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Old 12-28-2012, 03:45 AM   #1 (permalink)
Master EcoModder
christofoo's Avatar
Join Date: Mar 2012
Location: Salt Lake City
Posts: 292

00C - '00 Toyota Corolla
90 day: 43.54 mpg (US)
Thanks: 147
Thanked 190 Times in 73 Posts
Project: ECOfamily Civic and its Aero Hitch Box / Boat Tail

In order to make the Civic a more perfect family car, it needs better aerodynamics, additional cargo space, (and an improvement of ICE efficiency by some method: P&G/EOC for now, maybe a taller transmission on the horizon). An Aero Hitch Box and other mods will improve aerodynamics and increase cargo space.

Aero Hitch Box status :
  • Aero Hitch Box on the road! (5/15/2013)
  • Gap filler added to close sides and bottom to the car after coast-down showed a benefit. (6/28/2013)
  • Full boat tail (added Kammback and gap-filler window). (11/10/2013)
  • Added rear-wheel skirts. (2/8/14)
  • Kammback was damaged and Kamm-to-AHB-gap-filler-window was destroyed in a side-wind. Lesson: need downward force and maybe leading edge fish-scale for side-wind resistance. (4/20/14)
  • IMPORTANT: Magnets for Kammback attachment are a big no-no, according to the state of Utah. My Kammback has been shelved for now (6/2014)
  • The AHB lid flipped up due to operator error and did a lot of damage to the metalwork. Repaired (12/2014).

My best guess for Cd is around 0.30, but the error margin on my estimate is very wide.

Crr probably around 0.12 at 45-50 PSI. (Stupid Les Schwab. I really should have upgraded.) I also have some winter tires on here, generally Nov through Apr.

Lower-hanging mod to-do list:
  1. Low rolling resistance all-season tires.
  2. Remake driver-side rear-wheel skirt (it adds cross section area).
  3. Replace missing wheel blanks (winter mode).
  4. Adjustable grille block, cooling ducting
  5. Air dam (probably in the articulating style of cfg83)
  6. Side skirts and rear-wheel tails
  7. Windshield wiper cowl
  8. I keep trying to think of something I can do to correct the a-pillars. They strike me as quite bad. Acrylic half-cylinder additions? Or maybe just vertical acrylic fins? If I get around to it I'll mock it up and tuft test it.
  9. Maybe boat-tailing both side-mirrors, or else upgrading all the way to cameras (but I'd need to get an exception).

Tail-end to-do list:
  1. Additional engineering / repair to prevent future side-wind problems with the Kamm-back.
  2. Paint the whole AHB to stop the corrosion.
  3. Expecting to need a rear-quarter belly pan.

Original post:
This thread will probably mostly be about my forthcoming hitch-mounted cargo box boat-tail. Okay, not exactly the first time we've seen the general idea, but maybe the first project thread applicable to a sedan. Also I'll have some brief descriptions of other mods on our 97 family-of-four Civic, and of course results.

Getting right down to it; my plan for the Aero Hitch Box (avoiding the 'copyrighted' name ):

Green - the part I'm fabricating. (Black is the hitch receiver on the car.) I'm thinking strip reinforced aluminum sheet, rivet construction. However, that method hasn't got the wife test green light yet. I could probably get it done just as fast in plywood, plus foam/bondo, and it would be more likely to pass the wife test that way, but I expect that would be heavier and less durable.

I've sized the space from the bumper to the front of the box to give enough clearance for the trunk to open, plus a half-inch for good measure.

I'm probably going to want to put a caster on the main steel post that it will be on to minimize damage in the event of a departure angle violation, but I probably need to experiment in my driveway.

Now, I see some aerodynamic gaps here to fill. The only question is how far do I need to go to get good results? I expect this to require some testing to be sure about it.
Possible Gap Fill Remedies:
Opaque Half-Kammback (orange) with clear plastic side fillers (blue):

Full-Kammback with hinged window (or louvers):

All the remedies attach to the car, so you can imagine with the aero box off the car roughly fits a Prius profile with a full Kammback.

Any thoughts so far?

Hoping to get this done before spring, but you never know with me.


Random background notes, if you want them:
  • Hypermiling by itself has phenomenal ROI, but I find it relatively incompatible with long-haul family travel.
  • A high goal that I have on my mind is MPG retrofit of numerous existing vehicles; I always have an eye out for mass production and market compatibility, although I kind of doubt that I'm the right guy to pull the trigger on this type of fabrication, even if I had the right project for it.
  • I just got my long-haul family MPG up from about 36 to 42. The primary factor was P&G, which I had never done on a long-haul in this car before. That's 42 MPG at 70+ MPH in <35F with minimal aero mods. Not bad, eh? The other project I've got kicking around in my mind, which is more closely matched to my skill set for production purposes, is a P&G cruise control. I'm still in an info gathering stage though.


I will be editing this post for current status and index.

Last edited by christofoo; 12-26-2014 at 10:46 PM..
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