There is no guarantee that you will purge.
I don't purge no matter what I drink; no Ayahuasca, rue (including raw seeds) or cactus (also including raw chips) takes me to that territory. That said, some brews are more physical or cleansing (possibly via the lower end) than others.
The type of vine used is also important here, not just the amount. E.g. caupuri is more physical / purgative than the tucunaca types (white, cielo,...).
Chali is also known to be a good cleanser. So even if your vine is not particularly purgative, your leaf may well be enough to trigger the purge.
I don't know your level of experience, but if it's not very high, I wouldn't worry that much about 'purgative' ratios, but rather aim for a 'standard' (and perhaps somewhat conservative - Chali has the reputation of being unforgiving) dose and see what happens.