What is the best cat setup that passes inspections anywhere?

[Asbjorn]

So I have been struggling to figure out what the best street-legal track-ready cat setup would be for the N54 at around 400whp. I want to be able to pass both OBD and sniffer-based inspections while also keeping EGTs low, cat-life long and not having to worry about exhaust burbles if I ever decide to turn those up.

I initially thought using two-stage race-cats would be an option, the mid ones just had to be huge. Unfortunately I am told otherwise by Chinese cat suppliers today. Basically a typical high-flow catalytic converter is 300cell, whereas OEM cats are more than twice that.

So below is what I have concluded so far. The best option seems to be using high-flowers for the down-pipes to pass the OBD test, and keep a good EGT/Spool performance, while OEM mid cats are needed to pass sniff tests. The next best option seems to be just running OEM down-pipes and de-catted mid pipes. A final alternative is de-catted down-pipes in combination with OEM mids, but this requires that the O2 sensors be relocated to control the mid-pipe cats.

I would love to hear your opinions. My goal is to try and get it right this time.

Setup	EGTs	Cat-life on track	Spool	Restricts power? (@ 400whp)	Aggressive burbles?	Passes annual inspections (China only)?
OEM down, OEM mid (stock)	High	Bad	Bad	A minor concern	Risky	Yes (confirmed)
OEM down, high-flow mid	High	Bad	Not as bad	Not a concern at high rpm	Risky	Yes
OEM down, de-catted mid (M2 style setup)	High	Bad	Better	Not a concern at high rpm	Risky	Yes (confirmed)
High-flow down, OEM mid	Lower	Better	Good	Not a concern at high rpm	OK	Unknown (cat suppliers say yes)
High-flow down, high-flow mid (M4 style setup)	Very low	Better	Great	Not a concern	OK	Unknown (cat suppliers say "maybe")
High-flow down, de-catted mid	Very low	Better	Great	Not a concern	OK	No (confirmed, fails sniff test)
De-catted down, OEM mid (M4 GT4 style setup)	Very low	Best	Good	Not a concern	OK	No (fails OBD test unless O2 sensors are moved)
De-catted down, high-flow mid (the @fmorelli style setup)	Lowest	Best	Best	Not a concern	OK	No (fails sniff test)

 

[Mikejones1208]

Honestly just stick with stock, e85 will keep those egt's down, and if you have stock twins the spool difference between catted and non catted downpipes is negligible. Just pick up an extra set to bring with you to track days, if you blow one out or clog one it wont take you but maybe an hour to swap it out and theyre cheap and can be picked up all over the place

 

[Asbjorn]

Im on Chinese RON 98. No corn here. Also after-market turbos.
My main worry with clogging cats is that it might happen slowly over time?
Anyway, if sticking with stock is the right direction, I might as well keep my current setup (oem down, de-catted mid)

 

[Hydra Performance]

German-made HJS 200-cell cats are probably what you're after, but let me warn you, they don't come cheap...

 

[MDORPHN]

German-made HJS 200-cell cats are probably what you're after, but let me warn you, they don't come cheap...

Agree. I ran them my twin-screw supercharged '99 M Coupe. They flow well and do the job!

Neil

 

[RSL]

Im on Chinese RON 98. No corn here. Also after-market turbos.
My main worry with clogging cats is that it might happen slowly over time?
Anyway, if sticking with stock is the right direction, I might as well keep my current setup (oem down, de-catted mid)

Cobb catted and INA0S have never thrown a CEL for me with everything enabled/ready and I've been on them for 4+ years. In my testing, earlier roms seem more prone to throwing efficiency codes on high flows and do it sooner.

I've never had a sniffer test on them, but OBD cat ready is obviously automatic. I think they'd pass a sniffer too though (I'm on Cobb catted + stock mid cats), but obviously can't confirm.

Maybe get a few more track days on them and then pull the DPs to see what matrix looks like. If it's getting too hot at any point by now/then, I would expect you'd see something (probably need a scope for thorough look). If it's clean and straight, at least you know it's relatively safe for them. I'd still strongly consider high flows if you're on INA0S, but sniffer test is still an unknown.

