Tested: Mike Sleeter's KTM 350 SX-F 1

Article and Photos by Michael Lindsay

First-things-first, who's Mike Sleeter? Mike is an ex-pro/current pro (I don't think he can quite make up his mind), a family man, and one of KTM's main test riders. His main testing duties have varied from testing suspension and motors for the U.S. race team, to pre-production testing of new models. As such, Sleeter was one of the first guys to swing a leg over KTM's 350SX-F during its development stages. At that point, he became quite attached to the bike and proceeded to use one as his personal bike once they were released.

Rider: Dylan Crower

Once the bikes were in the public, he continued to see the bike improve, as KTM made some massive strides with the 350 over its first few years. Beyond that, he's been spoiled with the opportunity to also ride a factory race team prepped version of the 350SX-F. Which is part of the reason this project was born. Mike was looking to build himself a 350 that was more comparable to the race bikes he had ridden, so he could use it to compete in a few AMA Nationals and the Vet World Championships. Since KTM's in-house Factory Services program is extremely busy with the teams they service (plus, Mike's a nice guy that doesn't want to bug his co-workers), he decided to build one for himself. Using his vast connections and knowledge of the 350, he built something that he considered to be comparable to the factory bikes he had ridden, and be his ultimate anti-450 weapon.

Mike Sleeter's KTM 350 SX-F features:

Engine:

  1. Proven Moto cylinder head mods and reprogrammed stock ECU.
  2. DCR (Dan Crower Racing) billet intake and exhaust cams.
  3. Vertex high compression piston.
  4. FMF 4.1 Titanium exhaust system with MegaBomb header.
  5. Hinson pressure plate and clutch cover.
  6. DT-1 air filter with billet cage and oil filter.
  7. VP Fuels MR-12.
  8. Cometic gasket kit.

Chassis:

  • WP 48mm Cone Valve kit forks and Trax shock setup by KTM Factory Services.
  • KTM Powerparts titanium footpegs, PHDS bar mounts, and oversized front brake rotor.
  • Renthal intellilevers, bars, and sprockets, utilizing the stock gearing (14-50).
  • Nihilo Concepts aluminum gas cap, titanium brake tip, and axle blocks.
  • FASST Company bar inserts and rear brake return spring.
  • ODI MX V3 lock-on half-waffle grips.
  • Acerbis carbon fiber front brake rotor guard and full plastic kit

First Impressions

Factory or project KTM's are always interesting for me to do a walk-around of. As they've hit a higher popularity in recent years, the aftermarket options are finally growing for them. But still, the options are much less than the Japanese models. Typically, even the most built KTM doesn't look that much different on the outside.

In this case, the big ticket items are the engine package and the WP kit suspension. Beyond that, I did a little bit of searching and spotted just a few other aftermarket products. Nihilo Concepts is popular amongst KTM riders as their hard parts aren't only bling, but usually do have a feature that either makes the item tougher or easier to service. In this case, their aluminum gas cap and axle blocks fall into that category. Beyond that, the bike is still keeping it simple with some goodies from Renthal and the KTM's PowerParts catalog. Such as an oversized front brake rotor, cast titanium footpegs, and the PHDS bar mounts (which I love, as they are equipped on X-Trig's clamps which are on one of my personal rides). I also found FASST's anti-vibration bar inserts, which I had never actually tested before, but Mike is a firm believer in.

Outside of the suspension, the bike doesn't sound very trick for someone that spends a decent amount of time on some of the most insane factory bikes in the pits? The true work done to this bike became apparent once we finished with some photos and I swung a leg over it.

On the Track

First up, Sleeter's 350 has WP's version of kit suspension equipped. This includes the Trax shock and the 48mm version of their Cone Valve forks. The factory KTM team runs a 52mm version of this fork, but in recent years KTM's off-road team, amateur riders, and other smaller teams have adopted for the now available 48mm version. I won't go in-depth on what exactly a Cone Valve is, but if you want some info on the forks and Trax shock, go here. These units were set up by KTM/ WP's Factory Services program, which is available to the public.

