Well I finally got my Eisenmann 83mm race muffler. What i'm planning on doing is going to a local muffler shop and having them make me some custom piping from the headers back, no cats, no resonator. My question is, if I install the O2 sensors directly into the piping, will this work? If not, what do I have to do to make this setup work? Thanks in advance!

:dunno

You're going to get a cE light for sure. The post-cat O2 sensors are not going to get the proper readings.

And the cats are integrated into the headers, so you cant just have the muffler shop make new pipes, they'd have to make an entirely new set of headers.

So your telling me that there is no way to take off the cats without replacing the headers? THen how do you simply replace the cats when you buy aftermarket cats from lets say Supersprint? How do i get around having the lights come on and making everything run properly?

You'd have to replace the headers completely if yoy want to remove the cats... the cats are part of that assembly.

How do you get around the cE lights? Somebody will probably invent a set of O2 simulators that you could use on the car. I know there are a set for the E36 M3... I believe the E46 M3 uses the same 0v-5v O2 sensors instead of the typical 0v-1v O2 sensors on other cars.

However, I heard that the first attempt to use O2 simulators on a S54 powered MCoupe (E46 M3 engine) didn't work, so it's back to the drawing board.

MSpired, are you doing any engine modification or getting forced induction? If not, then you have no reason to replace/remove everything you're talking about; a simple muffler swap to the exhaust that you want will be more than what you need and alot cheaper too!

I appreciate the comments/opinions/suggestions, but I now what I want to do (take off the cats and get teh most HP), can anyone give me a technical answer please?

Originally posted by MSpired
I appreciate the comments/opinions/suggestions, but I now what I want to do (take off the cats and get teh most HP), can anyone give me a technical answer please?

What's wrong with the answers above? As far as I've been told ( I haven't actually been underneath an E46 M3 yet), the cats are integral with the tubular headers that come on the E46 M3. To remove the cats, you must remove the headers. That means buying some really expensive aftermarket headers to go in their place.

If that's not the case, then just remove them and go for it. If it is the case, you've gotta decide if the HUGE price for a new set of headers is worth the 2-5 horsepower you MIGHT gain. If you are expecting huge horsepower gains from removing the cats, you might as well look elsewhere.

Originally posted by MSpired
THen how do you simply replace the cats when you buy aftermarket cats from lets say Supersprint?

You don't. Take a look at the Supersprint website...they don't offer any cat replacement. They offer the rear exhaust, and two different center replacements, both of which attach to the stock cats.

They also don't offer headers, as the headers on the E46 are already tubular and pretty much optomized. You don't get 333 hp out of a 3.2 liter engine without optomizing everything, which is the reason you just aren't going to see much of a gain at all by trying to remove the cats.

Maybe try and get the exhaust manifold off a European Spec M3. The dealer may be able to get you one, but I am sure it is going to cost an arm and a leg...

ss headers for a e46 m3 do exist. how do i know? i have a set here that i ordered for a customer. unfortunately he's trying to sell them now cuz he needs $$$ for personal reasons. that's another story though.

but the headers do exist. and so does a cat replacement and race pipe for no cars. it replaces the section of pipe aft of the headers and before the secondary resonator.

on the headers, there are also only 2 o2 ports. so o2 sims will have to be used or ce lights will come on. also, an exh temp sensor bung needs to be put in too.

-alex