KTM has always been a company that has offered options and filled niches in the market. The 250XC is an off road oriented race bike while the 250SX is a Motocross bike. Also offered is the 250XC-w which is said to have a wider ratio transmission and be the most mellow version of the three. Swapping the head is a good upgrade on a 250XC.
|New SX Head|
While these bikes differ in more ways than one, the head is an area where KTM can easily change the characteristics of one bike compared to the other. Altering the compression of an engine can do a lot to the power of an engine. The SX has higher compression than the XC, and the XC higher than the XC-w. Higher compression generally makes more power, but can also make an engine less reliable and/or less rideable if not done properly or kept in check. Elevation gain actually lowers compression, so the compression an engine makes will tend to be more of an issue for those that ride at higher elevations. Having these heads that are interchangeable factory options made a nice easy and safe way to give my 2010 KTM 250XC a power boost. Since I always ride 4,000 or above, it brings it back to the compression range I'm looking for. I picked the head up for $164, add new o-rings for under ten bucks and some shipping and I was ready to go. The part numbers are almost identical, but do vary with one number. The 250 xc # is 548301063
00, 250 sx # 548301064
00, and the 250 xc-w # is 548301062
00. This really is an easy swap, just unbolt the old head and re-bolt and re-torque the new head. Be sure to get new o-rings any time you remove the head.
|Head removed, new o-rings|
It's a good idea to keep the stock head in case you ever want to go back. The higher compression gives a big boost to low-end and mid-range performance and torque. This upgrade won't make the bike into an SX and still maintains smoother more tractable power. To get closer to SX power you must combine the head with a new CDI unit. The kind of riding you do most along with your personal style and preferences will determine what kind of power upgrades you want to do. I like the feel of the SX head along with the red power valve spring and stock XC CDI unit. With this setup I ride most with the ignition mapping wire connected. In this configuration having the wire connected is more aggressive and it revs more free and spins the rear tire more easily. By disconnecting the wire, or flipping a switch in my case, the power will be a bit more mellow and take a little longer to wind up making it a little easier to ride in loose terrain. It seems as though with the stock power valve spring it's more aggressive with the wire disconnected. The SX CDI unit will make it rev more like an SX and tend to make it a little harder to ride on tight trails, but will give it a power boost. It adds horsepower and torque from the bottom to the top and should be combined with the SX head.
|Head comparison, old XC on left, new SX on right. The spark plug sits deeper on the SX because of shallower bowl.|
|Another comparison between the two. Notice the shallower bowl on the SX, pictured right.|
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