Alexander Rossi and Tony Kanaan were among three drivers to take part in IndyCar's first test at the Austin circuit that will join the series' schedule from 2019.
Andretti-Autosport driver Rossi and AJ Foyt's Kanaan were joined by an unnamed Carlin driver in a Firestone tyre test at the Formula 1 US Grand Prix venue on Monday.
Rossi completed 90 laps on the day, and tested a variety of tyre compounds as well as turbo boost levels.
Teams agreed not to disclose times, but Rossi described his run on the circuit with IndyCar's universal aerokit as "fantastic".
"With the various programmes Tony and I were doing, it was hard to tell where we were at comparatively," Rossi told Autosport.
"But I can tell you that our car around that track is awesome! I had a smile on my face for the entire 90 laps and the package is great.
"It's challenging, it's technical, but there's also a lot of high-speed corners. It's a perfect circuit for us.
"From Turn 1 to Turn 9 is just mega. The first bit of it is pretty close to flat and each one [corner] subsequently gets tighter so you kind of decelerate as you go through them and if you're a little bit off on the first one, you pay a big penalty six corners later!
"It's definitely a drivers' track."
Rossi, who was runner-up to Scott Dixon in the 2018 IndyCar standings, said he could not draw comparisons from his F1 experience at the circuit, having driven in FP1 for Caterham in 2013 before contesting the US Grand Prix with Marussia two years later.
"In 2015 in the Marussia, the whole time it was wet!" said Rossi, "and in 2013 driving for Caterham as test driver I did one free practice in the dry.
"But I honestly don't remember too much about that."
He added the test was primarily focused on providing Firestone with information and that he did not attempt to draft the other two cars or use the push-to-pass boost.
"I literally didn't see the other two all day when I was out on track," he said.
"Firestone wanted data and feedback on the tyres on a variety of length of runs, so they didn't want external influences, in order to get a true comparison between compounds.
"We weren't really told [by Honda engineers] what the deal was with the extra boost, but there wasn't a time when we changed a setting and suddenly found a huge bunch of lap time. It was active the whole time, I didn't use push to pass.
"It was just good to get out on track - and that track in particular.
"Austin is a strong addition to the IndyCar schedule, and I think we'll put on a good show for the fans, I really do."
Get unlimited access to the world’s best motorsport journalism with Autosport Plus