I remember seeing a website that dynoed and tested a 20B. Whe it was done they stated the the compression was 12.4:1. Is that correct and would yo be able to put those rotors into 13B housings and build up a functional motor. I can't remember the website though. Just a thought.

 

That seems pretty unlikely. The only way that would be possible is with custom made rotors. Rarely anyone makes custom rotors because there is usually no need to do it, and it costs thousands of dollars to do so.

However, if you did get a hold of that set of rotors, then yes, they would swap directly into a 13B.

 

Do a SEARCH in the 20B forum...