On 12As that little opening leads to a vertical gallery down to a passage that is open in both directions to similar galleries in the rotor housings. That allows air from the air pump to enter the hollow bolts (two in each rotor housing) to blow air into the exhaust stream that assures complete burning of any excess fuel that might have escaped

from the engine. These bolts pass through the stainless liners and stick up into the exhaust stream to no good help. In racing these hollow bolts are removed and replaced with solid aluminum bolts of same shape.

(from Racing Beat). Or you can cut the stock bolts down to match the liner and TIG the ends shut. So, at least on early engines that passage does nothing for racing or airplane use, but those holes must be plugged otherwise there is a path from outside the engine to inside the engine. If there is no air pump on the year you have, the opening may be vestigial and go nowhere. After market manifolds just have a land area that covers the hole. So, you could plate over it. Or fill it with epoxy.

 

It is common of Mazda and others to leave features on parts and pieces for years that are no longer used. Such as the shape and land area for the top mounted starter that most people have never even seen.

 

The builder may have plugged those holes, or the holes may not exist in 13B stuff. Just look into the exhaust ports.

 

Lynn E. Hanover

 

 

Joe,

 Mark is correct...............Do not recall if it is for EGR (exhaust gas recirculation) or intake manifold heat...........Definitely needs to be blocked off and

for our aircraft use ideally the opening in the exhaust insert  could be welded shut or otherwise closed off..............IMHO...............Lynn what say

you on this matter
 ??.....................

 

Kelly Troyer