After-market E38 Catalytic Converter

[Gigs]

My mechanic tells me that he will not install after-market E38 cats because they have a tendency to blow after 15,000 miles. He's been getting a lot of complaints about them. I spoke to a guy at BavAuto who said that after-market cats are fine as long as you replace both of them at the same time. Money is the main concern with my soon-to-happen wedding. I am willing to shell out the cash, but just hope to find a cheaper alternative of equal quality. Any thoughts on what I should do?

[Auraraptor]

My mechanic tells me that he will not install after-market E38 cats because they have a tendency to blow after 15,000 miles. He's been getting a lot of complaints about them. I spoke to a guy at BavAuto who said that after-market cats are fine as long as you replace both of them at the same time. Money is the main concern with my soon-to-happen wedding. I am willing to shell out the cash, but just hope to find a cheaper alternative of equal quality. Any thoughts on what I should do?

Rob Lev has an excellent high-flow cat setup for sale. I know when my cats go, those are what I am getting.

[Bread]

Rob Lev has an excellent high-flow cat setup for sale. I know when my cats go, those are what I am getting.

True, but they aren't cheaper by any means. Many people get the Magnaflow High Flow Catalytic Converter (2.25" inlet/2.25" outlet model # 53005) to replace the stock units. They're cheap and I haven't seen anybody post here about them failing.

They might even be the same one's Rob uses without all the high-flow piping that his kit includes??? Not sure.

[johngoga]

True, but they aren't cheaper by any means. Many people get the Magnaflow High Flow Catalytic Converter (2.25" inlet/2.25" outlet model # 53005) to replace the stock units. They're cheap and I haven't seen anybody post here about them failing.

They might even be the same one's Rob uses without all the high-flow piping that his kit includes??? Not sure.

I don't think so.

I am sure Rob's are build from scratch.

John

[Auraraptor]

I don't think so.

I am sure Rob's are build from scratch.

John

He uses Magnaflow High Flow 2.5 in 2.5 out.

[Auraraptor]

Good Read on cats:

http://www.randomtechnology.com/technical.html

[Auraraptor]

BTW A 53000 series cat will NOT work on a 750iL.

In fact, it is not ideal for the 740's 4.4 engine either, as the max it is designed for is a 4.2.

http://www.car-sound.com/catalog/universal/530.aspx
The 53000 Series universal is a small footprint round body universal for use with small displacement engines or as a front converter in dual converter systems.

That said, I am not sure if it is ok in dual, it doesn't say.

[johngoga]

He uses Magnaflow High Flow 2.5 in 2.5 out.

Wow, I was under the impression that he made those from scratch.

John

[Bread]

Wow, I was under the impression that he made those from scratch.

John

He made the pipes, but nobody can make a cat from scratch.

[Trey]

True, but they aren't cheaper by any means. Many people get the Magnaflow High Flow Catalytic Converter (2.25" inlet/2.25" outlet model # 53005) to replace the stock units. They're cheap and I haven't seen anybody post here about them failing.

They might even be the same one's Rob uses without all the high-flow piping that his kit includes??? Not sure.

Mine only lasted 7 months/8,000 miles. Just replaced them with DEC.

tw

[Mblaster]

He made the pipes, but nobody can make a cat from scratch.

IIRC the internal biscuits in ALL aftermarket hi-flow cats are made by the same company.

[Bread]

Mine only lasted 7 months/8,000 miles. Just replaced them with DEC.

tw

DEC?

Cat's don't fail on their own. Generally speaking they should last hundreds of thousands of miles if the engine is running properly. If they fail prematurely then the engine is having any number of issues including too rich fuel mixture, coolant being burnt, etc.. Things that will collect and clog up the internals.

[Trey]

DEC?

Cat's don't fail on their own. Generally speaking they should last hundreds of thousands of miles if the engine is running properly. If they fail prematurely then the engine is having any number of issues including too rich fuel mixture, coolant being burnt, etc.. Things that will collect and clog up the internals.

True, most don't fail. But these cars are notorious for failed cats. The Magnaflows that were put on as replacements for the originals were smaller than factory. They thought they'd work, but didn't last.

I believe the ones that were put on this time are DEC or some variation of that name. My indy has guaranteed them for a year, so I hope they last. They were about $1000 less than originals.

Regardless, I can't recommend Magnaflow as a replacement since I didn't have good luck with them. Everything with the engine checksout good - not the cause of mine failing.

tw

[Jfstu]

Hey Mblaster, that is one of the best looking cars BMW ever made. I have been looking for just the right one for years. How many miles do you have on it and how reliable has it been? I hear repairs for those things make my 740 look like a honda. Any truth to that?

