528i Catalytic Converters [Archive] - Bimmerfest - BMW Forums

: 528i Catalytic Converters

04-17-2005, 05:34 PM
Hey all,

I've been trying to find aftermarket catalytic converters for my '98 528i, and i found a couple magnaflow cats for $84 each at


I don't know the size of the 528i cat though, is it 2" in/out? or is it 2.25" in/out like the 540i?

TIY, I appreciate it


04-17-2005, 06:02 PM
Before you buy the universal cats, if you are buying new cat(s), you should talk to an experienced exhaust specialist before you install them. I tried an aftermarket cat, and had horrible results. I found a good exhaust guy and he informed me that the aftermarket cats he has installed on 540's have all failed after 6-8 months. I replaced my universal aftermarket cat with a direct fit unit. Although very expensive, I have a 5 yr, 50,000 mile warranty. These units just bolt on and away you go. I hope you check into this before you purchase them. Good luck!

540 M-Sport
04-17-2005, 06:03 PM
Instead of trying to "MacGyver" something up, why not buy a decent aftermarket cat that has all the proper fittings and end pipes so it will bolt right up, with a minimum of fuss?

I just did a "google" search and found these:

I have no idea if they are any good, but may be worth investigating.


04-19-2005, 03:16 AM
sorry to intrude... but i didnt want to make another thread for this.... but what does the resonator do and if i took it out would the sound of the exhaust be cooler?

04-19-2005, 12:13 PM
540 M Sport,

Unfortunately, the previous owner of my car "McGyvered" it up originally. By reading other posts, I tried to use a non-direct fit type cat, which was a HUGE mistake. I had to do what you recommended, and what I recommend to others that have had cat problems. Now, I have a correctly installed direct fit, fully warranted and functional cat on my car that meets the OBDII and Calif. EPA standards. You cannot "cheap out" and expect your cats to last very long.


No offense, but you don't need to remove the resonators on your car to make it "cool". The car itself speaks "Cool". Don't you agree?

540 M-Sport
04-19-2005, 05:29 PM
Glad to hear you got your car fixed correctly. Keep us posted if you have any further troubles with the aftermarket cat. I have seen threads that folks have had troubles with aftermarket cats causing "check engine" light to come on. Not sure why. Whether they are just poorly made, or if the BMW O2 sensors and system is just very sensitive to having the "correct" or factory cat.

04-20-2005, 08:11 AM
sorry to intrude... but i didnt want to make another thread for this.... but what does the resonator do and if i took it out would the sound of the exhaust be cooler?
The resonator is suppose to quiet down the exhaust note. One thing is for sure, it weighs like 40-50 lbs. and so just losing that weight could be a big deal!

04-20-2005, 12:52 PM
540 M Sport,

Yes, I'll keep everyone posted on this. BTW, the exhaust guy mentioned to me that he believes that the reason for the SES light coming back on is due to the smaller, universal cats becoming clogged and losing efficiency, or in my case, they were just not allowing the exhaust to flow correctly and triggering the SES light. All is well for now.