Secondary air injection
 

I was wondering if I could take the belt off of my my air pump on my S4 FC? The belt makes a lot of noise bc the pump isn't lined up properly with the other pulleys.... I know it puts air in the cat to help burn excess fuel but my cat is hollowed out anyway. I just wasnt sure if it did anything else?

That is one function of the air pump air. The other is that it mixes fresh air with exhaust via the ACV. Your car will probably smell worse, but it won't affect performance.

The air pump belt also spins the water pump pulley. When you remove that second belt, it can allow the pulley to slip and slow down the water pump. Common fixes are to run dual alternator belts (which requires a different pulley) or a yoohoo belt.

Well the car smells terrible anyway lol but it doesn't bother me, just the people behind me lol and ya I was worried about the water pump but I wasn't too sure how much it would effect it.... How much does a yoohoo belt go for?

It's a generic part. I seem to remember the part number floating around on the forum.
Or you can buy it from Pineapple racing.

Sweet thanks for the info!