Mark Winterbottom has topped the timing charts in a final practice run ahead of Saturday’s V8 Supercars race in Perth.

The reigning series champion edged white-hot Volvo man Scott McLaughlin to top spot in wet and slippery conditions.

Showers are forecast to hit this afternoon’s 120km race, which begins at 2:45pm (4:45pm AEST).

“The wet weather has been a weakness for me in the past so it’s nice to go out and top a session and have some fun,” he said.

Jamie Whincup, who has struggled with electrical problems so far at the meet, placed 14th.