To quench or no quench

The down side to the cnc heads in that particular application is, the low/mid-lift flow for those heads, as they come from SM, just isn’t very good.
Combine that with a cam that doesn’t have much lift, ports that are much bigger than factory heads, and a motor that isn’t very big...... and I don’t see how you’re ever going to generate enough velocity in the ports to get really effective cylinder filling.

Up thru .500 lift, it’s pretty easy to outflow the cnc SM heads with heads that have smaller runners.

Bowl blended J head vs ootb SM CNC:
Lift———J/SM
.100—— 67/63
.200——134/127
.300——190/167
.400——236/209
.450——250/228
.500——253/247

Which do think would be better on a 340 with a .470 lift [email protected] hyd cam?
Even if you were down 10cfm from those numbers in the .300-.500 range with the J head, it’s still a win.