Aug 8, 2019 update to the Chevrolet Corvette Z06 project car

Project Z06: Aero Comparo: Is it Worth it?

Photo courtesy Dave Green

At a recent track day in our Project Z06 at our local track—which happens to be Daytona International Speedway—we had the unique opportunity to run the high-speed high banks in two different configurations in very similar conditions. For one session, we kept all of our aero accessories from AJ Hartman Aero in place, including the swan neck mount rear Fulcrum wing and the front canards. For another session we removed the aero bits. What follows is some discussion on our best laps from the aero session and the non-aero session.

1. As we cross the start/finish line to begin our flying lap, we can immediately see a big difference. Our top speed without the aero bits is a good 7 mph faster than with the carbon fiber goodies. This is a powerful reminder that drag and downforce are basically the same thing. Downforce can just be thought of as drag with a directional vector. We can immediately see that we’re using some horsepower just to drag the aero gear through the air at high speed.

2, 3. But as we hit the brakes for Turn 1, we start to see the balance shift the other direction. Because of the additional stability provided by the downforce of the aero gear, we are able to delay our braking for Turn 1, and brake harder across the transition from the banking to the flat section.

4. Pointing the car into Turn 1, we also see quite a bit more speed from the high-downforce configuration.

5. At the exit of Turn 1, though, we see that the non-aero configuration has matched the exit speed of the aero-equipped Corvette. This one we’ll attribute to simple technique differences in those two laps, which brings us to an interesting point: Especially at lower speeds, where the aero components aren’t making massive downforce, you can occasionally produce some fairly similar corner exit speeds. The trick is doing it consistently. The additional aero grip is a highly stabilizing force for the chassis, which makes the car easier to drive at the limit, making consistent high g cornering more easily attainable.

6. Here we see approaching the apex of the low-speed, slippery Turn 3. While the wing is barely making over 100 pounds of downforce at these speeds at our angle of attack, we see a fairly better speed from the aero-aided car. Again, this could be driver technique differences lap to lap, but having that additional aero help certainly makes those techniques easier to execute consistently.

7. Now we’re heading out onto the west banking from Turn 6 and, oops, we got a terrible exit in the aero car. Our exit speed is 3 mph off the non-aero car. Certainly, the additional drag of the wing will hurt us as we accelerate into the long banking and back straight. Let’s see…

8. Hmm. Not too bad. By mid-way through the banking the aero car has made up almost all of the speed differential to the non-aero car. At 90 mph, the rear wing is producing over 200 pounds of downforce, but it’s only taking about 8 horsepower to push it through the air. This zone is a particularly “sweet spot” for the aero components, as they are producing very usable downforce, but the tradeoff is not so great in terms of drag.

9. But all good things must end, and when we hit 5th gear, the party sort of ends for our largely stock-motored Z06. When we shift into 5th gear at 140-ish mph, the rear wing is making nearly 600 pounds of downforce. But it’s also taking nearly 25 horsepower to pull it through the air. When we hit that tall 5th gear, the acceleration is noticeably reduced with the aero in place.

10. Nearing the braking zone on the back straight, the gap has closed a bit as the engine has climbed higher into the powerband. But the non-aero car still tops out faster than the aero configuration.

11. Time to brake for the bus stop chicane, and we see a very similar situation to what we saw going into Turn 1: More stability and more speed from the aero-aided car. We’ve got nearly 200 pounds of wing downforce on the rear of the aero car, making a more aggressive entry into the chicane much less dramatic than a slower, non-aero entry.

12. Exiting the bus stop, we see that additional entry speed has been carried all the way through the chicane, and we’re a full 9 mph faster as we get ready to head onto the east banking.

13. That additional exit speed has served us well, and as we approach the end of the east banking, that exit speed advantage of the aero car has translated into a 4 mph advantage as we near the top of 4th gear.

14. As we near the 4-5 shift at 140 mph, we can see the air beginning to take its toll, though. If you look at the flags, you can also see we’re rolling right into a headwind. That’s great for downforce, but on the wide-open front straight of Daytona, we’re not worried about downforce.

15. The 4-5 shift is another wall of wind that’s hard for our 380 wheel-horsepower C5 to break through. While the non-aero car keeps pulling strong, the aero car struggles—especially lower in 5th.

16. That headwind isn’t helping things, either, and as we near the start/finish line, the slicker, low-downforce configuration has a distinct top-speed advantage.

17. Across start/finish, and we’ve closed the speed gap a bit, but the top end advantage still goes to the slicker car.

So, what can we conclude here? Well, first of all, we’ll tell you that on the laps depicted, we were nearly a full second faster in the aero-equipped car than in the non-aero car. While the top speeds were reduced, we were more than making up for it in the corners—especially the higher speed cornering areas like the bus stop chicane.

