02' Exhaust Help? Any StangExpert will have input on this so please help!

[cughter]

Vehicle: 2002 Base 3.8L Mustang

Preface: Head gasket broke a few months ago and I guess water got into the first Cat Converter on the drivers side. It was fine for a month or so then somehow it cracked and it rattles when I drive and it popped up a code for it as well.
I'm just trying to figure out possible solutions and I have a few questions for any Mustang experts that might be able to answer them.

Questions:

1. The stock exhaust on this mustang has 2 small catalytic's near the header on each side, 2 medium sized catalytic's a bit lower on each side and 1 muffler. (correct me if I'm wrong.) However, a lot of the after market exhaust I've been looking at doesn't even have catalytic converters it looks like, just a muffler? My concern is: If I buy and install an after market exhaust system will I be able to pass emissions? That's the only thing I'm worried about really, I don't wanna spend that kind of money for it to be a waste.

2. If the answer to #1 is NO, then what modifications will need to be made in order for the car to pass emissions? (I mean, the stock exhaust has 4 O2 sensors on the midpipe and it looks to me like none of the aftermarket exhaust systems have O2 sensors, Do I need to drill a hole and install the sensors into the new midpipe myself?)

I'm just very confused and not very experienced with cars, any input would be extremely helpful.
Thanks guys!

3.

 

[Bullitt347]

The two small catalytic converters just after the exhaust manifolds/headers are called "pre-cat's" and the two larger ones down stream are your regular 2 way catalytic converters. Many manufactures did this back then before the now common 3 way catalytic converter came into being. If you actually have a damaged catalytic converter, then you can legally change it out. Since the "cat pipe" from the factory is a one piece item from the manifolds down, then all 4 cat's on that pipe can be changed out for a new "cat"pipe". I believe that y0u can upgrade to a more modern 3 way catalyst "cat pipe" that would have only 2 cat's in it, one for each bank. The 4 O2 sensors that are in the "cat pipe" are used in this fashion: The front O2 sensors (before the catalytic converter) are used to monitor if the engine is rich or lean and make or tell the ECU to make the appropriate corrections rich or lean as the case may be. This monitoring of the exhaust from the "upstream" O2 sensors happens hundreds of times a second. The rear O2 sensors (after cat) or downstream O2 sensors monitor the exhaust to see if the catalytic converter is doing it's job of cleaning up the exhaust. If the sensor reads the same ( same switch rate) as the upstream catalyst, then the ECU knows that the catalytic converters are not doing their job. ( result is a check engine light and a code of P0420) The rear O2 sensors also sample the exhaust hundreds of times a second, but usually only have to switch (rich/lean) about 1/100th the amount the upstream O2 sensors do. As a result the rear O2 sensors switch rate is about 1/100th of the front sensors. For the ECU to do it's job properly, it needs to see the rear O2 sensors. The aftermarket has produced rear O2 sensor "eliminators" that plug into where the rear O2 sensors would normally be, and they provide the correct voltage signal that the ECU likes to see. Best case legally for you is to install a new "cat pipe" that has the correct catalytic converters be that a stock 4 cat pipe, or a more modern cat pipe that has the newer 3 way cats. The newer 3 way cats do the same job as the older style pre-cat/2 way cat combo did. The illegal way to do it would be using a "off road" H or Y pipe that has no catalytic converters and using "MIL eliminators".
Just an added note: Modern 3 way catalytic converters are so free flowing that you have to be well over the 500 wheel horsepower level before they become any kind of a restriction to the engine. So do not buy into the BS that to make power you have to remove the cat's, this just is not true.

 

[jrod2423]

if you take your cats off and take them to a junkyard you might get enouugh to pay for the 2 new cats, but all depends on how many precious metals are left in them and what the price is on them at the moment.
also don't break open the cats before you go because the junkyard probably wont buy them, i think they still have to be sealed for a junkyard to accept them