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Brucey, I measured the top angle of your boattail and it looks like more than 15 degrees. If the airflow doesn't detach at the hatch/boattail transition line, then you'll probably see attached flow down the back, but that doesn't have to mean that everything is OK. From what I've read, the optimal angle is 10-12 deg. As it gets steeper the airflow stays attached but lift increases, until about 26-28 deg. when it detaches. In this case, detached may be better for fe than generating lift. Would it be possible to tilt the boattail upwards slightly?
This of course is a worst-case, I'm with the rest that you dip in mpg's is probably weather/fuel/random.
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e·co·mod·ding: the art of turning vehicles into what they should be
What matters is where you're going, not how fast.
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[Old] Piwoslaw's Peugeot 307sw modding thread
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