Making power out of the 318

66fs said

Or you could run 273 heads or 302 heads and port without the extra steps. But I still like 360 heads better for the air flow.

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Yes you could but how available are 273 heads and how much valve can you put in them?
Port flow volume is just part of the picture. Flow velocity is also important and where in the port you get that velocity. Flow volume and flow rate combine to generate port energy. This is the important number.