That’s closer than a lot of stuff I see.
If I tested a head that was advertised at 350, and it was 342 on my bench...... I’d call that pretty close.
I figure if nothing else, it’s a different radius plate being used.
I had a CNC ported head here that flowed about 50cfm less than advertised.
Yet, I’ve tested other cnc ported heads from that same supplier that flowed very close to the advertised numbers.
However, overall I see what I consider are fairly noteworthy differences often enough so that if I really want to know how it compares to other stuff I’ve tested....... I know I’m going to have to test it myself.