Here's the situation:

I hear rattling noise coming from the below the front/below car. The shop said it's the cat. So I need a direct replacement. It will be hooked up to the stock/oem exhaust. Which one do I get?

I'm thinking of getting 2 of the 2.25" in/out since I'm going to hook it up to the stock exhaust. Do I need to get the ones that accept an O2 sensor? TIA.<ul><li><a href="http://www.hottexhaust.com/search_results.asp?txtsearchParamTxt=&amp;txtsearchPar amCat=44&amp;txtsearchParamType=ALL&amp;iLevel=1&amp;txtsearch ParamMan=ALL&amp;txtsearchParamVen=ALL&amp;txtFromSearch=f romSearch&amp;btnSearch.x=1&amp;

If you want to go with a 2.25" inlet/outlet you should probably use the 94005.

Your muffler shop can install a O2 sensor bung after the cat, if necessary.

If I do purchase these Magnaflow cats, how much work and ($$$) will it cost to do the cutting/welding?

Here's my situation. My cats are f'ed up, so I just need to replace them. I have a stock exhaust, stock everything.

Also, a fellow AW'er recommended these "direct replacements." $280 for each.

What do you recommend? Thanks.<ul><li><a href="http://www.discountconverter.com/converters/audi/audi_direct_fit.cfm">http://www.discountconverter.com/converters/audi/audi_direct_fit.cfm</a></li></ul>

It should cost you under $100 to get them installed. Call around and get some prices or ask for a good place on your regional forum.

Some of the guys around here also like the catco cats as they are even cheaper than Magnaflow. Can't recommend a place to get them, though.<ul><li><a href="http://www.hottexhaust.com">This is where I got my Magnaflow cat</a></li></ul>

So, I get two 2.25" Magnaflow cats or do you recommended something else?

One other thing to mention, you'll probably have to replace the flex pipes, too, as they are right up against the cats. The exhaust shop should have these on hand.

I won't pass CA requirements with these, will I? I checked the Magnaflow website and they just released their 4300 series, which they say are CA OBD2 compliant.

to find out for sure which to use. The 50 state OBD2 compliant cats are more expensive.

i think my cats are on the down hill way and if i dont need to replace 2 o2 sensors and save a couple hundred $s new cats seam like even a better idea..