My son is eating 8oz every 4 hours. after every feeding he cries because he is still hungry, would moving him up to 9oz be over doing it?

Signals: You don't mention the kids age or weight which is important for feeds. The average kid will take 1/2 his weight (lb) as ounces every 4 hrs. Just because he cries doesn't mean he needs more. Hunger only happens with an empty stomach. You are mixing signals. He may want attention or cuddling or be uncomfortable from bloating. I never feed an infant more than 8oz/4h.