Also, stupid question but when you scribe lines outside the ports, how do you determine placement? Do you go by the port size of the heads? Putting a gasket down seems pretty arbitrary and inconsistent from side to side and even front to back.
You hit the nail on the head regarding many manifolds, and in our experience particula
rily the performer rpm's, in that no matter when moved towards the front of the engine at least 2 ports are badly blocked at the rear opposite and towards the rear to then correct 2 ports at the front opposite seem to be way off..... if ever a manifold that needs severe correction from OOTB it would be the BB Mopar Eddy Performer rpm's in our experience anyways.
The way we port match is this
* we scribe vertical lines on the head identifying the center dividers and pinch sides of the ports
* we put the manifold on the engine/heads with Head Gskts and layers of tape to simulate the .020" thick valley pan and bolt it down.
* We then scribe along the top of the manifold putting lines on the Head landmarking the tops of the Ports
* We then landmark the Port center divider/pinch side side lines from the head onto the Intake to locate when the Port lines up.
* remove the Intake and scribe the Port verticals from above
* measure down from the top lines identifying where the top of the intake sat to the top of the Port on each pair of Ports and transpose onto the Intake to locate the port tops.
Takes awhile....
but it's the only way we've found to have accurate location of the Ports to Grind to ?