Ryan Hunter-Reay, Josef Newgarden, and Sage Karam

The July 18 Iowa Corn 300 at Iowa Speedway proved to be a banner day for six of the eight American drivers racing in the Verizon IndyCar Series.

Ryan Hunter-Reay, the winningest active American driver, scored his first win of 2015 and 15th of his career. Hunter-Reay became the third American driver to win in the past four races, joining Graham Rahal and Josef Newgarden among the nine winners through 13 races this season.

Three race-winning Americans is the most in the series since 2011 when Hunter-Reay, Marco Andretti and Ed Carpenter recorded victories. Add Charlie Kimball's 2013 victory at Mid-Ohio Sports Car Course and six of the Americans currently competing in the series have won races.

The race-winning drivers aren't the only Americans making waves. At Iowa, Sunoco Rookie of the Year candidate Sage Karam scored his first podium finish -- the sixth-youngest driver ever to finish on the podium -- while fellow rookie Conor Daly has a best finish of sixth in his five races this season.

Newgarden completed the podium at Iowa Speedway for the first American sweep since Sam Hornish Jr., Marco Andretti and Michael Andretti finished 1-2-3 in the 2006 Indianapolis 500 Mile Race. Graham Rahal finished fourth for the first 1-4 American finish since 2001.

"I think it's always great when Americans do well," said Andretti Autosport owner Michael Andretti. "It's very important to note that it's an international series and there's international drivers. So when the Americans do well and they beat the rest of the world, it's always great."

A look at Americans currently competing in the Verizon IndyCar Series

Ryan Hunter-Reay, Andretti Autosport - 15-time Indy car race winner, who won the 2012 Verizon IndyCar Series title and 2014 Indianapolis 500. Winningest active American Indy car driver.

Ed Carpenter, CFH Racing - Co-owner/driver of CFH Racing is a three-time Indy car race winner and two-time Indianapolis 500 pole sitter.

Marco Andretti, Andretti Autosport - Third-generation driver from one of racing's most famous families is a two-time Indy car race winner. Only driver to complete every lap of every race in 2015 season.

Josef Newgarden, CFH Racing - Rising star has won his first two Indy car races and his first pole in what has been his breakout season. Was the 2011 Indy Lights champion.

Graham Rahal, Rahal Letterman Lanigan Racing - Son of 1986 Indianapolis 500 winner Bobby Rahal is having his best season in Indy car racing, scoring a win at Auto Club Speedway in June. Currently second in Verizon IndyCar Series championship standings.

Charlie Kimball, Chip Ganassi Racing - Scored his first win at Mid-Ohio Sports Car Course in 2013. Finished third in the Indianapolis 500 in May.

Sage Karam, Chip Ganassi Racing - At 20 years old, is youngest driver racing in the Verizon IndyCar Series. Has finished in the top five in two of his past three races and qualified a career-best third at Milwaukee. Was the 2013 Indy Lights champion.

Conor Daly, Schmidt Peterson Motorsports - Son of former Formula One and Indy car driver Derek Daly has performed as a super-sub in 2015. Finished a career-best sixth at Belle Isle 2 and led his first career laps.