Yamaha's Jorge Lorenzo was edged off the top spot by MotoGP rookie Marc Marquez during the final free practice sessions in Qatar by just 0.001s.
The defending world champion, who finished second behind Marquez in FP2 and FP3, evaluated a different chassis and set-up on his factory M1, setting his best lap in 1m 56.085s.
Lorenzo expects to improve further during final qualifying at Losail although he is yet to make up his mind over which chassis he will use for Sunday's opening round under the floodlights.
“I'm very happy with the changes we made on the bike because it improved a lot.
"In the last moments the track was better this evening, in the beginning it was very dirty,” he said.
“I think we can still improve the bike more tomorrow, we still haven't decided which chassis is better; today it is the new one, yesterday the old one.
“I'm very curious to see how the qualifying goes with the new formula, we will just be concentrating on making four fast laps, the maximum performance we can get.”