Indianpolis 500 testing: Helio Castroneves fastest on day three

The Team Penske driver ran a two-assisted lap at 227.514mph inside the first hour of running, and that speed would remain unbeaten when the session ended.

However he also set the fastest unassisted speed of 225.314mph during happy hour, helped by what appeared to be some previously unseen pieces of the Chevrolet superspeedway aero kit.

"It was a good day," said Castroneves, who is chasing his fourth victory at the 500.

"The car was super strong, super solid, felt comfortable. Now we've got to just keep working with this new aero kit.

"Today was basically the second day that we've been working constantly, but I like what I see."

Castroneves' Penske team-mate Simon Pagenaud was second-fastest for the day ahead of Scott Dixon, with Andretti's Justin Wilson slotting in behind the Kiwi as the fastest of the Honda drivers despite suffering an engine failure late in the day.

"I looked in the mirror and there was a lot of smoke coming out of the exhaust so, yeah, it's unfortunate," he said.

"I don't know any more than that right now. But, looking back over the day, I think we've had a pretty good day.

"The car's been quick, and I think there's more to come.

"There's a few tweaks we can try for going faster and also dealing better in traffic."

Wilson's engine failure followed a similar problem for Schmidt's James Jakes earlier in the day, while Simona de Silvestro's running was cut short when a fuel leak caused her car to catch fire.

"It's definitely unfortunate because the car is pretty burnt down, and it's really frustrating that it seems like fire follows me," said the Andretti driver.

"Until now, everything was working fine, and it's just annoying because it's a pretty big setback for us, but I have four great team-mates and that will make it easier for us to continue moving forward."

It is the third time that de Silvestro has faced a fire in an IndyCar. She suffered burns to her hands when her car began to burn after a crash at Texas in 2010, and endured similar injuries when her car flipped and ignited during practice for the Indy 500 a year later.

Elsewhere, James Davison made a surprise appearance to join a growing list of drivers to have steered Dale Coyne Racing's #19 entry this year, although it's understood that the Australian is yet to secure a deal to race the car.

The 28-year-old made his Indy 500 debut last year, when he finished 16th with KV Racing.

INDIANPOLIS PRACTICE RESULTS