My .02, and keeping this strictly in terms of factory BBM iron heads........
Provided the port work in the runner is adequately sized to keep up with the addition of a bigger valve(and the SSR is shaped to help curtail flow separation with the bigger valve) ...... and that the throat percentage between the two valve sizes will be retained....... at something in the .700” lift range for a flat port head(346/902/452)....... I’ll call it a 5-10cfm gain going from a 2.08 to a 2.14.
With a 906, the gain will be similar but will often occur at a lower lift, then just flat line from there........ or might even lose a few cfm at the higher lifts.
This would be for what I would consider a “normal” porting job.
On a “max effort” head, the results could be way different.
On something like in the pic(this is a 346 head), a 2.08 would be low/mid-270’s....... a 2.14 would be low/mid-280’s.
For the lesser ported heads, and under .600” lift combos, the bigger valve doesn’t change the “big number” that much, but really improves the area under the curve.
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