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Catalytic Converter Question - Downpipes, Aftermarket exhaust
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04-09-2012, 07:37 PM | #1 |
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Catalytic Converter Question - Downpipes, Aftermarket exhaust
Hey everyone, I need some suggestions for my situation. Awhile ago I bought an aftermarket exhaust after falling in love with the sound. It was a downpipe-back exhaust, so it removed the secondary cats.
Next, I fell in love with the idea of catless DPs for the performance gains. So once I install my new DPs I'll be completely catless which is a no-go for me as I can't feel right about just dumping all those fumes out the pipe when they could be treated. I need a catalytic setup that I can weld into the aftermarket exhaust that hopefully won't harm the performance gains from the catless DPs. I'm of course willing to sacrifice some performance in the name of treating the exhaust gases, and passing the sniffer test we have here in Ontario (very similar to California regulations as far as I know). I was thinking of getting a shop to cut the factory cats back a bit on their flanges to widen the opening to the size of the aftermarket exhaust (2.5") and weld the original secondary cats back in rather than purchasing something like the Magnaflow hi-flow cats as from what I've heard, they don't work all that well. Can anyone see any issues with this setup? Is there another setup I should be considering that will keep the car legal on the sniffer and not dumping really smelly fumes out the back? Any input would be appreciated! Thanks very much for your help! |
04-09-2012, 08:41 PM | #4 |
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Staying catless isn't an option for me. I hate the smell of a catless car and I just think it's irresponsible. Not to mention that if our finest catch a whiff of something like that I'll be walking away with a hefty fine for running catless and rightly so. One car might not make a large difference but it makes a difference. I'd like to try and do it legal, and responsibly because I'm sure there's a way - I just need some direction on how.
Anyone with any input on what cat setup I should go with (keeping catless DPs, but placing cats in the exhaust) let me know. Magnaflow hi-flow from what I've heard don't work that well with the sniffer, so how about cutting back the flange on the OEMs to make them a match for the exhaust diameter and weld those up? Would that affect the flow substantially? |
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04-09-2012, 08:55 PM | #5 |
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Not to be rude, but with your philosophy, you should just go back to stock downpipes. The secondary cats don't "catch" the majority of pollutants like the primary's do.
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04-09-2012, 09:06 PM | #6 | |
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Quote:
I want to be as responsible as possible while staying catless on the downpipes because of the performance gains that are possible there. I agree secondary cats in their stock configuration don't "catch" the majority of pollutants like the primary setup, but that's mostly because the primary's are doing 99% of the work and the secondary setup is there to catch the remaining amounts. If I were to reweld the secondary cats in an aftermarket exhaust (by cutting the flange to widen and match diameter) would this result in a passable setup by the sniffer? I understand that cats work best hot, so I imagine that I may have more initial emissions while the cats heat up as they're not as close to the engine as the DPs are. Would a catalytic preheater setup solve this? I'm just looking for options for my setup, I don't need to be swayed to reinstall my stock downpipes. Thanks! **EDIT: So that I'm clear, I don't believe there's a physical difference between the primary and secondary cats? They don't appear to be different but if they are, and I'd be better off welding in the original primary's I could do that instead? |
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04-09-2012, 09:46 PM | #7 |
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Cats require heat in order to function. They don't "filter" the fumes, they cause a chemical reaction that changes the fumes into CO2. Unless the cats are near the turbos then they won't have the heat necessary to function properly.
But yes, you can just weld some high flow cats in the midpipes to help with the smell. |
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04-09-2012, 09:51 PM | #8 | |
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I would imagine the mid-pipes get hot eventually? That's why I'm wondering if a pre-heater of sorts would help get them working well quickly? How do non-turbo cars have their cats setup? I'd think they'd end up further from the motor in an NA configuration? |
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04-09-2012, 10:22 PM | #9 | |
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On a NA car the first set of cats are typically mounted in the exhaust manifold just after the collecter. |
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04-09-2012, 10:31 PM | #10 | |
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Disappointing that they won't reach temperature, are you reasonably sure about that or guessing? |
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04-09-2012, 10:35 PM | #11 | |
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04-09-2012, 10:41 PM | #12 | |
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I remember reading somewhere that some 7 series were equipped with catalytic "pre-heaters" to help initial emissions on startup. I haven't been able to find any kind of aftermarket "pre-heater" through searches so far though. I'll have to look up an exhaust shop locally, maybe they'll have some more knowledge or have run into this setup before.. |
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04-10-2012, 06:38 AM | #14 |
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also interested in this question.
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04-10-2012, 07:50 AM | #15 |
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I dont think people are being rude, but being realistic. If you are truly interested in running a clean emissions vehicle, keep all the cats stock. If somehow you feel running without the secondary cats makes you 'clean enough'...Ok... Others feel their car without any cats is clean enough.
If you care more about the smell and if you can get caught, that is another story. |
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04-10-2012, 12:21 PM | #17 |
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Cars with no cats on them STINK. I'm too old for it, and the minimal performance gain just isn't worth it. Drive one in DC traffic then get out of your car an hour later. You will smell like exhaust fumes.
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04-10-2012, 07:06 PM | #18 | |
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I think I've decided on an approach to try. I'm going to get some cats welded in to the exhaust section near where the original secondary cats were. I'm also going to take some advice from others that have suggested heat wrapping the exhaust to the cats to keep most of that exhaust heat in so it reaches further back in the exhaust more quickly. I think this should cure the smell problem and as I've heard it's possible to keep it legal (pass sniffer test) with just secondary cats I think the heat wrap will help go the extra mile and heat the cats up more. Hopefully it works out! |
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04-11-2012, 07:01 AM | #19 |
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I have an AE cat back with high flow cats. Just ordered VRSF catless Dp's. With just the high flow AE secondary cats in place do you guys think that will smell bad as well?
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04-11-2012, 07:34 AM | #20 |
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Drives: '08 E90 335i, '99 E36 M3
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I have AR catless DPs with AE HFC's and there is almost no smell. When the car was fully catless, it smelled extremely bad.
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10-02-2012, 03:21 PM | #21 |
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AE Peformance Exhaust with AE 2nd HFC's
Hi guys,
Any photos of system installed ? Any vids of the sound ? Tried calling **********s and AE performance to ask abt the AE exhaust c/w 2nd HFC's and no joy. Do you AEP part numbers to help me out Thanks, Dave |
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10-03-2012, 11:36 AM | #22 |
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OP,
So did you not know this prior to getting your catless DPs installed? What were you expecting? Lol.....sigh. If it were me, I would just put back on the OEM exhaust, sell the catless exhaust and get an axle back exhaust.
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