KTM 250/300 EXC TPI and Honda SH125
Who says two-strokes are dead? Sure the introduction of Euro4 and its stringent emissions controls looked to have struck the final nail in the stroker coffin but where there’s a will – along with huge market share and financial gain to be had – there’s a way.
It’s taken 13 years of development but finally, here at the notorious Erzberg off-road venue in Austria, KTM are letting us ride their new Euro4 compliant fuel injected two-stroke enduro bikes – the KTM 250EXC TPI and the 300EXC TPI.
Gone is the need to pre-mix fuel, instead there is an oil tank which holds 700ml of black gold, which runs to the combustion chamber at an average of 80:1 fuel to oil ratio, meaning up to eight full fuel tanks per top-up – depending on your type of riding. It’ll transform longer rides, with no need to carry oil – so long as eight tanks will get you home. The injection technology also makes the bike incredibly frugal, using up to 30% less fuel than its carburetted predecessor. It also negates the need to jet for different conditions or altitude as the injection system and ECU automatically compensate, meaning it will run perfectly in sea-level dense woods up to the highest mountain climb.
I have to admit that I was slightly apprehensive about how it would ride, after all this is a bike designed to comply with bureaucratic edicts. So, has it lost the qualities that make KTM’S two-strokes so special? The current model range was the pinnacle of this with beautiful bottom-end power and torque combined with a blistering top end and explosive power when needed. And the new injected model delivers this same character and more. Blasting up the impossibly big and long hills of the Erzberg (the home of the Erzberg Rodeo and also the largest iron ore mine in Europe) the drive is incredible. A mixture of torque and outright bhp – a claimed 51bhp for the 250 and 54bhp for the 300 – make it an even better proposition for club riders through to extreme enduro competitors. There’s less smoke, crisper power with the only slight glitch being when you’re on a constantly increasing throttle where there is a small step in the power. I also felt the 300 ran a little rich at times when on small throttle openings.
How have they done it?
“There are two major areas which has made this possible,” says Michael Viertlmayr, Head of engine off-road and motocross R&D at KTM. “The first is having the best possible thermodynamics in the engine. A lot of effort has been put in to the shape of the combustion chamber, transfer ports and spray targeting and pattern of the injectors. Another crucial area is the design and shape of the exhaust.
‘Blasting up the impossibly big hills, the drive is incredible’
“The second aspect and even more important part is the engine management system. The control strategy has been developed over almost ten years and this is where the major know-how is located. We are able to detect flame out and cylinder charge cycle, and this is what you really need to understand to make a fuel-injected two-stroke bike work. The increase of the new ECUS and faster calculation time was a big benefit to us. This would not have been possible ten years ago because the calculation of the engine management system was not fast enough.”
Crisp power and control from the 300
HIGHLIGHTS O Fuel-injected two-stroke O 700ml oil tank O 80:1 fuel-to-oil ratio O 54bhp for the 300 O Incredible drive