Magnaflow Cat comments/info

[robnitro]

I used to have a Magnaflow 93006D 2.5" cat (the wider one, 7"). It got plugged up quick- when I saw that a straight pipe gave me less smoke/better boost response I did some research. Some other people have noticed that it clogs up and back-pressure goes up a lot (up to 9 psi!).

So, I rushed into bashing the ceramic matrix out, removed both and put the cat back on.

It started to be annoying to have the smell, especially idling in traffic. So, I saw a later thread that said he removed only 1 of the 2" thick matrices.... and back pressure was much less- and still it got rid of the stink. IMHO, the stock cat never gave me problems, and I believe because it was only ONE element in there... not 2.

So, I found one pretty cheap on the forum, but the narrower one, 94006D 2.5" (which has a body size of 6.5" instead of 7") and removed a matrix. It has been working great so far. The gutted 93006D cat is available, but I may use it as a "muffler" LOL.

FYI, to remove one matrix without breaking the other, get a long drill bit, and drill slowly until you feel it get way easy. STOP (you have about 3 inches to the next one that you don't want to break!). Repeat, make a couple of evenly spaced holes. Then be careful and use the drill bit to crack the element into pieces. Turn it upside down and it will fall out.

 

[turbocharged798]

I have read lots of reports of clogging on magnaflow diesel cats. They just plug up after a while. Bad design or something...

We really don't have any other options though.

 

[Fix_Until_Broke]

What's wrong with the OEM cat?

It's ~6" in diameter and seems to work OK

The ends are conical so just cut them back a little farther until they're at 2.5" or 3.0" or whatever size you're running and weld the pipe on.

 

[IndigoBlueWagon]

I have read lots of reports of clogging on magnaflow diesel cats. They just plug up after a while. Bad design or something...

We really don't have any other options though.

I've had a 2.5" Magnaflow on my wagon for 4 years, close to 100K. Absolutely no problems, and it's not like I'm not running any fuel.

 

[robnitro]

Yep, I remember you measured minimal backpressure with OEM. OEM worked well for me, but I thought the magnaflow would be better. After seeing issues crop up, that's when I saw the issues people had and tried catless.

I think the issue is that the stock cat has one element, wheras the magnaflow has 2 elements (one on each side). The pressure drop over one is probably good to clear out soot, but with 2, once one clogs, the second one ends up clogging because there's no concentration of pressure drop (like filters in series- they split the differential pressure).

Cross sectional area for OEM which you say is 6" round= 28 sq in.
Cross sectional area for 94006d (4 tall, 6.5 wide round edges) = 22 sq in
Cross sectional area for 93006d (4 tall, 7 wide round edges)= 24 sq in

So, that is why I think the stock CAT has less issues and why magnaflow is too restrictive with 2 elements in series!

What's wrong with the OEM cat?

It's ~6" in diameter and seems to work OK

The ends are conical so just cut them back a little farther until they're at 2.5" or 3.0" or whatever size you're running and weld the pipe on.

 

[IndigoBlueWagon]

Maybe you're over-fueled. I honestly haven't had any problems, nor have I heard any negative feedback from customers. Maybe they don't tell us.

 

[TDIJetta99]

They need sustained high EGT's once in a while to clear out soot.. I'm planning on putting some sort of converter on mine to clean it up some since it really stinks.. I definitely need something that can withstand a fair amount of soot since I'm a bit overfueled, and will be even more overfueled once I get the hardware straightened out..

Maybe I'll get some header wrap and wrap everything from the manifold down to the converter inlet to keep the converter hot enough to burn off soot..

 

[robnitro]

Just smoky on tip in until it started clogging. Someone else had the issue... he did what I just did w the element and has been ok, ill look for the thread.

I think my commute was partially to blame. I was doing only 8 miles a way, mostly stop n go, stoplights.

But the stock cat never gave me issues...?

Though I dont get why the stock cat has only one medium, where magnaflow has 2?

