One of the 64 heads started leaking coolant, that is when Hand made the switch to the 6x-4s. Rocky Rotella showed me that particular heads and let me look it over. Very nice looking port work, shouldn’t have been close to hitting a coolant passage. IRC it flowed just over 250 cfm @28” on the intake and slightly over 200 on the exh. The 64s are fairly well known to have smaller port volumes against other d ports, might explain why he had trouble.
I think Hand gained a fair amount of performance with the 6x-4 combo, almost 20 cfm on both the intake and the exhaust. 260 something on the intake and 220s over on the exhaust. There is a lot of flow potential on a 6x if you put in the work. IMHO they are a great head as cast though too, not unusual to see them out flow some of the older heads as cast. I tested one very early 6x-4 from a 76’ 350 that nearly made it to 220 cfm. Upper teens anyway, most of the older d ports I have tested barely made 200-210.
Last edited by Jay S; 10-16-2021 at 07:24 PM.
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