Starting in 1997, IRL cars were powered by 4.0 L V8, methanol burning engines. They were production-based and normally-aspirated engines. They were produced by Oldsmobile under the Aurora label, and Nissan under the Infiniti label. They produced around 700 horsepower. The engine rules changed in 2000. The displacement was dropped from 4.0L to 3.5L. The block no longer needed to be production-based. In 2004, the displacement was further reduced to 3.0L to curb top speeds.