Motocross Action Mag

ASK THE MXPERTS: IT’S NOT A TWO-STROKE PIPE, IT’S A TUMOR

Date Added: 24/07/2018 15:33 by Motocross Action Mag
24pts
Description:

The 2019 KTM four-stroke exhaust pipes have absolutely nothing in common with two-stroke expansion chambers. The bulge is a resonance chamber.

Dear MXA,
I was shocked to see the photos of the 2019 KTM 450SXF. I thought it was strange a couple years ago when their four-stroke pipes began to resemble two-stroke pipes, but now they are two-stroke pipes. I don’t understand how KTM can put a two-stroke pipe on their four-strokes and get it to work. What’s the deal?

We’ve been over this a million times, but people don’t always catch it the first 999,999 times. No surprise we probably answered questions about  2007 Honda CRF250 jetting specs every day (and we still get letters about how to jet one 11 years later).

The 2019 KTM four-stroke pipes are not two-stroke pipes, nor would a two-stroke pipe work on a four-stroke. The actual KTM four-stroke pipe is a normal-looking, constant-diameter tube. The part that reminds you of a two-stroke expansion chamber is a resonance chamber. It is stamped just like an expansion chamber and then welded over the four-stroke exhaust pipe (after a hole is drilled in the four-stroke pipe to allow excess exhaust to be sucked into the empty space of the resonance chamber). We find it hard to believe that you never noticed this before; although, on the 2018 450SXF Factory Edition and 2019 KTM four-strokes, the resonance chambers aremuch larger than it was in the past.

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