Verus - Carbon Rear Diffuser for 987.1 & 987.2
 

Verus Engineering Rear Diffuser

The Verus Engineering Carbon Fiber Rear Diffuser fits both the 987.1 and 987.2. It is manufactured out of three different diffuser main planes produced from 2x2 twill carbon fiber, which is autoclave cured for superior strength and weight properties (also known as dry carbon). The diffuser strakes are made out of a highly durable polyurethane for longevity and impacts. There is absolutely no drilling or fabrication required for installation of this rear diffuser.

The Verus Engineering Carbon Rear Diffuser improves vehicle performance with drag reduction and downforce production. It was designed in unison with our other components for the Cayman to create a well-rounded and balanced aerodynamic system.

Price : $1,649.95

Link to product page

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How did we start the development?

We started off with Gear One Performance contacting us. They wanted a full aero kit developed for their 987.2 for the track, but something that could still be driven on the street. The project started off with them driving the car to our shop in Indianapolis. We then got to work doing what we do best. We scanned the full car with the main purposes of creating a CFD model and using the scans to make manufactured components.
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Scanning the car
https://cimg0.ibsrv.net/gimg/rennlis...cc97d22f3f.png
Raw scan files of sections of the car

Creating CFD Model
Creating a CFD model from a scan is a long and tedious process. This is done with the combination of scanning software and CAD. This is the real bottleneck of developing an aerodynamic package for a scanned vehicle.
https://cimg1.ibsrv.net/gimg/rennlis...4e0aa9e48e.png
CFD Models

Getting an Aerodynamic Baseline
Analyzing the vehicle’s baseline is the first step in the development. This gives our team the starting point and locations where improvement can be developed. From there, we can make incremental changes while watching how these changes impact drag, downforce, and aerodynamic balance.
https://cimg0.ibsrv.net/gimg/rennlis...508a349ed1.png
CFD Baseline

Development Goals
The goal that we set out to achieve was an aerodynamic package that had good downforce for a heavily tracked Cayman but was also very street-able. Vehicles that are street-able need to watch ride height and all underbody aerodynamic components. The main concerns for street-ability were the front splitter and diffuser strakes.
Front Splitter:
The front splitter needs to be as short as possible while still creating enough downforce to balance out the rear wing. Having a short splitter means it is less likely to hit objects on the street and the vehicle can be setup with a lower static front ride height.
Diffuser Strakes:
Diffuser strakes can add a substantial amount of performance gain to the rear diffuser. However, they hang low on the rear of the car. To ensure this will not be an issue on the street, we made them out of a hard durable plastic. This will ensure proper function of a strake while not being concerned with damage by road obstacles.

Development Phase
From the stock analysis, we went through 25 major design changes, not including some minor changes in between.
https://cimg6.ibsrv.net/gimg/rennlis...19bfa593a7.png


Final Design
The whole system met our development goals, especially for a street-able, high downforce setup. The front splitter was kept to a minimum length with help from the dive planes. The rear diffuser strakes are designed to flex when impacted and also kept as high as possible to the chassis without negatively impacting performance. The rear wing airfoil and endplates were optimized for maximum performance with a low drag penalty. Each and every component was developed to work with each other in harmony for the best aerodynamic performance available in such a package while being well balanced.
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Final CFD


Performance
The downforce and drag of the total car is in the maps below. Each color plots a different wing angle, but at a fixed ride height of 90mm FRH and 205mm RRH measured from the front splitter to the ground in the front and from the rear diffuser to the ground in the rear. Also note the factory car made 140 lbs of lift at 120mph, which meant we had to overcome that lift to just start to make downforce.
https://cimg5.ibsrv.net/gimg/rennlis...08a69c153f.png
Downforce (standard)
https://cimg9.ibsrv.net/gimg/rennlis...410a1565c2.png
Drag (standard)
https://cimg0.ibsrv.net/gimg/rennlis...a2cf8767b2.png
Downforce (metric)
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Drag (metric)

Testing

Coast Down Testing

We followed the SAE standard of coast down testing as close as we could. We coasted down from 80mph to around 10mph with 3 different cases; wing at 0 degree, wing at 6 degrees, and wing at 12 degrees. The data was recorded using an AIM data logger and 4 runs were done and then averaged. Elevation changes were ignored because it could not be accurately calculated. Runs were made on the same day, at the same location, back to back.

1. The 0 degree angle of attack took the longest to coast down. This logically makes sense because it has the least amount of drag slowing it down.
2. The 12 and 6 degree angle of attack slow down quicker but they are close together. This also makes logical sense because the drag from 12-6 degrees is less overall than the drag from 0-6 degrees.

https://cimg3.ibsrv.net/gimg/rennlis...350be5ec55.png

From the coast down testing data, calculation of the coefficient of drag (cd) was completed. From this, the ability to compare simulated CFD drag to coast down testing drag was possible.

1. The real world (experiment) and CFD on the 12 degree angle of attack correlated extremely well.
2. At 6 degrees angle of attack, the real world experiment showed less overall drag than we calculated in CFD.
3. At 0 degree angle of attack, the real world experiment also showed less overall drag than calculated in CFD. However, with both 6 and 0 have similar trends, this most likely was early separation on part of the CFD model.
4. Overall, the real world results correlate well to CFD estimated data. The drag numbers are still very close even though 6 and 0 degree angle of attack are not as close as 12 degree angle of attack. It could also be a change in wind during the coast down test that caused the slight skew

https://cimg4.ibsrv.net/gimg/rennlis...bc2a427ec1.png


Track Testing
The aerodynamic kit was then fully tested on the track during the summer of 2018. The car was fashioned with a data acquisition system to collect data which included 3 laser ride height sensors. Ride heights correlated with downforce numbers when corrected for weight transfer and roll. We are still working on optimizing suspension setup to go with the added downforce.
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If you have any questions, please ask!

