The Frenchman topped the times comfortably on the second day of Formula 1 testing thanks to a series of short runs on the soft tyre in the afternoon.
Grosjean, who was also positive after the first day of pre-season running, told reporters in the Jerez paddock that the second day had confirmed his initial feelings.
"It's a little bit better in all areas," he said. "Generally speaking, after this day, we can say that the car is a good baseline.
"I was a bit cautious with what I said yesterday, but the feelings are better than last year.
"There is some more work that we are going to do on the car to improve some areas, but generally for a first try I am very happy with the car."
Grosjean will hand the Lotus over to team-mate Kimi Raikkonen for the second half of the test, and he said he is looking forward to hearing the former world champion's assessment of the car.
"We have some ideas for the future tests, and it will be good to have Kimi in the car to give us some feedback as well," he said.
"We can see if he feels the same as I do, and if he wants to go in the same direction as I do in terms of set-up."