IMHO, you need to prove and or improve the cylinder pressure. I run a proven 185psi on 87 octane with al. heads, with a Hughes 230*/.050 cam. I have run other cams from 223*/.050 to the MP292/509( around 239*/.050). As I changed duration or retimed them the pressure always moved around. Pressures below 140psi were always soft on the bottom.Over 200psi I had to run premium fuel.160 to 185 worked for me. I know this doesnt answer your question but I thought it was worth mentioning. Hope it helps. AJ
