RE: Max RPM's for a fully mod'ed Zen??
Yup, as an advanced tuner of zenoahs, Full mod engines when propped right and pipe length set right should run under load @ 16,500 to 17,500 RPM.
Most mod engines have a HP & Torque peak at @ 15 - 16K, but will slightly over rev at high hull speeds too @ rpm posted above.