Once on the bike, these units take on a much different feel than WP's stock hardware. The forks are much firmer, but at the same time, much more free feeling than the production fork settings I've tried. Even though desk life hasn't been as kind to me recently, I'm still a bit under Mike's setup weight. After a few laps, we made the most obvious adjustment and softened up the compression a few clicks. This is where I became a bit more impressed by how noticeable small adjustments were on these forks.

The shock also carries some unique features. The most obvious being the dual adjusters at the top of the shock body, which each service either high-speed or low-speed compression. This may sound like the shock that's located on your own bike, but by separating the two into separate adjusters, it lowers the impact they have on each other when making changes. The other feature is the Trax system, which detects when the pressure on the shock decreases (when the rear tire leaves the ground). This allows the shock to drop back through the stroke quicker, to re-obtain traction with the ground. This can be found to be quite helpful when accelerating across small chop that causes the rear-end to chatter and skip, ending with rear wheel spin. Overall, this kit suspension's characteristics leans more towards an aggressive rider that continually pushes throughout their motos.

As mentioned earlier, the motor side of Factory Services is a very busy place at the moment, with KTM's growing number of teams and support riders. So for this, Mike went outside of the race shop to work with a few people. The main man involved here was Matt Jory from Proven Moto (TLD's former in-house engine development specialist). Together, their main focus was to improve the usability of the 350's engine. In stock trim, the 350 loves to rev, and I mean LOVES to rev, but doesn't have enough bottom end to run higher gears and ride conservatively on rougher and slick terrains. This makes the 350 seem more like a over-the-top 250F than a true competitor to the 450. By focusing their efforts on this missing power, though, the bike came out with a more well-rounded powerband. The bike now felt much more like a tamed down 450 down low. The terrain of the track we rode has soft powder berms, with lots of high speed chop entering and exiting corners and slick portions hidden under the powder, that becomes more apparent as the day wore on. It's actually the same facility that I tested the stock 350 at this year, so it was a perfect comparison.

On the stock bike, I would catch myself downshifting to second gear much more often to find the power I would need, before shifting back to third to tackle the next obstacle. Sleeter's bike however could be treated much more like a 450 and be left in third gear, thanks to the generous amount of roll-on power to play with. This was advantageous for a few reasons. One, the bike would be more in the torque curve, allowing it to accelerate and track much more efficiently across the high-speed chatter bumps. Also, this hit was still less abrupt than the might of a 450 and wouldn't wear me out as quickly. This increased amount of low-end grunt was still followed by a fantastic mid-range, which led into even a bit more top-end than the stock motor had, as well. Having that much more top-end pull made it even more useful in tighter sections, where shifting up for just a split second or two was a waste of time and effort. This is especially true when comparing it to the early sign-off of the 450s it's meant to compete with.

This may sound like an exaggeration, but this really was one of the most enjoyable engines I've had the opportunity to try. Keep in mind, this 350 was built with the expectations to not only pull, but outride 450s at a few select nationals. One of them being Glen Helen, where it was put to the real test by holeshotting a field of 450s at the Dubya Vet World Championships.

Realistically, the amount of work done to the engine isn't overly extensive, as it didn't involve anything below the piston (save for a Hinson clutch). Matt from Proven took care of the cylinder head porting that was focused on low RPM gains. The compression was also raised through a bit of machining and surfacing of the head and cylinder, plus the inclusion of a high compression piston from Vertex (14.1:1 ratio). This was all mated together with a set of Billet cams from Daniel Crower Racing (DCR takes care of the cam duties for JGR and other major teams in the pits) that Matt did some custom timing with to continue to maximize low-end and mid-range power. Once the top end was back on the bike, it recieved a dyno tuning treatment that involved VP fuel's MR-12 and full titanium FMF exhaust system with MegaBomb header. Matt was also able to achieve the needed mapping revisions using the stock KTM ECU.

Beyond this, the work was minimal throughout the bike. Small things such as the larger front brake rotor complemented the Brembo's already excellent job at slowing you down. While the combination of the PHDS bar mounts and FASST CO's anti-vibration inserts almost leads you to believe that you're running a set of Fatbars, instead of Renthal's stiff but precise Twinwall handelbar.

