The amount of syrup you need will depend on the passionfruit flavour.
Tropical fruits are generally more tart than temperate kinds.
Add cold water or soda water, serve in long glasses garnished with a slice of orange. Serve in a punch bowl with plenty of ice, slices of lemon, pineapple pieces and sprigs of mint. Leave covered for an hour or so to allow flavours to develop. Add chilled ginger ale just before serving. Make about 30 punch glasses.