Dual exhaust for a 307 Olds

[megaladon6]

85cutlass: you can't compare your newer nissan to a 20yr old gm, or even a 20yr old nissan. the old cats were pretty easy to plug. newer ones can be worn out, esp by a rich condition yes, but they won't get highly restrictive.
old or new, burning oil is not good for them.
air tubes feed air from an air pump, driven by the accessory belt, into the exhaust manifolds. this provides extra O2 for the cats and dilutes the exhaust.

 

[kustomkyle]

Thanks for clearing that up. I've tried searching for information on what AIR tubes were and never found anything.

 

[85 Cutlass Brougham]

AIR stands for "Air Injection Reaction". It is the smog pump system, and the attendant parts of it.

 

[joe_padavano]

AIR stands for "Air Injection Reaction". It is the smog pump system, and the attendant parts of it.

The 307 A.I.R. system is designed to serve two purposes. When the engine is cold (before the O2 sensor warms up), air from the pump is sent to the injection tubes in the heads. This is intended to help reduce cold start emissions. After the O2 sensor warms up and the computer goes to closed loop mode, the air from the pump is diverted to the converter. This is intended to prevent the converter from overheating and melting the pellets. On my 86 307 this switching valve had failed, due to the check valves in the exhaust A.I.R. manifolds going bad an allowing hot exhaust gas to flow back into the switching valve.

Two suggestions. First, check the A.I.R. valves for proper function. Second, if you still have the original pellet style cat, replace it with a modern matrix style cat. These are much less prone to meltdown. Pypes Exhaust makes a nice high-flow cat that is low restriction.