thinking about DP/relocated Cat vs hi flow cat

**GreyGhost** · 11-02-2005 06:53 AM

I talked with the guys at stratmosphere who said that the cat was definitely the most restrictive part of the B6 exhaust system and recommended upgrading the cat before the exhaust. I was wondering about the true benefits of just a cat with stock exhaust, and whether a relocated cat with DP (ala MTM) was worth the extra dough. Also, anyone else know who makes a relocated cat/DP system that won't throw a CEL. Not interested in a test pipe...
TIA
Jeff

**Audi Skate Snow** · 11-02-2005 08:04 AM

stock cat your turbo is really restricted. it doesnt spool as fast. I would recomend doing a testpipe but you said you didnt want one. that way your turbo spools faster and you will make more power as well.

If anything just get a high flow cat and relocate it after the downpipe. that should help you out a bit. As far as CEL you would need the proper software to not throw the CEL

**teutonic_blur** · 11-02-2005 12:31 PM

Originally posted by GreyGhost
Not interested in a test pipe...

My kind of people

A long time ago Dr. Mike (bhvrdr) posted why MTM has the DP/relocated CAT approach. IIRC it had something to do with smoothing the airflow at a very critical point which is as it exits the turbo.

I don't think this arrangement causes a CEL. However, I would be a little bit concerned about the cat not passing readiness tests. Being so far from the turbo it will take a while for it to warm up. On the other hand, I've never heard Mike complaining about this.

Maybe he'll chime in.

I've always had my doubts about the benefits (besides the sound) of changing the exhaust system while having that CAT blocking things so what Stramosphere says makes a whole lot of sense to me.

**AvanTTix** · 11-02-2005 04:25 PM

i'm looking at doing getting a high flow cat too and probably the Milltek one since i've already got a Milltek...

i was talking to Michel (JetJockey) about that and his first suggestion was also to relocate the cat after the DP... however i believe the only way to do that is either going MTM or custom made... having already installed a Milltek i'll personally go w/ their high flow cat...

i'm curious to hear what more the guys at Stratmosphere told you... i'm assuming they suggested Milltek?

and i feel the same way as you do...

Originally posted by GreyGhost
Not interested in a test pipe...

**bhvrdr** · 11-02-2005 04:34 PM

Relocating a hiflow cat will aid in spoolup and removing that immediate restriction would conceivably even reduce the EGTs a bit. Jet's unit does pass all readiness codes and uses an MTM o2 relocation harness with the 100cpsi HKS race cat that doesnt throw a CEL (it's not in the programming apparently bc I throw a CEL with my testpipe).

If you dont want to spend the $1200 bucks or whatever it is, there are always cheaper quality HiFlow universal cats that may work (usually in the 200cps to 400cpsi range). You could run a testpipe, the downpipe, then have the universal hiflow mounted under the car. www.tantrumwerks.com has a photo of this setup on their site. Probably would run you about $700 all said and done for the labor, testpipe and hiflow. You'd neeed to source a specially designed o2 reloacator for our harness and i'm not sure where to get that. cheers! Mike

**A4Jared** · 11-02-2005 04:52 PM

Originally posted by bhvrdr
Jet's unit does pass all readiness codes and uses an MTM o2 relocation harness with the 100cpsi HKS race cat that doesnt throw a CEL (it's not in the programming apparently bc I throw a CEL with my testpipe).

You'd neeed to source a specially designed o2 reloacator for our harness and i'm not sure where to get that. cheers! Mike

How do you mean its not in the programming? I don't know how MTM does it, but for Dahlback, Stage II and up gets a much wider reading on the secondary 02 sensor, obviously because you're pushing more airflow and the sensor needs to understand that infortmation. Hell even that unfortunate stint where i had the test pipe on my car, I never through a CEL nor even a fault code. The HJS cat in the MTM downpipe is basically a test pipe, its about 85% hollow, I don't think there is any way that MTM doesn't change the accepted range of readings on that sensor. In fact I'm about 99% sure they do, which would explain why normally you wouldn't get a CEL but every once in a while you would, because most of hte time you were probably a hare outside the accepted but still tolerable range, and occasionally, probably in higher gears, you'd surpass that tolerable accepted range and get a fault or MIL.

Also, I believe you can purchase the lambda extention harness from Hoppen for about $100

**bhvrdr** · 11-02-2005 05:02 PM

All I can tell you is I get a CEL all the time with a testpipe and the MTM programming. Perhaps they do change some limits a bit, but apparently the HJS is not llike a hollow testpipe at all and sure the DBack programming is different. The HJS doesn't look very hollow at all if you look at all that precious metal material in there. If Hoppens sells that piece seperately, that would be great. I just havent know them to do it. cheers! Mike

**A4Jared** · 11-02-2005 05:09 PM

I thought you told me that you get a CEL occasionally with the test pipe...no matter, anyways, yes its not hollow like a test pipe but its still about 85% empty as most 100cpsi hi flow cats are. And yes Ken did tell me that he sells the lambda extension separately, in fact he offered to sell it to me when i had plans to buy the Dahlback Dp/HFC

**bhvrdr** · 11-02-2005 05:12 PM

I get CELs, I clear them, I get them again. Usually takes a couple days. Depends on weather and load I put on the car. HJS makes good stuff. ...

cheers! Mike

**GreyGhost** · 11-02-2005 05:33 PM

i'm curious to hear what more the guys at Stratmosphere told you... i'm assuming they suggested Milltek?

