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Old 03-02-2011, 12:48 AM   #1 (permalink)
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2004 Civic Kamm Sedan Back Project

OK, So here's what I'm thinking.

I drive across the country routinely now, and although the Civic is getting good mileage ~36 Hwy on average (Winter's killin me) I thought I might make a long haul Kamm Thingy to smooth out the airflow over the back of the car.

I know that now, flow gets shredded going down the back glass. I can see it when it rains & such, the air just doesn't blow from like 2 inches down.

So I figure this takes me from a 27% to 40% aft body. I'm about 2 inches low in the back due to my roof line taking a pretty sharp dive about 10 inches before the rear glass. If I try to get back on the "Curve" it just doesn’t seem to flow. Anyway, this shape beats the heck out of the Prius shape anyway.

The idea is to use this for the 4 days I travel 2,100 miles across country, then take it off and store it till I go back home.

I'm thinking of using redwood to build a frame, then 1 1/2 blue board polystyrene insulation as a skin. The whole thing will weigh like 20 Lbs tops. I'll put a small clear Lexan part in the vertical bit to give me a peek out the straight back. I'm going to attach it with some kind of clamp/hook thing on the leading edge of my trunk lid and keep the "contact points" limited to the back window and the tops of my rear light fixtures so I don't damage the paint on my trunk lid.

The redwood chunk and 4x8 blueboard should only be about $20.

I plan on using polyurethane adhesive in a caulk form along with screws to hold the foam in place. I'm not sure what to use as a body filler, I thought maybe just Bondo, and I don't know what to paint it with. I thought I could just paint it with spray paint made for plastic as a primer coat, then use regular enamel over that.

So here's the shape I'm going for.

Whatcha Think?? I'm hoping this will get me into the 40mpg range consistently at 70mph.






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Old 03-02-2011, 01:01 AM   #2 (permalink)
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Like the idea. But for 4 more mpg at 70 mph might also require smooth hubcaps, side wheel skirts and possibly an air dam. Clean up the underside and you'll see even better gains! Good luck.
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Old 03-02-2011, 10:27 AM   #3 (permalink)
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Originally Posted by vacationtime247 View Post
Like the idea. But for 4 more mpg at 70 mph might also require smooth hubcaps, side wheel skirts and possibly an air dam. Clean up the underside and you'll see even better gains! Good luck.
VT247
I like it and I hope you do it. But I'm with Vacationtime on this one. For highway driving I would do some major grill blocking/air dam to clean up the front end. I have gotten good results from a coroplast belly pan/skid plate combo. You could do these two mods and still have full use of your trunk and back window visibility and you can leave them on the car all the time.
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Old 03-02-2011, 10:49 AM   #4 (permalink)
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So let me get this straight....The drum beat on this web site is to modify the area where the most good can happen, the back. And you're saying spend my effort on the front & bottom? I already have an upper grill block in. I'm going to devise a way to get the thing on & off in 30 seconds, so the trunk will still be usable.
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Old 03-02-2011, 11:15 AM   #5 (permalink)
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Edit: I see you have an upper block already. The profile pictures don't show it, so it might be improved by making it flush to the outside bodywork.

I want to see your results.
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Old 03-02-2011, 12:55 PM   #6 (permalink)
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Getting the front done right first will improve the airflow all the way along the car, increasing the gains from the Kammback.

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I'm going to devise a way to get the thing on & off in 30 seconds, so the trunk will still be usable.
Maybe fasten the front half to the rear window, and have the rear half hinge up? I can imagine it sliding on a set of rails when the trunk opens.
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Old 03-02-2011, 01:03 PM   #7 (permalink)
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Aerohead says to make sure you have attached flow coming from the front or the mods at the rear won't be very effective so my personal rule-of-thumb has been to work from the front to the back. That said, you should have good attached flow over the roof so I guess it is personal preference what you do first. If you can make it quickly removable, hopefully we can see some A-B-A test results too.
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The power needed to push an object through a fluid increases as the cube of the velocity. Mechanical friction increases as the square, so increasing speed requires progressively more power.
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Old 03-03-2011, 05:49 PM   #8 (permalink)
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Quote:
Originally Posted by ChazInMT View Post
So let me get this straight....The drum beat on this web site is to modify the area where the most good can happen, the back. And you're saying spend my effort on the front & bottom? I already have an upper grill block in. I'm going to devise a way to get the thing on & off in 30 seconds, so the trunk will still be usable.
It's my opinion that the flow is okay for this project.
You might,just for simplicity,build two simple C-pillar buttresses exactly like you've drawn,mounted parallel.Then install a flat shelf spoiler,dead level,which extends from the top rear of the buttresses forward to as close as you dare get to the backlight.
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The buttresses will force the side flow to behave itself over the trunklid sides and the shelf will sculpt the attached-vortex which the air will just skip over as if it was a solid Kamm roofline.
The air captured under the shelf will just be a stagnant pool of air dragged along with the car.
--------------------------------------------------------------------------
She won't be glamorous but it's only three easy to build pieces joined and mounted.
If it is hinged at the rear with some sort of forward latch,it will flip up,allowing you to get into the trunk without removal.

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