Magnaflow cat converter question

[Dash01]

BMW 535ia, M30 engine:

For those who have replaced their OEM cat converter with Magnaflow or similar stainless steel units, can you please describe and/or show pics of exactly how you did it?

I imagine the old stock pipes would be cut and the Magnaflow spliced in with U-clamps or similar. What about the O2 sensor, the mounting brackets, etc.?

In my case, the Magnaflow or similar would then be mated to a Supersprint stainless muffler.

I'd like a better idea of all this before proceding.

[gale]

I did a custom job on mine a few months ago:

http://www.bimmer.info/forum/showpos...61&postcount=1

I have aftermarket headers & downtubes which caused me to temporarily remove the stock cat altogether, since there was only 16" to work with between the end of the downtubes & inlet to the stock resonnator.

Magnaflow has a universal 2" dual-in/dual-out universal cat that's rated for the m30 motor, part number 94008:

http://www.car-sound.com/02product/parts/94008.jpg

You can get them on ebay for $80 w/free shipping:

http://cgi.ebay.com/ebaymotors/Magna...spagenameZWDVW

You'll need to get an "X" or merge pipe with a bunge in it for the O2 sensor such as this one from my friend's 735iL:



Google Jegs or Summit for a possible source for that. I lucked out & the Harge downtubes were already merged with the O2 sensor bunge:



Just about any muffler shop could weld them up for you.

[alexander525]

have their been any noticable perforamnce differences with the headers? im really considering them but if they are a waste of time why bother..

[gale]

My "butt-o-meter" measured a noticable performance increase, especially low-mid range. It rev's more freely and needs less pedal for same power as before. It pulls strong past 6k without any effort. Can't say if that's from the headers or lack of a cat, prolly a little of both.

For an m50 with a 4-valve head, I would think the gains would be more significant, especially at the top end. On the other hand, just adding tube headers and nothing else, the gain will be marginal. It's the type of mod that will work best with the whole picture as in hotter cam, mild porting, MAF or bored throttle body, aftermarket exhaust, etc. Then things start getting expensive -- maybe time to consider forced induction.

[Jon K]

If you have an aftermarket exhaust (and usually no resonator, or very open resonators) hi-flow cats will make your setup louder.

Don't expect to feel any difference. You will actually probably lose low end torque but pick it up in the high end.