ASK THE MXPERTS: WHAT’S UP WITH THE KTM 450SXF EXPANSION CHAMBER?

 

The world’s first mating of a two-stroke expansion chamber and four-stroke exhaust system is not what this is about.

Dear MXA,
    I was shocked to see that KTM put a two-stroke-style exhaust pipe on the KTM 450SXF Factory Edition. I’ve never see a four-stroke pipe with cones in the mid-pipe before. My question is, how does it work?

The KTM 450SXF Factory Edition exhaust system works very well. Compared to last year’s KTM 450SXF it produces more horsepower from 5000 rpm to 6500 rpm and then again from 7500 rpm all the way to sign-off at 11,400 rpm. In the 1000 rpm range where it doesn’t make more horsepower than last year (6500 rpm to 7500 rpm), it doesn’t make less either. All around it produces a broader and more useable powerband that peaks, in our dyno runs, at 57.07 horsepower. However, it is not a “two-stroke-style” exhaust pipe. What you, and many others, are mistaking for cones in the mid-pipe of the Factory Edition is in fact a resonance chamber. Inside the bulging cones is a normal tube-style four-stroke pipe.  There are two holes drilled into the mid-pipe tube to bleed exhaust gases into the resonance chamber for more pick-up off the bottom and a one decibel reduction in exhaust note. The part that people are confused about is welded over the 450SXF exhaust pipe and is made out of two stamped halves. It does look cool though.