Hybrid unit cooling in 2022 WRC cars

After MSport, images from the 2022 WRC cars (or mule test cars) have been released through social media. All three teams have declared to be testing the new hybrid units, which constitutes the main modification for next season. For this reason, MSport and Toyota are using mule test cars, while Hyundai has started working with the new car (i20N), but stripped of most of the aero parts. One of the main concerns in this initial stage of the development test season of the 2022 WRC cars is to evaluate the hybrid unit performance, and this includes designing an adequate cooling system to keep it working at the optimal temperature range.

J.Hänninen, Toyota Yaris mule test car, 2022 pre-season development test, Viseu, May 2021 – picture by Pick Prego a fundo

Rear cooling air feeding

The location of the hybrid unit at the rear of the car, as per FIA designation, recommends installing the radiators also at the rear of the car, for what the cars have been modified to force an adequate amount of fresh air entering into the car’s rear. MSport also showed their initial design in the car used in the test developed near Barcelona some weeks ago, consisting of a rounded intake, located at the height of the rear of the door’s handle.

M.J.Wilson/S.Loudon, Ford Fiesta test mule car, 2022 pre-season development test, Bages, April 2021 – picture by Anna Solé Genescà

The side air intakes in the Toyota’s mule test car are bigger in size than those of the Fiesta. They are rectangular and reach up to the center of the rear window. Due to their bigger size, they ensure a higher amount of fresh air to enter into the rear of the car, but also a bigger drag (air resistance) due to the higher front area.

J.Hänninen, Toyota Yaris mule test car, 2022 pre-season development test, Viseu, May 2021 – picture by Luis Coimbra Photography

The Hyundai i20N car seen in the first test developed in the south of France included a third side air intake alternative. It was positioned at a higher position, in the location of the side window. It is a perfectly rectangular opening, and the pictures suggest that it has a smaller area than that of the Toyota, thus the air flowing on both sides of the car (and the rear wing) would be less perturbated.

Hyundai i20N mule test car, 2022 pre-season development test, South of France, May 2021 – picture by Hyundai Motorsports

The shape and location of these air intakes will surely change with the design of the new cars. In their current location, they have a significant impact on the efficiency of the rear wing, as they represent an obstacle for air flowing on both sides of the car. If less air reaches the side winglets of the rear wing, less downforce will be generated. And with the aero restrictions planned for 2022, any gram of downforce will be more than welcome, so the disturbance over the rear wing of the air intakes will have to be minimal.

The main objective in this initial stage of development is to ensure that enough air enters into the rear of the car to ensure adequate cooling of the hybrid unit. Once this objective is achieved, teams will work on the design of the air intakes to reduce the drag and their impact over the rear wing, as well as to minimise the pressure drop of air entering into the car, as the cooling efficiency depends on both (amount and pressure of air). Then, we will probably see more developed air intakes, similar to those used in Rallycross Supercars, such as we already reviewed in a previous post. Some of them are shown in the picture below. Note that they are all located at a lower position with respect to the initial proposals of WRC teams, and with minimal impact on the air flowing towards the rear wing.

Side air intakes of Peugeot 208 RX, Ford Fiesta RX, Mini RX and Hyundai i20 RX – Catalunya RX 2019

Side air intakes of Renault Clio RX, Renault Megane RX and Citroën DS3 RX – Catalunya RX 2019

Rear hot air venting

The air used for cooling the hybrid unit is removed in all three cars by a rear vent. The main difference is in the location of the rear vent. MSport included the vent in the upper part of the rear bumper, which forced them to relocate the exhaust gas pipe exit, as shown in the picture below.

A.Fourmaux/R.Jamoul, Ford Fiesta mule test car, 2022 pre-season development test, Bages, April 2021 – picture extracted from Jaume Soler video

Both Toyota and Hyundai have located the rear vent to a lower position: at the location of the (now forbidden) rear diffuser.

J.Hänninen, Toyota Yaris mule test car, 2022 pre-season development test, Finland, May 2021 – picture from The Teevoman’s video

To remove the hot air from the rear of the car, fans are placed behind the radiators. This solution is also used by all the RX supercars withth rear radiators. The picture below shows the use of one (Audi S1 RX), two (Renault Megane RX, Hyundai i20 RX or Peugeot 208 RX) or three (Mini RX) fans for this purpose.

From top to bottom: Audi S1 RX, Renault Megan RX and MIni RX, Catalunya RX, 2019

The solution implemented by Toyota and Hyundai follows the same principle of the exhaust blown diffuser, that is, to combine the energy from the air coming from the rear radiator fans with the energy of air removed from under the car (now without the beneficial effect of the rear diffuser).

J.Hänninen, Toyota Yaris mule test car, 2022 pre-season development test, Finland, May 2021 – picture from Toyota Gazoo Racing video

The result is a faster removal of air at the rear of the car (car’s wake) that translates into lower pressure, thus generating more downforce in this area. Also, drag can be reduced with a faster wake. It is a wise solution due to the lack of downforce caused by the removal of rear diffuser in the 2022 WRC cars, by regulation.

Once the hybrid unit cooling solutions are fully evaluated, the rest of the car, aero parts included, will be added by teams, hopefully in the next weeks. And we will review them, as usual.


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6 thoughts on “Hybrid unit cooling in 2022 WRC cars

  • 2021-05-28 at 19:06

    Thanks as usual. I had missed both the hybrid unit cooler for the Hyundai on the window and the Toyota rear vent exhaust blown type exit.

    • 2021-05-28 at 20:01

      Thank you, Lawrence. I’m sure that we will discover some more new details in the next tests.

  • 2021-05-30 at 23:32

    The Toyota doesn’t need brakes or rear spoiler with those massive air vents…

    • 2021-05-31 at 20:34

      You’re right, a small parachute at the rear and no brakes anymore!

  • 2021-05-31 at 12:09

    Yeah, I half-expected these rudimentary solutions to not be the final designs either. It’s likely the teams were just gathering internal data about how much air they could play and get away with under maximum load. Not only do I expect the teams to follow the WRX designs, I also think they’re going to take design clues from WEC and road cars where they use sculpted and scalloped roof scoops (instead of the current protruding one) to add more cooling ducts at the expense of cabin ventilation (which will likely come elsewhere from a relocated inlet). What do you think, Luis? Also, with the different weight and power curve, is Pirelli developing yet another new profile & construction? I remember F1, Moto2, and WEC having to get used to new tire profile along with engine regulation changes.

    • 2021-06-01 at 16:06

      Sure, Kevin, they will take any useful idea from any other racecar competitions to get an optimal hybrid unit cooling, but they need to keep cabin ventilation intact, for the crews to deal with hot events such as Greece or Turkey.
      I can’t help you regarding Pirelli, have no information, but I’m sure they keep working to continuously improve their tyres, especially after the usage we saw in Portugal, rather than because of regulation changes.


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