What is this air pump for on these engines. (I have a 88 N/A) I looked under the hood yesterday and I saw this airpump and it said do not remove on it (I'm guessing just for emmision reasons). Also, I keep reading about 5 and 6-port stuff with back pressure from the exhaust, what is this all about?

 

The air pump supplies air to the catalytic converters and exhaust manifold to help with emissions. This air allows unburned fuel to be burned in the manifold supplies cooling air to the cats to help both cool them and provide oxygen for the reaction that converts the nasty stuff to CO2.

The aux ports are a whole other discussion. Best to check the factory service manual for a good diagram of the induction system. This is also covered in the Haynes.

 

In short, they 5th and 6th ports (aux ports) open at high rpm for more power. They are only operated by the air pump in 89-91 cars, so you shouldn't worry about it. There was just a discussion about this a few days ago, try searching for it.

 

but the 88 and lower are controlled by back pressure from hte exhuast.... right ??

 

There is argument as to whether they are controlled by exhaust backpressure or velocity but yes, they are opened by the exhaust.

 

Yeah I Learnd Sumthin

 

As a side note, my RB header is ideally set to measure exhaust velocity; the aux port tube sticks down into the center of the exhaust pipe and points directly at the exhaust port (think pitot tube). That's not the ideal setup to measure overall backpressure by a long shot!



Maybe the stock S4 had enough backpressure, but I don't think that's the case here.

 

So if I were to straight pipe the exhaust then this 5/6 port stuff wouldn't work right I suppose? What if I just left a muffler and the rest straight pipe? Also, if I removed the air pump that wouldn't effect anything other than emmissions right? I'm lucky..... we don't have emmisions down here!!!

 

It's doubtfull that a muffler alone would open the aux ports.

If you remove the air pump, you also need to block off the ACV, remove the cats and get a duel alternator belt pully.