Just as it had promised in March, KTM has launched a two-stroke, fuel-injection engine that is expected to present a strong challenge to the four-strokes. The new single-cylinder engine is designed to provide the best of both worlds since it is offered in capacities of 250 and 300 cc and at the same time conforms to the most stringent emission standards.
KTM, an Austrian motorbike maker, made its name in the glory days of two-stroke cross-country competition motorcycles and it appears set to abide by this tradition, even it means going against the current. The company is positioning the new engine as a designing paradigm shift but the reality is that there was no need of reinventing the wheel when building an oil-burning engine that is environment friendly as required by modern laws.
Indeed, the newly-launched enduro 250 and 300 EXC TPI motorbikes that promote the engine are mostly founded on the two-stroke EXC range from last year; only the main parts that control the fuel and breathing aspects of the engine have changed.
The main thrust of KTM’s new technology is the replacement of the Mikuni carburetor used in basic EXC models with the now-patented TPI(Transfer Port Injection) system. The new system feeds the cylinder through a pair of downdraft injectors that squirt atomized fuel onto transfer parts located on the back of the engine cylinder. The fuel is then mixed with air and oil that is delivered via a throttle body created by Italian experts Dell' Orto.
The entire system is controlled by a new and accurate engine management system (EMS) built by Synerject. Using several electronic sensors, the system defines the precise amount of fuel that will be sprayed on the ports at any particular time, while a different injector in the throttle mechanism mixes small amounts of oil with inflowing air so as to lubricate the moving parts of the engine.
KTM says that the new injection system eliminates all the usual flaws that previously made two-stroke engines to be criticized for being environmental hazards. The EXC TPI single-cylinder engine ensures a broad range of power delivery, low oil and fuel consumption and problem-free cold starts. In addition, it will not require to be adjusted according to the altitude.
The oil is held inside a tiny reservoir beneath the central frame beam. According to KTM, the new engine operates on a fuel-to-oil ratio of 80:1, unlike the normal two-stroke engines that need an average ratio of 40:1. Essentially, the capacity of the oil container’s 1.2 gallons (0.7 liters) is sufficient for about five 2.4-gallon(9-liter) tanks of fuel. This cuts the quantity of smoke emitted by the exhaust by almost 50 percent when compared to pre-mix systems.
In 2018, KTM will build two variations of EXC TPI. One will have a capacity of 249 cc while the other one will have 293.2 cc, with the cylinder bore being the only difference. Their engine performance figures have not been revealed but the full trim package weighs 227 pounds(103kilograms) without fuel.
The new enduros are alike to the introductory 2017 EXC models in all other respects. Their construction is based on KTM’S trademark chromium-molybdenum(25CrMo4 ) double-cradle steel-alloy frame and a sub-frame made of lightweight aluminum. There is also an adjustable suspension (WP Xplor) that incorporates a PDS rear shock ,inverted 48-millimeter forks and Brembo brakes. Included in the list of standard equipment is a 6-speed transmission that is paired with the bike maker’s own DDS clutch that utilizes a damped diaphragm steel basket system in place of the normal coil springs.
The two enduro bikes will be available in June. Their pricing information has not been released, but seemingly the two EXC TPI are likely to be priced at the same range as their 4-stroke engine equivalents.
KTM considers this change to be a key investment that is directly correlated to similar developments in the world of enduro racing. Two of its leading riders, Christophe Nambotin(a three-time World Enduro champion) and Johnny walker (well-known for his exploits in Extreme Enduro) are now competing using two-stroke engine bikes. Both of them are expected to change over to the newly-unveiled fuel-injected models in the coming year.
Both bikes (the 250 and 300 EXC TPI) are in compliance with Euro 4 emission standards, which demonstrates that all that was needed to bring two-stroke engines up to date was the application of simplified and recognized technology and, most critically, the will to proceed in this direction. It will be quite fascinating to observe how the other manufacturers will react and whether KTM introduces two-stroke-engined versions in other segments of the market.