Im not huge on FCs yet, but i had a question for you guys

How many cats are there on a N/A FCs, i think theres 2? and is both crucial for passing smog? or just the main one?

Thanks guys

 

Mine had 3 but you can pass with just a main one. You'll most likely need a new one.

 

Theres 2 pre cat's and a main cat!

Here in Cali if the ref knows you've removed the pre cats he'll fail you. But Ive never had that happen to me!

 

You can always just use a large metal pipe/rod and some elbow-grease on the inside of the pre-cats in order to pass visual inspection, but keep them from failing and free up some airflow

 

I hollowed out the 1st and 2nd precats. It passed cali smog with flying colors. 88 GXL 130k. To answer your ? FC N/A's have 3 cats.

 

Ive also passed without pre-cats.

 

You should pass without the pre-cats. They shouldn't be doing anything when the main cat is at operating temperature.

The pre-cats get hot, and up to operating temperature very quickly due to their size and position. This reduces emissions created at and after startup. After a short period the main cat will fire off, and start functioning. Somewhere around this point the pre-cats become too hot to function properly, and you are basically running on just the main cat. This is why you will pass smog with the pre-cats gutted.

 

the S4's have 3 cats while the S5's have 2.

I don't know about the ACTUAL numbers WITH only the pre-cat. The pre-cat is the "stock header" btw (in case there was a confusion)

 

Wrong the 2 pre cats are after the header and they bolt up to the header. This is of course on an s4.

 

My stock S5 exhaust sure as heck looks like it's got 3 cats.

 

On an S5 the middle section is essentially a straight pipe (my '89 was this way anyhow). The first section has some sort of mesh stuff in it that acts as a pre-cat. When I replaced the three sections from the manifold back to the y-pipe on my car (I used this Magnaflow combo), I found that the mesh stuff had come loose from the pre-cat and lodged against the front of the brick in the main cat.