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Brucepick,
I think the idea is creating a flow of air over the vehicle that closely matches what might be accomplished with a Kamm back. The extended trunk simulates the 15 or 10 degree angles people seek with Kamm backs. That's if I understood correctly.
I attempted an A/B/A test tonight of a design like the pics of my car I posted a few posts back on this thread. The difference was in elevating the surface with one inch blocks of foam. My test was cut short by traffic and cooling weather as the sun set. I got a pair of "A" runs (with mod attached) and a pair of "B" runs (without mod). The average of the "A" runs was 46.88 mpg and of the "B" runs 46.85. It is possible that I overstated one "B" run by 3 mpg through transposing a 6 as a 9. If that is true then the "B" run was 46.10. A difference of 0.88 mpg is not all that much. My speed was fairly low (52mph). I also have attempted several coast-down tests from 45mph, and these too have been equivocal, with a possible but uncertain ever-so-slight advantage to the spoiler. I think the speeds are not high enough for either test. I also think the flat spoiler might be too short. It extends about 9" off the tail for the trunk. I'm thinking I need a longer route, and 60mph to see this for sure, and I might attempt that this weekend. Tips?
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See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.
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