As soon as DL has 9000 engines delivered to customers more info will come in regarding their performance with a cannister or pipe. Frankly the stock setup works so well most users won't go to the hassle of a longer system. It is quite loud though.

Basically, the exhaust port has the same dimensions as the DA (and a few other engines, btw). A 50cc engine "tuned" to swing a certain size prop in a certain RPM range and possessing a certain diameter header will ALWAYS require a certain length pipe.

Most of the "improvement" in power seen using a cannister arises because a cannister typically flows much better than the side-dump or pitts style muffler it replaced. Most of the cannisters don't give much of a "tuning" effect (although some do). In fact a sharp tuning peak is not desired because it makes the throttle more difficult to manage. We desire a nice, broad power curve without any peakiness.

Soarrich, you probably need to follow the experience of others who use a cannister on a 50cc engine and use the same header length. If your pipe tunnel isn't long enough it may be worth modifying to give you the exhaust length you desire. This should require only minor surgery on the airframe.