O.S. Engine 91RZ-H DH Ringed Piston Rear Exhaust Helicopter Engine  [OSMG1979]

Scale-Focused Power: O.S. Engine 91RZ-H DH Overview

Model helicopter builders who aim for accurate looks and consistent performance will appreciate the O.S. Engine 91RZ-H DH. The rear-exhaust architecture keeps exhaust runs low-profile so canopies retain true scale contours.

Performance Specs and Tuning Notes

The 91RZ-H DH offers 0.91 cubic inches of displacement and produces about 3.3 hp at 15,000 rpm, with a practical operating range from 2,000 up to 16,000 RPM. New intake porting and a modified crankcase contribute to steady combustion and smoother throttle transitions.

Two Heat Sink Heads for Different Setups

Pilots can pick either the larger blue anodized head for aggressive cooling or the smaller squared die-cast head for confined installations. The choice helps match cooling capacity to flying conditions and canopy space.

Designed to Fit Inside Scale Canopies

The rear-exhaust layout means the muffler and pipework are tucked away, preserving the silhouette of scale helicopter fuselages while keeping exhaust flow efficient.

For scale modelers who want a neat installation and reliable midrange response, the O.S. Engine 91RZ-H DH offers a practical balance of fitting options and tuned internals.