let me start off by saying i have been reading on this pre-cat issue for about 3-4 hours this week so i have searched.

I am thinking about buying a friend mazda 6 3.0 ... its a 03 with 130k on it ... it has the vacume leak pcv valve problem i think. He said i could buy it for 2k.

My only issue is the cats...

I am not worried about no emissions or none of that my state doesn't check all that.

My question is can i gutt both front pre-cats and cutt off both rear cats and the motor run fine... I am also not worried about the checkin engine light coming on this is just going to be a cheap gas saving car.

also is the metal easy to cut and weld back on the precats?

 

READ: https://www.mazdaforum.com/forum/gen...effects-30404/
LOOK AT MY PICS: Mazda Forum - Mazda Enthusiast Forums - UseYourNoggin's Album: 2006 Mazda 6 V6 3.0 Exhaust, Stock & Modified

FROM FIRST THREAD TO READ LINK: Removing a catalytic converter will result, at most, in 5 HP in power improvement. However, hollowing out a catalytic converter will cause resonance problems. The symptom is most often seen as a hesitation, popping, or backfire at or about 3,200-3,500 RPM. Upon hard acceleration, the engine will appear to cut out for a split second as RPMs drop and a split second later recover and continue past 3,200-3,500 RPM. Additional symptoms are a loud and continual popping sound when the vehicle is allowed to decelerate under load and a whooshing sound that is delayed from or following the engine speed. This is due to the open chamber within the hollowed out catalytic converter case. It loads up and releases pressure in the exhaust system that acts almost as a capacitor. The open chamber allows the formation of standing waves within the chamber which reflects back toward the engine and causes the hesitation and miss in the RPM range.
The symptoms become more pronounced as the exhaust system is made freer flowing, meaning that hollowing out a cat with the stock exhaust may cause mild annoyance, while it becomes a serious problem when a header and performance exhaust system are installed, mimicking a ignition miss or backfire. This is probably the best reason not to hollow out a catalytic converter.

My .02: When you look at my pics you'll see how they are attached. They are actually 1 assembly which is part of the exhaust manifold.
You can probably remove from past pre-cats and jam something in there to unclog cat or clean it as per video in one of the threads you read.

If you try to remove bits and don't know if you got them all, you should do this first before starting car as bits can re-enter engine intake via the EGR:

READ: EGR_BYPASS Post 98, 108, 183, 187, 208. Great NY is the Mazda Guru on that site.
This is post #108: the egr has 2 points that it is connected to. one in the EGR which is mounted on the Intake manifold and the other end of the pipe is connected to a port on the leftmost runner of the rear exhaust manifold.
cut the EGR pipe up by the EGR valve and leave about an inch of pipe. then remove the pipe from the exhaust manifold. slide the pipe out of the nut that held the pipe to the exhaust manifold. stick a penny inside the nut with some Ultra copper gasket maker. I think someone tried using a penny and it melted. screw the nut back onto the port on the exhaust manifold. done, u have now capped the exhaust manifold port for the EGR. you arent plugging the manifold. just the port for the EGR.
now run a heater hose from the EGR valve to the intake. DONE.

MY EXPLANATION: Buy cutting the steel hose from behind the EGR and removing the rest of the solid hose that goes to exhaust manifold (source of exhaust), you've completely eliminated the exhaust from re-entering intake manifold. You fill in what you've cut with a plug or maybe just bend the tube?
Now the short steel hose sticking out of your EGR valve (where the exhaust originally came from) is not hot!. Attach some heater hose to it and run a line to the intake, before the MAF sensor. Some people put in just before the air filter with nipple attachments, elbows. Not sure on hose selection as it is subject to vaccuum now.
Now the EGR still works according to the ECU, but it is passing air instead of exhaust. Not sure on side effects of too much oxygen when EGR cycles.
I sent the above to another member and he thinks NOX values may be higher. Your O2 sensor may give you cel since your pre-cat is gutted or gone! You may need some O2 simulators to stop cel.

With the EGR by-pass you are guaranteed no catalytic converter bits will re-enter your intake manifold.

 

Why would you want to gut the catalytic converters? Are they causing a problem? If they don't cause a problem I would not mess with them. Without functioning catalytic converters the O2 sensors will give false readings and the computer will try to make up for it. It won't be able to do so hence you will get the CEL. Apparently you are not afraid of that. But how would you know if the engine is running right or not?
You should at least monitor the fuel consumption. Almost always the the fuel consumption will go up if something is awry.

I would keep it as close to stock as possible and run 1 gal of laquer thinner (NOT PAINT THINNER!!)on 1/2 tank of gas for about 100 miles. That will clean the deposits out of the engine AND the catalytic converter. I would do this only once every 100K or so.

You may be an 03junky, but that doesn't mean you have to have a junky 03.