Removing catalytic converters on a 2000 v6 Mustang?

Question

I live in Oklahoma, so we don't have to get emissions checked. I have a 2000 v6 3.8l Mustang. I bought the car for $3500 at 70k miles (it was a really good) so I don't want to spend more money than I have already done with maintenance (around $1000/ brakes, other stuff, etc) to make the car "better".

Would removing the catalytic converters cause any negative effects on the engine? Would it affect how it runs in a negative way? I'm not to worried about the ECU popping up a code, because I could always take my ECU to get flashed (tuned) to run without the catalytic converters.

Answer 1

The catalytic converter is there to make your exhaust cleaner. It does nothing critical to the proper running of the engine itself. If you remove it, all that will happen is that you'll get dirtier exhaust and an error code P0420 (Catalyst System Efficiency Below Threshold (Bank 1)), which is to be expected because the "catalyst system" has been removed.

If you reflash the ECU to ignore this error, you won't have to worry about it ever again. I got the same error in my Subaru Forester after I had the downpipe decatted. When I reflashed the ECU, the error no longer popped up and it didn't affect my performance in any way. In fact, turbo spool is quicker because the exhaust is less restrictive now ;)

Answer 2

tl;dr: I can't find any evidence that removing the catalytic converters on this model will improve the car. It will definitely confuse the ECU (and obviously pollute more).

I've looked hard for any dyno sheets that show any concrete evidence that cat delete alone will add power.

Removing the cats is something that I would almost never recommend outside of certain specific circumstances:

1. Removing a pre-turbo cat on an early 2000s WRX. Those fail after years of use and will suck all kinds of turbo breaking yuck into the turbine.
2. Building a race exhaust from the ground up where cats aren't required anyway.

Downsides:

1. Louder: this might be something that appeals to you. However, I find the tinny cat delete sounds to be like a drill in my brain.
2. Confused ECU: the ECU will almost certainly throw codes due to the change in airflow and composition. On my car, a confused ECU means lower performance.
3. The exhaust fumes will be illegal in many states: unless you're planning to live in one place forever, you should consider whether it's going to be worth the hassle when you decide to move or even drive out of state. Local ordinances will win if they don't like your new volume and non-catted exhaust smell.
4. Also, as Fred Wilson reminds me, it is against federal law to remove or replace a functional OEM catalytic converter.
5. Hidden costs: getting any benefit from a no-cat exhaust will require tuning. This, this isn't really a zero cost solution.

Practical recommendations for other ways to get cheap fun:

1. Get a cheap intake. Better airflow up front will certainly help.
2. Remove the muffler / replace with minimal required: a lower weight muffler will likely sound much more fun than no cats. If I could get away without mine, I would. :-)
3. Remove weight in the car: can you replace the spare tire and jack with a can of fix a flat?
4. Better tires: are you driving on the original tires? Dump them for something new but affordable and be impressed.