KTM Two-Stroke Engine Innovation

KTM have done many things for motorcycling since emerging in 1953 with a Rotax-engined two-stroke enduro motorcycle. The biggest off-road manufacturer by a good amount of units, KTM are fast becoming a giant in the road legal motorcycle industry, if they aren’t already.

Despite booming adventure bike sales and MotoGP projects, at their core is off-road, at the core of off-road is enduro, and at the very core of enduro is the two-stroke. Without the two-stroke engine, enduro is half cut.

The problem for two-stroke engines is emissions laws that are putting the thumb screws on smokey engines. Off-road manufacturers have been working hard to design more lean-burning carburetor engines but ultimately they are doomed.

Except they’re not, thanks to a little engine KTM have been developing. The new KTM engine is a 300cc Transfer Port Injection (TPI) engine and developed for well over a decade – the project began 13 years ago but took a back seat for a couple of years during the global recession.

Initially going down a cul-de-sac with EFI scooter and marine engines, using air-assisted direct fuel injection, KTM admit development has been tough on this patent-pending TPI system. How you start from nothing to develop two-stroke injection and software to deliver the fuel and air in ever way a carburetor can, in every conceivable riding condition, boggles the mind. That’s why it took so long. Thinking about the last half-dozen times I’ve been out on a motorcycle I can’t imagine how you would arrive at the settings to make a motorcycle mimic a carburetor two-stroke…

Yet KTM have. At any altitude, in any weather, the TPI engine means no more jetting problems caused by conditions. It’s also easier to live with and no more complex than a ‘normal’ two-stroke. A separate oil system (mixing 1:80 ratio) means no more pre-mixing fuel – oil top-ups will most likely come every five or six petrol fill-ups. In races the new KTM TPI two-stroke engine is more economical too – 20 to 30 percent, KTM claim – though it depends on riding conditions and the heaviness of your throttle hand.

The big difference is the linear power delivery. There’s no sudden powerband pulling your arms off, just tractable power. This means you can find grip more easily because the throttle link to the rear wheel is more precise. Motorcycles which grip better, are easier to ride and burn less fuel – it’s hard to not like that. Unlike a carburetor two-stroke the new TPI never needs a good rev-out to clear the smoke, however it does get mildly fluffy. It doesn’t smoke anything like as much, however. TPI motorcycles are about 3 kilogram heavier, though you’d be heard-pushed to feel it.