These modifications result in an improvement of Cd from 0.37 (estimated based on similar car shape) to 0.245 (measured via coast down tests) .
Note rear end of boattail is near horizontal, and beginning of boattail has same slope as rear at junction. Note also how about half of the rear ends as a 180 degree ledge. I believe this helps, but have not tested. Note also how minimally drag in a crosswind should be affected. You should be able to see the rear wheel skirt is a mini-teardrop shape. Wheel covers have clear pvc screwed on and heatshrunk a little, cheaper than racing rims (ship quicker too).
Note smooth contour of grille blocking:
Front deflector is as low as possible to the ground without bumping anywhere on my commute. Yes, I'd probably do a nice compound curve if I knew how to do so ala Burt Rutan, but I only know how to work aluminium at present.
Undertray consists of two 0.6mm aluminium sheets (same as all other shiny bits) screwed into the chassis, the panels under the door, each other, and the two bumpers. Joined by duct tape. Segments are cut out for suspension bits, tow ring, sump plug. (Not sure what to do about oil draining, maybe remove some of the duct tape join for draining. Should really have some heat proof insulation between panels and exhaust to stop rattling at idle. Note rear deflectors.
Note extension beyond for purpose of ease of flow separation. Should cut the bolts to a less ugly size, oh well.
LHS mirror replacement bits. A bit of rubber from Clark Rubber, and some aluminium. Yes, I know it should smoothly contour back, might fix it someday. Should be a good improvement anyhow.
Only planned mods to go are front wheel skirts and some gap sealing. Maybe bigger tires in lieu of a taller fifth gear. Maybe clear mini-boattails for the side indicators.