So True, Bob.  One reason while I may  be panting in anticipation (I will not be holding my breath {:>)).  Interesting, I had always thought the 12A had long preceded the 13B so far as used in Mazda vehicles. 

 

Ed.

The first engines were the 10As. Many had three holes for an exhaust port. Wide spread in Australia

and still many running around. The 12A was the same thing but 10MM wider rotors. 

 

The early 10As and 12As from the 70s had a smaller bell housing and a top mounted starter. A big heavy sucker.

The apex seals were solid carbon pieces. The irons had the same case bolt pattern, with 2 extra bolts.

 

Later 12As had the larger bellhousing bolt pattern of the modern engine. The RX-4 and pickup truck had

13Bs, with the larger (modern) bellhousing, but I don't know what year that was. The 13B is the same thing but with 10MM wider rotors.

 

12A, 13B and probably 10A irons can be interchanged for various advantages. The rear iron determines the mounting bolt pattern (bellhousing). In the 80s case "O" rings were moved to the irons, but are now back in the rotor housings in the Renesis engine.

 

Renesis rotors (10:1 compression) can be run in a 13B by machining the apex seal grooves to accept the 13B apex seals. The taller apex seal is required to maintain its shape over the exhaust port.

 

The 16X will go back to the 12A rotor width, but have more stroke.

 

I am not in favor of supporting the entire engine and reduction by holding onto the front cover. The engines are not very stiff. Early engines were mounted by holding onto the front cover and the tail end of the transmission. When stressed the front cover will crack through the mounting stud holes. Later engines have the mounts bolted to the center iron, so that the engine is not in bending. Very high output engines have a thick plate bolted on in place of the oil pan rail, to help keep the engine from changing shape.

 

In the very fast National Champion RX-7 from years ago, the builder had added center iron mounts where none existed. He said it made more power, with less engine flex. Since his car was the fastest in the US for several years, I started believing him.

 

High boost engines use added alignment dowels along each case bolt on the combustion side of the engine. This to keep the rotor housing from flexing with each combustion event, and to add shear strength to the stack so that the two stock dowels will not shear off, or break out their holes in the rear iron. The rest of the bolts are oversized in thickness and fitted in reamed holes to add stiffness.

 

All of this is to keep 600 to 1,000 HP turbo engines alive and well. At a mear 200 HP or less, nothing at all is required.

 

But the flat plate on the pan rail mounting system is good news anyway. Tech Welding and the Cozy Girls have very nice mounting plates and engine mounts.

 

 

Lynn E. Hanover