After delivering a nearly flawless introduction of its Chevy- and Honda-built energy recovery systems (ERS) last weekend at Mid-Ohio, the next big test for the NTT IndyCar Series’ hybrid powertrains happens this weekend at Iowa Speedway where another first—hybrid open-wheel cars on an oval—will take place.

The challenge posed to the ERS units will come from the unrelenting heat each of the 27 hybrids will face as most of the 250-lap nighttime race will start with ambient temperature close to 90F and taper off to the low 80s by the checkered flag. While the high midwestern heat and humidity are a significant factor, the compact track with short straights and near-constant action around the circuit means most drivers will be unable to run in clean air for long stretches to cool the ERS.