The Thor 303 is the highest displacement engine in the Polini Thor series. Its cylinder, crankshaft, carburetor, airbox, CDI, and exhaust system have all been completely redesigned to improve performance and in-flight safety.
Delivering 38 HP at 8000 RPM, the Thor 303 can generate up to 265 lbs of static thrust with a 63-inch propeller.
At a cruising RPM of 4500, it consumes just 0.8 gallons per hour, producing approximately 66 lbs of thrust in level flight.
Thor 303 with Manual Flash Starter
Thor 303 with Electric + Manual Flash Starter
Thor 303 Dual Spark (Dual Ignition)
The Dual Spark version meets top-tier aviation safety standards and comes with electric and manual starters, dual CDI units, and fully independent redundant ignitions.
The Thor 303 is the product of 3 years of development, including dyno bench testing and real-world flights by Polini’s team of professional pilots. Every engine is tested and inspected individually before delivery.
Displacement: 281 cc
Bore × Stroke: 2.99 × 2.44 inches (76 × 62 mm)
Static Thrust: 265 lbs with a 63-inch prop
Design: 5 transfer ports for high and balanced output across all RPM
Head: Optimized combustion chamber for faster flame front
Polini developed a lightweight, low-noise exhaust specifically for the Thor 303. Its compact expansion chamber improves performance across all RPM ranges. Mounted with a spherical joint, the muffler allows free movement and reduces vibration—extending durability.
Resistant to changes in altitude, humidity, and pressure
Stable fuel delivery across different climates
Includes a manual drain valve to empty fuel and prevent leakage
Optional Polini starter control for safe engine start
Allows precise tuning for smooth, powerful output
Fluid-dynamically optimized to stabilize airflow
Features an S-curve design to reduce turbulence
Uses polyurethane foam with 30 PPI (pores per inch)
Split-design allows easy access and replacement during service
Compact Radiator Size: 14 × 7.9 inches (355 × 200 mm)
18-core high-efficiency radiator with expansion tank
Pressure cap rated to 20 psi (1.4 bar)
Driven by a 1.18-inch (30 mm) mechanical water pump
Blue silicone hoses with Polini branding
Thermostat prevents temps from dropping below 140°F (60°C)
Polini's custom reed valve setup includes 6 carbon-fiber petals, engineered for precise and responsive airflow throughout the full RPM range. The intake leads directly to the crankcase for optimized performance.
Cast aluminum with high-silicon content
CNC-machined for perfect tolerances
Reinforced in high-stress areas
TBO (Time Between Overhaul): up to 400 hours
Constructed from high-grade steel
Precision-balanced to eliminate vibrations
Fitted with high-performance bearings
CNC-controlled production ensures perfect centering
Integrated centrifugal clutch (prop stays idle at low RPM for safety)
Two reduction ratios available:
2.8:1 for 55-inch (140 cm) propellers
3.2:1 for larger props
Helical gear design reverses prop rotation and softens torque
Balancing countershaft reduces piston-induced vibrations for smoother flight
Custom CDI system with auto-advancing timing based on RPM
Smooth throttle response and easy starts
Dual Spark Version: Includes 2 CDIs, 2 stators, 2 coils, and 2 spark plugs for maximum redundancy and reliability
Manual pull-start system with ergonomic handle
Reinforced internals for extended life
Available on all versions (including those with electric start)
All Thor engines, including the 303, use the same mounting points. This simplifies frame design and allows easy upgrades across the entire Thor lineup. Engines come fully assembled with all mounting hardware and, for electric versions, plug-and-play wiring and battery.
Due to its power, the Thor 303 is ideal for:
Single or tandem trikes
Delta trikes
Three-axis ultralights
UAVs (Unmanned Aerial Vehicles)
For single-seat paramotors, this engine is recommended for experienced pilots and competition use only (e.g. slalom racing).
The Thor 303 is the highest displacement engine in the Polini Thor series. Its cylinder, crankshaft, carburetor, airbox, CDI, and exhaust system have all been completely redesigned to improve performance and in-flight safety.
Delivering 38 HP at 8000 RPM, the Thor 303 can generate up to 265 lbs of static thrust with a 63-inch propeller.
At a cruising RPM of 4500, it consumes just 0.8 gallons per hour, producing approximately 66 lbs of thrust in level flight.
Thor 303 with Manual Flash Starter
Thor 303 with Electric + Manual Flash Starter
Thor 303 Dual Spark (Dual Ignition)
The Dual Spark version meets top-tier aviation safety standards and comes with electric and manual starters, dual CDI units, and fully independent redundant ignitions.
The Thor 303 is the product of 3 years of development, including dyno bench testing and real-world flights by Polini’s team of professional pilots. Every engine is tested and inspected individually before delivery.
Displacement: 281 cc
Bore × Stroke: 2.99 × 2.44 inches (76 × 62 mm)
Static Thrust: 265 lbs with a 63-inch prop
Design: 5 transfer ports for high and balanced output across all RPM
Head: Optimized combustion chamber for faster flame front
Polini developed a lightweight, low-noise exhaust specifically for the Thor 303. Its compact expansion chamber improves performance across all RPM ranges. Mounted with a spherical joint, the muffler allows free movement and reduces vibration—extending durability.
Resistant to changes in altitude, humidity, and pressure
Stable fuel delivery across different climates
Includes a manual drain valve to empty fuel and prevent leakage
Optional Polini starter control for safe engine start
Allows precise tuning for smooth, powerful output
Fluid-dynamically optimized to stabilize airflow
Features an S-curve design to reduce turbulence
Uses polyurethane foam with 30 PPI (pores per inch)
Split-design allows easy access and replacement during service
Compact Radiator Size: 14 × 7.9 inches (355 × 200 mm)
18-core high-efficiency radiator with expansion tank
Pressure cap rated to 20 psi (1.4 bar)
Driven by a 1.18-inch (30 mm) mechanical water pump
Blue silicone hoses with Polini branding
Thermostat prevents temps from dropping below 140°F (60°C)
Polini's custom reed valve setup includes 6 carbon-fiber petals, engineered for precise and responsive airflow throughout the full RPM range. The intake leads directly to the crankcase for optimized performance.
Cast aluminum with high-silicon content
CNC-machined for perfect tolerances
Reinforced in high-stress areas
TBO (Time Between Overhaul): up to 400 hours
Constructed from high-grade steel
Precision-balanced to eliminate vibrations
Fitted with high-performance bearings
CNC-controlled production ensures perfect centering
Integrated centrifugal clutch (prop stays idle at low RPM for safety)
Two reduction ratios available:
2.8:1 for 55-inch (140 cm) propellers
3.2:1 for larger props
Helical gear design reverses prop rotation and softens torque
Balancing countershaft reduces piston-induced vibrations for smoother flight
Custom CDI system with auto-advancing timing based on RPM
Smooth throttle response and easy starts
Dual Spark Version: Includes 2 CDIs, 2 stators, 2 coils, and 2 spark plugs for maximum redundancy and reliability
Manual pull-start system with ergonomic handle
Reinforced internals for extended life
Available on all versions (including those with electric start)
All Thor engines, including the 303, use the same mounting points. This simplifies frame design and allows easy upgrades across the entire Thor lineup. Engines come fully assembled with all mounting hardware and, for electric versions, plug-and-play wiring and battery.
Due to its power, the Thor 303 is ideal for:
Single or tandem trikes
Delta trikes
Three-axis ultralights
UAVs (Unmanned Aerial Vehicles)
For single-seat paramotors, this engine is recommended for experienced pilots and competition use only (e.g. slalom racing).
