Exhaust Expansion Chambers - in laymans terms (how it works)



All right Fellas. I ve seen numerous posts on Exhaust chambers on multiple threads and thought I could lay it out in easy to understand detail.

Two strokes are all about the exhaust. When combustion occurs in a two stroke, the piston is pushed down by the expanding gases uncovering the exhaust port. The exhaust gas rushes out into the header pipe and a pressure wave is created. This wave can be either positive or negative in pressure. If it is a positive wave and hits a change in diameter in the tubing of the exhaust pipe it changes to a negative wave. Hit another change in diameter and the wave changes back to positive. This wave pressure can be as high as seven pounds per square inch (Both positive and negative waves) and can travel over 1500 feet per second..

If the pipe is made just right, a wave with negative pressure reaches the exhaust port just as it is fully open. This sucks the exhaust AND part of the new intake charge into the exhaust pipe. Then, just before the piston closes the exhaust port, this negative wave changes to a positive wave and pushes the fresh intake fuel charge BACK into the cylinder. All this happens in three to four thousands of a second. This sort of supercharges the engine, giving the high power out put of a two stroke engine. Without that properly designed exhaust pipe called an "Expansion Chamber", the two stroke engine will have no real power!

There is only one draw back to all this and that is that this supercharging only happens at the specific RPM that the pipe was designed for. Running the engine at any RPM above or below the designed RPM and the supercharging effect will be much less effective. That is why two strokes have such a narrow power band.

The length of pipe between the exhaust port and the expansion chamber determines at what rpm your power will be at .
Lengthening or shortening thid header pipe will make the power band kick in at iethr a highr or lower rpm will affect

One problem with two stroke exhausts is that they can get plugged up with carbon from the oil used to lubricate the engine. The bike will start easily but just will not rev up. This is especially true of quiet exhausts. If the exhaust has removable baffles or is fiberglass packed, you can easily clean them and replace the fiberglass packing. If the baffles are not removable it is much harder to clean them. Many stock two stroke exhausts have non removable baffles or have only one or two baffles that are removable. The different baffles collect the unburned carbon and plug up but you can't easily get to them.
Our pipes have removable baffles but its something to think about if you plan o n switching pipes.

Hope this helps abit



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