Tested: Twisted Development/Fasthouse KTM 250 SX-F 17

No matter how much faster a 450 might be, there's nothing quite like the overall rideability of a 250 four-stroke. Because of this, there are riders that choose to make them their everyday weapon, even when regularly lining up against a gate of 450s. Once such machine, a 2016 KTM 250 SX-F, belongs to our regular video guy, Joe Carlino.

Included among the events that he rides each year, are the Mammoth Mountain Vet week and the Vet Nationals. Because of that, we planned to put together a package to get his KTM up to the power and the handling needed to take on the elevation, hills, and general roughness that comes with these events. Why put in all that effort? Like we mentioned before, a well-built 250F is an absolute joy to ride...and race.

So kicking things off, we started with one simple fact, this bike would be racing a field of 450s (at altitude in some cases), meaning we needed to make some serious power. To do so, we wanted to take the opportunity to work with an engine builder that's had to develop race motors for 250Fs at the pro level. Enter Twisted Development's Jamie Ellis. Jamie came through the ranks as a mechanic for YOT, later transitioning into the engine building side and eventually becoming the guy behind the power at Rockstar Racing during their Suzuki and KTM years. Because of this, Jamie has had a lot of experience developing and tuning engines with some serious resources.

Thanks to the level of parts the current KTMs are using, Jamie's mods were limited in number, but very affective. First off, he started with a very in-depth cylinder head port job, adding in copper beryllium valve seats when he was done. After that, he added a custom piston of his own design and only available through Twisted Development, and that's all for his internal mods! What about cams? Not in this bike, as the KTM factory teams actually uses the production cams and that's what Jamie believes in as well for this application. Before we threw the bike on the dyno, though, we snagged a DDS (Damped Diaphragm Steel) clutch kit from Hinson Racing to install. The DDS clutch, which is found in KTM's 450 SX-F, has been adapted by Hinson to help take some of the strain off the 250 and 350 SX-F's transmissions, while still putting the power to the ground effectively. Lastly, FMF provided a full titanium/carbon RCT 4.1 exhaust system, with a special low-boy header which was developed with the Troy Lee Designs/Red Bull/KTM team for more bottom-end performance. This head pipe is actually available to the public as an option now, if you ask for it.

Once everything was installed, Jamie took the bike for some serious dyno time, creating fully custom engine maps with a full programable Vortex ECU. Once all the hard parts and VP race fuel have been added, this custom mapping really unlocks all the performance capability from the machine. While many tuners offer engine mapping to ECUs, Jamie is one of the few that will spend hours on a dyno, tuning the bike perfectly for air-to-fuel ratio and working at small increases in throttle position (5-10% jumps) to ensure the bike is crisp and responsive at all times. This is one of the key features that make race team engines so much better than what's usually available to the public, pure R&D and dyno time.

Moving over to the chassis and suspension side of things, it's quick to see that this 250 SX-F is equipped with a set of WP's 48mm Cone Valve forks. This 2016 model originally came with WP's 4CS forks, but even after multiple avenues of modification Joe wasn't overall thrilled with the stockers. But after a day on a set of CV forks, he found the answer he was looking for. The forks were picked up used at a good price, then taken to Factory Connection to be freshened and add some settings to better match the stock shock they had already modified.

Beyond these major upgrades, it was down to a few trick but helpful pieces. A set of Raptor titanium pegs were equipped, as the stock footpeg's traction was one of the only major complaints with the stock setup. Also, a set of X-Trig's ROCS clamps were added to hold the WP CV forks in place. These triple clamps were for a long time the choice of factory KTM worldwide, as their adjustable steering stem offset, and six optional bar mount positions offer a large amount of overall adjustment. The PHDS bar mount system also allows the benefits of a solid mount and rubber mount in one. The PHDS cushions eliminate the vibration and allow a little flex, while the mounts themselves are mounted solidly to the top of the triple clamp, allowing it to hold up to some abuse during a crash. Their newest ROCS design splits the top and bottom mounting bolt on each clamping surface, allowing the X-Trig clamps to run a lower torque rating on their bolts, while still providing the necessary clamping force. This allows the clamp to flex more in the right places, as many aftermarket billet clamps are actually more rigid than the stock cast aluminum versions. As we saw with Ken Roczen jumping back to his stock clamps from works billet ones this summer, which shows that they can be too stiff for some rider's tastes. Lastly, the clamps are now available in orange for the KTMs through Technical Touch USA, as they used to only be available through KTM's PowerParts catalog in that color.

