Officials estimated that the change would reduce top speeds by 10 miles per hour.
Brian Barnhart, IRL's senior vice president of operations, said in a statement: "We have been gathering data and studying ways to slow the cars down without compromising the highly competitive racing we have in the IndyCar Series.
"We believe these changes to the cars and engines will accomplish that goal."
Indycar
IndyCar ready to welcome back spectators
19/06/2020 AT 15:09
IRL driver Tony Renna was killed in a one-car crash during a test run at the Indianapolis Motor Speedway two months ago.
Sweden's Kenny Brack, the 1998 series champion and 1999 Indy 500 winner, is still recovering after sustaining multiple fractures in a crash at the Texas 500 IRL race in October.
Mario Andretti, the 1969 Indy 500 winner, escaped injury when the 63-year-old's car flipped over at high speed and almost reached the top of a catch fence during a private test session at the Indianapolis Motor Speedway in April.
Indycar
Will Power first Australian to win Indy 500
27/05/2018 AT 23:24
Indycar
Andretti: ‘What will propel Indycar into future’
07/04/2018 AT 19:02