By Abhishek Takle

SEPANG, Malaysia, Sept 29 (Reuters) - McLaren's Fernando Alonso is set to start Sunday's Formula One Malaysian Grand Prix from the back of the grid as he tries out an upgraded Honda power unit in practice on Friday.

Rules permit a driver to use no more than five complete power units and their constituent components over the course of a season.

Running the upgraded power unit will result in Alonso taking on new variants of five of the six components that comprise it, which will cost the Spaniard 30 places on the 22-car Sepang grid.

The double world champion took a similarly hefty engine-related penalty in last month's Belgian Grand Prix at the Spa-Francorchamps circuit, where he also exceeded his permitted allocation of power unit parts.

"We knew these penalties would come," said Alonso, who lost some of his allocation of power units to reliability issues earlier in the season.

"One of the best places was Spa because of the conditions of our engines at that point. The second best was maybe Malaysia because the weather could play a big factor in the race..."

Honda, engine suppliers to the Woking-based McLaren squad, have made steady progress after a difficult renewal of their once-dominant partnership last season.

The upgrade they have brought to Malaysia this weekend is the latest in a spate of enhancements they have been making to the engine over the course of the year.

The latest change features a lighter engine block and a redesigned exhaust aimed at boosting the power unit's efficiency, a Honda spokesperson said.

Alonso will run it during Friday's opening practice session, with Honda deciding whether to leave it in the car for the second 90-minute session in the afternoon.

They will revert to their old-specification power unit for Saturday's qualifying and the race.

Alonso finished seventh in Belgium, despite having started dead last, and is targeting another points finish on Sunday.

"That's the target for both cars," he said. "Even if I start last then hopefully we can recover places quite soon."

The 35-year-old, who took his first pole position in Malaysia and has won the race three times, is 11th in the drivers' standings.

Team mate Jenson Button, celebrating his 300th grand prix start this weekend is 19 points adrift in 15th.

(Editing by Amlan Chakraborty)