Test Pipe Smell, Ideas to fix under $200 :)
10-15-2013, 08:00 AM
#82
First, please don't take my long *** response below as argumentative, though I'm sure it could easily come across that way (because internet).
I'm actually quite happy to see someone reply with intelligible points.
And also know that I pretty much fully agree with all of your points here, I'm just offering my perspective on those points. Not trying to say you are wrong or prove you wrong in your comments
Fantastic (and accurate) points dude. The point about the OEM cat's being far enough away isn't entirely true IMHO
Though they aren't as close as some are, they're still more than close enough to be a notable restriction to exhaust velocity.
I'd like to point out the use of the word velocity, not flow. The OEM cat's flow quite well, and when speaking about flow, you're right, the HFC design will flow more than a single HFC in the Y pipe because there are 2 pathways and therefore less of a bottleneck.
However the farther back in the exhaust stream a restriction, or 'pressure drop' is, the less it impacts the velocity and scavenging, and thusly, the less impact it has on overall performance.
That's not to say this setup will give more power than HFC's. Making more power isn't the point of what I'm doing here or what I'm claiming.
And it's also not to say that this setup is LESS restrictive than HFC's, but I'd wager to say it's roughly the same as far as overall performance is concerned. Again of course, this is all speculation without testing.
I would point out that Motordyne did all that research and chose to do it the same way I have done it, but I don't know the actual reasons he chose to do it this way. I am only speculating.
Regarding longevity, you bring up extremely valid points that honestly I didn't fully consider.
But the less the cat is working, the longer it will last, right?
The lower the temps the longer it will last, you only have to ask any FI guys (especially turbo) how long the cat's lasted to know heat will kill them. Both HFC and OEM.
Regarding needing a certain temperature to operate correctly, you're absolutely right, I believe that's why they created Pre-Cats in the first place. To operate when cold. Luckily for me, and most of the enthusiasts the modify the exhaust, I don't care about cold temp emissions, I only want the smell gone when I'm driving the car, and this have achieved that for me. I can only say that this setup WORKS. And that's all I need to know.
A few minutes on Google will answer this for you better than I can by linking threads. "Nissan Cat failure" should suffice, and leave you with hours of reading if you have any inclination.
I haven't heard much about the Stillen, glad to hear they are using quality components. Price isn't really any more than the other HFC's on the market from what I've just looked at though so maybe this is a very good option for those who want a bolt-on setup! Thanks!
Great track record, I did my research on them. Long life without issues on many FI cars and as OEM replacements. What would you suggest as a replacement that is high quality then?
I'm actually quite happy to see someone reply with intelligible points.
And also know that I pretty much fully agree with all of your points here, I'm just offering my perspective on those points. Not trying to say you are wrong or prove you wrong in your comments
Not true. A pressure drop is a pressure drop. And the OEM cats are far enough from the engine to not affect scavenging and so are the HFC on the market.
You've got all of the flow going through one cat versus the flow going through two cats so if anything, while your cat is some what larger, your solution likely creates more pressure drop and therefore less power.
Catalyst works more efficiently at higher temperatures until a certain point (different for every catalyst) where activity starts to drop off. The temperature has to be extremely high to affect the catalyst life. You will only see lower efficiently due to the lower temperature at that location here, not extended life.
You've got all of the flow going through one cat versus the flow going through two cats so if anything, while your cat is some what larger, your solution likely creates more pressure drop and therefore less power.
Catalyst works more efficiently at higher temperatures until a certain point (different for every catalyst) where activity starts to drop off. The temperature has to be extremely high to affect the catalyst life. You will only see lower efficiently due to the lower temperature at that location here, not extended life.
Fantastic (and accurate) points dude. The point about the OEM cat's being far enough away isn't entirely true IMHO
Though they aren't as close as some are, they're still more than close enough to be a notable restriction to exhaust velocity.
I'd like to point out the use of the word velocity, not flow. The OEM cat's flow quite well, and when speaking about flow, you're right, the HFC design will flow more than a single HFC in the Y pipe because there are 2 pathways and therefore less of a bottleneck.
However the farther back in the exhaust stream a restriction, or 'pressure drop' is, the less it impacts the velocity and scavenging, and thusly, the less impact it has on overall performance.
That's not to say this setup will give more power than HFC's. Making more power isn't the point of what I'm doing here or what I'm claiming.
And it's also not to say that this setup is LESS restrictive than HFC's, but I'd wager to say it's roughly the same as far as overall performance is concerned. Again of course, this is all speculation without testing.
I would point out that Motordyne did all that research and chose to do it the same way I have done it, but I don't know the actual reasons he chose to do it this way. I am only speculating.
Regarding longevity, you bring up extremely valid points that honestly I didn't fully consider.
But the less the cat is working, the longer it will last, right?
The lower the temps the longer it will last, you only have to ask any FI guys (especially turbo) how long the cat's lasted to know heat will kill them. Both HFC and OEM.
Regarding needing a certain temperature to operate correctly, you're absolutely right, I believe that's why they created Pre-Cats in the first place. To operate when cold. Luckily for me, and most of the enthusiasts the modify the exhaust, I don't care about cold temp emissions, I only want the smell gone when I'm driving the car, and this have achieved that for me. I can only say that this setup WORKS. And that's all I need to know.
