What is the difference between "early 13B" and  "late(??) 13B"?

 

 

The early 13Bs had the compression and water seals in the rotor housing just like the 12As.

 

Later this was changed to the seal grooves being cut into the irons, and the sides of the rotor housings being flat. The irons often break through the bottom of the seal groove when run too hot. There is not enough material (cast iron) around the outside of that groove.

 

When left sitting for ages, they can even rust through that groove and fail sitting still.

 

The Renesis  engine has the grooves in the rotor housings again, where God intended them to be all along. 

 

There are a number of options, where you can mix and match irons and housings to achieve differing outcomes. For example a 12A center iron to get the biggest primary ports and turbo end irons to get the biggest secondary ports. So, you could run two throttle bodies, and at lower power and on the ground have a docile quiet tame engine, and at full song with two throttle bodies have the end irons bridge ported and doing over 200 HP when flat out.

 

Race engines have all irons bridge ported because there is no need for full power below 7,000 RPM. 

 

You cannot build up anything with no seals but you can run two seals facing each other. Racers do it anyway with no problems. I would dyno that one a lot before installing it in a

plane.

 

Lynn E. Hanover