SPA-FRANCORCHAMPS, Belgium (AP) Lewis Hamilton increased the pace on quicker tires and posted the fastest time in the second practice session for the Belgian Grand Prix on Friday.
The Mercedes driver was second quickest behind Ferrari's Kimi Raikkonen in the morning practice, but that was with Raikkonen on ultra softs and Hamilton on the slightly slower softs.
With both on ultra softs in P2, Hamilton showed extra pace, clocking .262 seconds clear of Raikkonen and .427 ahead of Mercedes teammate Valtteri Bottas.
''The car felt strong straight out of the box,'' said Hamilton, who has won four races this season.
Mercedes upgraded the engines on both cars for this weekend, meaning it has made its fourth specification change on the power unit. Any further changes this season will incur penalties.
Ferrari has kept its third engine and has another permitted change remaining over the eight races following Belgium.
''We made some good steps with the set-up right from the start of P1, which is a really encouraging way to kick off the weekend,'' Hamilton said.
But he added a note of caution with regard to the car's actual race speed compared to Ferrari: ''It looks tight at the top on the long-run pace.''
In a further boost for Hamilton, championship leader Sebastian Vettel was only fifth behind Red Bull's Max Verstappen in P2.
Toward the end, a thunderstorm drenched the vast seven-kilometer (4.3-mile) Spa circuit that cuts through the forest of Ardennes, enveloping it in darkness.
''Aquaplaning already,'' Red Bull's Daniel Ricciardo said.
Ricciardo then sought refuge in the team garage, along with the other drivers, as the session petered out.
Because of its location, the Spa track is famed for its micro-climate, meaning it can be sunny on one side and raining on the other.
''It's going to be usual Spa weather,'' Red Bull team principal Christian Horner said. ''Bring your sun cream and your umbrella.''
The third practice is on Saturday morning followed by qualifying, where Hamilton looks to equal F1 great Michael Schumacher's pole position record of 68.
Vettel leads Hamilton in their title fight by 14 points.
Raikkonen went quickest in the morning after having repairs on his Ferrari. The Finnish driver went into the garage for about 20 minutes after an apparent suspension problem, but came back and overtook Hamilton's time.
The first practice was interrupted after about 20 minutes when Felipe Massa lost control of his Williams and went off track into the gravel, buckling a couple of wheels. Massa, who missed the Hungarian GP last month because of vertigo, sat out P2 because the team had to change his chassis.
When P1 restarted, Mercedes teammate Valtteri Bottas also went into the gravel. After some small repairs, he placed sixth fastest.
Bottas, who has won two races and finished on the podium in the last five, was less upbeat than Hamilton.
''We had some trouble setting up the car and I didn't feel too comfortable in the beginning. In the end it was getting better, we made quite big steps,'' Bottas said. ''The performance of our car in general is looking good. However, there is still a lot of margin to optimize the car.''
The 19-year-old Verstappen, meanwhile, is going to enjoy huge support, with up to 80,000 Dutch fans flocking over the Belgian border to cheer him on over the weekend. That is four times more than came to see the Dutchman race last year.
''It's brilliant to see so much orange around the place. Everything's sold out, rammed. To see so much support for Max is quite phenomenal,'' Horner said. ''He's had a lot of bad luck so far this season, and where better for it to change than at effectively his home grand prix?''