Down where the bike contacts the ground are a set of Pirelli's newest moto tires, the MX32 front and MX32 Pro rear. These tires were born for a simple reason: When dealing with the top racers with all the choices in the world, Pirelli found most still want a set of tires that can be run throughout the day, on changing conditions but with consistent traction. Of course, this bodes well for the average consumer who values this more than anyone. Considering most tracks in Southern California are prepped constantly, the dirt starts somewhat loamy in the mornings but due to the nature of the dirt itself, ends up quite hard-packed by the end of the day. This is where the MX32 Pro shines, allowing confidence and consistency through these moderately changing tracks. With the Pirelli being the tire of choice, a new set of hoops were needed to mount them to. Thus, a set of DID rims were laced up to Talon Ultralight hubs by the crew from Dubya. After all, why go this far and not add a gorgeous wheelset, that's also stronger than stock?

Lastly, was the overall look of the bike. Joe is a huge fan of the Fasthouse crew, so we got together with one of their designers to put their spin on the well-liked neon orange and blue look, common amongst KTM's 250 teams. All said and done, in typical FastHouse fashion, the bike really pops but in the most simple and old-school cool way.

Words from the owner:

Joe Carlino - Honestly, I love the way the KTM 250 SX-F handles, as the all-around feel and characteristics are spot on for my liking. But as most people know, the bike is meant to be ridden more in the mid-to-top range, and this is what I wanted to add to. My goal for this build was not only add power, but to place as much of it as possible to the roll on punch. After talking with the guys at Twisted Development, and hearing their experience and capabilities, I knew this was the place to go. Honestly, I was stressing on the reliability of the engine though, as I wanted to be able to ride twice a week and not have to rebuild the engine every month. With this in mind, Jamie suggested we stick with stock cams and bore, just bump up the compression with his custom high-comp piston, some heavy head work, and what I consider to be his magical ECU mapping. We settled on a 25-hour maintenance interval for the top-end, which I feel is perfectly fine for a 250F that is a complete monster!

The outcome? Completely spot-on and more. The mods gained me all the bottom-end punch I wanted, allowing me to ride almost any corner in at least third gear. But that wasn't the end to it, because I barely have to up shift as I can let it rev to the 14,000 RPM limiter while making some insane top-end power! Honestly the biggest surprise is not only how responsive this bike is at the crack of the throttle, but how responsive it is at any RPM with any amount of throttle input. The mapping work Twisted put it really is worth every penny as I didn't think a bike could run this crisp.

Also, this is my first time owning a full Hinson clutch and after feeling the difference in traction, it makes me believe why nearly all the top factory riders use them. The way the cushions on the new DDS clutch work help take away just of odd slip or lurch with the extra power. It just feels like my hand and throttle are directly connected to the rear tire, with the tire directly stuck to the ground. How good is it? A top five start against a field of 450s at Mammoth good.

The suspension was a tough sell at first, as I didn't want to spend the cash on WP's Cone Valve forks. Due to a great deal I found on a used set, though, I finally said yes. While not even set up for me, I could tell on my first ride I made the right choice. To get them perfect, I dropped them off at Factory Connection, which I've been using for the last three years and we were able to hit the mark right away. The most noticeable change with these forks over the 4CS is the bottom resistance, while keeping the initial feel supple but responsive. They're soft initially, but when you smash into something they just take the blow, where stockers tend to give you that metal-on-metal bottoming clunk. Where the forks also shine that many people don’t talk about is confidence in turns. Because the balance between soaking up the bumps but holding up in the stroke gave me front-end traction I just wasn't used to. Lastly is the overall adjustability of the forks, with sensitive compression and rebound, along with the preload adjustments. These forks, along with becoming more studious with suspension, have really allowed me to dial in the bike easily from track-to-track quickly and effectively.

Another cool feature was the Honda-style Showa steering damper that Moto Whips welded the frame mount for me to use on my KTM. This wasn't for high-speed stability, but to keep the front tire from being so twitchy in corners at low-speed and track easier at my skill level. Finally, beyond the clamps, wheels, and custom seat cover from SDG, the awesome one-off look the Fasthouse crew put together for me really completes the look of the bike.

All-in-all the build was very successful for me, as the suspension upgrades and the engine mods gave me more confidence and performance than I could ever need.

Credit: Joe Carlino
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