Massive air dam on '98 Geo Metro (Firefly), A-B-A coastdown test; Update: version 2

[MetroMPG]

Yeah, wood's not the ideal material to be doing car mods. But I didn't have any brackets on hand or metal to make some.

It took about 2 hours, altogether.

[Daox]

I really like that yours extends down farther than mine. I still have 6 inches of clearance! 4 would be fine with me.

[MetroMPG]

So, after a week of having the new air dam on the car and several drives under my belt, some observations:

• I've scraped it on bumps & driveways maybe 3 or 4 times. That's much less than the one I had on the Civic (3.5 inches clearance vs. 5). Have you seen the OEM air dam height on the Chevy Volt? They must scrape a lot.
• My Extremely Scientific and Accurate Butt-o-Meter says the car coasts further and my Non-Confirmation Bias Seeking Eye says the ScanGauge seems to be reporting better MPG at steady speed.

I was able to make a MPG comparison of a pre-air dam vs. post-air dam round trip...

• 76.8 mpg US (no air dam) round trip (87 km / 54 miles)
• 82.5 mpg US (air dam) same round trip

And that was with a 3.2 km/h (2 mph) higher average speed with the air dam on (low 30's avg mph; max of low 50's; cruising between 45-50). Similar weather & traffic conditions (mostly deserted country roads with more than a few stops & turns).

Big disclaimer: unfortunately I changed another major variable to confound these results because I also put RE92 low rolling resistance tires on the car in between the two trips.

I think I may do an A-B-A of this air dam though. It seems like it may show up above the normal noise of testing variability.

[Xist]

How does one calibrate one's butt?

[MetroMPG]

Originally Posted by Xist

How does one calibrate one's butt?

Why, against a known good butt, of course!

Version 3 of the air dam, as applied to my winter beater 2000 Metro...



Strips of Coroplast are also screwed underneath the main "bumper" portion of the bumper to take the upper screws through the air dam. No unsightly holes, should I ever want to reverse the mod.





This one is closest to the one tested, with the exception that I haven't made any grille openings in it yet. Since it's now winter conditions, I'm going to leave just half of the upper bumper-hood gap open instead.

From thread: http://ecomodder.com/forum/showthrea...orn-34102.html

[gone-ot]

And...the "Science Project" continues ! ! !

In my best Celine Dion voice: "The Science Will Go On ! ! !"

[Xist]

Originally Posted by MetroMPG

Why, against a known good butt, of course!

Somehow, my criteria for a good butt have little to do with measuring gravitational forces.

Originally Posted by MetroMPG

Strips of Coroplast are also screwed underneath the main "bumper" portion of the bumper to take the upper screws through the air dam. No unsightly holes, should I ever want to reverse the mod.

Please clarify. You may choose to use hand puppets or hideous Paint sketches.

You have layers of coroplast attached to your bumper? How are those attached? Is that ABS?

[MetroMPG]

Clarified! Hideous paint sketch! Maybe?




So the screw holes into the bumper are all on underneath surfaces.

The screws through the vertical face of the air dam itself go into the corrugation of the horizontal supporting coroplast that's attached to the bumper.

[Xist]

Is that ABS?

[Handsome Jack]

sweet!!! this is the kind of post I needed for encouragement!