WE RIDE DUBACH RACING DEVELOPMENT’S KTM 350SXF

February 19, 2012
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You’ve probably heard so much about the 2011-12 KTM 350SXF that your mind is on overload. By some pundits, the KTM 350SXF has been heralded as the second coming, and the ballyhoo was accompanied by a successful race debut in the hands of 450 World Champion Antonio Cairoli. Historically, aftermarket hop-up companies don’t put KTMs on their “must-do” lists when it comes to making project bikes. Not so after 2011. Every company immediately started working on KTM 350SXF parts, pieces and paraphernalia. Why? Because of all the bikes offered in 2011-12, the KTM 350SXF is selling.

Doug Dubach became a believer when, in record time, DR.D (Dubach Racing Development) ran out of 350SXF pipes, including their entire production run of stainless steel, titanium and carbon fiber systems. Amazingly, racers had pre-ordered pipes before they even laid hands on their bikes.

Like most aftermarket companies, DR.D was excited to get the latest thing and try to make it better. The high demand for exhaust systems not only sweetened the deal, but DR.D was quick to predict that the KTM 350SXF would be embraced by Vet class riders. This is important, because Vet racers are more likely to be able to afford a cool new bike, less likely to adhere to traditional engine displacement class structures, and more likely to buy aftermarket parts. Early in the game, DR.D back-burnered some Japanese-built bike projects to go full-speed ahead with testing of their KTM products.

To make the most of KTM’s popular mid-size racer, DR.D focused on the engine and had Enzo work on the suspension.

As for MXA, we had spent more time on the KTM 350SXF than virtually anyone outside of the KTM R&D department. We aren’t telling tales out of school by saying that we were hoping for a little more from the 350SXF. Don’t get us wrong; many of the orange helmet crew loved to race the bike. But virtually every MXA test rider hoped that it would fall a lot closer to the 250 side of the spectrum on weight and a little closer to the 450 side on power.

When Doug Dubach told us he was working on a 350SXF project, we were excited. We had been tinkering with and tuning our KTM 350SXF for the last two seaosns and had made a few discoveries?but hadn’t kicked out the jams in terms of engine development. So, we were eager to get together with one of the sport’s most famous factory test riders to compare notes. Best of all, Doug was willing to hand over his full-race KTM 350SXF so that the MXA gang could test it, play with it and race it.

SHOP TALK: DID THEY COVER THE BASES?

DR.D teamed up with Malcolm Smith Motorsports on a joint project that both hoped would hit a home run with buyers. Malcolm Smith’s shop is one of the nation’s most famous motorcycle dealerships.

FIRST BASE: First base for DR.D was to hone the 350SXF engine’s power delivery. They felt that the 350′s cam profile was sufficiently aggressive and that the compression ratio was more than high enough at 13.5:1. DR.D’s goal wasn’t to build a time bomb, but to depend on exhaust tuning to maintain the durability of the stocker while showcasing DR.D’s bread and butter?their exhaust pipe.

Engine mods were relegated to degreeing the stock cam and porting the head. The cam timing was outsourced, but DR.D performed the head porting in-house. You won’t find the service advertised on www.dubachracing.com, but if you send in your cylinder head, they will port it, recut the valve seats and inspect the valve train. DR.D didn’t notice a huge difference on the dyno with just these mods.

Naturally, most of DR.D’s attention was focused on the exhaust system, and our project bike got the titanium version. Most MXA test riders prefer to stick with stainless steel systems because they offer more bang for the buck, but on their project bike DR.D wanted to mount their top-of-the-line system. Doug felt that the KTM 350SXF had good spots and bad spots, but wasn’t as unified as it needed to be. Doug believed that by adding more midrange and top-end power, he could define the working zone of the 350SXF.

Most DR.D full titanium systems cost $869.00, while carbon systems cost $919.00. The Ti systems for the 2010/2011/2012 YZ450F and 2011-12 KTM 350/450 cost $919.00. We understand the increased complexity of the Yamaha’s loop-de-loop midpipe, but we’re not sure about the KTM.

 
Enzo handled the suspension chores, and tried to make the 350XF work without going to stiffer springs. It didn’t work.
 

SECOND BASE: Second base was covered by Enzo Suspension, which Doug Dubach has had a long relationship with. On the bill were suspension revalving (front and rear) and stiffer fork springs (0.49 from 0.46 kg/mm). In testing, Doug’s first goal was to get the 350SXF suspension to stay up in the stroke and keep the forks from diving when entering turns.

THIRD BASE : At third base were some carefully chosen performance aftermarket accessories. A Turn Tech 2.5-amp battery was aptly chosen as an affordable way to shed almost three pounds. Hinson got the call for clutch duty and supplied an inner hub and clutch cover.

