I need new Cats

[Mark 178]

OK, so I've got the rotten eggs/sulfur smell coming from my exhaust after spirited driving.... I know this usually means the cats are on the way out, so:

What's the best option?

- Replace with OEM

- Replace with aftermarket

- Remove and replace with resonators

- Remove entirely and replace with straight pipe

And should I replace the back section of the exhaust at the same time? (not that finances really allow at the moment)

Cheers, Mark.

[*Glenn* 854]

Go 3rd option thats what I did

You only have to replace cats with cats when you have pre & after cat oxy sensors

Aftermarket cats are $375 each fitted

Just replace the cats with dogs (resonators)

Cheers

Glenn

BTW..the smell could be running too lean...have you had it scanned ??

Edited June 18, 2008 by botanymotorworx

[Mark 178]

Cheers Glenn... will go with the dogs option then!

Haven't had it scanned, but I'll do that first before I start hacking up my exhaust.

[Apex 693]

OK, so I've got the rotten eggs/sulfur smell coming from my exhaust after spirited driving.... I know this usually means the cats are on the way out, so:

What's the best option?

- Replace with OEM

- Replace with aftermarket

- Remove and replace with resonators

- Remove entirely and replace with straight pipe

And should I replace the back section of the exhaust at the same time? (not that finances really allow at the moment)

Cheers, Mark.

My car has made that smell since new.. Are you sure there is a problem?

You could always look at a sport-catalytic converter also.

[steve R 0]

Straight pipes!

[Lubed 55]

You say you only get the smell after "spirited" driving which means your exhuast temp will go higher than normal driving which will burn off residue from the cat.Chances are your cat is fine, if it is not rattling or blocked then leave it in to do its intended job.

[Mark 178]

All good points guys... I can't hear rattling or anything and I don't think it's affecting performance so maybe next time it happens I'll just close my eyes and think of Rotorua!

[Yuen 16]

If only you were in Auckland Mark... I've got just what you need!

[Mark 178]

If only you were in Auckland Mark... I've got just what you need!

And what exactly would that be Yuen?

[Yuen 16]

And what exactly would that be Yuen?

Full de-catted 328 exhaust system, so has M52 manifolds, resonators in place of cats, and 328 exhaust with ACS tip. I also have brand new gaskets. Would go well with the diffuser... and I got it for my M50B20 so it should work for your M50B25.

[dcm17 0]

Im looking to get rid of my cats just because I feel I want the car to breath better. Is there any advantage in replacing the cats with a resonator or am I just wasting time?

I just put a K&N panel filter up front so now its time for the back end

[Mark 178]

Im looking to get rid of my cats just because I feel I want the car to breath better. Is there any advantage in replacing the cats with a resonator or am I just wasting time?

I just put a K&N panel filter up front so now its time for the back end

If your 323i still has the stock exhaust you'll get good gains by replacing it with the cat back section from a 325i or 328i. Heaps of them about too and you can bolt it up in your garage (need the help of a mate though)

[pureboiracer 0]

all cats do is drain power and cause problems.... ohh and help exhuast gas polution but thats no biggie. so if i were you i would take them out and put dogs or pipes in weather they were stuffed or not

[martyyn 2]

all cats do is drain power and cause problems.... ohh and help exhuast gas polution but thats no biggie

Which is why BMW fit them to pretty much every car they make

If your going to make a statement like that you really need to have something to back it up with.

[pureboiracer 0]

Which is why BMW fit them to pretty much every car they make

If your going to make a statement like that you really need to have something to back it up with.

they fit them because they have too. they wouldnt pass emissions standards otherwise. unless its a aftermarket high flow cat it will drain power. its a known fact

[martyyn 2]

they fit them because they have too. they wouldnt pass emissions standards otherwise. unless its a aftermarket high flow cat it will drain power. its a known fact

Ahhh so they do do something other than drain power, they cut emissions.

What about all the problems you claim they cause. There must be thousands of people on here with them but only a handful of people who have had trouble.

Im not trying to pick a fight, just wanting some stats to back up your comments that they do nothing but cause problems.

[Apex 693]

Speaking from experience I wouldn’t go removing a catalytic converter if your car has a sensor on or after it, it could cause all sorts of problems

[swiggs 0]

Ok i am speaking from experience.

I had a problem with my cat. Well i have two but one of them disintegrated and was causing my engine to stall/ ordered some new ones but would have been ten days before they come into the country. so i had my garage take both cats out and put a straight through pipe in and earth out the o2 sensors.

But the car then was running rich, I mean super rich, i remember seeing on my screen read out 28L/100km. NOt good. It was the o2 sensors playing up. We rerouted them and it worked fine. We got around the problem by disconecting the MAF sensor(the car will then just run on the computer average from the previous 100,000 km) But by doing this alone we lost alot of power at low end but solved the fuel and rich problem. So we also disconected the backpressure line on the inlet manifold so to get more air at lower revs. This worked a jem.

Now the sound from just having the straight through pipes was alright at idle, a definate lower pitch, and when just crusing at low speeds there was a pleasent low drone, not irritating by no means. But the downside was when i accelerated heavy it sounded like a bloody skyline cackling away. Was horrible!! Sounded so tinny and cheap.

And for power to be honest I didnt notice any increase in power for acceleration, if anything i did notice that it changed gear more firm in the touque zone.

But as soon as we got the cats back in when they arrived and hooked everything up it was fine.

Cats shouldnt cause an issue at all. but like everything they do need to be replaced when they age, BIG deal really. If you want to free the exaust up by doing a simple mod you should look at doing the rear mufflers. I did this after the cat debarco. Didnt change the tips or anything as I like how the 740 conseals them but it sounds great, clean under acceleration and slightly more powerful and slightly cheaper to run.

My advice if you cant afford new cats is to replace with free flow baffels (as i hate cackly sounds from cars). But be very carelull with the o2 sensors and get indapendant advice on this. BMW has so many electrical systems in place that when u mess with one it trowes the whole car out of kilter.

Hope that helps