The Cup racer manual cambelt procedure does not specify slackening of the cam pulleys. I have all 3 of the Renault timing tools and timed my cup racer motor up as per Fred, the timing was correct as you would expect. But last night I did the cambelt on my 172 cup and decided to see if it could be done without slackening of the pulleys as per the Cup racer manual.
Locked the crank and cams off, replaced the belt and re-tensioned, marked the cam pulleys and removed the locking tools, rotated the motor 5-6 times clockwise. Refitted the crank locking pin, checked the marks I had made on the cam pulleys and they all line up, checked the tensioner marks still lined up, refitted the cam locking tool with a light tap from a rubber mallet. So everything still lined up and the belt was still correctly tensioned.
Whether I was just lucky i dont know but why does the racer manual not specify slackening of the pulleys? I think if the cam pulleys have not been touched since they car left the factory then there shouldnt be a reason to slacken the pulleys aslong as you are using a genuine belt.