I have a few questions on Magnaflows highflo cat. first off whats the difference between it being oval and round? my 2nd question is the oval one has an option 2 come with or without an air tube, what does this air tube do? newb questions i know but i wanna make a smart choice between these 3. Thanx in advance guys. Catback to come in 2-3 weeks!

 

well the air tube comes from the air pump which blows air into the cat.