01. Engine & Exhaust
The 250cc 2-stroke engine has plenty 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, 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. With Euro IV homologation, it's not only considerately green, but leaves the competition green with envy too.
The KTM 250 EXC TPI cylinder has a bore of 66,4 mm and is fitted with a sophisticated power valve, which provides really smooth and controllable power characteristics. For the EFI application the cylinder features two lateral domes which hold the fuel injectors that supply 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 less emissions, a more efficient combustion and reduced fuel consumption. A little tube in the back of the cylinder is connected with an intake pressure sensor, which supplies pressure data to the control unit. The cylinders feature 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. Last but not least the models allow the use of a more widely available type of traditional spark plug.
Crankcases and engine covers
The compact engine cases are manufactured using a high pressure die-cast production process which helps with weight reduction, while retaining strength and durability. The design allows for optimal shaft arrangements close to the center of gravity, resulting in ideal mass centralization and easier ride-ability. Plus, the engine covers feature a smart surface structure which reduces wear caused by the rider's boots, keeping them looking as fresh as the day you bought your EXC.
The KTM 250 EXC TPI is fitted with 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 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 the TPI 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 and water temperature plus a new additional ambient air pressure sensor. Thanks to altitude and temperature compensation the rider does not need to worry about fiddling around with the jetting anymore. Should the rider decide to mount a radiator fan from the KTM PowerParts program, it will be controlled directly by the EMS without needing to add an additional thermal switch.
Say goodbye to numb feet and hands. This engine design allows the implementation of a lateral balancer shaft in order to keep the vibrations to a minimum. You know what that means: more comfort, less fatigue, bigger smiles.
The KTM 250 EXC TPI 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.
Pre-mixing 2-stroke fuel is a thing of the past for KTM EXC TPI owners. The 2-stroke range is fitted with an oil tank featuring flexible mountings, which greatly improve durability and reliability. In addition, a mesh filter helps prevent dirt getting into the oil pump. Mounted below the oil tank, the oil pump 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. The filler cap assembly for the oil tank is located between the fuel tank and steering head, utilizing a hose in the upper frame tube to transfer the oil to the storage container. With an average fuel-to-oil ratio of 1:80, the oil capacity of about 0.7 liters is sufficient for at least five tanks of fuel.
The TPI engine is fitted with a 39 mm throttle body made by Dell`Orto. The airflow is regulated by a butterfly connected with a twin-cable throttle cam, which is operated by the handlebar throttle assembly. A throttle position sensor provides airflow data to the control unit. The idle system allows the idle speed to be set more precisely via the bypass screw. Also, the cold start system provides a better supply of extra air when opening a bypass. Oil supplied by the electronically controlled oil pump via an oil intake tube is mixed with the incoming air to lubricate the moving engine parts.
To accommodate the power requirements of the engine management system, the TPI models are fitted with a powerful 196 W alternator and a voltage regulator. The same as can be found on the EXC-F 4-stroke models.
Maintaining the optimal engine temperature is crucial to ensuring consistent horsepower throughout the ride. The KTM 250 EXC TPI features radiators which are mounted close to the center of gravity and match the design of the shrouds perfectly, in order to achieve perfect ergonomics. By using CFD technology (computational fluid dynamics) together with a clever coolant circuit routing, the innovative system ensures the optimum engine temperature for the highest performance, no matter what the conditions. Above all, the delta distributor, integrated into the frame triangle, features a large center tube, making the coolant flow from the cylinder head to the radiators highly efficient. The radiators also feature special protectors that don't only serve as protection from flying rocks and debris but also as a brace that disperses energy around the radiators in the event of an impact.
When it comes to power delivery and performance, the exhaust plays a key role and packs a punch that is hard to beat. The 250 cc and 300 cc models feature HD exhaust pipes (heavy-duty) made by using an innovative 3D stamping process which produces a ribbed surface finish. This makes the pipe much stronger, with better resistance against rocks, while also helping to reduce noise drastically. The silencer features a compact shape and end cap with internal designs individually developed for each model, while it is mounted using an aluminum mounting bracket. In addition, the exhaust's shape provides slim ergonomics and more ground clearance, while a perforated inner silencer tube works with lighter damping material for efficient and durable noise reduction.