Friday, January 21, 2022
Home » Product Reviews » O.S. Engines 55HZ-R

O.S. Engines 55HZ-R

Supercharge Your 50-Size Heli

The HZ-R shares the exact same specs as the popular 55HZ-H but adds the OS Demand Regulator System (DRS) at the fuel inlet to supply fuel based upon the engine RPM. The DRS uses crankcase pressure coupled with a check valve to pressurize the fuel supply creating a high-pressure system that provides constant supply of fuel, unlike like fuel systems that utilize muffler pressure that change as the tank drains.

The 55HZ-R will drop in to any of today’s popular 50-size helicopters while using the same mounting holes as any conventional 50-size helicopter engine. The fit and finish of O.S. engines has always impressed me but the new helicopter engines take this to the next level with beautifully machined and anodized heads with attractive laser engraved graphics.

To test the engine I used a Hatori SAB- 55 muffler that has been specifically designed to maximize torque and power in the new larger-displacement engines and installed it in the new JR Vibe NEX (see the review in this issue). I used Byron Fuels Rotor Rage 30% Nitro Masters Blend.


I followed the O.S. break-in procedure first, fully closing the needle valves and then opening them to the prescribed two turns for the main needle and one turn for the mid-range needle. Excited to bring this engine to life, I fueled up my heli and went through my pre-flight checklist one more time to ensure everything was properly connected, that all controls were working in their proper directions and in particular, that the throttle was indeed at low throttle at low stick and full at high stick and that I could completely close the carb using the throttle trim lever on my transmitter. Once confirmed, I toggled throttle hold on then off to trigger my SwitchGlo igniter and applied the starter. After a few seconds, the engine started to fire but needed a bit more throttle trim to make it idle smoothly and consistently. On the next try, it fired right up and was ready for flight.

I lifted off into hover and confirmed a nice rich condition, plenty of thick smoke and the occasional drop of oil from the muffler. After hovering for a brief period, I hit throttle hold, landed and checked the engine temperature with my infrared thermometer. I confirmed that the engine was indeed running rich and that it was getting warm, but not hot. The goal for the breakin process is to generate some heat to properly condition the piston ring and sleeve and to allow all other working parts to mate together. Running rich ensures that plenty of oil and fuel are running through the engine, keeping the reasonable temperature with plenty of lubrication. I found that the factory-suggested setting for break-in was perfect. I ran another five tanks through the engine, leaning it just a few clicks with each tank as I approached a more optimum needle setting.


Throughout the break-in process, the engine ran flawlessly. I had no reason to touch the idle mixture and I was now ready to tune the high and mid-range needles. To tune the high-speed needle, I start by flying in fast forward flight at full throttle and note the smoke trail and performance during pull ups and loops. If the smoke gets thin or the engine sags, I’ll richen the mixture, if the engine bogs with thick smoke, then it’s too rich and I’ll lean the mixture. I land frequently during this tuning to ensure that the motor is not getting too hot which would indicate a lean condition. Once I am satisfied with the high end, I’ll tune the mid-range by doing a series of tic-tocs. If the smoke gets thin, the engine sags or the engine over-speeds when I stop pushing the heli, I’ll richen the midrange, if it takes a long time to recover or it loses head speed, then I’ll lean out the mid-range.

The 55HZ-R was very easy to tune, taking less than a tank to find a happy location for the high and mid-range needle valves. After many flights, I know I am still not at peak performance yet. I choose to take a very conservative approach to tuning a new engine. However, the 55HZ-R is definitely delivering plenty of power. Over the next few weeks, I’ll lean it out a few more clicks and in time I’ll be able to enjoy the maximum power this engine can deliver.

It was very encouraging to know that even with the slightly rich mixture, the 55HZ-R was delivering huge power and consistent performance in all attitudes. The 55HZ-R did not care what the fuel level in the tank was, It didn’t matter whether I was cranking along in a backward inverted hurricane or in sustained tic-tocs, the motor was equally happy at the beginning of the tank right through the end of the tank.


DISPLACEMENT: .55 (8.93 cc)

BORE: .91 in. (23mm)

STROKE: .85 in. (21.5mm)

PRACTICAL RPM: 2,000 – 20,000

POWER OUTPUT: 2.1 hp @ 17,000rpm

WEIGHT: 15.13 oz. (429g)

FUEL: Byron Fuels Rotor Rage 30% Nitro Masters Blend

Author’s Opinion: Developed for demanding 3D flight, the O.S. 55HZ-R borrows technology from its 90-size big brother offering consistent full-power from a full tank to fumes. So, if you’re tired of tuning rich for the first half of your tank so your engine will run properly during the second half, the new O.S. 55HZ-R will adjust your tuning methods and your attitude, suddenly you’ll find you’re an optimist. That half-empty tank is now half-full as you push the limits all tank long.


Because the 55HZ-R’s performance was so consistent throughout each flight, I’ll leave you with just one word of caution, “fuel.” Be careful that you don’t run out! With the Demand Regulator System (DRS) your engine will not warn you by going lean when your supply is running low; it will now run full bore until it sucks the last drop out of the tank. You don’t need to ask me how I know this, just smile and tell me how much you like my new rotor blades. When you buy your O.S. 55HZ-R, remember this; low to the ground in a high-speed maneuver with lots of cyclic and collective input is a bad time to run out of fuel.


Hatori USA, (716) 297-3295

O.S. Engines, distributed exclusively by Great Planes Model Distributors, (800) 682-8948

SwitchGlo, (818) 709-0268