What is the biggest cam i can go with on stock unported heads?

 

Bigger is not the answer. The choice depends on several factors.

Pick up this months Chevy Hi Performance on the news stands now to help answer that question.

http://chevyhiperformance.com/toc/ch_toc/
You'll see the header for the article your looking for at the top on the cover photo and on the left in the list of articles under Tech.