 

[TDIJetta99]

different brand.. Stock has one long medium, magnaflow has 2 short ones..

 

[robnitro]

Thanks
How long is the OEM cat element? I didn't cut mine open when I tossed it.
The magnaflow is about 2 inches thick each.

Maybe you can use the 93 (7 inch wide) series, like you said in another thread it seemed to have bigger holes than the 94 series. Drill some holes in it, or maybe find one of those ebay
I forgot to mention, I also drilled 8 evenly spaced 3/8" holes in the element that I kept in the cat. I figured might as well try, hey it might just have a little bit of stink.
Greatfully, the stink isn't there at all when the engine/cat are warmed up!


http://forums.tdiclub.com/showthread.php?p=3490051&highlight=cat#post3490051
Here's the thread where vwdsmguy , keebler145, cgdoig mentioned issues with their magnaflow cats. In another thread, chippednotbroken had removed his cat and smoke went away. I will keep a lookout to see how my replacement "half cat" does.

Just to clarify how important exhaust pressure is on a turbo here's some EMP calculations.
Let's say you are running 29 psi, that a pressure ratio of 2 (to atmosphere).
Let's say the turbo is great and needs the same EMP ratio, so ratio of 2.
Without any backpressure past the turbo, you would need 29 psi EMP to do PR of 2.
Now with a clogged cat backpressure of 10 psi, you would need (14.5+10)*2= 49 psi EMP!
10 psi increase in the exhaust backpressure made emp go up by 20 psi! (Like keebler mentioned in the thread).
That's why downpipes help so much and why I think the cats don't affect people much at all to notice until they change turbos.

 

[eddie_1]

I've been running the Magnaflow High Flow Cat 93006D for exactly 3 years. No problems whatsoever. This is supposed to be for a truck and if people are still managing to clog it, it is quite an achievement. The RC tune did not use the EDC15 smoke limiter and by way of the 'dump and run' method, why I was able to black out at least 2 lanes of traffic back then. But thankfully that was many moons ago.

 

[darkhorse]

I managed to clog my Magnaflow 2.5" cat. back when I was smokey & trying to sort out my build. The first element was over 1/2 plugged.

 

[kiwibru]

Four years and 50k miles on mine. No issues. Good tune, air and balanced fuel load with calibrated injectors seem to have a lot to do with clogging or not. Perhaps too the Italian tune-up helps.

 

[Alcaid]

Bumping an old thread instead of writing a new one:

How much HP has anyone run with these Magnaflow diesel catalytic converters? I need to silence my car more than what one muffler does today as GTB20 turbine lets too much noise pass. And why not make it "road legal" with a cat if there isn't much of a down side to it?

 

[eddie_1]

Hey Norge, how are you? Uten Cat stoppe Norge! With so few people around and lots of sound absorbing woods, can anybody even hear cars? They made me do a Noise Measurement in Germany,when i brought the jetta. The limit was 75dBA. I was able to meet it with the Magnaflow Cat and Magnaflow inline Muffler.

 

[IndigoBlueWagon]

Magnaflow is no longer selling CATs in the US. Don't know about Europe.

 

[robnitro]

The problem is that the stock cat is round of cross sectional area A, with one thick element of about 3 inches (approx?) So the volume of restrictive material is of volume 3A (area x thickness).
The magnaflow big version that fits, has a similar area A (oval instead of round- thats why it looks bigger but has similar volume) but 2 elements of 2 inch thickness. So it takes up volume of 2A + 2A ... about volume of 4A.

The magnaflow with only one element (which is what I did to reduce backpressure and cloggability (if thats a word, lol) has volume 2A which is less than the stocker 3A.

I used my other magnaflow cat that I gutted way back as a muffler, with a flex pipe to 45 exhaust tip out right below the back bumper.. works great!

