Pumba

On Monday, October 1st, I drove my 2002 C5 Z6 from my home in southeast Michigan to Mooresville, North Carolina. That was so I could be at the Aerodyn A2 Wind Tunnel on Tuesday, the 2nd.
I arrived at the A2 tunnel at 9:00 a.m. and was greeted by Geoff Eaker. Jeff is the Operations Manager of the A2 tunnel.

I have tried to upload a picture of Geoff and my Z6 in the tunnel, but the "improvements" made to this website don't allow that.

After we had my car properly situated in the tunnel we proceeded with nine different runs during the next two hours.

Again, the website's changes don't allow me to show you the results for the nine runs we made that morning. It seems, that the powers-to-be have made this website useless for the posting of detailed how-to articles with pictures.

jumpmanmb87

So the car was in a wind tunnel for? What did you improve? anything on the car for better aero on track time I'm guessing?

gimp

Are you having trouble with uploading images, or do they not allow linking images/articles?

Pumba

I have posted several detailed How-To articles with pictures on the previous version of the website, which to me was a much better version. On this version, which seems to have been designed for people who want to read and post using the 4 inch screen on their phones, I cannot download and display any pictures which are necessary for a good How-To article.

Pumba

I took my Z6 down to the A2 wind tunnel so I could see what sort of lift or down force I have on it with my front splitter, my vented hood, my side skirts, and my rear spoiler. I use the car for open road races in the 120 mph class, 1/2 mile and 1 mile acceleration runs, and to a lesser extent HPDE track days.

I ended up with one minor change to the rear spoiler, which added down force to the rear, so that now both the front and rear of the car have downforce, and a Cd of .389.

But the details of the nine wind tunnel runs were what was a learning experience. Plus I have a 3.2 GB video which shows the use of a smoke wand, and where the air goes around and through the car while it was in the tunnel.

gimp

Try it on desktop and try hitting the "go advanced" button below the quick reply.

Bossdog

Could you post the video on youtube and post the link here? I think it would be fascinating!
I've been debating putting a vent on my hood for Track days/HPDE's

GCG

Plus 1 here

YYZ06

I agree.

sperkins

In for results. I was talking to someone at the track this weekend about using that company since it's not too far from me.
Overall, do you think it was a worthwhile experience?
Do you feel they used your time effectively?

grantv

Surprised someone hasn't said that the Z is less aerodynamic...

Pumba

Here is the YouTube Video -

Pumba

Yes, I think it was very worthwhile to go to the A2 tunnel. Geoff Eaker was very helpful. He constructed the 1" rear spoiler and the two 9" rear spoilers out of his own material.

Pumba

I am still not pleased with the new format for posting pictures. But here goes:

Run 1) The first thing we tested during our nine runs was my Z as it arrived at the A2 tunnel - Result, Cd of .389, with 223 lbs. of down force on the front and 102 lbs. of lift on the rear. Project top speed - 217 mph.
Run 2) The second run we taped a 5-inch high rear spoiler on top of my Cafaro rear spoiler - Result, Cd of .535, with 187 lbs. of down force on the front and 764 lbs. of down force on the rear. Project top speed - 199 mph.
Run 3) The third run we removed the 5-inch rear spoiler and taped a 1-inch square edged rear spoiler to the top rear edge of the Cafaro spoiler. Result, Cd of .409, with 211 lbs. of down force on the front and 103 lbs. of down force on the rear. Projected top speed of 210 mph.
Run 4) The fourth run we removed the 1-inch taped on rear spoiler and taped two 1/2 inch square edged rear spoilers on the left and right edge of the Cafaro rear spoiler. Result, Cd of .395, with 225 lbs. of down force on the front and 55 lbs. of lift on the rear.
Run 5) The fifth run we removed the two 9" rear spoiler pieces. Next, I removed the 1/2" of washers at the center post of my front splitter, making its front edge parallel to the ground instead of being tipped down. Result, Cd of .394, with 250 lbs. of down force on the front and 127 lbs. of lift on the rear.
Run 6) During the process of removing the washers from the center post of the front splitter we moved the car on the test bed. We repositioned the car to its original location.
Run 7) The seventh run we folded the side-view mirrors in to the side of the car. Result, Cd of .390, with 270 lbs. of down force on the front and 152 lbs. of lift on the rear.
Run 8) The eighth run we taped over the upper portion of the grille. Result, Cd of .375, with 395 lbs. of down force on the front and 201 lbs. of lift on the rear.
Run 9) The ninth run we put the mirrors back to their OEM position, removed the tape across the grille, and lowered the side windows. Result, Cd of .423, with 275 lbs. of down force on the front end and 132 lbs. of lift on the rear.

