91HZ  | Specification:
- Displacement : 0.912 cu in (14.95 cc)
- Bore: 1.091 in (27.7 mm)
- Stroke: 0.976 in (24.8 mm)
- Practical R.P.M: 2,000-16,000
- Output: 3.4 hp @ 15,000 rpm
- Weight: 21.8 oz (618 g)
- Includes: 61B carburetor, muffler, in-flight needle valve adjustment arm & #8 glow plug | 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.
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 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. |
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