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 :thumbup: .
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.

Ooo, nice results. Did you put them in the coast-down calculator to see what kind of Cd reduction that implies?

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.

thanks bill

No, I haven't got that far yet. Too busy at work today.

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.

I just put it back on.

Sorry, the best I can do right now is direct you to my garage pics :o . 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.

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 :).

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!!

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"!

Now that's a compliment :) .

I did some more calculations. It appears the kammback improves Cd by about .05 :thumbup: . 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)