Sorry for the dumb question. I've looked and looked but nothing.

Which holes are are primary and secondary on 12a intake manifold. The center holes or outside holes. Also what is the rectangular hole in the middle for?

 

Center holes are primary and on the SA 12A that center hole is for the exhaust manifold which allows hot exhaust gas to heat it up to help burn off pollution. Usually needs to be plugged or covered when using an aftermarket intake.

 

the rectangular port takes the air pump air to the exhaust ports, Mazda calls it 'Port Air' its kind of like an EGR in reverse, its adding fresh air to the end of the exhaust stroke. makes it run better, and cuts emissions very drastically

 

Ah, so I had it backwards. My bad.

 

Thanks a lot. Picked up a spare 12a to rebuild. Guy said it just got harder and harder to start. Apex seals look good from what I can see in the exhaust ports.