When we sat down and looked at data from other laps and roughed together a theoretical fastest lap, we also saw that the aero car outran the non-aero car, but by a slightly smaller margin.

In our situation, we’d say that on track where we never had to shift into 5th gear, it’s a no-brainer. The high-downforce configuration will smoke the low-drag configuration nine ways to Sunday. But as soon as you spend a considerable amount of time in 5th gear, there’s some math to be done. Armed with this knowledge, on subsequent trips to Daytona, we may take a look at prevailing winds—a stiff breeze off the ocean that would reduce downforce through the infield kink and increase drag down the back straight might make us rethink the aero aids. Even so, we’d probably run both configurations in different sessions to assess the conditions of the day.

But in literally any other situation, where terminal speeds are more typical of the types of tracks we see, there’s really no debate—the AJ Hartman aero bits increase both cornering speed and drivability.

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Comments
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stafford1500
stafford1500 Dork
8/7/19 11:50 a.m.

Whew, I think my job is still safe. Just gotta keep finding efficient downforce to make it fun. Thanks for the descriptions of the effects...

bmxr
bmxr New Reader
8/7/19 12:14 p.m.

Great story. I’d love to see the test repeated at Homestead on the infield configuration where you spend little to no time in overdrive, and at Sebring where extra grip and stability can be really helpful. 

Patientzero
Patientzero Reader
8/7/19 12:55 p.m.

How many laps were done with and without?  Maybe I missed it.

slowbird
slowbird Reader
8/7/19 1:07 p.m.

This is why I like the Daytona roval so much. It's got the big open banks, and also the tricky, flat infield section, that makes low and high downforce configurations both have pros and cons. It's a real balancing act to find the right setup for ultimate pace, both over a lap and over 24 hours. (Speaking not from real-world experience, but from watching the pros do it and some sim-racing time as well.)

David S. Wallens
David S. Wallens Editorial Director
8/7/19 2:01 p.m.
stafford1500 said:

Whew, I think my job is still safe. Just gotta keep finding efficient downforce to make it fun. Thanks for the descriptions of the effects...

How do we make the wing retract for the oval? 

captainawesome
captainawesome Reader
8/7/19 2:59 p.m.

Is there any tuning to the suspension with the added downforce vs without? I would assume spring rates may need upped, but I know diddly.

z31maniac
z31maniac MegaDork
8/7/19 3:16 p.m.
David S. Wallens said:
stafford1500 said:

Whew, I think my job is still safe. Just gotta keep finding efficient downforce to make it fun. Thanks for the descriptions of the effects...

How do we make the wing retract for the oval? 

Talk to Moti at Blackbird and check out the DRS system he had previously installed on Creampuff?

NickD
NickD PowerDork
8/7/19 3:30 p.m.
z31maniac said:
David S. Wallens said:
stafford1500 said:

Whew, I think my job is still safe. Just gotta keep finding efficient downforce to make it fun. Thanks for the descriptions of the effects...

How do we make the wing retract for the oval? 

Talk to Moti at Blackbird and check out the DRS system he had previously installed on Creampuff?

Or be like Chaparral and make the angle of attack variable with a foot pedal

JG Pasterjak
JG Pasterjak Production/Art Director
8/7/19 4:11 p.m.
captainawesome said:

Is there any tuning to the suspension with the added downforce vs without? I would assume spring rates may need upped, but I know diddly.

The first time we ran at Daytona with the wing, we pushed the rear fenders down into the tires on the banking. Luckily we caught it before any major damage occurred, but to answer your question, yes you need to take aero loads into account when it comes to spring rates. How much? Well, that could be the subject of a book, but a quick place to start would be with some shock travel tests using zip ties on the shafts. Knowing how far your suspension is traveling under load can ive you a good idea of where to start for adjusting spring rates and bump stops.

frenchyd
frenchyd UberDork
8/7/19 4:45 p.m.

In reply to JG Pasterjak :

Things like this is one of the prime reasons I keep subscribing.  Nice article and very well done! 

BMG905
BMG905 None
8/8/19 8:52 a.m.

Were the Aero loads applied through the bodywork or directly to the chassis?

Would it be possible to mount the Wing element in the rear so that the force was applied directly to the frame?

 

JG Pasterjak
JG Pasterjak Production/Art Director
8/8/19 1:04 p.m.
BMG905 said:

Were the Aero loads applied through the bodywork or directly to the chassis?

Would it be possible to mount the Wing element in the rear so that the force was applied directly to the frame?

 

Rear bumper beam. It's about the furthest rearward structural member there is on the car, plus the wing is cantileivered behind the swan necks. There's a LOT of leverage. 

Jerry From LA
Jerry From LA SuperDork
8/8/19 2:39 p.m.

