Borg-Warner makes the turbos for all three IndyCar engine suppliers, Chevrolet, Honda and Lotus, but the engine makers provide two compressor shrouds of their own design for homolgation by the series. Honda's singe-turbo engine is down on power compared to Chevrolet's and Lotus' twin-turbo motors, and Chevrolet has won all every race so far and taken all pole positions this season. Honda had a new shroud ready for the Long Beach GP and IndyCar allowed the change, but Chevy protested so Honda wasn't permitted to make the switch.
A three-man panel was selected to hear Chevy's appeal, and their verdict in favor of Honda means that the Japanese automaker was permitted to swap the shroud before this weekend's São Paulo race. The new shroud is said to be worth 10 to 15 more horsepower, but in the end, Chevrolet-powered racers managed to finish in seven of the top 10 positions.
Chevy had been contesting the ability to make an engine change at this point in the season, when there are no constant-parity clauses in the regulations and IndyCar has an agreed date in mid-June for such alterations to create parity. Honda's argument was that an agreement in 2010 that was meant to prevent turbo wars does allow the change it sought to make. The panel supported Honda's interpretation of the parity argument.
Chevy has said it will not appeal the decision. Now it's up to the Honda-powered drivers fitted with the new 0.74 A/R compressor cover to show they can do better than second place.