So how much will a Trick Flow cylinder head change effect performance? Can't tell you that yet. But we are beginning to get feedback on changing from a OOTB RPM head to a ported RPM head.
On a RPM head/RPM intake to a ported 2.14/1.81 RPM head and a Victor intake that went from 266 cfm @ .500" lift to 295 cfm and from 278 cfm @ .600" lift to 314 cfm, That car went from 11.75 ET to 11.07.
A 4000# B-body with OOTB RPM heads, a RPM manifold and a 511 B-engine, went to a 440 using the same cam, same compression, ported 2.14/1.81 RPM heads and ported RPM manifold, completely skipped the 12's and went from 13.05 to 11.80.
These Trick Flow heads are going to be as good.......as long as you are able to build an engine that can support them.