I would like to buy the magnaflow hi flow cat..There re 3 options,round,ovel and ovel with air tube...What exactly is this air tube for and do I need it?

AFAIK only manual trans cars have the air tube.
If you don't have a smog pump/air pump, to inject air into the cat, on the engine then you don't need it.

Actually, all of the cars had the AIR system from the factory for certain years....my '88 IROC has the system and it is an auto trans car. I actually just finished installing Hooker 2055 headers with AIR and a Dynomax high flow 3" cat that also has the AIR tube. Not that big of a deal......

I have a 91 v6 firebird..this means I need the one with the air tube right?

Some cars inject the air into the exhaust manifold at the heads. The best thing to do is look under the car at the CAT that you have now. If it has a small tube coming off of it that goes back up toward the engine, than you need one with an air tube.

Parts America only lists the air tube for '91's with manual trans.


http://www.partsamerica.com/SelectPa...tic+Converters

I will check that out thanks...

By the way.What size Do I need?
I have a dynomax catback (2.5 inch) I think..Does that mean I need the 2½ inch in/out cat?

IIRC the y-pipe is a 2-1/4". So 2-1/4" inlet 2-1/2" outlet.

Wtf?

The only cats i see listed in the mag are the same sizes in and out...such as 2"in/out2½in/out and 3inch in/out

That's the trouble with having a V6. The magazines never list anything that fits! Only stuff for V8's.

edit: I've got a CATCO high flow cat on my car. Bought it from Summit on their web site. If you read the sticky at the top of this board on "what's the best exhaust" you'll see there isn't much difference between any of the after market cats.

So I need 2¼ in and 2½ out right?

I'll call up Magnaflow to see if they have that size..If not i'll go with catco or whatever else is available