Final Thoughts

The 350SX-F, in my opinion, is truly a fun bike to ride and even race in stock form. But it definitely leaves some potential on the table when it comes to its capabilities as a race bike. This bike however, gave me a completely different opinion of its capabilities with the work that was done. Some may look at this as quite the extensive build when looking at the big picture. For me, I see the engine as the crowning achievement. I wish I had it. Realistically, in the days of four-strokes, this engine didn't involve any bottom end work and kept it relegated to a few key pieces that made a massive difference.

Although I'm lucky enough to have a little bit of everything when it comes to suspension, I usually lean towards spending your money on a revalve/re-spring of the stock components. In this case, WP's kit suspension can definitely be defined as an improvement over what the KTM has in the stock unit's capabilities. Even though I would always preach suspension over motor work, in this case I was torn, as I would most likely choose the motor package when it came to the big ticket items.

About the Test Rider

Michael Lindsay- is a born-and-raised moto freak and gearhead from the heart of motocross in Southern California. First swinging a leg over a bike at the age of five, he immediately caught the racing bug, spending nearly every weekend behind a gate… and a lot of time on the couch while injured. While swinging back and forth between moto and the off-road scene, giving him a wide range of experience on the bike. Of course, all of this led to one thing: Lindsay loves working on his bikes almost as much as he loves talking about them. When he’s not in the Vital MX forum or writing his latest product review, you can find him out at the track taking dirt naps, snapping some pictures, or drooling over the latest parts for his bike. With an outspoken personality, gearhead background, and as Vital MX’s guru for product, Michael is here to share his unbiased opinion.

Product List

Proven Moto: Cylinder head porting and epoxy $440.00, machining and resurfacing cylinder/ head $160.00, dyno tune/ ECU remap $195.00, labor for engine cleaning, rebuild, setting critical engine measurements (deck height and custom cam timing), and dyno chassis services $895.00.
ProvenMoto.com / 801-477-0171

Daniel Crower Racing (DCR): Billet intake and exhaust cams $377.00 each.
DanielCrowerRacing.com / 951-296-9669

FMF: Titanium/carbon RCT 4.1 exhaust with titanium MegaBomb header $949.99.
FMFracing.com / 310-631-4363

WP Factory Services: WP 48mm Cone Valve kit forks $3,149.99 and Trax shock $2,000 (springs not included).
WPfactoryservices.com / 951-234-2254

Hinson: Pressure plate $179.99 and clutch cover $169.99.
HinsonRacing.com / 909-946-2942

Nihilo Concepts: Billet gas cap $49.99, chain blocks $59.95, holeshot fork guard bracket $11.95. and frame grip tape $18.95.
NihiloConcepts.com / 855-464-4456

One Industries: One ID Graphics kit
OneIndustries.com / 808-663-5567

Vertex: 14.1:1 high compression piston $243.58.
VertexPistons.com / 515-270-2302

KTM PowerParts: Cast titanium footpegs $329.99, PHDS bar mounts $199.99, floating front brake rotor $179.99.
Shop.KTM.com/PowerParts

FASST Co: Rear brake return spring $19.99 and anti-vibration bar inserts $59.99.
FASSTco.com / 877-306-1801

VP Fuels: MR-12
VPracingfuels.com / 210-635-7744

Renthal: Twinwall handlebars $119.99, Gen2 front brake lever $89.99, Gen2 clutch lever $89.99, front sprocket $25.99, and rear sprocket $79.99.
Renthal.com / 877-736-8425

DT-1 Filters: Aluminum air filter cage $129.99, air filter $28.95, oil filter $7.99.
DT1Filters.com / 559-651-4120

Cometic: Top-end gasket kit $60.84.
Cometic.com / 800-752-9850

Acerbis: Plastic kit $199.95 and carbon front brake rotor guard $189.95.
Acerbis.com / 800-659-1440

ODI: MX V2 lock-on half-waffle grips $24.95.
ODIgrips.com / 951-786-4755

Dubya: Re-laced stock hubs with Excel rims.
DubyaUSA.com / 714-279-0220

Dunlop: MX32F 80/100-21 front tire and MX32 120/80-19 rear tire.
DunlopMotorcycle.com

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