 

[ShocknAwe]

Agree. I ran them my twin-screw supercharged '99 M Coupe. They flow well and do the job!

Neil

Can they be used in the mids to good effect? Wondering if a single 200 cell would work in a 3.5" midsection.

 

[MDORPHN]

As I understand it, BMW put cats in the downpipes 'cause they heat up quickly more quickly than the mid-pipe cats and take care of emissions upon cold start. I don't know whether a single 200 cell would do the trick and imagine it would depend in large part on the specific manner that the emissions testing is preformed.

Neil

 

[doublespaces]

I have pitched this concept multiple times over the years, but never sat down and did it myself. But what we need to begin doing is running test pipes. Then weld some flanges onto your oem cats and bolt them onto the mid pipe when it comes time for emissions.

Myself on the otherhand, I am going to work out some sort of valved combination to flip back and forth between a quiet, catted(not smelly) exhaust and a straight pipe.

 

[ShocknAwe]

I have pitched this concept multiple times over the years, but never sat down and did it myself. But what we need to begin doing is running test pipes. Then weld some flanges onto your oem cats and bolt them onto the mid pipe when it comes time for emissions.

Myself on the otherhand, I am going to work out some sort of valved combination to flip back and forth between a quiet, catted(not smelly) exhaust and a straight pipe.

Great idea. Did test pipes on previous cars, but never had them fabbed in with flanges for quick swaps.

 

[doublespaces]

Great idea. Did test pipes on previous cars, but never had them fabbed in with flanges for quick swaps.

Re-using the mid pipe cats would result in an awful and ugly outcome just based on the shape of the inlet/outlet but it would function and you'd only need it temporarily. Vbands would make it a nice easy swap.

 

[fmorelli]

Actually my setup, the last one listed in the graph, passes sniff test and sets no codes. I have catlees downpipes, custom exhaust with mid-pipes housing 200 cell Magnaflow 49 state CARB approved catalysts. I relocated the downpipe post-cat 02 sensors to behind the midpipe cats, extending the harness with Deutsch connectors.

Filippo

 

[Asbjorn]

So based on your comments I looked into higher quality high-flowing cats again. While the first suppliers I talked to said no high-flowers can pass chinese inspections, some others I talked to today said it is possible.

I am told that if I install a large 400cell mid-cat, I should be able to pass sniff tests. If I combine this with my 200cell down pipe, I should be able to pass OBD inspections as well. Otherwise I can swap in new 400cells on my down-pipes. I got a quote for USD 70 per cat, with a guaranteed money back in case of no pass. These are euro 4 cats btw. They also provide 600cell euro 6 cats at triple the price, but then they are hardly high-flowers anymore.

I have no idea how HJS makes 200 cell cats that pass inspections in all Euro categories. They are used in many high flow aftermarket down-pipes for BMWs in China. I got a quote for USD 1200/pc for HJS (just the cat). Im sure I can get them cheaper - if not in China then next time im in Europe. But I will certainly try the cheaper china cats first...

 

[Asbjorn]

So as I was about to order the 400 cell mid pipe cat, the supplier changed his mind.

Now they say only a 800 cell cat would be able to pass in China. So that's basically an OEM cat, not a high flow type.

They now claim that no 200-600 cell cat would do the job in China... same as three other local suppliers have said.

So now it is either 200cell down pipe + 800 cell mid pipe, or 800cell down + de-catted mid, or the @fmorelli config but with a 800 cell mid pipe.

 

[MDORPHN]

Trying to distinguish your OBD and emissions concerns. OBD can be addressed with some electronic trickery. The emissions testing, however, will require cats or different fuel. Do you know the procedures they use to test emissions and what the standards are?

Neil

 

[Torgus]

As I understand it, BMW put cats in the downpipes 'cause they heat up quickly more quickly than the mid-pipe cats and take care of emissions upon cold start. I don't know whether a single 200 cell would do the trick and imagine it would depend in large part on the specific manner that the emissions testing is preformed.

Neil

That is my understanding as well. I would think a decent quality cat in the exhaust would allow the car to pass, once it is heated up of course. Just where most cars have their cats.

