Draft:KTM SXF 450 ENGINE
Motorcycle engine production line
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The KTM 450 SX-F engine is a high-performance 449.9 cc liquid-cooled single-cylinder four-stroke racing engine developed by KTM for motocross competition motorcycles. It powers the KTM 450 SX‑F and related competition models such as the KTM 450 XC‑F and KTM 450 SMR.
Submission declined on 16 April 2026 by ThatTrainGuy1945 (talk).
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Comment: The entire text should not be bolded. Also note lack of references in-text and unreferenced references. 🚂ThatTrainGuy1945 Peep peep! 02:02, 16 April 2026 (UTC)
The engine is known for its extremely high power-to-weight ratio, producing over 63 horsepower at the front sprocket while weighing around 26.8 kg (59 lb) for the 2023 onward engine, including the electric starter. The design emphasizes lightweight components, centralized mass, and high-revving performance for motocross racing.
Design
The engine uses a single-cylinder configuration with a single overhead camshaft (SOHC) operating four titanium valves.
The cylinder is inclined slightly rearward within the chassis to improve mass centralization and rear wheel traction.
Cylinder head
The cylinder head is designed for high airflow and low mass.
Key features include:
• 4 titanium valves
• DLC-coated finger followers
• Lightweight camshaft
• High-flow intake ports
Valve diameters:
| Intake | ~40 mm |
| Exhaust | ~33 mm |
The maximum engine RPM (rev limit) for the modern KTM 450 SX-F (2023-2026 models) is approximately 11,200 to 11,400 RPM
Piston
The engine uses a forged aluminum box-type piston produced by suppliers such as CP‑Carrillo.
Features:
• Extremely short skirt
• Low reciprocating mass
• High compression ratio (13.1:1)
The lightweight piston contributes to the engine’s rapid throttle response.
Crankshaft
The crankshaft assembly is designed for minimal inertia.
Characteristics:
• Plain big-end bearing
• Press-fit crank assembly
• Optimized balancing factor
The reduced rotating mass allows the engine to accelerate quickly but still maintain stability at high rpm.
Fuel system
From 2013 onwards Fuel delivery is handled by a Keihin electronic fuel injection system 44mm produced by Keihin Corporation.
Lubrication
The engine uses a pressure-fed lubrication system with multiple oil pumps:
• Pressure pump
• Scavenge pump
This ensures consistent lubrication under high-G motocross conditions.
Cooling system
Cooling is provided by dual aluminum radiators mounted on the chassis.
Features include:
• High-flow water pump
• Large coolant passages in cylinder head
• Thermostat-less racing cooling design
Technical specifications
| Specification | Value |
| Engine type | Single-cylinder, 4-stroke |
| Displacement | 449.9 cc |
| Bore | 95 mm |
| Stroke | 63.4 mm |
| Compression ratio | 13.1:1 |
| Valvetrain | SOHC, 4 valves |
| Fuel system | Keihin EFI |
| Maximum power | ~63 hp (at rear wheel) |
| Maximum rpm | ~11,400 rpm |
| Engine weight | ~26.8 kg |
| Transmission | 5-speed |
The engine is rotated backwards by 2 degrees. This lowers the countershaft sprocket by 3mm, which in turn lessens chain torque under acceleration. The compression ratio is upped from 13.75 to 14.1, and peak power is 59.85 horsepower.
Applications
The engine platform is used in several KTM competition motorcycles:
• KTM 450 SX‑F (motocross)
• KTM 450 XC‑F (cross-country)
• KTM 450 SMR (supermoto)
Racing use
The engine has powered multiple championship-winning motorcycles in the AMA Supercross Championship and the FIM Motocross World Championship.
Professional teams often modify the engine with:
• Race ECU maps
• Titanium exhaust systems
• Higher compression pistons
• Ported cylinder heads
The KTM 450 SX-F engine is one of the most extreme production single-cylinder engines ever built for motocross.
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