I imagine another 200 horsepower would swing the results more towards the aero end with higher top speeds and greater leverage.

deaconblue
deaconblue New Reader
8/9/19 11:09 a.m.

Keep seeing different wheels on this car - are you still using the narrower OEM Z06 rims or are those just older photos? Autocross vs open track setup?

Did you get the oil cooler setup on the car before heading to Daytona, if so how well did it work?

JG Pasterjak
JG Pasterjak Production/Art Director
8/9/19 12:12 p.m.
Jerry From LA said:

I imagine another 200 horsepower would swing the results more towards the aero end with higher top speeds and greater leverage.

I like the way you think

JG Pasterjak
JG Pasterjak Production/Art Director
8/9/19 12:16 p.m.
deaconblue said:

Keep seeing different wheels on this car - are you still using the narrower OEM Z06 rims or are those just older photos? Autocross vs open track setup?

Did you get the oil cooler setup on the car before heading to Daytona, if so how well did it work?

The autocross setup is 18x11F and 18x12R Momos with 315/335 Rivals. The track rubber is 315 R1S on 10.5" Z06 rears all around. At some point we'll get another wider set for teh track wheels, but wheels ain't exactly cheap for this car. The lead shot in this story is with the Rivals because we ran a couple sessions in the rain and they were the only thing we had handy with tread on them.

And we haven't gotten the oil cooler mounted yet. Improved has some brackets designed, but they wanted to wait until we got our headers installed to finalize the adapter and hose configurations. The E85 has cut coolant and oil temps by a good 15-20 degrees, though.

deaconblue
deaconblue New Reader
8/9/19 2:42 p.m.
JG Pasterjak said:
deaconblue said:

Keep seeing different wheels on this car - are you still using the narrower OEM Z06 rims or are those just older photos? Autocross vs open track setup?

Did you get the oil cooler setup on the car before heading to Daytona, if so how well did it work?

The autocross setup is 18x11F and 18x12R Momos with 315/335 Rivals. The track rubber is 315 R1S on 10.5" Z06 rears all around. At some point we'll get another wider set for teh track wheels, but wheels ain't exactly cheap for this car. The lead shot in this story is with the Rivals because we ran a couple sessions in the rain and they were the only thing we had handy with tread on them.

And we haven't gotten the oil cooler mounted yet. Improved has some brackets designed, but they wanted to wait until we got our headers installed to finalize the adapter and hose configurations. The E85 has cut coolant and oil temps by a good 15-20 degrees, though.

Wow didn't realize the E85 would make that much difference in the oil and coolant temps out on the track!  I would need to go from 36->46 lbs/hr injectors and swap in an E85 compatible 340 L/hr pump at the power level in my C5 to work with the flex fuel kit.  I really like running the E85 in the wife's 2.0L Turbo Ecotec LHU (factory flex fuel) - it makes a noticeable different with the summer's high heat and humidity

frenchyd
frenchyd UberDork
8/10/19 2:54 a.m.

In reply to JG Pasterjak :

Please may we have some more, SIR! 

How about comparing the same budget spent on various area’s? Brakes, power improvements, handling etc.  

It properly should be on a GRM size  budget, maybe around your Miata?  Then we can each scale it up or down according to our own budget and vehicle.  

Your article on fuel myths  did exactly that.  Scale the results of that to ChevyV8, or whatever motor and you have an idea of how those fuels will personally impact each subscriber.  

My first suggestion would be compression versus flow on cylinder cylinder head porting.  In other words, baseline the engine.  Then increase compression via pistons, Versus ported cylinder head.  

 

 

6pak72
6pak72 New Reader
8/14/19 8:56 a.m.

In reply to JG Pasterjak :

Really love the ComparemyLaps here, and your take-apart. Great driving, great analysis - it’s helping with my aero modelling for an ST-class Miata.

PLEASE get a TPS and BPS trace going - I’d love to see the traces!! 

Robbie
Robbie UltimaDork
8/14/19 9:11 a.m.
NickD said:
z31maniac said:
David S. Wallens said:
stafford1500 said:

Whew, I think my job is still safe. Just gotta keep finding efficient downforce to make it fun. Thanks for the descriptions of the effects...

How do we make the wing retract for the oval? 

Talk to Moti at Blackbird and check out the DRS system he had previously installed on Creampuff?

Or be like Chaparral and make the angle of attack variable with a foot pedal

I think the best approach is to make a hole in the cabin near the drivers knee that if covered will direct high speed air into the wing path and stall the wing, therefore reducing drag and downforce. Bonus is that when uncovered it fills the cabin with cool fresh air for the drivers comfort.

frenchyd
frenchyd UberDork
8/14/19 1:10 p.m.

In reply to JG Pasterjak :

Enzo Ferrari; “ Aero is for those who can’t build a powerful engine”. 

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