 

[Asbjorn]

Trying to distinguish your OBD and emissions concerns. OBD can be addressed with some electronic trickery. The emissions testing, however, will require cats or different fuel. Do you know the procedures they use to test emissions and what the standards are?

Neil

When I was running 200cell down-pipes only, the test that failed is called "double idle speed test", CO(%) and HC was too high. Lambda was also low, but only by 0.02. I dont know if measured with OBD or sniffer. I have seen both OBD and sniffing equipment used during annual inspections in China previously, but nowadays they don't let you observe their testing methods.

 

[Torgus]

Perhaps have an exhaust shop weld on some flanges, as stated above, then install a massive cat. Uninstall after you pass emissions and replace with straight pipe. Buy a cheap cat and use two in series vs. a high quality one? Make sure the car is VERY warm before going in for emissions testing so the cats are working best. That way you could get away with no cats in the DPs year round...

 

[fmorelli]

I assure you, beyond running factory BMW exhaust there is no black and white answer. Cells are not the only thing. Quality is also a big factor since platinum group metals used as an active part of the catalytic conversion. So one could have a billion cell, super restrictive core with crap coating and have it not pass emissions. Omar mentioned some brand that he's aware of (no clue what Lebanon does for emissions or Omar's direct experience dealing with this stuff), but might now hurt to ask @Hydra Performance for more info.

Knowing the test methods would certainly help. The cats are put right after the turbos since heat helps with the conversion process. If the engine is warm, the mid pipe configuration will be warm. Downpipe cats are a cold start emissions thing - much like the BS air pumps used during cold start for some cars. Any M54 owner, for example, has dealt with a dying $350 air pump (worthless junk) or better yet clogged air pump passage ways in the head (rendering the head useless on an emissions car). This crap has gone on for a long time.

So back to the subject, unfortunately you are just not going to know what works in your locale without trying stuff. I was the first guy (I know, at least) that did the mid-pipe cat conversion with 02 sensors. I had some funny errors early on but I believe it was because so much got changed in my car and an adaptation reset seem to solve the issue. I've done a driving sniff test and passed, I've also passed OBD2 plug-in.

Another possible factor is tuning - I don't know if a tune could run a cleaner scenario - cold and warm. You can ask @BQTuning about that.

Another possible consideration is to run a mid-pipe setup that allows you to swap cats if you needed to. Sure that could get expensive. But the reality is, and there is no getting around it, unless someone with the exact setup you have is successful in China you have little proof of what will work. So you might get it on the first try, second try, or not at all. That's the trade-off space. Using a modular mid-pipe configuration with a swaged, slip-on configuration and band clamp at both ends.

Here are some photos of my installation. I did this in the first stage of build on my car, as I knew downpipe cats were the heat devil. Yeah I hate heat. The J-bungs are vibrant. They do pull the post-cat 02 sensors a bit out of the flow (reduces chances of setting codes) but as @jyamona has informed us, their data is used to adjust the front 02 sensor data for aging. Jake has talked about having a mod that removes that from happening - for those not running post-cat sensors or the few people like me that have built a "legal" exhaust.

. . . .

Hope this helps anyone reading along.

As a side note, one would wonder what a China's people do with such restrictive emissions requirements - OE catalyst systems can cost $2-3k. New cars are not cheap, and the value of a car that doesn't pass emissions can't be much. While there is certainly plenty of wealth in China, there is lots of poverty. I get lots of people don't own cars, but I have to imagine lots of people that do own cars can't afford these kinds of issues. In the USA I consider it a burden on lower income people - they are more likely to own older cars and get caught up in emissions issues. Draconian states like Virginia, where I live, continue to run emissions programs that strip cars from these folks, with a huge operating cost to do so, while the impact of those cars given their small percentage on our environment is rather nominal. Virginia considers 3,000 lbs of garbage in the landfill, cost of program, and burden on lower income people a net plus over a less than perfect emissions profile. I digress. In VA one can get an emissions waiver after spending $815 at a certified emissions repair center ... and even then it is good for 2 years, in which one has to spend $815 again to prove it cannot be repaired in that price range. Simply stupid.

