Quote:
Originally Posted by superchow
We currently get about 37-38mpg on the freeway. 40 mpg would justify the undertaking, 45mpg at high freeway speeds would earn me a back massage from wifey. 
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Funny
When you consider that my "partial boat tail" - the
permanent Kammback I'm constructing - was worth a 2.3% mpg increase at 55 mph in cruder prototype form, I think a larger, more complete boat tail could double that at least. So, I don't think +2 mpg is a stretch. Not quite back massage territory though.
The challenge for you is that your car is a notchback. You've got flow separation happening part way down your rear window. Ideally you want a boat tail to be a surface that shepherds
already attached flow down toward a point. This will be much harder to do on your car than on, say, a hatchback.
You could just accept that there will be an entrained vortex at the base of the rear glass and hope for reattachment on the extended decklid/boat tail, but it's not
as good as the full meal deal.