The Amelung Modellbau website used to state that the ZDZ rpm/prop numbers were derived from engines using tuned pipes set at full length - not optimized (shortened) for max power. Since they don't sell or use in-cowl mufflers in Europe, it doesn't really make any sense for them to quote power figures with the kind of exhausts we use in the US. Still, most users are able to duplicate their results using the J&A mufflers. On the other hand, RCShowcase could provide more info on their website for the in-cowl mufflers (a wider selection of prop numbers). Since Imac is driving us towards the European noise standards, the European style pipes and tuned cans are likely to become much more popular in the US.

Here's some more data from Topmodel. Click on pricelist, ZDZ, specs, then click on performance propeller chart.

http://www.topmodel.fr/cat/a_catalog_frame.htm