Filippo

 

[Asbjorn]

I assure you, beyond running factory BMW exhaust there is no black and white answer. Cells are not the only thing. Quality is also a big factor since platinum group metals used as an active part of the catalytic conversion. So one could have a billion cell, super restrictive core with crap coating and have it not pass emissions. Omar mentioned some brand that he's aware of (no clue what Lebanon does for emissions or Omar's direct experience dealing with this stuff), but might now hurt to ask @Hydra Performance for more info.

Knowing the test methods would certainly help. The cats are put right after the turbos since heat helps with the conversion process. If the engine is warm, the mid pipe configuration will be warm. Downpipe cats are a cold start emissions thing - much like the BS air pumps used during cold start for some cars. Any M54 owner, for example, has dealt with a dying $350 air pump (worthless junk) or better yet clogged air pump passage ways in the head (rendering the head useless on an emissions car). This crap has gone on for a long time.

So back to the subject, unfortunately you are just not going to know what works in your locale without trying stuff. I was the first guy (I know, at least) that did the mid-pipe cat conversion with 02 sensors. I had some funny errors early on but I believe it was because so much got changed in my car and an adaptation reset seem to solve the issue. I've done a driving sniff test and passed, I've also passed OBD2 plug-in.

Another possible factor is tuning - I don't know if a tune could run a cleaner scenario - cold and warm. You can ask @BQTuning about that.

Another possible consideration is to run a mid-pipe setup that allows you to swap cats if you needed to. Sure that could get expensive. But the reality is, and there is no getting around it, unless someone with the exact setup you have is successful in China you have little proof of what will work. So you might get it on the first try, second try, or not at all. That's the trade-off space. Using a modular mid-pipe configuration with a swaged, slip-on configuration and band clamp at both ends.

Here are some photos of my installation. I did this in the first stage of build on my car, as I knew downpipe cats were the heat devil. Yeah I hate heat. The J-bungs are vibrant. They do pull the post-cat 02 sensors a bit out of the flow (reduces chances of setting codes) but as @jyamona has informed us, their data is used to adjust the front 02 sensor data for aging. Jake has talked about having a mod that removes that from happening - for those not running post-cat sensors or the few people like me that have built a "legal" exhaust.

View attachment 26569 . View attachment 26570 . View attachment 26571 . View attachment 26572 . View attachment 26573

Hope this helps anyone reading along.

As a side note, one would wonder what a China's people do with such restrictive emissions requirements - OE catalyst systems can cost $2-3k. New cars are not cheap, and the value of a car that doesn't pass emissions can't be much. While there is certainly plenty of wealth in China, there is lots of poverty. I get lots of people don't own cars, but I have to imagine lots of people that do own cars can't afford these kinds of issues. In the USA I consider it a burden on lower income people - they are more likely to own older cars and get caught up in emissions issues. Draconian states like Virginia, where I live, continue to run emissions programs that strip cars from these folks, with a huge operating cost to do so, while the impact of those cars given their small percentage on our environment is rather nominal. Virginia considers 3,000 lbs of garbage in the landfill, cost of program, and burden on lower income people a net plus over a less than perfect emissions profile. I digress. In VA one can get an emissions waiver after spending $815 at a certified emissions repair center ... and even then it is good for 2 years, in which one has to spend $815 again to prove it cannot be repaired in that price range. Simply stupid.

Filippo

Excellent comment.

Regarding quality and size... I asked about imported 200 cell cats, and they still said it wouldn't work in China. I asked how big a 200 cell cat must be to make it work, they said it isn't possible. I asked how much I need to pay for a 200 cell cat to make it work. Same answer... grrr

But to answer your last question. Even putting aftermarket wheels on a car in china will make it fail annual inspections, so people usually just pay "extra". It is the easiest thing to do, and everyone does it. Except me...

Perhaps have an exhaust shop weld on some flanges, as stated above, then install a massive cat. Uninstall after you pass emissions and replace with straight pipe. Buy a cheap cat and use two in series vs. a high quality one? Make sure the car is VERY warm before going in for emissions testing so the cats are working best. That way you could get away with no cats in the DPs year round...

I really want to find the best street-legal track-ready permanent setup. Also there is just no way to make sure the car is warm, as it may be parked for an hour before they pick it up (they keep the keys while you wait).