{HEAD ~ The inlet chamber} has {TAIL ~ inlet ports} communicating with exhaust pipes respectively and the outlet chamber has an outlet port communicating with a downstream exhaust pipe 
has
{ HEAD ~ The inlet chamber } has { TAIL ~ inlet ports } communicating with exhaust pipes respectively and the outlet chamber has an outlet port communicating with a downstream exhaust pipe
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH