So I hear people saying to really build a N/A engine you should get new hears. In the mag they advertise 165cc, 185cc,205cc.....I presume these are the size of the openings. What are some good heads? what do the sizes equate to as far as application? My long term goal is to S/c to about 500HP. I know about the bottom end, but not about the top end. any help would be appreciated. thanks