After the runs were completed, we did 18 minutes of smoke wand testing to verify several flow items. At that point, Geoff and I talked and he suggested that I return the Z to the configuration before Run 1, and that I should add a 1/2-inch square edged rear spoiler addition on the top of the Cafaro rear spoiler. My last picture shows that addition to my car.

TrackAire

Pumba,
Thank you very much for doing this.....your video is by far the most informative regarding the smoke wand test that I have seen. If you're ever in NorCal, let me know as steak dinner is on me!!

I have a couple of comments & questions to ask you.
1. What was the wind speed during the smoke wand test?
2. It appears that the front fender vent openings are not venting outward at all and it looks as if they are actually pulling air into them causing stagnant air flow. Is that correct? Any thoughts?
3. The rear brake duct openings may be contributing to rear lift due to the air actually venting out the gas cap cover and body seams. I saw very minimal smoke come out the rear of the wheel well, on the ground or out the spokes of the wheel. Not what I expected.
4. The high pressure at the base of he windshield is huge.....actually pushing air forward towards the center of the hood. Anybody lifting the rear of the hood for adding cooling at high speeds is going to be disappointed.
5. Your bug eye headlights do not appear to be hurting air flow over the fender in the least.....is that what you've concluded?
6. It looks as if your vented hood is doing it's job getting some under hood air and pressure out, hard to say if it is hurting the Cd or effecting the downforce one way or another. Any thoughts?
7. The air turbulence behind the rear bumper is an issue, lots of lift and drag there.....During the summer if we have these little gnats that will actually get splattered on the back of my rear bumper when driving at spirited speeds. Very noticeable on a yellow car if you look closely.

Please post any other videos, pics of data of the test. Thanks again!!

Pumba

Question 1) The wind speed in the tunnel during the smoke wand exercise was 30 mph.

Question 2) Correct. The front fender vents are not contributing any positive air flow. Removing the closeout panels that GM installed in those was one of the first things I did to my Z. Geoff and I talked about that and we concluded that with my vented hood, I could close them off completely and not hurt the aero or cooling of the car at all.

Question 3) I have removed the rear brake cooling ducts. Instead, behind the screen on each side I have installed two small coolers that came with the L.G. Motorsports pinion driven trans and diff coolers. I need to build a closeout panel from the back of each screen to the front edge of each of the coolers so I force the air into the coolers.

Question 4) I agree. The Black Dog Speed Shop hood I purchased has greatly improved my cooling. My Z is used as a street car 95% of the time. My coolant temperature cruising at 77 mph with a 90 degree F ambient use to be 197 degrees F. With the addition of the hood's vents, I now have coolant temps of 174 to 178 degrees F.

Question 5) Exactly, those headlights are from Radio Flyer Innovations. George Argel, Radio Flyer's guru, and I installed them in the spring of 2017. They feature both low beam and high beam 5K HID bulbs. Compared to the standard C5 lights these are an order of magnitude brighter. Geoff and I also noticed that they did not hurt the aero.

Question 6) The front of the hood's vented area I believe is causing the air to rise from what would be the flow with a standard C5 hood. Seeing as the hood only weighs 16 lbs. compared to the 42 lbs. of a C5 hood, and the fact that it is relieving all of the front end lift a C5 normally has, and it has improved the cooling greatly, I am sold on keeping it.

Question 7) Geoff and I talked about that. During Run 5 I changed the angle of my front splitter and the aero did not improve. Geoff suggested that the original angle of my front splitter was causing the air that was hitting the front of the splitter to be forced around the Z, instead of under the Z. He commented after the smoke wand work that he noted very little disturbance of the air coming under my car and he thought that my front splitter and it's angle was the reason for this.

Thanks for your comments.

Pumba

Where in northern California are you located? I haven't had a good steak in a long time.

charger21

How do you have your front splitter mounted. Is it mounted to a undertray that is mounted to the frame?

Pumba

My front splitter was designed by Ross Aquilini. Ross is a Designer who works for Ford Motor Company. On the side he has an autoclave in his garage where he make carbon-fiber parts. As part of my front splitter package, he made a composite part that follows the bottom inside edge of my Tiger Shark front fascia. This part is very strong and stiff. On its bottom are nine fastener attaching points. So the load from the splitter is distributed evenly across the entire front fascia.

I have had my Z at 180 mph + and the fascia has not been negatively affected.

charger21

I just wonder if a frame mounted splitter/undertray would have changed things a bit up front.