Again, this is not true. Stillen uses high quality metallic cores. On my car, they provided a significant power (almost equal to test pipes) and were clean enough that I almost could have passed the sniffer (no detectable smell except at WOT). Sure they aren't cheap but my Stillen HFC are still going strong in a buddy's car.
Great track record, I did my research on them. Long life without issues on many FI cars and as OEM replacements. What would you suggest as a replacement that is high quality then?
10-15-2013, 08:06 AM
#83
The whole point of this thread was to present options.
This one is a safe, cheap, reliable option for people (especially FI cars) that want to get rid of the smell.
There's parts in a build that some people want to do custom, or themselves, and there's parts that people want to pay someone to do, or pay for the parts to just bolt up.
Neither way is wrong. I'm only offering an alternative idea to purchasing traditional HFC's. Take it or leave it.
This one is a safe, cheap, reliable option for people (especially FI cars) that want to get rid of the smell.
There's parts in a build that some people want to do custom, or themselves, and there's parts that people want to pay someone to do, or pay for the parts to just bolt up.
Neither way is wrong. I'm only offering an alternative idea to purchasing traditional HFC's. Take it or leave it.
10-21-2013, 12:02 PM
#84
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Though they aren't as close as some are, they're still more than close enough to be a notable restriction to exhaust velocity.
I'd like to point out the use of the word velocity, not flow. The OEM cat's flow quite well, and when speaking about flow, you're right, the HFC design will flow more than a single HFC in the Y pipe because there are 2 pathways and therefore less of a bottleneck.
However the farther back in the exhaust stream a restriction, or 'pressure drop' is, the less it impacts the velocity and scavenging, and thusly, the less impact it has on overall performance.
That's not to say this setup will give more power than HFC's. Making more power isn't the point of what I'm doing here or what I'm claiming.
I'd like to point out the use of the word velocity, not flow. The OEM cat's flow quite well, and when speaking about flow, you're right, the HFC design will flow more than a single HFC in the Y pipe because there are 2 pathways and therefore less of a bottleneck.
However the farther back in the exhaust stream a restriction, or 'pressure drop' is, the less it impacts the velocity and scavenging, and thusly, the less impact it has on overall performance.
That's not to say this setup will give more power than HFC's. Making more power isn't the point of what I'm doing here or what I'm claiming.
It IS possible for the cat to impact scavenging. However, the OEM cats and their location are far enough downstream that this is not an issue.
Regarding longevity, you bring up extremely valid points that honestly I didn't fully consider.
But the less the cat is working, the longer it will last, right?
The lower the temps the longer it will last, you only have to ask any FI guys (especially turbo) how long the cat's lasted to know heat will kill them. Both HFC and OEM.
But the less the cat is working, the longer it will last, right?
The lower the temps the longer it will last, you only have to ask any FI guys (especially turbo) how long the cat's lasted to know heat will kill them. Both HFC and OEM.
http://www.hjsna.com/
They are very expensive though. My $2500 Fabspeed X-pipe for my M3 has two HJS cats. The bulk of that cost is the cats.
For the record, I am not ragging on your setup. It is cheap and works great for what you want. Hell, you can replace that cat 6 or 7 times before you've spent what a good one would cost and that likely won't happen. I too use HFC for the smell. And my GF's 370Z has Berks on it so I get it. No need to defend your setup or the motivation.
It's just that I am a mechanical engineer and I deal with catalyst beds and high temperature gas flows that have cross sections the size of a small house on a daily basis. So I am just trying to make sure you have the correct technical info in here.
10-21-2013, 01:15 PM
#85
Regarding the info you posted above about the OEM cat's being far enough away that their only impact on performance is their restriction, can you offer any proof/theory on this? The stock cat's seem plenty close enough to impact scavenging and velocity. They're bolted almost immediately on the "collector" (term used very loosely on stock DE) of the exhaust manifold.
Looking at a set of Long tubes would show the collector doesn't even start until after the Stock placement of the Pre-Cat and Cat pipe.
Even on a set of shorty headers the collector is IMMEDIATELY before the flange where the Pre-cat/cat pipe mounts up.
I'm not an engineer, but it seems pretty obvious that this placement is close enough to notably impact the exhaust velocity and scavenging by placing a large restriction and pipe diameter change pretty much at the scavenging point of the manifold/header.
Not being argumentative, I am just looking at it (physically, I've looked at this setup on and off these cars multiple times), and I cannot possibly see how this placement is anywhere near far enough away not to have an effect.
Last edited by TunerMax; 10-21-2013 at 01:18 PM.
10-22-2013, 08:44 AM
#86
Thanks for the info dude! Yeah definitely not spending that much, as you said, I could buy 6-7 of these for that price. And this one works, so, meh. lol.
Regarding the info you posted above about the OEM cat's being far enough away that their only impact on performance is their restriction, can you offer any proof/theory on this? The stock cat's seem plenty close enough to impact scavenging and velocity. They're bolted almost immediately on the "collector" (term used very loosely on stock DE) of the exhaust manifold.
