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Discussion Starter · #1 ·
Guys,

After researching a fair bit and finding little to no info re the cats, i decided to give it a go and see what happens.

My reasons as follows:

1. Complete decat was out of the question for many reasons.
2. Yes the 3.6 m5 ceramic cats are rock solid however after 20 years, like anything else do become backed up. No questions about it.
3. I found the highest possible flowing racing cats with what the clacify at 100 cell CPSI cells per square inch. Standard e34 m5 ceramic cats are 400CPSI. Lets face it, Cat technology has come a long way in 20years. Also look for metal substrate.

4. When the old cats were removed, up against the light with a torch in one end, you cannot see any light whatsoever.
5. New cats, hardley block any light whatsoever. Chalk and cheese.
6. End result, little louder, engine breathes much better, much more response, maybe a few more HP.
7. For what its worth, highly recommended. About $600 AUD all up.

Befor and after Pics.

p.s. Eisenmann coming right up with pipes straight through to cats (gettin rid of the resinator)


These things are FULL with carbon and shi^ knows what else. They also weight alot.




Much Better.

 

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Anyone in the Chicago area known for good exhaust advice? I have so much to learn and need a shop that's willing to talk. Nice work ^.
 

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I would love a set. Here in CA we have high Smog Regulations. So I'm going to smog it then replace. Just in case. It would be nice to find something similar here in the US. :)
 

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i know i have an impending replacement sooner or later, i will certainly be looking into a pair of these! how much lighter would you say these new cats are? does anyone know how a racing cat will stand up to emissions testing vs. stock?
 

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Those look great. Did you have an O2 sensor before? If so, do you still have one?
 

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Discussion Starter · #9 ·
Hi Guys,

I would say these most definately stand upto emissions testing. Obviously each country is differennt but i would hardly worry about the.

In terms of weight, i would say at minimum each of these cats are 5-6 times lighter than the factory unit.

Yes most definately had an o2 sensor and yes the cats were cut off just before the o2 sensor x pipe thus not affecting it.

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A good bit of advice if doing this project.

Replacing the o2 sensor is a bit of a PITA because they are very tight and it is impossible to get a spanner/socker or any such tool onto it with the exchaust in place. Thus meaning to change the o2 sensor you need to drop cat section of the exchaust from the extractors/headers, which is easy enough but may leak if undone and not sealed 100% again.

Bottom line, if doing the cat changes, once the shop cut the old cats off (you will be able to physically pull the exhaust section low enough by hand to get a shifter or open end spanner onto the o2) , its literally a 5 minute job to change the o2 sensor and run the cable to the lower side of the motor, ITS VERY EASY.

My o2 sersor was original 180k and car was running dangeriously lean, even causing the mass air sensor code. Once replaced beautifull, no more MAF code.

DO NOT do away with your o2 sensor. All m5's fuel and igniton systems run in closed loop communication to richen and lean off the AIR/FUEL mixtures and the o2 sensor is a crucial part of that system. along with the MAF, coolent temp sensor, air box intake temp sensor, injectors, fuel presure reg, fuel pump and a number of other sensors around the engine.
 
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