Quote:
Originally Posted by California98Civic
That is a good looking DIY mod. And a 6% FE gain is cool. I'm hoping for 0.5-1% FE gains with this trunk lid. Looking at your Kamm makes me feel like giving the lid up. But I want to finish what I started. I want to know methodically if it can work and how well or poorly. Are you still running your Kamm? What are the windows made of? On the curve-cut in coroplast, I hear you. I bought tin snips, curved, for the coroplast cuts. But I'm still not confident I'll get a great line. I'm patient. I'll work up a model of that section in card board first. Ultimately, I know I want to build whatever is final in durable materials (lightweight fiberglass).
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I think a 1% gain should be doable (but a change that small is hard to discount from being driving variation). You should be able to perform coast down testing. You just need a flat stretch of road, no traffic, and a way to take data. I have gotten quite good results with coast down testing. I can give you a template to work from that translates speed into Cd and Crr. It's just a modified one from instructables, but fits my needs much better.
The Kamm is off the car for now. I still have it, but the Duck brand duct tape started to lose it's adheasive qualities after we had a bunch of days over 105 degrees that summer. I have considered re-building it out of better materials, and making it attach in a nicer way, but I think if I do anything, it would be getting some Nashua brand foil backed duct tape (heavy duty and holds like a mother!), do a bit of cutting to make it fit a bit better, and foil tape it to my car. Maybe paint the foil, maybe get some more of the Duck brand duct tape (I got another brand of white duct tape, and it sucked! Duck brand was quite good in my opinion) and tape over the foil. A caution on the Nashua tape, it holds so well that it can be very difficult to remove, especially if you prepped the surface to any degree...
The windows are made of thin acrylic that I got at Hobby Lobby for around $4 with a 40% off coupon (they have coupons quite regularly). Plexiglass is acrylic, Lexan is Polycarbonate. I have a good amount of Lexan, and have been trying to figure out how to easily make either a more permanent kamm back, or a full out boat tail, but too many other aero projects (and other projects) take priority for the time being. The placement of the windows in the kammback was crucial! I had just enough of the acrylic to make the three small windows you see, so I planned them out well to give maximum visibility around the car. I am glad I took my time and thought it out, since the correct placement meant I could see the road behind me with the horizontal window, and I could see the traffic to the side of me with the side windows.
If you ever get to the point where you are going to build a kamm back, and want some pointers, let me know. I remember enough of how I had done the build that I may be helpful.