Looking at a set of Long tubes would show the collector doesn't even start until after the Stock placement of the Pre-Cat and Cat pipe.
Even on a set of shorty headers the collector is IMMEDIATELY before the flange where the Pre-cat/cat pipe mounts up.
I'm not an engineer, but it seems pretty obvious that this placement is close enough to notably impact the exhaust velocity and scavenging by placing a large restriction and pipe diameter change pretty much at the scavenging point of the manifold/header.
Not being argumentative, I am just looking at it (physically, I've looked at this setup on and off these cars multiple times), and I cannot possibly see how this placement is anywhere near far enough away not to have an effect.
Regarding the info you posted above about the OEM cat's being far enough away that their only impact on performance is their restriction, can you offer any proof/theory on this? The stock cat's seem plenty close enough to impact scavenging and velocity. They're bolted almost immediately on the "collector" (term used very loosely on stock DE) of the exhaust manifold.
Looking at a set of Long tubes would show the collector doesn't even start until after the Stock placement of the Pre-Cat and Cat pipe.
Even on a set of shorty headers the collector is IMMEDIATELY before the flange where the Pre-cat/cat pipe mounts up.
I'm not an engineer, but it seems pretty obvious that this placement is close enough to notably impact the exhaust velocity and scavenging by placing a large restriction and pipe diameter change pretty much at the scavenging point of the manifold/header.
Not being argumentative, I am just looking at it (physically, I've looked at this setup on and off these cars multiple times), and I cannot possibly see how this placement is anywhere near far enough away not to have an effect.
10-28-2013, 01:15 PM
#89
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It looks to me like there is almost 10 diameters between the "collector" and the face of the first catalyst module. Ten diameters is a rule of thumb that is used to ensure that flow is "fully developed" meaning the effects of a disturbance will be mostly mixed out. There will likely be no hint of the individual pressure pulses that affect scavenging at the catalyst face.
Scavenging is a function of the high velocity pulse creating a lower pressure in the primary and "pulling" the remaining exhaust out of the cylinder. So the cat's distance from the collector is not related to scavenging, it's more a function of the primaries.
Because catalysts usually present a significant obstacle to flow, it tends spread out as evenly as possible across the face of the catalyst. I would think that this *could* cause exhaust reversion if the cats are close to the collector depending upon valve timing (overlap). While I guess this isn't technically "scavenging" this is what I was referring to earlier. However, the 350Z catalyst is plenty far enough downstream from the "collector" that it's effects will not propagate upstream that far.
Scavenging is a function of the high velocity pulse creating a lower pressure in the primary and "pulling" the remaining exhaust out of the cylinder. So the cat's distance from the collector is not related to scavenging, it's more a function of the primaries.
Because catalysts usually present a significant obstacle to flow, it tends spread out as evenly as possible across the face of the catalyst. I would think that this *could* cause exhaust reversion if the cats are close to the collector depending upon valve timing (overlap). While I guess this isn't technically "scavenging" this is what I was referring to earlier. However, the 350Z catalyst is plenty far enough downstream from the "collector" that it's effects will not propagate upstream that far.
Thanks for the info dude! Yeah definitely not spending that much, as you said, I could buy 6-7 of these for that price. And this one works, so, meh. lol.
Regarding the info you posted above about the OEM cat's being far enough away that their only impact on performance is their restriction, can you offer any proof/theory on this? The stock cat's seem plenty close enough to impact scavenging and velocity. They're bolted almost immediately on the "collector" (term used very loosely on stock DE) of the exhaust manifold.
Looking at a set of Long tubes would show the collector doesn't even start until after the Stock placement of the Pre-Cat and Cat pipe.
Even on a set of shorty headers the collector is IMMEDIATELY before the flange where the Pre-cat/cat pipe mounts up.
I'm not an engineer, but it seems pretty obvious that this placement is close enough to notably impact the exhaust velocity and scavenging by placing a large restriction and pipe diameter change pretty much at the scavenging point of the manifold/header.
Not being argumentative, I am just looking at it (physically, I've looked at this setup on and off these cars multiple times), and I cannot possibly see how this placement is anywhere near far enough away not to have an effect.
Regarding the info you posted above about the OEM cat's being far enough away that their only impact on performance is their restriction, can you offer any proof/theory on this? The stock cat's seem plenty close enough to impact scavenging and velocity. They're bolted almost immediately on the "collector" (term used very loosely on stock DE) of the exhaust manifold.
Looking at a set of Long tubes would show the collector doesn't even start until after the Stock placement of the Pre-Cat and Cat pipe.
Even on a set of shorty headers the collector is IMMEDIATELY before the flange where the Pre-cat/cat pipe mounts up.
I'm not an engineer, but it seems pretty obvious that this placement is close enough to notably impact the exhaust velocity and scavenging by placing a large restriction and pipe diameter change pretty much at the scavenging point of the manifold/header.
Not being argumentative, I am just looking at it (physically, I've looked at this setup on and off these cars multiple times), and I cannot possibly see how this placement is anywhere near far enough away not to have an effect.
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