Matrix mini undertray
 

My parents have a 2003 Matrix. They average about 30 mpg with it doing mostly highway driving. There's one little detail about it that's been driving me nuts. The front bumper.

http://i606.photobucket.com/albums/t...ix/matrix1.jpg

There's a huge gap!

http://i606.photobucket.com/albums/t...ix/matrix2.jpg

It's so big, I could stand in it if I wanted to.

http://i606.photobucket.com/albums/t...ix/matrix4.jpg

That's got to make all sorts of stupid votexes and lets air that goes in the lower grill dodge the radiator. So, this past weekend, I made filled the gap. Bolting a plate to the lower edge of the bumper was an easy decision. The rear mounting point required at least five minutes of thought.

The factory under trays start at the bottom of the radiator and go down a bit and back a bit. They are mounted very securely. You can see them here infront of the oil pan and transmission pan.

http://i606.photobucket.com/albums/t...ix/matrix5.jpg

I bolted the back edge of my new panel to the factory trays. The panel is made of an aluminum realistate sign I got for free from a scrap yard, and some left over chunks of street sign from my previous project, also obtained from a scrap yard.

http://i606.photobucket.com/albums/t...x/matrix10.jpg

The panel ends about an inch further back than the original tray, but still give enough room to get at the oil filter. That means I wont have to remove it for oil changes.

http://i606.photobucket.com/albums/t...ix/matrix9.jpg

The whole thing was painted black before final mounting. I don't know if the fuel milage was improved at all, but at least the ground can't be seen through the front grill anymore.

Good show. Would be even mo better ifn those gaps at the sides of the realtor signs were filled in, preferably with fairings for the front wheels. For such installation, keep in mind the slipstream from the bow wave flows outboard by ~60 degrees (see Hucho pp. 142 & 183.), meaning the airflow hitting the front wheels impinges at a steep angle, meaning the wheel fairings need to be canted in accordingly, i.e., pigeon-toed.

While you're at it, may as well fill in those useless cosmetic slots at the outer curves of the bumper cover. (Those just add drag, since the air flowing around those curves is probably the fastest air the car feels. Drag increases exponentially with speed, so that is a particularly bad place to put lumps & bumps in the breeze.)

Might could make dimples in Coroplast by laying out on flat concrete floor, then heating a bunch of billiard balls in the oven, and placing them on the Coroplast where you want dimples. Heated balls would spot-melt Coroplast to make dimples. Or, just use styrofoam for the panel, and scoop out dimples with hotwire.

FWIW, Porsche had dimpled forward undertray surface on one of its 911 models a few years back. May have been cosmetic though.

Mythbusters dimpled a whole car body, seemed to be pretty significant improvement.

Nice job, Why not just do a partial belly pan, say just past the front axle? that is what I did to my Matrix and it has the same effect, just over the whole engine. it also keeps the snow out when going over/ through drifts :)

Laziness. That was the last of my signs, and I really don't want to have to remove anything to change the oil. I'll probably make it wider as suggested when I get some more metal.