[taylor99ss]

I understand our cars (e9x) have 2 sets of cats. One set on the DP's and another along the exhaust path. Im currently looking to purchase a catless exhaust system, but i know in the near future im going to upgrade and get cat-less DP's. Is this a recommended set up? If i were to have cats on the car, which location is the best? at the DP or along the exhaust? something tells me its better to have cat-less DP's and keep the cats along the exhaust. Also, if I have no cats, isnt my car illegal?

please help.

thank you

[vasillalov]

Things you have to consider when going fully catless:

1. It is a federal crime to tamper with emissions systems. If caught you can face a $5K fine for first offense (someone correct me on the dollar amount) and more for repeated offences.

2. How strict are your emissions testing stations. Some will perform visual checks, use tail pipe sniffers and other tools to detect problems. Others will simply scan your ECU to look for stored emissions related codes.

3. Some people report bad smell when stopped at a red light.

4. You will need either an O2 Simulator or another way of tricking your car computer into thinking the cats are still there and working.

Personally, I went fully catless and I have BMS O2 Simulator (see signature for mod list). I've been running this setup since April of this year and the car has been running great!

It should be noted that I have kept all of my original hardware in the garage. If needed, I can always re-install everything, pass emissions and then revert back to my aftermarket hardware. Also, in Chicago we have scan-only emission testing stations. My ECU has not codes so I am confident I will pass without any problems. Another thing is that in the state of Illinois, and possibly other states, a vehicle is not due for inspection until 4 years have passed from the original sales date. For my 2008 model, this means that I won't be due for emissions till 2012.

Finally, I have can definitely smell my exhaust when I am stopped at a red light. However, it is nothing like the "rotten egg" smell most people describe it as. It is somewhat strong, but not something I will consider a foul smell.

Having said that, I recommend going completely catless only if you feel confident that you will not have problems passing emissions down the line.

[forza1976]

no cats means there could be issues passing emissions.

Running fully catless is quite a bit louder all together. Running without the primary cats (DP cats) does produce more noise but it's not obnoxious.

If I were to do it, I'd run the secondary cats with catless dp's

[Daya]

I am running AR catted DP, Borla catless MP and BMW O2 sim. No codes, drone, or smell.

[scrufy]

Dunno about Texas but in California you have smog test bi-yearly. You need to put them on or it won't pass. Simple as that, some inspect and fail visually but my Vette used to fail anyway on the emissions regardless. Yes, it is also illegal, I don't know the specifics on that so I won't waste everyones time by spouting off my opinion as if it is true law, lol, like I have seen in a few other threads...

[Doug007]

Texas just checks for codes on the OBDII system. No SES light and you'll be fine.

[WWM3]

Does a car need just one set of cats to pass emissions or does one need both sets? Like if you just remove one set at mid pipe or on DPs?

[Doug007]

You either need:

1. Cats in the downpipes between the two sets of O2 sensors, or
2. A O2 sensor fix to fool the OBDII system

In states that use exhaust sniffers for late model cars you may not be able to get away without both sets of cats (can be replaced with high flow versions).

In states that just check the OBDII system, you just need the O2 sensor fix (BMS sells one and it's built into the PROcede). Midpipe cats don't have downstream O2 sensors so you can get away without them. You can probably get away with fully cattless with an O2 fix at most emissions stations.

[cstavaru]

Originally Posted by Doug007

You either need:

1. Cats in the downpipes between the two sets of O2 sensors, or
2. A O2 sensor fix to fool the OBDII system

In states that use exhaust sniffers for late model cars you may not be able to get away without both sets of cats (can be replaced with high flow versions).

In states that just check the OBDII system, you just need the O2 sensor fix (BMS sells one and it's built into the PROcede). Midpipe cats don't have downstream O2 sensors so you can get away without them. You can probably get away with fully cattless with an O2 fix at most emissions stations.

I think the best setup is to eliminate the downpipe cats and relocate the O2 sensors behind the midpipe cats.

[WWM3]

Originally Posted by cstavaru

I think the best setup is to eliminate the downpipe cats and relocate the O2 sensors behind the midpipe cats.

Anyone running this setup?

[igom3]

Originally Posted by scrufy

Dunno about Texas but in California you have smog test bi-yearly. You need to put them on or it won't pass. Simple as that, some inspect and fail visually but my Vette used to fail anyway on the emissions regardless. Yes, it is also illegal, I don't know the specifics on that so I won't waste everyones time by spouting off my opinion as if it is true law, lol, like I have seen in a few other threads...

Not if you buy new car. No smog for seven years.