With EGR on, it's a bit loud at idle, but once the engine is warm (dynamic EGR off), the exhaust is very quiet at idle. Under load it varies depending on how the vanes are positioned... WOT at full boost gets loud because the vanes open up. Part throttle is pretty quiet, because the vanes stay half closed.
Check n75 duty cycle basic settings to hear the difference at idle.

 

[Alcaid]

Hey Norge, how are you? Uten Cat stoppe Norge! With so few people around and lots of sound absorbing woods, can anybody even hear cars? They made me do a Noise Measurement in Germany,when i brought the jetta. The limit was 75dBA. I was able to meet it with the Magnaflow Cat and Magnaflow inline Muffler.

Well, we have to do a technical control every second year (EU control) and if car was equipped with cat when stock it is a requirement. Mine is way noisier than that, had it tested at a trackday but don't remember the number, the loudest diesel for sure

Magnaflow is no longer selling CATs in the US. Don't know about Europe.

They are still all over the web (summitracing, amazon, etc.) so should be possible to get hold of one?

The problem is that the stock cat is round of cross sectional area A, with one thick element of about 3 inches (approx?) So the volume of restrictive material is of volume 3A (area x thickness).
The magnaflow big version that fits, has a similar area A (oval instead of round- thats why it looks bigger but has similar volume) but 2 elements of 2 inch thickness. So it takes up volume of 2A + 2A ... about volume of 4A.

The magnaflow with only one element (which is what I did to reduce backpressure and cloggability (if thats a word, lol) has volume 2A which is less than the stocker 3A.

I used my other magnaflow cat that I gutted way back as a muffler, with a flex pipe to 45 exhaust tip out right below the back bumper.. works great!

With EGR on, it's a bit loud at idle, but once the engine is warm (dynamic EGR off), the exhaust is very quiet at idle. Under load it varies depending on how the vanes are positioned... WOT at full boost gets loud because the vanes open up. Part throttle is pretty quiet, because the vanes stay half closed.
Check n75 duty cycle basic settings to hear the difference at idle.

That's worrying if there is more restriction in it than stock I don't have an EGR system at all

Might just put an extra silencer on for now on my 2.5" system and put the stock exhaust system on when it's time for technical control, easy swap on these 4Motion Golfs! (lift all up in one piece, attach a few rubber hangers and bolt to downpipe with 3 bolts, job done )

 

[robnitro]

Yeah, someone found the stocker to be less restrictive... but because the magnaflow has 2x honeycomb elements. Remove one and it works fine..a tiny bit more smell.

 

[IndigoBlueWagon]

The only Diesel cats Magnaflow shows on their site are truck CATs that are 3.5" entry and exit or larger. We used to carry 2", 2.25", and 2.5" CATs from them but none of those are available. I don't think a truck CAT would fit in a TDI. Retailers may have existing stock, but I'd see if they actually have a product to ship.

 

[Alcaid]

Check out www.magnaflow.eu instead

 

[IndigoBlueWagon]

There you go. When I spoke to them at SEMA they said they were pulling them off the market because they didn't want to deal with the EPA. Doesn't rule out Europe, although it doesn't help us. We've found another manufacturer, anyway, the their products fit in our cars better.

 

[AnniBooster]

There you go. When I spoke to them at SEMA they said they were pulling them off the market because they didn't want to deal with the EPA. Doesn't rule out Europe, although it doesn't help us. We've found another manufacturer, anyway, the their products fit in our cars better.

In the UK we are now stuck with a visual check for a CAT as well as a smoke test on our annual MOTs. I had been looking at the Magnaflow options to go on my 2.5" exhaust that I have on my 2260'd ARL with 783s.

Are there any CATs that don't detract from performance and spool? Or is this just wishful thinking?

 

[IndigoBlueWagon]

I don't think the magnaflow detracts in any Measurable way. I've had a 2.5" CAT on my wagon for several years, no muffler. I don't see anything unusual with boost or EGTs, and this car has always made good power.