Thanks for the input guys.

Re stratmosphere, basically they just said that the cat was the most restrictive component and that they just received a new HFC for the B6 recently. He said using the old B5 HFC for the B6 would likely fail, and that the new HFC would last much longer. Pricing was $900, sorry don't remember the cell count ?100. Given the choice between upgrading the cat or exhaust first, he definitely said that he'd go with the Cat. Also, he's the first person I've heard say that the B6 exhaust was actually pretty good!

So, I'm toying with the idea of the MTM DP/Cat (which they do sell separately) with a flange to my stock exhaust for now...the MTM piece looks pretty sweet from Jared's photos.

**turbo** · 11-02-2005 05:34 PM

I did a test pipe with stock exhaust and noticed no gains untill I put my cat back exhaust on.
Also I have no Cell with test pipe W/ Revo

**bhvrdr** · 11-02-2005 05:35 PM

Probably a derrivative of the one they now use for the B7. They say it is a 200cell now.

cheers! Mike

**EBG 18T** · 11-02-2005 05:39 PM

Originally posted by turbo
I did a test pipe with stock exhaust and noticed no gains untill I put my cat back exhaust on.
Also I have no Cell with test pipe W/ Revo

interesting. DenverNoob has posted several dyno's showing that the test pipe made the biggest improvment. He gained twice as much from the testpipe as he did from the exhaust.

**turbo** · 11-02-2005 05:46 PM

Well all I can say is I felt no gain with just a test pipe.
and I drove the car for 7 days with stock exhaust and a test pipe.
why would I give BS info?I do not sell Exhaust or eneything for that matter.
just telling you what I know from my experience.

**turbo** · 11-02-2005 05:48 PM

did he do a dyno with stock cat and aftermarket exhaust?

**bhvrdr** · 11-02-2005 06:06 PM

15hp is not really going to be easily "felt" cheers! Mike

**A4Jared** · 11-02-2005 07:23 PM

Mike: no sweat bro. Just trying to get the story straight.

Thats interesting that Pete said that b5 Milltek HFC might fail, did he give any reason?

**initiala4** · 11-02-2005 08:25 PM

<---- Has Milltek HFC

**AvanTTix** · 11-02-2005 08:37 PM

how do you like it?

not sure whether you had the exhaust first and then installed the HFC, but if you did, did you notice a difference in the sound of the exhaust?

**initiala4** · 11-02-2005 08:39 PM

Mmmm i have to say it does feel faster? or like the rpm moves faster...sound is a tad bit louder for sure. CEL...havnt got any. Milltek uses HJS cat also...200cell if i am not wrong.

**AvanTTix** · 11-02-2005 08:42 PM

thanks for the info... i'm definitively adding this to my list of parts to get w/ my "BTish" upgrade...

**initiala4** · 11-02-2005 08:52 PM

Originally posted by Avantéix
thanks for the info... i'm definitively adding this to my list of parts to get w/ my "BTish" upgrade...

ahhh ic ic...someday i will get KO4 and some sort of IC...just got clutch and new flywheel in!

**GreyGhost** · 11-03-2005 06:11 AM

If you dont want to spend the $1200 bucks or whatever it is, there are always cheaper quality HiFlow universal cats that may work (usually in the 200cps to 400cpsi range). You could run a testpipe, the downpipe, then have the universal hiflow mounted under the car. www.tantrumwerks.com has a photo of this setup on their site. Probably would run you about $700 all said and done for the labor, testpipe and hiflow. You'd neeed to source a specially designed o2 reloacator for our harness and i'm not sure where to get that. cheers! Mike [/B][/QUOTE]

just got a chance to look at their website,
interesting option, but the Cat is 400 cell, likely not as good flow as a 100-200 cell I presume...

A4jared, no didn't have a chance to ask stratmosphere why the B5 Cat would likely fail

**EBG 18T** · 11-03-2005 06:49 AM

Originally posted by turbo
Well all I can say is I felt no gain with just a test pipe.
and I drove the car for 7 days with stock exhaust and a test pipe.
why would I give BS info?I do not sell Exhaust or eneything for that matter.
just telling you what I know from my experience.

I never stated i didn't believe you. All i said was 'interesting', there is no reason to read into anything any deeper.

As for your second question. No he doesn't. He added the exhaust a few months later.

