Air Dam and Front Undertray

[Bill in Houston]

Thanks, Brelandt!

[Bill in Houston]

Well, after a month of air dam and front undertray use, it seems that it has not improved my highway mileage. It may have actually lowered it. It definitely does keep the front end more stable at speed. So maybe it is actually causing some downforce, which I would gladly trade for higher mileage.

So here's my question. If I use a manometer and find out that the air pressure above the undertray is higher than the air pressure below, is there something that I can do that would allow me to trade downforce for lower Cd? Like maybe lowering the back edge of the undertray?

I will probably try it no matter what, but just wondered if anyone thought I had a chance of being successful. ;-)

Update:
In mid June I did lower the trailing edge of the undertray a little closer to the ground. It seems to make less downforce now. I assume that this improves my Cd.

Thanks for the input!

[atomicradish]

It looks great especially considering your frugality.

Fortunately for me, I have no need for an airdam. My car is already quite low to the ground.

[Bill in Houston]

For the sake of completeness, this is a link to the coast down testing that I eventually did. Show something like 10% improvement in Cd.

http://www.gassavers.org/showthread.php?t=4419

[fabrio]

i looked your job Bill: very good!

[Bill in Houston]

Thanks!

[fabrio]

you have made a job much cleaning up (professional), and the result of your test is indicative about quality of modification.
I have written a simple excels for to calculate the acceleration or drag: it is necessary to read the GPS NMEA after a procedure equals to Coast-down Test, but at the moment, it is not capable of CD result, but to calculate only complessive resistance (drag+rolling resistence)

[Bill in Houston]

Do a few runs coasting from 65 mph to 60 mph.
Do a few runs coasting from 15 to 10 mph.
Dump the data to Excel. For the high speed runs and the low speed runs, plot speed vs time and draw the best-fit line. From that best fit, figure out what to put into the calculator at http://web.archive.org/web/200408030...DownCalcs.html
That calculator will calculate your Crr and CdA separately.

[fabrio]

yes, the algorithm is simple.
it must calculate the negative acceleration in high speed (that it allows to obtain the sum of all the resistances), after, it must calculate the negative acceleration in slow speed (that it allows to obtain only the rolling resistance)

for last, it is necessary to embezzle the CRR at the total resistance, the result value, it is the aerodynamic drag!

in my excels file, this I have not still implemented it, only, because, I have not still had way to make a test with the car

[johnf36]

I am new here but thought I would help with a source for VG's if you have not found them yet.
http://www.vortekz.com
and here is a picture of the car, I am getting started on side skirts when I found the site.