[Bread]

True, most don't fail. But these cars are notorious for failed cats. The Magnaflows that were put on as replacements for the originals were smaller than factory. They thought they'd work, but didn't last.

I believe the ones that were put on this time are DEC or some variation of that name. My indy has guaranteed them for a year, so I hope they last. They were about $1000 less than originals.

Regardless, I can't recommend Magnaflow as a replacement since I didn't have good luck with them. Everything with the engine checksout good - not the cause of mine failing.

tw

Well it's certainly good to have options. Do you have any information for the DEC units? Part numbers or something like that? I'd like to have options when mine go out Thanks for the input.

[Rob Levinson]

Make cats from scratch? Nooo... I very specifically used the Magnaflow 94100 series because they are certified OBD-II compliant.



That's something which is very important to me, to keep the car clean and legal (or at least within what a reasonable law should be). Why use an "illegal" cat when a legal one is the same price and performance? Why risk the hassle if some inspector ever questions the installation?

I have not officially offered the cat section for sale just yet... as we're so tied up with other projects at the moment, I do not want to make anyone wait. As soon as I build them and have them in stock, then they will be offered.

It's a pretty neat system. The altered pipe size and longer secondary V section do seem to add to torque production.



- Rob

[Rob Levinson]

Forgot the most important part in the thread above, got distracted by a phone call.

The 94100-series cats are each rated for displacement up to 6.2l. So with 2 of them, you have 12.4l of capacity. The extended concept is that if you were to supercharge or turbocharge your 750, the cats have enough capacity to handle approximately 20psi of boost.

- Rob

[Auraraptor]

Rob, I know your cat lead in tube is 2.5 inches, but how wide is your post header tube?

I am thinking of getting the G Power header unit and matting it to your cat unit. (after/if I get satisfied with Magnaflows). I need to get more details on the G power unit, though. This may actually seem like the most cost-effective option, but it is still in the air yet.

[Rob Levinson]

Rob, I know your cat lead in tube is 2.5 inches, but how wide is your post header tube?

I am thinking of getting the G Power header unit and matting it to your cat unit. (after/if I get satisfied with Magnaflows). I need to get more details on the G power unit, though. This may actually seem like the most cost-effective option, but it is still in the air yet.

I posted a bunch of technical details about this in another thread, but here's the short version:

OE post-header pips has an ID of 1.9"... it looks much bigger because it's a double-walled pipe. My new pipes are 2" and configured exactly the same length before the "V" as the OE.

This sizing is more than sufficient for this size motor; for comparison reference, the contemporary E36 M3 with 3.2l of displacent used similar sizing, and it had another 1200rpm. If you think about each half of the V12 as a 2.7l 6-cylinder, dual 2" leading to a single 2.5" is more than sufficient.

Of course, size alone is a simplistic way of looking at the situation that does not tell the whole story. In my experience, the very critical post-manifold tuning that BMW does is often spot-on. The primary inefficiencies come from the cat size/type and various crimps or restrictions that are manufacturing or sound compromises. With the shorter Magnaflow cats placed strategically, we get a longer secondary-V pipe length for effective retention of exhaust velocity before hitting the cats.

- Rob

[Shinobi'sZ]

So Rob,
I need a passenger side Cat for my 1998 740il. Who has the best price on one of these? If it is a complete bolt in I can do it myself, or have the muffler shop weld in a new one.
Thanks

[Rob Levinson]

So Rob,
I need a passenger side Cat for my 1998 740il. Who has the best price on one of these? If it is a complete bolt in I can do it myself, or have the muffler shop weld in a new one.
Thanks

I would not suggest you use just one side of a performance cat setup, you will have more restriction on the OE side.

- Rob

[Shinobi'sZ]

I would not suggest you use just one side of a performance cat setup, you will have more restriction on the OE side.

- Rob

Ok how about a price on both.

Thanks

[daverehm]

I am also looking to replace mine. How much would it cost and can I install myself?????

[khajdiddy]

I need to replace my Cats tooo... DAMMIT my regular mechanic gave me an estimate of $1,000. And of course its not coverd by my extended warranty. I have 107,XXX miles on my car so its way over the 80,000 or 8 years replacement warranty. Anyone know of any good shops that will install the magnaflow in the northjersey area cuz my mechanic is in denial and says he cant install it. boooOOooo!!

[Jfstu]

Can someone (Rob) give an estimate for the replacement of the cats with the aftermarket ones you mention? Also, is it safe to assume that if you keeps your oxygen sensors fresh you wont have to worry about the cats failing?