Ted Eaton asked me to post the details of our recent discussions, regarding two of his articles, as well as my questions, regarding piston valve reliefs and metric rings.

While comparing the dyno sheets of two of Ted's engines/w very similar specs, I noticed that the "HP to the Cubic Inch" engine made 45.9 hp and 29.9 lb/ft more than the "Modified" engine. I asked Ted to explain why. Ted replied that the "HP" engine used metric rings. "I typically see 25-30 hp increase, when using metric rings." He also stated that the "HP" engine's static compression was 9.57:1 vs 8.75:1 for the "Modified" engine. When asked about oil consumption, ted replied, "No oil consumption or smoking issues with metric rings, but cylinder wall finish is critical. Modern technology requires modern machine work."

Regarding the need for piston valve reliefs, Ted replied, "You are generally safe up to 0.535" lift." "Changing lobe centerline or advancing/retarding cam can change valve/piston clearance." Bore size typically not a player, but notching cylinder edges when lift goes past 0.535 for iron heads, and for unshrouding intake valves on aluminum heads. 
Ted expects members, who have had experience with these issues, to chime in.