In the FMT, a german leading magazine, they did a comparison of a few smaller gassers.
For the ZDZ 40 with a tuned muffler they got:
18*8 9000
18*10 8100
18*12 7500
19*12 6900
20*10 6400
20*12 5600
21*10 5200

These number seems to be comparable to mine.
The RCS website claims 7400 on a 20*10
and the Amelung (German distributer) site claims 6900 on a 22*10
These are totally different numbers .