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