MODERN-DAY KTM 380 PROJECT: BEHIND THE BUILD

You gotta love a motorcycle that makes people look. Bob Casper’s KTM 380SX Factory Edition is like that. What’s even better, it makes people listen too. This is a dirt bike that confuses onlookers on so many levels. On initial contact it prompts about three questions in the first millisecond: Was that Ryan Dungey? Was that a Factory Edition? Hey, was that a two-stroke? No, yes, yes. The object is Bob Casper’s KTM 380SX, a custom merging of a highly desirable modern bike and a somewhat forgotten cult bike.

REMEMBER THE 380?

At the close of the 20th century, open-class two-strokes were cashing out and heading for the door. They were still offered, but they weren’t selling well. Four-strokes were coming and 250 two-strokes were more fun. The 500cc two-stroke was simply too hard to ride, but there was an attempt at finding a more manageable displacement from several makers. KTM was always the king of odd-ball engine sizes. There was a 550, which turned out to be a movement in the wrong direction. There was a 350, and much later there was a 360. All were flawed in some way. The last stand of KTM’s open-class two-stroke was actually the best.  In 1998 the forgettable 360 was replaced by a 380. It was actually 368cc in displacement, but KTM engineers put so much effort into making it different from the previous year’s 360, they had to give it a different name. By 2000 it was a genuinely good motorcycle, but no one cared. There was no future for the open class.

Dungey2RF-copy
If you look long and hard enough, you can find anything on eBay. The suspension is Showa’s A-kit from just a few years back.

Some people, however, didn’t forget. Bob Casper is one of those. He’s a 50-something motocrosser with a thing for two-strokes. He has several Honda CR250s of various ages, and he recently built his own aluminum-framed CR500. He rode that bike for a while, but it had a bit too much power, too much vibration and was too much like a 30-year-old Honda 500. Then he saw the ad on KTMTalk.com—a 2013 Factory Edition, or the “Dungey Replica” as people called it then, with a 2000 KTM 380SX motor. His perfect bike already existed and he didn’t even have to build it.

It turned out that Jimmy Wilbourne, a like-minded two-stroke fan in Alabama, had the same idea. He merged the 380 motor with a current (at the time) chassis. It wasn’t the easiest project, but then no engine swap is a bolt-on operation. The whole lower cradle had to be cut out of the original 380 frame because the four-stroke chassis was too tight down there. The 380 has a large resonance chamber in the exhaust manifold that made things difficult, but the rest of the motor fit nicely. The air intake from the 250SX two-stroke was essential, a plate was used to fill the gap left by the fuel pump, and the Doma pipe was easily modified. The ignition from a 250SX was also used. Within a month Bob had sold his Honda AF500 and the Dungey two-stroke was his.

Making the motor fit requied that the cradle from the original frame came with it.
Making the motor fit required that the cradle from the original frame came with it.

THE TRIALS OF FRAME CHANGING

Just because a motor fits into a different frame doesn’t mean it will work. Manufacturers spend a great deal of time working out the smallest details about how a motor sits in any given frame. That point was illustrated a few years ago when aftermarket kits for the Yamaha YZ450F became very popular. They moved the motor forward mere millimeters, and it made all the difference in the world. From year to year motorcycle makers change headstays and motor mounts to fine-tune a bike’s handling. It all goes into the soup. So, Bob continued with the project after it arrived in California. No one was crazy about the KTM’s suspension in 2013, so he found a used set of Showa A-kit suspension. The fork was the factory version of the single-spring SFF unit. From there Steve Piattoni at Shock Therapy helped him make it all work. KTM’s Factory Services wheels were used, and fresh Dunlop MX32s were mounted up.

We got a chance to ride it after it was sorted out. Actually, there probably wasn’t much sorting done—at least we’re sure there was no engine relocation involved. Jimmy and Bob were just lucky. The bike turned out to be one of the best-handling open two-strokes ever. It seemed about 30 pounds lighter than the 500s of long ago. It felt lighter than a modern 450 for that matter, although there’s probably not much difference in the actual weight. But, there’s certainly less rotational mass than either a 450 four-stroke or a 500 two-stroke.

The “Dungey Dragon” has a 2000 KTM 380SX motor in a 2013 KTM 250SX-F chassis.
The “Dungey Dragon” has a 2000 KTM 380SX motor in a 2013 KTM 250SX-F chassis.

As far as power goes, the 380 was still plenty fast. It can hang with any of today’s 450s in a muscle contest. As you might expect, the workable part of the power bank was narrower than that of a 450, but it was still wider and smoother than we anticipated. It just didn’t like to be over-revved. You shift early, unless you really want to get to the next turn quickly and are willing to hold on tight.

The nicest part was that we weren’t afraid of the throttle. Yes, it made a lot of power, but not so much that it got in the way. When you weren’t twisting it hard, you could ride at very low rpm without any fear of stalling. That’s something that modern four-strokes still haven’t worked out. Some aspects of the bike, on the other hand, were stark reminders that you’re dealing with 20-year-old technology. It took a mighty kick and an iron foot to start. Vibration was a little intense at higher revs, and traction wasn’t always so easy to find. If you got a little carried away with the throttle, it might keep on spinning until you back off and start all over again.

KTM Factory Services wheels found their way onto the Dragon.
KTM Factory Services wheels found their way onto the Dragon.

Overall, though, we loved it. We just wish there were more 380 motors laying around in need of a modern frame. We’re not saying that it was better, faster or more competitive than a modern bike, but we do believe that if open two-strokes were this good back in the day, perhaps we would still be riding them now.

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