Pipeline: We left no stone unturned in our pipe search.
Broad beam: Horsepower was ample with the 300 kit, so we
installed a flywheel weight to broaden the power.
2014 KTM 300SX the PowerParts catalog, but it isn’t really necessary. Q: WHAT ABOUT THE EXHAUST PIPE?
A: In 2012, we ran Pro Circuit’s 300XC exhaust system with a Pro Circuit KTM 250SX R-304 shorty silencer.
But, since that was on the KTM 300XC engine, we
decided to thoroughly test three different pipe options.
So, we put the stock KTM 250SX exhaust pipe, a Pro
Circuit 250SX exhaust, and a Pro Circuit 300XC pipe
through the wringer. In all three cases, we ran the pipes
with the R-304 shorty muffler because we had previously
found this silencer to be superior to the stock silencer.
Q: WHICH PIPE MADE THE MOST
HORSEPOWER? WHICH PIPE DID THE TEST
A: For background info, our 2014 KTM 250SX made
49. 10 horsepower on the dyno before we put the 300cc
kit on. Here are what the three pipes did on the dyno
and on the track.
Pro Circuit 300XC pipe. Peak horsepower with this
pipe was upped to 51. 26 horsepower. More significant, at
7000 rpm, the pipe produced the most horsepower of any
pipe we tested ( 5. 5 horsepower more than a stock 250SX
engine at seven grand). It was also the most effective at
taking the dip out of the powerband where the power
valve opened. It also had the most over-rev on top. This
was the pipe of choice for every Novice and Vet test
Pro Circuit 250SX pipe. Peak horsepower with
this pipe was boosted to 50. 48 horsepower. It made the
smallest peak power gains of the three pipes we tested
but still made 4.8-horsepower more than a stock 250SX
engine at seven grand. None of the test riders liked this
pipe on our 300SX kit engine because it had a big dip at
the power-valve opening and fell off on top. It felt very
Stock KTM 250SX exhaust. Peak horsepower with
the stock pipe was a massive 52. 21 horsepower, but at
7000 rpm, the stock pipe gave up one horse to the Pro
Circuit 300XC pipe while still making 4. 3 more
horsepower than the stock 250SX engine. Strangely, the
effect of less horsepower at 7000 rpm and amazing peak
horsepower at 8200 rpm resulted in a pipe that MXA’s
Pro test riders loved. It hit the hardest of all three pipes,
and that hit was exaggerated by the fact that it came
out of nowhere. Our Novice and Vet test riders hated
this pipe because it was hard to keep on the pipe, and
when it hit, it induced lots of wheelies and wheelspin.
Pro Circuit 304 long silencer. As a final test, we
mounted Pro Circuit’s long 300XC 304 silencer on the
300XC pipe. It made 49. 76 horsepower at peak, which
wasn’t very good, but even worse, it peaked 300 rpm
sooner and fell off at 8000 rpm, whereas the shorter
R-304 silencer didn’t start to lose significant over-rev until
8700 rpm. The long silencer was a buzzkill. We would
never run it for motocross. Oddly, Pro Circuit does not
list the R-304 shorty silencer as a 300XC part, but it fits
Q: WHAT ELSE DID WE DO TO OUR 300SX
A: We ran a 9-ounce Steahly flywheel weight. This
was another part that the AMA Pro riders thought was
unnecessary but the Novice and Vet riders loved. Steahly
also makes an 11-ounce flywheel weight for this bike.