Pitchcar is NOT compatible with Carabande. The track pieces will not snap together.
You could use the different games together if you jumped from the Carabande track to the Pitchcar track and then used the Pitchar jump to get back on the Carabande track. (phew)
If you have Pitchcar, buy the 'extension' pack.
If you have Carabande, buy the 'Action Set'.
I know that pitchcar and carabande are not compatible. But according to the Levalet site (the folks who are also the North American distributors of the game), the extension is not compatible with the first edition of pitchcar from Ferti. My inquiry is to whether Ferti actually did more than 1 edition of pitchcar because I do not believe they did.