Why are 318's low HP and torque?

Be careful as there is not alot of room for high lift cams in stock 318 heads. We use this cam with 600 cfm, Ed performer, headers and electronic ignition. http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=625&sb=2

Their program says 300hp 360tq. We did cut down the guides and put positive seals on our 302's, this went in our 92 truck no computer control.