cargo van additions

[bikenfool]

how do you make this styrofoam fastback tapers?

[Hersbird]

I figured a 3"x18"x18" block of foam shaved into a wedge and covered in epoxy like a surfboard and glued on the roof behind the vent. One block would make 2 wedges. The epoxy is a little pricey, I might try protecting the foam and then using fiberglass resin instead. The front of the vent needs a 1/4 round cylinder shape as well. Go from a 1.2 CD for the square block of a vent down to a .15 CD airfoil shape.