First off, a ZDZ uses a disk valve intake system, and the difference in how the engine operates versus a reed-valve induction engine is noteworthy. With a reed-valve engine, the intake pulses to the carbuetor mirror very closely the exhaust scavenging pulses, but with a disk valve engine, the valve is open at low rpm when it should not be (or a reed valve would be closed) making the scavenging and intake event of a disk valve rely on the exhaust event a bit differently, an in fact causing reversion from positive pressure pulses when the disk is open at the wrong time.

Also, remember that the BME's intake ports for the 102 and 105 are based on some very conservative "weedy" jugs, and that the combustion chamber and exhaust port are not designed with any type of "tuned" scavenging in mind. So, for the BME, having a short header, along with a free-flowing large canister style muffler, is more of an advantage than it would be for the ZDZ. Not to say that a ZDZ would not benefit from this style of exhaust, it does, but the older BME wil not gain as much from a fuly tuned system, the way a ZDZ would, but a more conservative exhaust will yield better results than a conservative setup would for the ZDZ (in theory). It all comes back to the necessity to "balance" the intake and exhaust events in the engine.

Basically, a 4-5" header on the BME 102/105, combined with the 50cc or 70cc Pefa canister muffler, will yield a decent power increase, but not at the expense of mid-range characteristics. The exhaust event is short, less than 150 degrees, and attempting to crutch it for a lot of upper rpm power will only cause it to run very poorly and have poor transition characteristics. Stick to a conservative setup, and the engine will easily wake up to the tune of 200-300 rpm, while not losing mid-range smoothness. This is true for any engine, but for the early BME's, with their limited intake and exhaust porting designs, it's a bit more important.