**EBG 18T** · 11-03-2005 06:51 AM

Originally posted by initiala4
Mmmm i have to say it does feel faster? or like the rpm moves faster...sound is a tad bit louder for sure. CEL...havnt got any. Milltek uses HJS cat also...200cell if i am not wrong.

How was the fitment? Did it fit ok with the Milltek exhaust?

This sounds very tempting. I might have to go on the list of goodies for 2006.

**initiala4** · 11-03-2005 08:36 AM

Originally posted by EBG 18T
How was the fitment? Did it fit ok with the Milltek exhaust?

This sounds very tempting. I might have to go on the list of goodies for 2006.

Fitment wasnt an issue since Milltek changed alittle bit in their design for catback. I am pretty sure most manufature tries to resolve their issues on their product. Pretty much the high flow cat fits onto the downpipe.

**A4NCAR** · 11-03-2005 09:38 AM

Originally posted by GreyGhost
I talked with the guys at stratmosphere who said that the cat was definitely the most restrictive part of the B6 exhaust system and recommended upgrading the cat before the exhaust. I was wondering about the true benefits of just a cat with stock exhaust, and whether a relocated cat with DP (ala MTM) was worth the extra dough. Also, anyone else know who makes a relocated cat/DP system that won't throw a CEL. Not interested in a test pipe...
TIA
Jeff

It is, and an aftermarket HFC will help with escaping gas and temps right after the turbo, but it'll still just bottle-neck at the OEM exhaust. That's why people with aftermarket exhaust already installed, then install a TP or HFC, notice a bit more difference.

If you're not going to go TP (which I wouldn't recommend - emissions pollution), then look at Milltek HFC or MTM DP/Relocated CAT. I'd do the whole MTM exhaust IMHO (76mm --> 70mm turboback w/ HJS 100 cell CAT). Milltek uses HJS CAT also, but I think it's a 200 cpsi for our app. I'm pretty certain OE CAT is 400 cpsi. Also, HJS has a higher standard, better metalurgy application process for their CAT's (quality/quantity of precious metals used..etc), so even though it is 100/200 cpsi, it works better then expected. It is said that there should be no problem passing CA smog/emissions tests (although I've never been able to confirm that myself, nor the "No CEL" with the MTM DP/CAT).

HJS Motor Sport

Milltek

From HJS:

Left:
Metal carrier
105 x 74,5 mm with
100 cpsi SM-winding
(motor sport)

Right:
Metal carrier
105 x 74,5 mm with
400 cpsi S-winding
(series)

From Milltek:

Standard Cat vs. Milltek Sport Hi-Flow Sports Cat

Your original catalytic converter will typically have 400 or 600 cells per square inch (cpsi), these original cats are restrictive in their flow, typically allowing an open area of around 55-65%.

A Milltek Sport Hi-flow Sports Cat which will be fully integrated into a large bore downpipe, has only 100-200 cpsi depending on application. These cats have an open area of between 75-85%, thus reducing back pressure substantially and increasing flow rates, all very desirable for extracting more performance, especially on turbocharged engines. Emission levels are maintained at legal limits by careful selection of the volume of the metallic substrate. Lamda probe positions remain unchanged from the original equipment. "

**teutonic_blur** · 11-03-2005 02:34 PM

This thread is a keeper.

**cuco33** · 11-04-2005 07:01 AM

lots of info here...

does having a test pipe make the car sound.... ricey?
cuz i'm not tree hugger but 800+ for relocated high flow cat is kind of pricey just to save the world when these gas guzzling SUVs are on the road

**GreyGhost** · 11-08-2005 10:06 AM

just wanted to make sure I wasn't spreading false info. I talked again with the guys at Stratmosphere. My bad...the B5 HFC will NOT fail if installed on the B6, but often causes CEL's. They redesigned the B6 HFC, still 200 cell, still made by HJS, but it should not throw a CEL.

**AvanTTix** · 11-12-2005 12:11 PM

Originally posted by GreyGhost
They redesigned the B6 HFC, still 200 cell, still made by HJS, but it should not throw a CEL.

just out of curiousity...

how come they only show one version on their website for the HFC then?

**Saturnine** · 11-12-2005 02:50 PM

I had the Tantrumwerks HFC a while back, but decided to sell it because it threw a CEL.. It was a truly nice piece, built very well but it wasnt that much different than the stock cat as far as dia goes..

**GreyGhost** · 11-12-2005 05:19 PM

Originally posted by Avantéix
just out of curiousity...

how come they only show one version on their website for the HFC then?

no problem...apparently they just received the new HFC so that's probably why it's not on their web site yet. They had to look around to make sure they had actually received it, so it's quite new...

**AvanTTix** · 11-12-2005 05:48 PM

well i actually asked Stratmosphere and here's Bob's answer:

There is in fact a different cat for the B6 A4. Our stock number is MSAU279. The B5 A4 is a MSAU241. They are different ! You will have no CEL's. If you wish to order online, please make a note of the B6 A4, or mention MSAU279.

We have these in stock.

once i get my addy in SF i'm gonna order myself one...