Thanks,
Paul

Wow, amazing work!

Parts backed by science. :cheers:

We are looking for a final test fit of the front splitter for the 987.2 for the final package to be ready. We only have a 987.1 so waiting for a 987.2 local to us for install for instructions.

Thank you, we worked hard on it!

We have an install video installing the diffuser. Check it out to see how easy it would be to install yourself.

Video Link to Youtube

You guys actually get it. I've pulled engines and trans and bolted on complete suspensions but that doesn't mean I'm a full race shop. Instructions are a factor in where I spend my money. Great video

Wow, this is incredibly impressive!

Thank you! When we release the full kit as a package, we will have even more of a write along with how to set up the car properly for the track. Setting up and aero car is a little different than a car with mechanical grip only.

Thank you!

Will you have a few different packages? For example, one without the large wing so you can use the diffuser & front splitter with the stock Cayman S "pop-up" wing? Or will the balance be completely off with that setup?

We will sell everything individually and as 2 packages.

Package 1:
Rear Diffuser with underbody panel and dive planes
This was science out to give a good overall balance to the car while improving aerodynamics. This wouldn't cause any driveability issues or ride height issues on the street.

Package 2:
Rear Diffuser and underbody panel, dive planes, front splitter with air dam, ducktail mount for wing, and rear wing
This is the high downforce (still very efficient) kit that will totally transform the car. This kit is also very streetable because the front splitter isn't super low and is very durable. This kit makes around 1000lbs of downforce at 120mph depending on the static car setup. We will have a setup packet for this kit which helps properly set the car up at the track. Balance is adjusted via the rear wing.

Paul, I'm probably going for the high downforce package, wallet permitting. The guys that I track with that have the big wing on the back just create more understeer. Its at a higher speed but the problem still exists. Clearly these guys are buying parts and putting them on the car vs your total solution. Can you talk about how the package works to increase front grip as part of an overall package?

Yes, I can. The first product we developed was the dive planes for the car. This was specifically done to help with an understeer problem on GearOne Performance's 987.2. They had another company front splitter and rear wing setup. We actually feel the front splitter they had actually hurt front-end downforce over the stock setup and caused part of the aero problem. I think there is a big misconception on many aero components and how they actually work on the car. Without the solid theoretically knowledge and real-world testing, it is very easy to make mistakes to the detriment of the car. The dive planes we designed and optimized with a goal of shifting aero balance forward as much as possible. Dive planes are better as an aerodynamic balance device than making big downforce numbers. They are just too small to make large downforce gains, but they are great at shifting aero balance.

https://cimg9.ibsrv.net/gimg/rennlis...96075d51f7.png
The image above shows why you do not need a large force to impact aero balance. Think of it as a ratchet with a socket. The longer the ratchet, the easier it is to break a bolt loose.

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This is a track map of our dive planes installed on GearOne Performance's 987.2 with their old aero setup.

This is a quote specifically from the owner of the car:
"I spent the morning sessions getting my lap times consistent enough to have a baseline. Then, during lunch break I installed the canards having drilled the holes the night before. These things actually made a huge difference. I was skeptical at first that adding canards wouldn't make much of a difference. Where the front end felt a little unstable and pushed the car is now solidly planted with the canards installed. The higher speed corners where you're typically a little hesitant to push the car to the very edge were completely changed now that I had more confidence in the front grip at those speeds. After testing the waters a little bit, I was able to carry much more speed through turns 3 and 4 and coming on to the straight. Those few mph at the beginning of the straight obviously translated into a significantly quicker lap time. After looking at the lap data from my AIM it confirmed what I felt out on track. The inside line on this picture is with the canards installed and the outside is without them. As you can see by the heat map I'm able to carry a lot more speed through the faster corners and get on the power much earlier coming on to the straight. "

The performance on a completely stock car without and then with our dive planes at 100mph is below.
Downforce = 62.5 lbs
Drag = 10 lbs
Moved aero balance forward by 30mm

Now onto the other front aero device, the front splitter. Our front splitter is actually a splitter and an air dam. The main splitter was used to create a large area of low pressure. Force equals pressure times area and with that equation, the lower the pressure and the larger the area will increase downforce. We also used the splitter to feed the factory front diffusers to increase downforce further. This is huge to actually have the car balance out. The air dam's purpose is to allow us to have the splitter exactly where we need it and help direct airflow around the front end of the car. The air dam also helpt the flow of the dive planes further which was an added benefit.


https://cimg6.ibsrv.net/gimg/rennlis...e39e774d80.jpg

The drag side shows where the drag is created. Red/yellow to grey is where drag is created on the color spectrum. This shows the surfaces directly working agthe ainst forward motion of the car. Purple/Blue to grey is not working against the forward motion of the car. The force would have a vector in the direction the car is traveling. Grey is neutral and doesn't act in either direction.

The downforce side shows where downforce is created. Purple/blue to grey are areas creating downforce. This force is pulling the car down towards the surface of the ground allowing more grip for the tires. Red/yellow to grey is causing lift which wants to pull the car off the ground.

The dive planes and the front splitter is what helps balance the car with the large downforce created by the diffuser and rear wing. The balance can be tuned with adjustment of the rear wing. Aerodynamic balance is very much a driver feel type of thing also. On the science side, the aero balance location (center of pressure, CoP) needs to be behind the center of gravity, CG (location point of the weight of the car). This is for vehicle stability and can cause issues if it is not right. How much further back the CoP needs to be behind the CG is very much driver feel. Because the Porsche has a CG point fairly rearward being mid-engine, more rear downforce is needed than front downforce.

Hopefully this answers all your questions. If you have any more, feel free to ask or contact us directly.

Thanks,
Paul