Flow numbers DO mean a LOT!!!!
That's one set of data we have to compare one head to another.
Flow numbers give us at least some data to compare.
As far as intake -vs- exhaust, that is yet another variable that is open to interperetation, and can vary with type of induction & exhaust used.
Perhaps nearly as important as overall flow numbers, is having each port flow the same as the rest do. The home port job without a flow bench may yield ports that vary 1030% between like ports, meaning you may have one port flowing 300CFM and another flowing 270CFM. Try to get correct mixture distribution with that!!! Not gonna happen, never will run to full potential.
So having a set of flowed heads (& intake) is EXTREMELY important to extracting max performance by allowing equal mixture distribution and tuning to the edge without getting a lean & detonating cylinder.
Speaking of balancing the flow, a stockcar wrench I knew would use pingpong balls to shove into the primary header pipes to check for equal length - each pipe should hold the same number of balls.
Also, rust inside of the primaries can reduce diameter and flow enough to be measured on the dyno.
