The ZDZ50 (NOT the NG series) is a example of tuned port design.
If you study the intake/exhaust releationship -this is obvious.
When these engines were first released -I found that they ran like gangbusters- simply because I use a header and some kind of can (tuned or non tuned.)
Those who elected a restrictive in cowl setup did not get the design advantages of this engine.
Good power but not the high output it was capable of delivering.
The NG series use a different port/sleeve piston setup which flows in a different manner.
It is more tolerant of the restricted exhaust ( also has lower exhaust timing.)
Overall power on this setup is as good as anything I have seen in this size engine.
On correct tuned setup -it is really a treat.
On these engines (both series ) they respond better with larger cans .
Especially on larger prop loadings.
I see more people here using headers and cans/tuned stuff also.
this also goes for the other brands of engines.
Noise has really become an issue---