3 per week and 1 bonus as available in each unlocked group.
Each engram group is released to be unlocked with each week of the program that passes. Meaning the first group is available to be unlocked during the first week, the second group is available to be unlocked the following week, etc.
Within each group, you may use (3) three can codes to unlock the first three engrams within the group. The fourth engram is a bonus that can be unlocked with a Rockstar Zero Carb Hunter edition.
Once you have unlocked all engrams from the available group, any additional entries during the same week, will not unlock anymore engrams, until the following week when the group is available.
However, EVERY CAN CODE ENTRY will give you additional entries for the Daily, Weekly, and Grand Prize entries.