Looks like an "anti- reversion chamber" to keep consumed/exhausted gases from re entering the combustion chamber. it has a cone shapped pc inside and directs any unwanted backflow of dead gases to the sides, within the pipe chamber instead of flowing directly back thru the center of the pipe and back into the cylinder during cycles of low pressure.
http://wiki.clubcivicquebec.com/imag...on_chamber.jpg