Accord aero mods, 4.25% increase, more to come
 

Starting point: 2005 Honda Accord EX sedan 2.4L 4-cylinder 5-speed automatic.

Mods tested:
- full upper grill block
- partial lower grill block
- panel closing the gap between the intake and bottom of radiator housing
- airdam (extending as low as lowest point on vehicle)
- partial undertray (20 inches / 50cm back from nose, doesn't quite reach wheels)
- mirrors folded back

Untested mods:
- rear wheel skirts
- smooth wheel covers
- larger OD tires
- sealed gaps around headlights/front panels (silicone) and hood (foam insulation strips)
- deleted mirrors

Total intake area of 54 square inches / 350 square centimeters, but I hadn't sealed the edges of the blocks yet.

Pic as tested:
http://i78.photobucket.com/albums/j1...psa9613308.jpg

A-B-A-B tested at 55mph / 88km/h, sunny and dry, temp 51F to 57F (~10-14C) during testing, winds somewhat gusty, sustained from 0 to 6 mph (10km/h). Test section 1.6 miles/2.5km long, straight, somewhat level. Longer and more level would have been better but there are limited nearby options living in the mountains of rural western Montana.
It's a 15 mile drive for me to get to the test site, and on top of that I did a couple warm-up runs while picking out turn-around points before gathering data, so the car should have been as warmed up as it could get.
I finally have cruise control! Set once at 55mph and left for the duration of the testing, engine never turned off.
24 passes, with half heading east and half heading west. 4 passes stock, 8 passes mods, 8 passes stock, 4 passes mods. Was only overtaken twice, and since it was once with mods and once stock, and I was going so much slower than the passers, and the numbers didn't stand out as odd, I left them in.

Results: 43.2, 45.2, 43.4, 45.2 mpg, for a 4.27% increase. Coolant temp rose less than 1F average, 2F at most (may change in summer).

Given the peculiar driving profiles while testing (measuring only a single, not quite level stretch of highway over and over) I'm not sure that this is an indicator of overall fuel economy, but with A-B-A-B testing, 24 passes, and pretty consistent figures, I'm confident the improvement figure is valid.

Original data for any interested: https://docs.google.com/spreadsheets...it?usp=sharing

Pic of Accord as currently modded:
http://i78.photobucket.com/albums/j1...ps2adzuews.jpg

Stock picture, for reference:
http://i78.photobucket.com/albums/j1...ps23bb9c13.jpg

Please let me know if the above pictures don't load; photobucket has been iffy on direct-linking images, it seems.

Some pics of fabrication and detail shots of the structure can be seen in this album (linking the album to not clutter the post with images). Honda Photos by IstasPuma | Photobucket

Construction material details: Total added mass from the mods is less than 8 pounds / 4kg.
Materials used are:
- galvanized sheet steel (do not remember the gauge, but it was sold as roof flashing)
- slotted hex washer head sheet metal screws, size 8x3/4 (take a 1/4" socket, or flat-head screwdriver)
- 3/16" outer diameter pop rivets (for permanent connections, such as the front undertray to the airdam, and the supporting bar for the undertray)
- 1/4"x3/4" flat aluminum bar (for supporting the upper edge of the upper grill block, as well as lower edge of future rear wheel skirts)
- aluminum L-bar (I forget the dimensions, but for supporting sheet metal across the width of a car I'd recommend the height be at least 3/4")
- >=1" outer diameter foam pipe insulation (for rounding transition from airdam to undertray without complex metalworking)
- Gorilla glue (for attaching pipe insulation)
- 3/16"x3/4" tight-fit open cell foam tape (for sealing the edges of the grill blocks)
- regular hubcaps plus 17" aluminum pizza pans

Planned mods:
- full undertray

Possible mods:
- warm-air intake (possibly adjustable)
- wheel spats/boattails
- air deflector for wipers
- maaaaaaaaybe kammback

The pictures loaded fine for me, the air dam and grill block look awesome!

Thank you very much!

Have you thought about smooth wheel covers yet? You might get another few percent more mpg's.

They are something I definitely will do; the only thing is, I don't think the alloy wheels can take hubcaps. I'd like to get a set of steel wheels, but that would be money. I'd like to make the alloy rims smooth, but that would involve things I'm not entirely comfortable with, like epoxying plastic panels into the openings, or drilling holes into the tops of the lugs and epoxying nuts into them as attachment points. If you have an easier (and reversible, and pothole/sun/wind proof) solution, please let me know. :)

MikeyJD: Ahh, zip ties. I want to avoid them as I worry about them weakening due to age, flexing, and exposure to the sun, and worry about wobble if the cover starts out, or shifts, off-balance.

On second thought, maybe I will give it a shot. Coroplast can't do too much damage if it flies off at highway speed, right? Right?

FREAKING AWESOME!!!!!! You transformed the looks of the car completely!!!

I use zip ties in place of the fender clips to hold the various panels and front bumper of my insight. No problems with them breaking, stretching, etc.

Body panels and front bumper are not subjected to 800+ rpm and are (somewhat) insulated from the shock of road bumps by the suspension, but I will take this as encouragement too. And thank you very much! :)