TWO-STROKE DI­RECT IN­JEC­TION

It’s taken 13 years, but with the new 300 EXC TPI, KTM have made stro­kers planet-friendly

Motorcycle News (UK) - - Garage -

“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.

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