Grosjean has been running the Australia spec car for the entire weekend, while teammate Kevin Magnussen has been driving the up-to-date version.
The Frenchman was the faster of the two in qualifying, getting himself into sixth place, where he is set to start tomorrow's race barring any potential penalties.
After Friday practice, Grosjean called the old-spec Haas car 'outstanding' and is happy the pace carried over into qualifying.
"It's been a good weekend up to now," he said. "Yesterday we were happy with the very hot conditions, something that we wanted to check and understand.
"The old package seems to be working very well, Kevin was not so happy with both packages yesterday.
"This morning, he was flying in cooler conditions and I was like 'ah, maybe I should have gone for the new car'. Then in qualifying, it was equal and the midfield, there was like four hundredths between four cars, which his exciting.
"In Q3 I got the best out of car. It's quite impressive that a car that is that old - not in general but in Formula 1 - is capable of delivering such a good result.
"Now we need to understand the differences between the packages and why Kevin was so competitive this morning and maybe lost a bit of that."
Haas has not scored points in the last four races, and are currently sitting ninth in the constructors' standings, ahead of only backmarkers Williams.