Quote:
Originally Posted by Cd
Ill let the experts take the floor on the question about the vacuum pressure being good or bad.
I was guessing based on a comment from an aero engineer that worked on the UCLA Future Car over a decade ago. The link is dead now, but there was a PDF write up about a partial boat-tail that was created for the car. At the tail end a section was hollowed out - the reason being that it created a bit of vacuum pressure at the tail end and pulled the wake in farther.
As far as having a downward slope to the extention, it might not do a thing, but i can't help but think of the back end of the dodge ESX-3 ( which had a fantastic Cd in the twenties. ( Note the trunk section )
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Odd looking car, eh? Wonder how well it works. Of course, my car looks bizarre these days. Here is a rough diagram of the build, which is better but not great. It is still three inches above the stock lid, but is tapered better for the tumblehome and at the trailing edge. The bottom row of my widow tufts is under it. Attached with magnets under the lid, its gaps still need to be sealed with ugly tape! My fabrication skills are just not yet up to this challenge. It seems like it might be making an improvement, but if it is, the difference is marginal and hard to measure, maybe 2%. I would post a photo but I took it off to use the trunk for lumber. With my seats and moldings out of the back. Ten foot boards slide in easily. Yay! Car didn't feel very heavy either, since I was only replacing the deleted stock weight. Yay.