Yeah some custom $$$ machine work on the rotating assembly. Always thought the poly heads were interesting. Those were ported to 275 cfm and put on an LA block. 550hp at a conservative 30 degrees timing on pump gas, 600 on race fuel. Shows that head cfm rating is not the end all be all of what goes on inside an engine. Wonder how they would do on a 408 or 390 shortblock. People struggle to get those numbers with the latest and greatest, moved pushrod, offset rocker gear, ported, big $$ heads out there, and the company that specializes in splayed valve heads(Trick Flow) just introduced another "SR" la replacement head.:BangHead: