ORIGINAL: Mr Cajun Gator
Zenoahs are very good engines, for less of a cost, the CY engine is the engine of my choice. The CY is basically the same as the zenoah, except the CY out of the box has more HP. The ports are cut larger at the factory, it is easily upgraded.
This is not correct. For identical displacement, the Zenoah makes more power in each case.
The Zenoah G230RC outperforms the Chung Yang CY23RC.
The Zenoah G260RC and G270RC (same displacement with 4-bolt head) outperform the Chung Yang CY26RC.
Chung Yang does offer: a 26.9cc engine - the CY27RC; a 28.5cc engine - the GP290, and a 28.9cc engine - the CY29RC. Zenoah does not currently offer any stock motors of these displacements (which have bores of either 35mm or 36mm), as the largest stock Zenoah bore is 34mm.
All else equal, however, a Zenoah will outperform and outlast a CY by a substantial margin.
I've sold more than ten thousand CY and Zenoah engines, so I have plenty of real-world data and experience on this topic.