what part of the rpm band will the 4 port exceed the 6 port in power output? both fully ported and assuming racing beat header and exhaust and idential intake and fuel delivery sytems?

 

very upper range due to the sheer size you can port the 4 port

 

seems like there is no range to work the motor in through the gears then unless you want to ride around in 2nd or 3rd gear at 8 K RPM?

 

The 6 port 12a motor did not make it to the states but did exist. Also there mazda use to have a bus that was powered by an old 13b. I'm pretty sure the only place you'll find those are in the museums if they still exist

 

The 6 port was created in an attempt to have more control in meeting the fuel economy and emissions regulations (in short). All the GSL SE 13B's were 6 port, and all were N/A. The 4 port can be just as "driveable" as a 6 port. That derives from your choice of intake configuration and tuning issues. IMHO the 4 port is better.