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Old 12-14-2013, 10:04 AM   #1 (permalink)
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Open rear KammBack??

I haven't read all the success stories but have noted a lot of concern over rear window visibility -- I am interested in KammBack mods and question whether anyone has road test data with the rear face closed off vs a fully open rear face. I have a thought that a fully open rear face might be just as effective, and possibly even better than a closed off rear face -- anyone have any data??

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Old 12-14-2013, 10:18 AM   #2 (permalink)
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I am unsure how much better a closed off face would be compared to an open faced kamm, but closing it off is better as an open face would allow wind to get under the kamm and cause drag as seen in 2000neon's thread
http://ecomodder.com/forum/showthrea...tml#post326694
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Old 12-14-2013, 01:35 PM   #3 (permalink)
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open/closed

Quote:
Originally Posted by jesdreamer View Post
I haven't read all the success stories but have noted a lot of concern over rear window visibility -- I am interested in KammBack mods and question whether anyone has road test data with the rear face closed off vs a fully open rear face. I have a thought that a fully open rear face might be just as effective, and possibly even better than a closed off rear face -- anyone have any data??
*A few years back,one of our European members reported on a Kamm-back he constructed for his Nissan pickup.He tested with both 'open' and 'closed' and said that there was some mpg penalty with the 'open' back.
*A neighbor ran an open boat-tailed box cavity on his Westfalia Vanagon and got high 20s mpg.He had no intention of enclosing it,so we have no comparative data for that one.
*Wolf Heinrich Hucho claims that,short of a proper,enclosed boat tail,that an open box-cavity is one of the few aft-body mods which actually help mpg.
*At one point GM claimed that rear separated flow,colliding with the vehicle's back provided some forward thrust and they configured the rear of the Corvette to capitalize on this effect.
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If your Kamm-back is properly boat-tailed,you're going to produce decelerating flow,with pressure regain over it's entire length,which will energize the wake region,lowering base pressure,and cutting pressure drag (the entire premise of streamlining).
Even if you lose the minute quantity of thrust,you've pretty much won the game.
*You might consider a full-length horizontal shelf under your backlight,reaching all the way aft as it will help keep the glass from back-soiling during inclement weather.
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Old 12-14-2013, 02:46 PM   #4 (permalink)
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My Firefly's Kammback is open:

http://ecomodder.com/forum/showthrea...sion-3518.html

I never tried enclosing it to see if there was any more benefit.
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Old 12-14-2013, 05:55 PM   #5 (permalink)
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Quote:
Originally Posted by aerohead View Post
keep the glass from back-soiling during inclement weather.
I get this with my open one. It does keep the frost off well though.

My visibility was regained by lowering the front end (only) 2".

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