TWO-STROKE DIRECT INJECTION
It’s taken 13 years, but with the new 300 EXC TPI, KTM have made strokers planet-friendly
“We began our direct fuel injection (DFI) project in 2004 and started out with Orbital, an Australian firm that had focused on marine applications. There aren’t the same size issues on a speedboat as on a bike, so their design meant we’d have to create a new frame.
“The air-assisted DFI system with injection straight into the combustion chamber looked promising in terms of consumption and emissions. But getting those figures meant lean mixtures and there were issues with piston durability.
“Then we looked at a system from Graz University in Austria. This was much simpler and the fuel injection pressure was much lower, just 3.5 bar, the same as a four-stroke. This was one of the project goals, as it reduces complexity and weight from the fuel supply system.
“This system was better, but it was still not at the level of the carburated bikes because of poor fuel/air mix and atomisation. But in 2014 we moved the injectors into the transfer ports ( Transfer Port Injection or TPI) and found there were no downsides in emissions or fuel consumption, but much better rideability.
“Now, in the new 250/300 EXC TPI we have a bike with more or less the same torque as before, but we can run it leaner for better response and we don’t have to run it rich as we can set every map point. Its first competitive test was at the Roof of Africa race where the course goes up by 2000m. The team loved the fact that they didn’t need to mess around with the jetting and all the rider had to do was select from two preloaded maps.”
All the fun of a two-stroke with none of the planet-strangling fumes
Two-strokes are back with KTM’S clever 300
Michael Viertlmayr Head of Offroad Engine Research and Development at KTM. He joined the TPI project two-and-a-half years ago.