Depending on what you are calling a normal boa..... BCC females can get quite large up to 13 feet from what i undersand havent seen one that big, anyway bci (like columbian) boas usually stay under 10 feet most males usually not much more than 7. I talked with a nice guy that breeds central americans @ the phoenix reptile expo in november he said they rarly pushed over 6 ft but again i am not sure on this....