To all the aero geniuses/creative inventors....

[Raccoonjoe]

OK...time to revive this thread.

After a Friday evening fueled mainly by Cap't 'n' Cokes, Julie is now proudly sporting a Coroplast belly pan. It goes from the air dam, angled down to the front axle, terminating just barely behind the axle
*working on pics, will post in garage soon*

Here's my problem. We went up to the lake this weekend, roughly 150 miles round trip....95% highway. It was a little faster than I usually drive on the way up (roughly 70), about normal speed on the way back (55). However, I did a rough calculation of my MPG, and came up with 18.5. Why would this be down from my normal 19.5-20.5??

Ideas would be great....I'm going to leave it in place for this week, and run some normal miles commuting. We'll see if it makes a difference there.

*edit* Forgot to mention something else. I noticed that engine bay temps seem to have risen a great deal, while coolant temps seem to have dropped. Anyone else noticed anything similar??

[Bill in Houston]

Speed kills (MPG)

My front undertray, in its initial configuration, created pretty noticeable downforce, and didn't help mileage a lot, or may have actually decreased highway mpg. I lowered the rear edge of it and now it makes less downforce and my mileage seems to have improved.

It will be good to see your photos.

[Raccoonjoe]

OK, photos are in the garage now. Basically, you get to see a before shot, then 2 afters.....also one looking in from the drivers front wheel-well.

I wouldn't think I'm getting downforce...actually expecting some lift out of the undertray. The front of the tray is about 8" from the ground, while the back is roughly 6" (maybe a little higher on the right side....)

[Bill in Houston]

Ya, it looks like it would make a little lift. I'm gonna blame your mileage drop on the speed, and see how the next tank goes. Hmm...

[sonyhome]

If you make a curve that goes towards the ground it makes lift?
Doesn't it increase the distance the air travels to the back of the car, making the wind faster and therefore would create down force (aka lift that goes towards the ground)?

Aerodynamic 101

[brucepick]

Is the leading edge of coroplast snug against the existing material so it doesn't catch air?

And consider extending existing air dam closer to the ground. If belly sheet slopes down towards the rear then you're better off adding a piece to the air dam to make it reach closer to ground, and having a belly pan that's more level. Because the air dam extension will push air off to the sides away from the car. Down-sloping belly sheet grabs that air and attempts to compress it which causes lift and turbulence.

Just my two cents worth.