OSM18750OS OS Engines MAX 105HZ-R without silencerNitro Helicopter Engine, 1. 05 Size w o Silencer Product Information The biggest, pure helicopter engine that OS have ever made delivers the levels of torque and power demanded by top fliers for both '3D' and sports applications. The 15% increase in capacity offers a big increase over the . 91 class engines yet still fits in mounts designed for that class. Modification to the cooling shroud is also unlikely. The distinctive 'blue anodised' cylinder