At what power level can i expect to see power plateau from lack of flow in the head?

What's the max power people have seen while using cams and valvetrain but with not other work on the head on an Evo 8 or 9?

 

Around 600ish whp.

 

+1

 

Actually, I recall some dyno data that shows the hp figures beginning to diverge as low as 250whp. Nevertheless, a port job that improves flow at all valve lifts and maintains decent port velocity will outpower a stock head 10 times out of 10, regardless of turbo size and just about everything else.

 

^ + 1,000,000,000,000

hell, a good valve job on a stock unported cyl. head will improve the flow throughout the lift range = more power!

 

The stock head its pretty good ...but like Ted B said a port flow does help a lot.
Cheers.