MXA’S ULTIMATE KTM 300SX MOTOCROSS BIKE VIDEO: HOW DARE WE SPEND $20 GRAND ON A KTM 300SX
To build the ultimate KTM 300SX, MXA started with a box-stock 2020 KTM 250SX, then ordered a KTM Power Parts 300 upgrade kits (cylinder, head, rings, gaskets, blask boxetc), which we sent to Dicks Racing to have the head milled and groove. Dick also taper-bored the stock carb from 38mm to 42mm, added a Quad Flow torque wing and made mods to the slide, float bowl and jets. The pipe was an Italian-made Scalvini cone pipe with Pro Circuit 304R silencer.
To ensure that we could accurately gauge what we gained or lost in the power department, we dyno’ed our KTM 250SX before we started and dyno’ed the KTM 300SX version after it had been broken in. First off, at no point on the dyno curve did the KTM 250SX come anywhere near the power of the 300SX engine. At 6000 rpm, the 300SX made 33.37 horsepower to the 250SX’s 31.54. At 7000 rpm, the 300SX made 43.75 horsepower to the 250SX’s 40.91, and the same pattern followed across the rev range. In fact, at 8000 rpm, the KTM 300SX produced 4.25 more horses than the 250SX.
On the track, that power advantage didn’t come across as brutish; instead, it felt more manageable, easier to keep hooked up and blessed with more top, more peak and more over-rev. All in all, the 300SX power plant was a plus on all accounts. Best of all, not a single part on our bike was unobtainable. Most came from the KTM Power Parts catalog or well-known KTM affiliates.
For the suspension, we added WP Xact Cone Valve Pro Series forks and Trax shock, but before we installed them we had AEO Powersports KTM in Temecula, California, have Mark Johnson revalve the forks and shock, replaced the chrome Cone Valve fork legs with $810 coated fork legs, and added a $450 REP Suspension shock linkage. We then slid them forks into KTM Power Parts orange split triple clamps from the 2020-1/2 KTM Factory Edition with Xtrig PHDS bar mounts.
The rolling chassis got KTM Power Parts orange-anodized Factory wheels (laced cross-three on the front), cool DeCal Works custom graphics and lots of added touches.
When you start with a $9000 KTM 250SX two-stroke, add a $960 Power Parts 300 upgrade kit, send the top-end and carb out to be ported milled and massaged to the tune of $1000, add $350 exhaust pipe and $135 silencer, $400 shock linkage, $900 KTM Power Parts wheels, $650 Power Parts triple clamps, $220 Xtrig bar mounts, $220 worth of Hoosier tires and $6000 worth of WP Cone Valve Pro Series Spring forks and Traxx shock (plus $810 of coatings, and over $1000 worth of suspension work)—you have a $20,000 KTM 300SX.
We built it to show what could be done—you don’t have to spend that much or even like the idea of a $20,000 two-stroke, but the world is full of them.