The CFD Development of Ken Block’s Hoonipigasus Porsche

Bargeboard Aerodynamics:

A major hurdle in the aerodynamic design was the fact that the car was significantly wider than the factory 60’s 911, and we were running the factory roof and doors in their original position. The tire sits around 10 inches out from the side of the door, and this creates a large open area of dirty airflow. The dirty airflow creates a large amount of drag and makes flow off the rear quarter panels terrible. Since we were already starting with a higher drag set up because of the factory windshield angle, gutters, and the overall width of the car, we needed to look for ways to clean up the car as much as possible.

The bargeboard was an area we threw a large amount of brute force computing at to help clean up the flow. We went through so many design iterations from simple to complex designs with the car at multiple attitudes and yaw angles and ended up with the design you see. The final design ended up being a two-airfoil design. Each airfoil changes angles independently and changes chord length throughout which then connects at the top. This then mounts directly to the floor.

The bargeboard on this application is basically a complex airflow conditioner. It takes the dirty air coming out of the fender well and off the front tire and cleans it up as much as possible while also pushing the airflow outboard. This significantly cleans up the airflow around the door and rear quarter panel.

Radiator Ducting:

Proper airflow through the cooling system is critical. There are two main items that were necessary to get airflow to and those were the radiator and the charge air cooler. The radiator is located in the front of the car and is designed and manufactured by PWR North America. We work closely with them and are able to get air-side pressure drop values to use for CFD purposes to properly analyze how the heat exchanger affects the airflow. We use a Darcy-Forchheimer model along with the porous flow to simulate. Using this allows us to optimize the inlet and outlet ducting for the radiator. This was very important as we had to increase the inlet opening and change the bottom surface of the inlet duct to get proper pressure distribution. We shaped the outlet duct to get airflow from the radiator to flow outboard and down to limit interactions with the rear wing.


  1. Thanks for sharing this Mike, and thank you to Paul/Verus for detailing elements of the aero development.

    I hope all involved in the project have a great time at Pikes Peak!

  2. This is such an awesome article, written in a way to make something very complex fairly easy to understand for someone with a limited understanding of aerodynamics such as myself.

  3. Are there any rules against moveable aero? Seems like this would be a perfect application of sliding side skirts and possibly even fan driven suction for low speed downforce.

      1. So sad that this didn’t get to make a run due to the engine failure. Hopefully they do some real shakedowns before next year’s race.

  4. How effective are the NACA ducts at cooling the engine/gearbox? Does it affect the pressure flow under the car thru the diffuser?

  5. Pretty effective, but more testing is still needed. No real change to the diffuser based on before and after CFD runs.

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