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Message: <blockquote data-quote="96blak54" data-source="post: 1543839" data-attributes="member: 14727">The positives i see are brand new castings, bronze valve guides, and the promise of excellent machine work.Id be curious to know if that casting is as good or better than Ford. The bronze guide is the way to go if you want to run the engine on the edge.A stock head can run a 1.840" intake valve on the original seat. Again im curious if the bigger valve gets a bigger seat, because the original seat material gets a bit skimpy for the big valve.Surely the sparkplug holes are revised 9thread! I didnt see that info, could have missed it, but it be dumb not to be 9threads.Looks like they are honest with flowbench numbers. 219cfm at .500lift for the cnc ported version and big valves is very conservative especially for $1050 per head for the bigger valve version. I remember inflated flowbench numbers wayback when 2v modulars were hot and companies competed for your dollars. Promises of great potential with their product only to discover minimal hp gains over stock. The money spent didnt justify the hp gain. Honestly alot of that still holds truth today with these modulars. Especially with them FB hero's.If you had a newer set(05-11) of stock pi heads that are in excellent shape, took them to a machine shop, had them prepared like the heads from promax, you would be out roughly the same amount of money. Keep in mind that pi head ports are known to stall after .500 lift and if you take note of there own flowbench numbers you notice only a 15cfm improvement for more lift and a bigger valve.I can see the stock version being worth the money. Not so much for the bigger valve vesrion</blockquote>