01. Engine & Exhaust
The 250cc 2-stroke engine has plenty of power and torque but remains light enough for riders to muscle their way through the toughest obstacles. Thanks to state-of-the-art engineering, innovative 2-stroke design, and revolutionary TPI fuel injection technology, and a 13:52 re-gear, the powerplant is even more refined than ever before. The compact and lightweight 2-stroke is a great choice for offroad riders who want usable enduro performance that is ready to conquer in the most extreme terrain.
The cylinder on the KTM 250 EXC SIX DAYS has a bore of 72 mm and is fitted with a sophisticated power valve, providing ultra-smooth and controllable power characteristics. Being fuel-injected, the cylinder features two lateral domes which hold the fuel injectors, supplying fuel to the rear transfer ports. The downstream injection guarantees excellent atomization of the fuel with the upstreaming air. Thus, the loss of unburnt fuel is minimal for fewer emissions, more efficient combustion, and reduced fuel consumption. The cylinder also features a state-of-the-art power valve unit with a sophisticated mechanism for the lateral support exhaust ports. The exhaust port layout increases engine performance, while the upper contour of the exhaust port has been machined to ensure more accurate port timing.
Crankcases and engine covers
These compact engine cases are manufactured using a high-pressure die-cast production process which helps with weight reduction but maintains strength and durability. This design also allows for optimal shaft arrangements close to the center of gravity, resulting in ideal mass centralization and ride-ability.
The KTM 250 EXC SIX DAYS makes use of a robust 6-speed transmission made by PANKL RACING SYSTEMS. The gears are made of a strong, forged raw material, ensuring the highest durability and reliability level. Another highlight of the KTM 250 EXC TPI transmission is the no-dirt gear shifter. Similar to the footpeg design, it prevents the build-up of dirt and ensures the next gear is always available, no matter what the conditions.
Engine management system
The engine management system (EMS) of all 2-stroke EXC models features a control unit located below the seat. The ECU defines the ignition timing while the amount of fuel to inject is based on several sensor readings such as intake air pressure, throttle position, water temperature , and ambient air pressure. Thanks to altitude and temperature compensation, re-jetting is a thing of the past, meaning more time twisting throttles and less time turning screws. Should the rider decide to mount a radiator fan from the KTM PowerParts, it will be controlled directly by the EMS without needing to add an additional thermal switch.
The KTM 250 EXC engine design allows for the implementation of a lateral balancer shaft in order to keep engine vibrations to a minimum. This means riders can focus on the obstacles ahead of them, with out distraction. After all, more comfort equals less fatigue.
The KTM 250 EXC SIX DAYS employs the KTM-developed DDS clutch (damped diaphragm steel) with a wear-free steel basket, extremely heat resistant clutch plates and nitrated steel liners. This clever design employs a diaphragm spring instead of the usual coil springs, making for considerably easier clutch action. A diaphragm spring also leaves sufficient space for a damping system to be integrated into the clutch hub. The goal is traction, but without compromising durability. Light operation and a 'telepathic' level of control come standard with this hydraulic Brembo actuated clutch. Additionally, this model comes with clutch slave cylinder protection.
Pre-mixing 2-stroke fuel is a thing of the past for KTM EXC TPI owners. The 2-stroke enduro range is fitted with a frame-mounted oil tank featuring flexible mountings, which greatly improves durability and reliability. In addition, a mesh filter preventss dirt from getting into the oil pumpand into the fuel. This works in conjunction with the oil pump, that delivers the lubricant directly to the throttle body, where it is mixed with the incoming air to lubricate the piston and crankshaft. Using engine speed and throttle position sensor data, the engine management's precise electronic control of the oil pump ensures that the ideal amount of oil for any given conditions is used. With an average fuel-to-oil ratio of 1:80, an oil capacity of about 0.7 liters is sufficient for at least five tanks of fuel.
The KTM 250 EXC engine is fitted with a 39 mm throttle body made by Dell`Orto. These regulate the airflow via a butterfly connected with a twin-cable throttle cam, which is operated by the handlebar throttle assembly, supported by a throttle position sensor that provides airflow data to the control unit. What all this means is, riders can precisely set the idle speed via the bypass screw, as well as easier cold starts.
In order to accommodate the power requirements of the engine management system, all KTM EXC models are fitted with a powerful 196 W alternator and voltage regulator to ensure all systems are always powered up.
Keeping the engine cool when the going gets tough comes courtesy of a pair of radiators, mounted close to the center of gravity. These make use of CFD technology (Computational Fluid Dynamics) and clever coolant circuit routing, achieving optimum engine temperature for the highest performance, in all conditions. Above all, the delta distributor, integrated into the frame triangle, features a large center tube for highly efficient coolant flow. The radiators also benefit from plastic protection fins that serve as protection from flying rocks and debris, as well as a brace that disperses energy around the radiators in the event of an impact.
There's more to it than 'braaaap!'. The exhaust plays a key role in packing that signature 2-stroke punch. The KTM 250 EXC models feature heavy-duty exhaust headers made using an innovative 3D stamping process that produces a ribbed surface finish. This makes the pipe much stronger, with better impact resistance, while also helping to reduce noise. The silencer features a compact shape and end cap with a signature SIX DAY logo for extra impact.