Our Cylinder Works 270SX-F project in phase one did increase power down low and in the midrange, but not so much on top. Going bigger usually means more performance, but that doesn’t mean the increase in performance will be in the places you want it. The last performance item we added was a billetproof clutch kit from Hinson Racing that included an inner hub, pressure plate, fiber drive plates, steel drive plates, springs and a CNC-machined clutch cover that is hard-anodized. Map two is made to work on pump gas and provide reliable performance. Map one is designed to run on a mixture of race gas and provide the most performance. Jamie simplified things by installing just two maps for us. Although the Vortex ECU has the capacity to store 10 different mapping possibilities, we are thankful that Twisted Development knows that can be confusing for the average guy. The Vortex 10 Map ECU we used plugs directly into our KTM 250SX-F standard wiring harness and works with all the standard engine sensors, such as ECT (Engine Coolant Temperature), IAT (Intake Air Temperature), MAP (Manifold Absolute Pressure), TPS (Throttle Position Sensor), and CPS (Crank Position Sensor) to adjust fuel and spark timing in all weather, altitude and load conditions. A complete Hinson billetproof clutch, Cylinder Works big-bore kit, FMF exhaust and some magic from Twisted Development transformed our KTM powerplant. With the head modifications complete and installed back on the bike, Jamie headed to the dyno armed with his computer to figure out mapping. Twisted also ported the head for more flow to optimize performance gains of the increased bore size and cut the valve seats to new specifications. This will ensure proper compression, delivering the best fuel burn possible. Cutting the head combustion chamber to match the new +3mm big-bore kit was first on the list, but that was just the beginning. Jamie is the mad scientist behind much of what goes on at Twisted Development, and before he got on the computer and started figuring out new maps for our 250SX-F project, he had to do some head modifications.
While we had the bike apart, we sent the main frame to Chris Johnson at San Diego Powder Coating for some bright orange coating. We found some neglected bearings that didn’t need to be replaced but were definitely in need of some TLC and grease. Because the bike was used, we decided to tear it all the way down for an in-depth inspection, and it’s a good thing we did. Factory Connection did re-valve both ends internally, trying to increase rider comfort on small chop, but we weren’t done with the chassis yet. Our target setup was geared towards a vet intermediate rider, so we retained the use of a stock shock spring and used pretty much stock air settings in the AER-48 fork. All oil, seals and bushings were replaced. Factory Connection went through the suspension completely. We had a set of AER-48 air forks, so we put those on right away. If you remember, 2016 was the last year of WP 4CS forks. The 2016–’18 chassis and engine configuration are almost identical, or at least close enough for what we had planned. We found a 2016 KTM 250SX-F in decent shape online, so we bought it. We might have to break a few rules along the way, but that is okay with us Test rider Spencer Clark was all smiles after riding our KTM big-bore project.
We decided to see if we could make the previous-generation 250SX-F better than the current model for the average rider. The stock KTM is a pro-level machine that’s a little demanding for amateurs. In 2019 KTM made huge changes to the 250SX-F, and now with the shootout results published, the story isn’t that different.
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