Can anyone explain why the exhaust scavenging on a 2-stroke using an "expansion chamber", is not carried over to the 4-stroke engine. I remember reading that on some of the older Corvettes they used an exhaust maifold they called a "rams horn", although I've not seen it it sounds like the shape of the expansion chamber I used on 2-stroke engines. Can anyone explain how an expansion chamber scavenges the exhaust? Any help would be appreciated.

4-strokes have an entire stroke devoted to expelling exhaust gases, hence no need. (the strokes: 1-intake, 2-compression, 3-power, 4-EXHAUST) Although the concept is close when people are tuning their exhaust systems to have the correct amount of backpressure, so that the departing pulse helps pull exhaust gases out of the combustion chamber.

the "rams horn" manifold is only called that because of the way it looks. the front and rear ports drop down below then loop back up to connect to the center two ports. the manifolds found on the camaros are sometimes called log manifolds because they're shaped like a log, ei. a straight chamber from front to back with the four ports all in-line.