I've read about the scavenging effect a bunch of times, but I have no idea what it is. Anyone define this for me?
What is scavenging?
- Thread starter nofxfan125
- Start date
The 2 stroke headpipe is designed to create a area of pressure and large volume , as the exhaust gas exits the head under the initial restriction it creates velocity , then the chamber gets bigger and allows the exhaust gas to slow down and expand ( expansion chamber ) then its compressed again and is forced out the silencer . The expansion chamber does 2 jobs , it creates vacuum and back pressure . The vacuum is created at the end of the headpipe where its diameter is decreased and this is where the scavenging effect happends , the backpressure occurs in the fat section where the scavenged exhaust expands and creates a backwards pressure wave that gives resistance to the combustion chamber so the current fuel air mixture isn't sucked out . In the normal 2 stroke cycle there is a point where the intake and exhaust ports are open at the same time , which creates velocity for the incoming charge and without the exhaust being designed the way it is , much of the fuel air mix would be sucked through the chamber without ever being burned . Hopefully that makes sense .
Would like to add to Blastard's statement and stress what an important role the shape, angle and timing of the transfer ports play in scavenging. There is some good reading on this at MacDizzy's Two Stroke Technology Exchange - TRX - YFS - YFZ - Glamis Sand Dunes
