Polini Thor 303

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SKU: thor303

Polini Thor 303



Polini Motori presents the new Thor 303, a concentration of power and technology.

An innovative engine with important novelties that result into reliability, power. Reduced weights, reduced aerodynamic section and moderated depth.


It is the Polini engine of the THOR family with the largest displacement and comes with a completely redesigned thermal unit, crankshaft, carburetor, air box, CDI and exhaust system to ensure greater performance and safety in flight.

With its 38 horsepower at 8000 RPM the THOR 303 is capable of offering over 120 kg of static thrust with a 160 cm * propeller .

The consumption is only 3 liters per hour at 4500 rpm , which corresponds to about 30 kg of static thrust , the mean value of level flight.

The THOR 303 is available in three versions :

  • THOR 303 with manual “flash starter”
  • THOR 303 with both electric and manual “flash starter”
  • THOR 303 Dual Spark

The Dual Spark version is designed to meet the highest aviation safety standards . It is supplied with electric and manual “flash starter” and is equipped with 2 CDI and 2 totally independent and redundant ignitions .

Flight safety
The THOR 303 is the result of three years of work, design and testing in the modern Polini test benches and in flight with our national and international professional pilots. An accurate work that continues even in the moment of production, when every single engine is subjected to careful testing and verification in all its parts before being delivered to the customer .

The thermal unit
The cylinder was designed and built specifically for aeronautical use, using the best modern technologies. The actual displacement stands at 281 cubic centimeters with a 76mm bore and 62mm stroke .
The cylinder is equipped with 5 intake ports to ensure precise and stable performance at all rotation speeds, promising a fluid and powerful delivery capable of offering over 120 kg of static thrust with a 160 cm propeller *.
The head is designed with a special combustion chamber that speeds up the flame front.

The muffler
From the experience gained over the years with 2-stroke engines, the new exhaust system has been designed , designed to enhance performance and at the same time ensure low noise . Compact and light, it is the subject of extensive testing and research to find the perfect combination of expansion and gas flows. The result is a muffler that ensures stable and progressive delivery at all revs . The suspension fixing and the spherical joint system guarantee freedom of movement and at the same time eliminate any type of vibration, guaranteeing the duration of the drain over time .

The carburettor
The Polini THOR 303 is equipped with the Orto VHST 28 mm carburettor .
The carburettor technology makes the engine much less sensitive to changes in atmospheric pressure, humidity and altitude, ensuring greater stability and minimizing any setting interventions. This carburetor can be equipped with the Polini starter control, essential for starting the engine in total safety .
Thanks to all these advantages, combined with various setting possibilities, the Orto carburetor perfectly meets the needs of all pilots , thanks to the very high precision, fluidity and power delivery.
For transport: the carburetor is equipped with a special valve that allows all the fuel contained inside to be drained, also allowing a horizontal position to prevent the petrol from escaping from the vents.

Air box
The THOR 303 is equipped with an air box born from an in-depth fluid-dynamic study with the aim of optimizing the speed of the air inside it to guarantee the ideal pressure to feed the carburetor at every rotation speed. By reproducing an S-shaped circuit that stabilizes turbulence, the new air box allows for linear, smooth and constant delivery . Completely openable and inspectable, inside there is a support frame for the new 30 PPI (pores per inch) open cell polyurethane foam filter mat : this support frame is designed to have a fastening capable of preventing over time the mat to move or collapse on itself.
Furthermore, thefilter box that can be opened in two halves with just two screws, making it easy to replace during routine maintenance .

Cooling system and water pump
In THOR 303 the cooling is ensured by a compact radiator of 18 elements by the size of only 355X200 mm equipped with an expansion tank provided with valve cap with 1.4 bar, which allows the system to self-l expansion of the liquid inside without burdening the other components
The circulation of the liquid is entrusted to a specific 30 mm mechanical pump housed on the countershaft. This system allows to keep the temperatures of the thermal unit always under control even in heavy applications, allowing the engine to be used for a long time and under stress without overheating. With a view to greater attention to design, pre-shaped tubes in blue silicone customized “Polini THOR” have been chosen , which guarantee greater durability over time.
As standard, for greater safety, the engine is equipped with a thermostat, which prevents the liquid temperature from dropping below 60 °.

