Air Dam experiments

[Siestarider]

Stock ST air dam on my ride, lip is 3" above pavement. I am still on stock suspension, but on 16" wheels. Pic shows extension grafted on.

I grafted a 2" extension on using 4" vinyl baseboard from Home Depot, secured with screws and wingnuts from behind the OEM air dam. Mod left me 1" clearance to pavement.

Assuming commonly referenced frontal section for ST is 22.9 square feet, this modification added one square foot, for a 4.4% increase in frontal area.

Before mounting the extension I ran 4 data logs, two in each direction on same flat road; then did same after mounting the extension. Nothing else changed, even same tank of gas.

During the acceleration part of the logging, I found little difference between original and extended air dams, average time from 2500 to 6500 rpm full throttle between the two air dam configurations was less than 1% favoring the OEM air dam.

During coast down, conducted by lifting throttle at 6600 rpm and car in neutral, then logging time to coast from 85 mph to 45 mph (Accessport has a vehicle speed log option), the air dam extension provided 5.5% more coast time. I was actually trying to coast down to 30 mph but public roads do present challenges, so 85-45 was best I could gather for all 8 logs.

So, my interpretation is this mod can increase frontal area and increase aerodynamic efficiency at same time. If you drive long distances at highway speeds, it should be reflected in better gas mileage.

If you lower suspension 1", some of this effect should accrue.

If you track and have straights, extending your air dam might provide a little more speed. I think I will leave it on for now and see what next track day (Dec 19) data show.

 

[RAAMaudio]

Great experiment

You might want to video it to see how well it holds position, not tucking back reducing effectiveness.

C5, C6 and likely C7 Vettes have air dams similar to the FiST for good reason, my highly modded C6 even in widebody conversion still got 28MPG when taking it easy on the road.

Reducing the height above the road directs air flow around and over the car decreasing lift and turbulence but at some point it may add drag as down force is increased which is purely speculation at to how much it adds unless published by GM. It would be great if you could gather data on several different heights

Another way to increase down force is to lower the front of the car more than the rear, a slight rake can make a nice improvement and it will lower the air damn in the process.

Looking forward to your results, very much appreciate your doing this

 

[RAAMaudio]

This should be an interesting GRM article I could not open earlier due to slow bandwidth but looks like I can now

Supposed to be by a race car aero expert.

https://grassrootsmotorsports.com/articles/downforce-sorcery/

Update:

I can read the text now it seems, will do so and see if the video will load as well, OK, does not show as a video, I will check again, might be a 2 part or more series.

I found the video(actually a podcast, no video at least on my end) I could not download earlier, have not watched it yet but going to if I can now, full time RVing does have some limitations on data flow......

https://grassrootsmotorsports.com/articles/podcast-episode-27-aero-engineer-steve-stafford/

 

[Siestarider]

Finally found time to read it, great article and thanks for posting. Since my car is a DD, it will never see a diffuser. Or any other mod that makes it look unusual, a big part of our car's fun for me on street is looking innocent. But diffusers look so cool. Bet if you put one on, functional or not, every hotrod that comes by will want a try at you.

Makes me think about our hatch "wing" and how much aero effect it actually has. Have to put the manometer to use, maybe get a little insight on that question.

I just found a way to mount my cheapie Gopro to car exterior, was going to use it to record yarn aero, but you are right, my vinyl air dam extension probably bends back at speed. May as well try to get some video of it when I try the yarn pics.

But first, I am going to finish my battery and WW fluid relocation to rear tire well. Or maybe play more with exhaust, its still too loud for me. Or do some more manometer testing. Oh, and Santa is bringing me a Cyborg. I love this car.

 

[RAAMaudio]

I fully understand, I like my cars as low key as possible and right now I love my exhaust but a bit to loud to be as stealthy as I prefer.

I was going to build a real diffuser, notch the trunk floor, etc...but follow the stock contour of the rear trim and not stick out to far or to low, paint it satin black, hopefully not show to much. Then build a more radical one with qtr turn fasteners so I could swap them out easily for the track.

Rear spoiler does not do much and adding a Guerney flap only creates more issues as the holes with lips in it will create swirls, according to a real race shop manager that looked over my car and we talked about all this. I want to use a real wing by fortifying the stock or none ST spoiler with mounts on top to not to obvious so I can take it on and off for the track.

My splitter/full length undertray is fairly effective but I was going to make an aluminum section with quick release mounts I could install for the track and make it much more effective.

Looking forward to the pics of the results of the extension for sure

I really need to install a rear washer resv and pump, I had the stock unit out most of the time I have had the car, it is back in for now but just put a little fluid in it at a time. I was going to use the line that feeds the rear washer from the front of the car to take care of the front and delete the rear wiper and washer, the rear wiper does not weigh all that much but everything adds up.

Having had the first Cyborg and at times wishing I had kept it as things developed making it better and better but now $$$$$ into the first DHM EFR and now changing to a GTX or with the recent great results GT2560 or 54.....I might go that route as only need so much HP to get the job done and a wider power band is more power more of the time often resulting in a faster car in real world and road race track use.

If I am being repetitive I have a reason, I am a bit brain dead, put in a ton of work getting out of the snow and into CA on a migration to AZ for the winter in our RV and with a major knee issue where I can barely walk....for now, I will get over it!

Have a wonderful weekend, I know I will

 

[the duke]

in.