The reigning MotoGP champion was second behind Honda's rookie Marc Marquez in both Friday practice sessions.
The 2013-specification Yamaha frame had been a clear improvement in Jerez testing, said Lorenzo, but the situation was less clear cut in Qatar.
"In Jerez it was more stable. Here there is no difference," he said when asked by AUTOSPORT how the new chassis compared.
"In practice I went faster with the old one. We still haven't decided. There's not too much difference, that's the situation."
Lorenzo said he was more interested in perfecting a race set-up on Saturday rather than an all-out push for pole.
"We need to improve the bike when the tyre drops off, and to save the tyres," he said.
"This is our main goal for tomorrow: to concentrate on the race. Obviously I want to do a fast lap [in qualifying], but the important thing is consistent pace."
He added that he was "satisfied but not relaxed" about his practice performances as he expects a very close fight at the front.
"I don't trust anyone because we can get some surprises," Lorenzo said.
"Marquez and the Hondas are very strong, Valentino [Rossi] is very fast, Cal [Crutchlow] is very fast."
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