Just the area around the new carburettor is a little bigger and may require adjustmenst to the cooling shroud.

This entirely new engine shares almost nothing with the 50SX-H and has some new features not seen on an engine of this size before. The rear bearing is now designed to resist corrosion, the new 40L carburettor has three adjustments to cater for idle, mid range and full power. Until now, these features were the domain of .61 class engines or bigger. The throttle arm has four leaves so that push pull control is easy from any direction. The heatsink head is bigger for improved cooling as well.

For the first time, O.S is also offering a matching tuned muffler as an option part and has been optimised to extract the maximum performance from the 55HZ Hyper. Part number X-OS72144000.

Once set for the fuel demands of your model/type of fuel and muffler, there is rarely any need to change those settings again.

The main mechanics of the engine itself are the same as the regulat Max 55HZ.

A Thermo insulator is installed on the carburetor mounting spigot and helps shut out engine heat to the carburettor, which in turn ensures a stable fuel/air mixture.

The 91HZ-PS is equipped with a new, bigger capacity PD-08 pump and matched 61B-P carburettor plus integral regulator, which assures a consistent fuel supply irrespective of violent changes in model attitude.

Combined with O.S. pump system, internal parts improvements same as the 91HZ contribute to stable power output and smoother higher engine performance.

It is purely a matter of personal choice for the pilot. What other manufacturer gives you that level of choice in one engine size? Mechanically, the Max 91HZ-R is identical to the other engines in the Max 91HZ range.

Advanatges over 120 size heli engines of other makes:

1) Uses same main gear ratio as .91 class engines
2) Vibration levels the same as the 91HZ so does not tend to break heli parts.
3) Easy carburettor adjustment that stays in tune.
4) Crankcase is noticeably cooler
5) More torque in the mid range
6) Velocity stack on carburettor sucks cool, undisturbed air from the fan flow.
7) Longer run time per tank
8) 105HZ with 15% nitro is similar power to a 91HZ with 30% nitro.

General internal design is very similar to the 91HZ series and draws on OS's deep experience in creating the best helicopter engines for all classes.

Like the 91HZ-R 3D, the new 105HZ-R utilises the OS 'DRS' fuel delivery system to cope with the extreme manouevres of modern 3D flight.

Advanatges over 120 size heli engines of other makes:

1) Uses same main gear ratio as .91 class engines
2) Vibration levels the same as the 91HZ so does not tend to break heli parts.
3) Easy carburettor adjustment that stays in tune.
4) Crankcase is noticeably cooler
5) More torque in the mid range for 3D
6) Velocity stack on carburettor sucks cool, undisturbed air from the fan flow.
7) Longer run time per tank
8) 105HZ with 15% nitro is similar power to a 91HZ with 30% nitro.