swirl port heads

Can somebody show the part of the port on one of these ''swirl port'' 308 heads that makes them swirl, and how it's different than all the other x,j,587,596, heads?

Also, can anybody show me the swirl inducing portion of the 302 int port and how it's different from the 675 318 heads?

It would be nice to know the info given has some proof to back it, thanks.