are boat tails for hatchbacks & sedans?
 

I have a 2002 2 door echo sedan, i have done a partial grill block and am going to do rear wheel skirts and belly pan, i saw wind tunnel pictures for a hatch and a sedan , the sedan had less than half the turbulance/drag at the rear of the car, how much benifit is in aero modding my echo rear, and what shape ,,,like the aero civic? the ford fusion hydrogen 999 speed record car has a funny car style rearwing on it. does that work cause it looks alot better than a boat tail.

That Ford: 2007 Ford Fusion Hydrogen 999 Land Speed Record - Ford Fusion Hydrogen 999 Marks Milestone 6 - 1280x960 - Wallpaper

Aero is too tricky for definitive answers to your question, but you can get a better sense of the possibilities by reading this site.

moonmonkey -

Here's a little text from the same site to go with Bob's URL (but no aero stuff mentioned) :

2008 Ford Fusion Hydrogen 999 Land Speed Record

CarloSW2

Moonmonkey - Boattails have been added to sedans, for example wagonman76's 4-door Celebrity iirc.
But before you go there try a few other mods, like rear wheel skirts and a full bellypan, both of which improve the airflow on the 'tail if and when you decide to add it.
You may also try a partial roof extension without sacrificing functionality, as in Groar's Uglyback.

...someone needs to "point" him to that aero article where the typically aero "drag" losses were summarized. That should give him some idea as to how much "gain" is possible with various modifications.

...anybody recall that article?

funny car
 

I have VHS video of a car with the funny car style extension running flat out at El Mirage Dry Lake,California during a pre-Speed Week warm up with SCTA.
Anyway,El Mirage is reaaaaaaaaaaaaaaal dirty,and you can see the entire wake exposed by the dust.
The area above the spoiler is completely clear,indicating attached flow( if not over a locked-vortex ) and complete "dirt" below and behind indicating that the wake is isolated to the area below and aft of the panel.
Short of a tail,this would definitely be one way to go.
You might shoot for a 15-degree angle from rear edge of spoiler up to top of roof over the backlight and trunk.
When GM set the land speed record with EV-1 their boat tail tailcone created a 15-degree angle,so it appears to be a good compromise angle.
One caveat,would be to "soften" the rear edge with rubber so as not lacerate some un-suspecting mindless automaton,wandering aimlessly by muttering incantations.
Cogito,ergo imodifi!

See Attched Image: Appears that the Fusion is about a 12 degree angle when looked at from this perspective. Aerohead, is this the correct way to use a deck lid spoiler to achieve this locked-vortex you are talking about?