O.S Engines OS91HZ 91HZ Engine
[OS91HZ]

The next champion in F3C competition!

With back-to-back FAI world championships in 2005 and 2007, the 91SZ-H was a winner by anyone's standards. Now there's the 91HZ – a 91SZ-H redesigned with the help and advice of the world's top pilots. It offers the tuning ease and performance consistency of the multi-time world champion and design innovations that promote improved cooling, a tighter compression seal – and tuning ease!

• The narrow profile of the heat sink head helps the 91HZ fit completely inside cooling shrouds without cutting or losing cooling power!
• Two heat sinks – one on the head, another on the crankcase – allow airflow to carry away heat and maintain performance.
• Better overall balance reduces engine noise and promotes smoother, stronger performance.
• The new 61B carb takes consistency to the next level. Dependability features start with an insulating ring which prevents crankcase heat from affecting carb settings. A generous use of O-ring seals – two on the main needle, one on the rotor – prevents air leaks and power fluctuations.
• In-flight control of the needle valve ensures smooth, consistent runs.

Five holes in the top of the lightweight piston route gases to the piston ring from within, resulting in a tighter seal and minimum blow-by. This effectively transfers more combustion energy to the crankshaft and produces more power than ever before.

There's no need to fabricate an arm to make in-flight needle adjustments – the 91HZ already includes one. Just install for an easy way to enjoy more tuning flexibility in-flight!

A heat sink machined into the end of the crankcase increases cooling and improves performance.