deflectors in front of the front wheels to divert air outward would help.

- Wheel skirts (exterior) in the back to keep air from rushing into the rear vaccuum would help.

- Wheel skirts (interior) in the front would keep the flow underneath the car

- Vertical lengthwise channels would keep air flow uniform and.... but here is an anomoly... a diffuser to reduce velocity in the back would be counter to the data.... want to speed up in this case?

- Any spoiler up front that moves air up instead of down should help (smoother streamlining above).

- Lowering the car should help.

This is starting to make sense :-)

For the coup de gras, a properly channeled underbody with an electric fan assist in the rear, velocity driven by delta air pressures between the under rear and the behind.... equalize ????
I have all of these changes that you mentioned in progress. I just have to install it all. Did you see my Photoshopped picture that I did on my car .... or do we just think alike ?

( By the way )
I too have thought of an electric fan system which would blow air from the back of the car*. It could be powered by you cigarette lighter / AC outlet .
It would really look stupid though.
Imagine driving behind someone with a fan blowing back at you.

( * To get rid of vacuum at the back of the car. )
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Old 06-28-2007, 09:49 AM   #29
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Based on the Autospeed articles, I bought a couple of Dwyer magnehelic gauges off Ebay. I have 0-0.5" H2O, 0-5" H2O, and 0-30" H20 gauges. Between the three I am getting some very interesting information at quite low speeds on my '98 Saturn. Using inexpensive gauges like this can add a lot to the knowledge gained from tuft testing. It's really nice for determining if the pressure behind your radiator increases (bad for cooling flow) or decreases (good for cooling flow) when you add a belly pan, and that sort of thing.

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Old 06-28-2007, 11:43 AM   #30
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Interesting.... what sort of pressure deltas do you see around the exterior of the car at speed? versus inside of the car, etc?

Let is have a look at some of the data... it would be interesting.
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