For years, Doug Dubach’s go-to tire combo was a Dunlop 756 in the rear and a 745 in the front. With these two tires discontinued, Doug switched to an MX51 in the rear and MX71 in the front. Most MXA test riders could live with this tire setup, although we opted for an MX31 front tire for deep loam and softer dirt.

HOME BASE: Bringing the project home were Renthal TwinWall handlebars and Kevlar grips, DeCal Works T-7 custom graphics, Motul lubricants, and a DR.D hour meter. Renthal also supplied the sprocket combo (with an extra tooth on the rear to help the bike rev through the powerband quicker).


Doug Dubach’s goal wasn’t to turn the KTM?350SXF into a fire-breather, but rather to give it one unified powerband?instead of two distinctly different ones that come with stock.

TEST RIDE: PUT IT THROUGH ITS PACES

The MXA wrecking crew put DR.D’s KTM 350SXF to the test in the most difficult situations we could find in SoCal. We drag raced up the steep hills at Glen Helen, hammered Competitive Edge’s Supercross track, powered through mud at Racetown and, most important, we lined up behind the starting gate and raced the bike in competition. In doing so, we found exactly where the bike’s strengths and weaknesses lie.

Low-end power felt a little stronger than stock on the DR.D 350, but for all intents and purposes, it was still best to skip straight to the midrange?which was significantly improved over the stocker. Trying to eke out every pony we could when chasing 450s and charging down straights required getting to the high-rpm sweet spot as soon as possible. In stock trim, the 350SXF has two powerbands?a slow, torquey low-end and a revving, high-rpm top-end. That might sound good on paper, but it is kind of schizo on the track. We preferred one powerband over two. The biggest perk of the DR.D powerband for some was more forgiving shifting points. The DR.D 350 was more forgiving if you came out of the turn in a taller gear or shifted sooner.

We were excited to do some Supercross riding on the 350SXF to see how it matched up against the traditional 450cc Supercross bike. The DR.D 350SXF had its merits. It felt light and lively around the technical course, and it was comfortable at speed. There were places where a 450 could be a handful, but it was hard to deny that the abundant low-end torque of the 450 was incredibly useful for hooking up on hardpack, jumping out of a turn, and shifting up in a whoop section. The DR.D 350SXF’s titanium pipe and lightweight battery helped make the KTM 350SXF about five pounds lighter, but to be truly competitive in Supercross, the 350SXF needs to lose another five pounds.

Indoors or out, the MXA test riders were comfortable with the bend of the Renthal TwinWall handlebars, but they were split on rigidity. Our Intermediate and Novice testers thought the bars were too stiff, but our Pros loved that trait.

From the factory, the 2011 KTM 350SXF is sprung like an enduro bike. Even featherweight test riders thought that it needed to be stiffer. As a rule of thumb, MXA recommends dropping the stock 0.46 fork springs and 5.4 kg/mm shock spring for 0.50 and 5.7 springs (luckily in 2012, KTM made these changes for us). DR.D didn’t change the shock spring, but they did stiffen up the forks. The biggest difference was in the Enzo valving. The front forks were great at handling hard G-outs, big bumps and whoops, but when the speeds got faster and straightaways started to get choppy, the forks beat us up. We softened the compression considerably to try to find a happy medium.

As for the shock, we don’t think anyone under 150 pounds can run the stock 5.4 kg/mm shock spring from the 2011 and will need the 5.7 from the 2012. Since Enzo kept the stock spring rate and tried to control movement with valving, the shock tended to feel very dead. We think that a stiffer shock spring would bring some life back to the rear end.


DR.D exhaust systems come with a magnesium end cap, a healthy dose of midrange power and an AMA-legal bark.

VERDICT: INCARCERATED OR VENERATED?

For a racer, the stock KTM 350SXF’s usable powerband doesn’t start to work until 9000 rpm and up. It must be ridden like a 250F (albeit a very powerful one). It can never be raced successfully as a mid-sized 450. It isn’t strong enough below 9000 rpm to be short-shifted. This is an all-or-nothing engine. MXA test riders either hated this engine or loved it; there was no middle ground.

DR.D’s KTM 350SXF powerband is much better than the stocker because the beefed-up mid-and-up powerband expands the working zone of the engine. The power is broader, not so single-minded, and while it’s no midrange monster, it does get started sooner. The DR.D version of the KTM 350SXF isn’t the ultimate racing weapon, but it is a nice shove in the right direction. If you plan to race a 2011-2012 KTM 350SXF, you should consider hopping it up to enhance and expand its existing powerband. Otherwise, just buy a KTM 450SXF.

For more information, go to www.dubachracing.com.

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