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Old 08-02-2007, 12:06 PM   #1
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tested my kammback

I needed to retape my kammback so I decided to do a test with and without it from 55-45 mph average of 2 bi-directional runs each.

Here are some preliminary results of the coast down testing.

Same test mile used for mega airdam test, 95 f, 30.03" hg, winds from west around 5 mph, no airdam installed all other aero appliances in place , test mass 1981 lbs.

With kammback = 15.86 seconds.

Without kammback = 14.14 seconds.

from 55-50 mph

with = 7.97 sec.

without = 7.16 sec.

So kammback is a good add on .
I still need to clean my hatch and reattatch the thing.

Disclaimer...I didn't follow the best testing procedures due to time and space limitations (and some laziness). I should have posted this in the experiments section but it wasn't proper enough IMO.
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Old 08-02-2007, 12:51 PM   #2
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Ooo, nice results. Did you put them in the coast-down calculator to see what kind of Cd reduction that implies?
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Old 08-02-2007, 01:04 PM   #3
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Can you post a pic here of the current configuration? I think you just have the side pieces with a hollow center - correct?

I don't think I have the nerve to build one for my "brick" - it would be huge, and would have to have a clean join to the main body as well as to the liftgate. But I'd like to see yours again in this thread.
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 08-02-2007, 01:06 PM   #4
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thanks bill

Quote:
Did you put them in the coast-down calculator to see what kind of Cd reduction that implies?
No, I haven't got that far yet. Too busy at work today.
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Old 08-02-2007, 01:51 PM   #5
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jwxr7 - I like it. At first I thought it hindered you rearward vision, but I can see by your pics in the garage that it really doesn't block it too much.

brucepick - Your correct, it would be fairly large on a 245 hatch. But you might get away with just fastening it to the hatch alone. The d-pillars aren't very wide in the back so laminar sep. would be minimal. Just an idea.
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Old 08-02-2007, 02:09 PM   #6
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I just put it back on.

Quote:
Can you post a pic here of the current configuration?
Sorry, the best I can do right now is direct you to my garage pics . I'm not photo literate. It is one long piece bent to make the sides and a support was cut to fit the middle. BTW the airdam in some of those pics is the 7" version which is now trimmed to 4".
I would like a better more permanent way of attatchment, but the tape works for now. I may try different angles sometime too.

Quote:
jwxr7 - I like it. At first I thought it hindered you rearward vision, but I can see by your pics in the garage that it really doesn't block it too much.
Thanks, yeah It really doesn't obstruct rear view (unless you want to see up behind you ). In fact it makes a nice sun shade while parked .
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Old 08-02-2007, 02:25 PM   #7
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I'd really like to make one up. When I take off my temporary coroplast air dam I'll see what kind of gunk the duct tape leaves behind and how much of a PITA to clean it off. My car's not gorgeous but it would be worse with tape gunk residue all over.

I had a full sheet coroplast, 4' x 8'. I thought that was big enough to build nearly anything but I used it all for the temporary air dam + the belly pan to go with it. No free coroplast till electon day, dang. Plywood??? Not with duct tape. Frustration!!
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 08-02-2007, 02:35 PM   #8
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I just added a couple current pics (top two) to my garage. One shows 4" airdam.
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Old 08-02-2007, 02:45 PM   #9
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Quote:
Originally Posted by jwxr7 View Post
I just added a couple current pics (top two) to my garage. One shows 4" airdam.
Cool! In the first pic, the side view, it looks "factory"!
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Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.

Now driving '97 Civic HX; tires ~ 50 psi. '89 Volvo 240 = semi-retired.
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Old 08-02-2007, 02:58 PM   #10
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Quote:
Originally Posted by brucepick View Post
Cool! In the first pic, the side view, it looks "factory"!
Now that's a compliment .

I did some more calculations. It appears the kammback improves Cd by about .05 . And average road load is reduced from 63.18 lbs to 56.75 lbs between 55-50 mph by using the kammback. (I love when i can use physics for real life stuff)
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