Reed valve
The engine is equipped with a reed valve with direct entry into the crankcase . The reed valve pack, expressly designed by the Polini R&D department, is designed to maximize performance. This result is obtained thanks to the use of 6 carbon fiber blades with calibrated elasticity to react uniformly to all speeds .

Motor casing
The casings of the THOR 303 are made of die-cast aluminum with a high silicon content . Thanks to this alloy and to the production process controlled during all phases (foundry, painting, mechanical processing on sophisticated CNC machines) , stable, long-lasting mechanical performance and low weight are achieved . The crankcase design has been optimized to be essential and reinforced in the points of greatest stress.

Motor shaft
The choice of the best steels and heat treatments , combined with perfect centering , eliminates parasitic vibrations due to imbalances which over time could lead to premature wear or failures. Thanks to the use of numerical control machines and latest generation measuring instruments, the sizing is maintained within predetermined tolerances with maximum precision . The whole is completed by high quality bearings positioned on the connecting rod and in the crankcase .

Countershaft, reduction gear and clutch
In the front half casing there are the housing of the centrifugal clutch system , the mechanical reduction and the balancing countershaft , all in an oil bath .

The centrifugal clutch allows the propeller to remain immobile when the engine is at idle speed and to maximize the safety of the pilot in the pre-flight phases.
The new THOR 303 is equipped with two different reductions for the propellers : 2.8 (recommended for props up to 140 cm) and 3.2 (for props over 140 cm) . The reduction is mechanical with helical teeth. This system reverses the direction of rotation of the propeller with respect to the rotation of the crankshaft, significantly reducing the overturning torque.
The balance shaft reduces vibration deriving from the imbalance generated by the oscillation of the piston which, passing from the lower dead center to the upper one, moves its mass at each rotation cycle of the engine, thus ensuring maximum flight comfort.

Electronic ignition
The ignition is electronic of the capacitive type , governed by a CDI unit expressly designed for the THOR 303 engine . The CDI unit allows you to automatically adjust the degrees of advance of the engine according to the rotation speed, allowing an easy and smooth start and a delivery that is always prompt and linear.

Flash starter
The THOR 303 is equipped with the most updated version of the renowned flash starter , a system that guarantees immediate and simplified starting of the engine.
In the latest version, critical points have been reinforced and centering has been improved, improving their operability and guaranteeing a longer operating life. In addition, an ergonomic handle allows a safer and more stable grip during the ignition phase.

THOR 303 Dual Spark
This version uses two completely independent electronic ignition systems , managed by 2 CDI, 2 stators, 2 coils and 2 completely redundant and independent spark plugs, ensuring better performance and greater safety during use .
The standard capacitive electronic ignition is combined with a second ignition that reads the signal through a dedicated pick-up and sends it to the secondary CDI, which controls the secondary coil and spark plug.

Fixing system
Polini Motori has decided to keep the same fixing system on the whole range of THOR crash bars . Manufacturers can thus produce a frame that can accommodate the entire range , significantly reducing both production costs and delivery times .
Riders can change the THOR model without having to replace or modify the chassis.
Like the whole THOR range, the THOR 303 is also sold complete with all its parts, completely assembled and ready to be installed on the frame with extreme simplicity.. Even in the versions with electric or DS start, the engine comes equipped with electrical wiring and plug and play battery as standard.

Given the high power, the THOR 303 finds its maximum expression on single and two-seater trike, delta trike, three-axle single-seater and UAV (Unmanned aerial vehicle) .
As for the use in a single-seat paramotor, it is recommended for experienced pilots and is unparalleled in slalom race

Additional information

Weight 70 lbs
Dimensions 14 × 27 × 19 in

2.8, 3.2

Start Type



Dual Spark, Single Spark

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