Tripper511

Im looking to purchase a high flow catalytic converter on ebay. The seller says that it won't come with the air tube unless specified. Im not sure what the air tube does, so if anyone can explain this to me before I buy it, it would help a lot. thanks.

v8nate92RS

If your car came with a stock cat that has the air tube, you will need to buy an aftermarket cat with the air tube if you want to stay emissions legal. It is part of the A.I.R. system that recirculates exhaust gases to reduce emissions.

Apeiron

The A.I.R. system actually pumps fresh air into the exhaust to to reduce CO and HC emissions.

v8nate92RS

Yes, and works together with EGR to reduce emissions.

Apeiron

Yes, but they're not dependant on each other. some cars came with one or the other but not both.

v8nate92RS

You are quite right.

DanTheMan_smlk

so what happens if u buy a cat without the air tube when your car is supposed to have one?

IROCThe5.7L

Just let the tube hang I imagine.

v8nate92RS

You are no longer emissions legal. Effects are probably non-existent to minimal as far as it messing with the performance of the engine.

DanTheMan_smlk

ok, thanks

thirdgenbird

letting your air tube just hang has absolutely no adverse effects at all. here in iowa we have no emissions checks so when my cat went out i just had a pipe put in to replace it and the air tube just hangs. someday i would like to put headers on and eliminate the air system all together.

OUTATIME GTA

iTrader: (2)

Is it okay if the tube is plugged if it' just hanging?
I took out my cat and it is hanging and plugged by weld.
I wasn't sure it it affected airpump or performance.

DanTheMan_smlk

what exactly does the system do? Pump air into the manifolds so it seems like less exhaust gas is comming out? Fake emissions?

five7kid

iTrader: (14)

A.I.R. provides additional oxygen to complete the reaction of unburned fuel and promote the conversion of noxious compounds, to reduce undersireable emissions.

It does not "dilute" the exhaust, it does not recirculate exhaust gases (it is completely independant of the EGR system - EGR cools the combustion temperatures under certain conditions to reduce the formation of nitrogen oxide compounds).

A.I.R. is routed to the manifolds in open loop operation and during certain closed loop conditions in some systems. It is routed to the cat during closed loop operation to avoid giving the O2 sensor false indications.

DanTheMan_smlk

but its ok to take it off then right? Will it give my O2 sensor bad signals?

Apeiron

Removing the A.I.R. system won't affect the O2 sensor at all.

DanTheMan_smlk

ok, what can i use for a screw on cap to the air tubes on my edelbrocks?

five7kid

iTrader: (14)

A screw-on pipe thread cap.

JPrevost

Pumping air into the manifolds is to warm up the oxygen sensor (non-heated ones like what comes stock on thirdgens) and to warm up the first brick in the cat. When closed loop is ready the air pump will direct all air flow into the middle of the cat to give the second brick IT'S needed oxygen to do it's job. Do a search on howstuffworks.com about cats, it'll tell you everything you need to know and then some.
Removing the air going to the middle of the cat WILL effect your emissions, not by much, but it will none the less. If you can pass without it then good, if not, oh well.
You don't want to leave that pipe open. It will be an exhaust leak and you could easily fail inspection for it. Plug it up if you're not going to use it.

DanTheMan_smlk

no emissions here

Jetmeck

iTrader: (3)

Then you can remove the tube and air pump and clean up your engine bay.

bonz

So does the air tubes going to the manifolds only turn on on engine start up or do they come on more often.