I've been building and tuning some of the worlds most powerful true street rotaries for 20+ years ......... I've never really had this "issue" personally nor seen on engines running in the upper stratosphere of power I am used to obtaining that have been tuned and set up correctly
(eg, non BDC or HC tuned or built lol).
It must be more of a thing seen by people who have poor cooling systems? or *stupid* AFR settings the would over heat any engine (even at far less power).
Put in a decent radiator
Do proper exhaust shielding
Keep water temperature at 77~78deg C
Use AFR of 10.8:1 @ full load
Use water injection
Use Mazda Factory 2mm apex seals
You wont have any of these "problems"
However, I have seen these marks with brand new rotor housings using inferior after market apex seals and springs (to stock) on a few engines built by experts that I have had here after only completing run in of 600miles! (engines never been boosted or seen over 5000rpm) and power levels less than 150bhp....... much more from the apex seal not staying in contact with the rotor housing than anything to do with heat or distortion of the housing.
I 100% agree with Libor, get a handle on your coolant temp and you wont have these issues, in my experience, also use stock Mazda 2mm apex seals as they are most compatible with rotor housings and actually seal far better on the rotor housing in this area especially.
