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bmwbav
bmwbav Reader
8/14/15 2:11 p.m.

In reply to Trackmouse:

Of course it matters, it's on the Internet!

bmwbav
bmwbav Reader
8/14/15 2:21 p.m.
alfadriver wrote:
bmwbav wrote: In reply to alfadriver: Wow, Thank you for such a detailed response! I'm using MS3 with speed density fuel control on a modern BMW V8 engine, WB O2 sensor. It's targeted to Stoich. Not concerned with start-up emissions, the car is almost 45 years old. (1971 BMW Bavaria) It's tuned well enough, but A/F ratios do move around quite a bit. Am I reading that right that being rich lowers exhaust temp, but may overstress the cat?
No, it won't stress the catalyst. Unless it misfires. Trucks with trailers run very rich going up passes for as long as the pass is, and it won't damage anything.
Honestly I haven't data logged it for a while, It's been running this way for over a year. I just haven't made time to get on a dyno since it works well enough for street use and occasional track days. That said, it does have a fairly consistent misfire under load at higher RPM's, probably tuned too rich or conservatively. It's never lean in that range of operation, It could also be timing related.(Megasquirt sucks for diagnosing that type of stuff) It doesn't really cause issues on the street, as I would be doing something illegal to hit that part of the power band.
You need to deal with the misfire at some point- at high speed and loads- that will burn up the cat really quickly. As in a few seconds- picture the lost power you notice from the misfire, and ALL of that lost energy is being released in the catalyst. Not good.
I am really concerned with additional heat. It's a big engine squeezed into a pretty small car with some components close to the headers/manifolds. So, I'm going to see heat increases on anything upstream of the cats? I was planning on putting them under my feet and passengers feet, probably 2-3 feet from the manifolds. If it's more like 4 feet, is that substantial?
You should not seem much of a temp increase upstream of the cat. Some, but not enough to really worry about. 2-3 feet will be ok- 4 feet would be stretching it if you do a lot of stop an go driving- as the idling will cool things down. But that should be ok. On turbo cars- the turbo is acts just like a 2 foot stretch of pipe, and we can make that work well.

Again, thanks so much for the knowledge!

So, here's what I've absorbed.

  1. Fix my damn misfire (Need to anyway)
  2. As long as A/F is in a semi-sane operating range, the cat will handle it
  3. Location - closer will keep it at operating temp better

So, final clarifying question about location..

I live in the bay area, so, yes, there is a bit of stop and go :) Having it further away will cool it down while idling, is that a terrible thing?

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/14/15 2:24 p.m.

In reply to bmwbav:

Not terrible- just that cooling it down reduces the effectiveness. For a car that has no catalyst- it's still better than nothing by a very wide margin. It will warm back up quickly enough. You might smell it.

(one has to put my view into some perspective- my job is to try to meet low emissions, for 150k miles. Some of the suggestions come from that work- and you really need 80's-90's goodness to be good.)

bmwbav
bmwbav Reader
8/14/15 2:43 p.m.

In reply to alfadriver:

Fair enough, thank you!

Toebra
Toebra Reader
8/14/15 6:25 p.m.

High flow cat, excellent, great idea, unless you live in Kalifornia, where it is OEM or it is not street legal.

Desy
Desy New Reader
8/15/15 1:47 a.m.

What about cars with 2 or more? Sure the single CAT test shows results, but lets add another variable.

For instance, the OEM exhaust system on my car (2014 tC) has lots of variations of exhaust diameter. This provided great low end torque and feel. But when I removed the midpipe for a aftermarket unit it upgraded the size to a 2.25" stainless system removed 1 CAT and had 1 20" resonator in line. The results? Less low end torque, but after about 3500RPM's much better flow and pull going through the mid-upper power band. So I went from 2 CATS and a resonator to 1 Cat, 1 resonator, and a larger consistent pipe.

novaderrik
novaderrik UltimaDork
8/15/15 7:07 a.m.

if you need a cat converter to keep your exhaust from smelling like gas, then you have tuning issues.

jsquared
jsquared Reader
8/21/15 8:46 p.m.
alfadriver said:
bmwbav said: In reply to alfadriver: Wow, Thank you for such a detailed response! I'm using MS3 with speed density fuel control on a modern BMW V8 engine, WB O2 sensor. It's targeted to Stoich. Not concerned with start-up emissions, the car is almost 45 years old. (1971 BMW Bavaria) It's tuned well enough, but A/F ratios do move around quite a bit. Am I reading that right that being rich lowers exhaust temp, but may overstress the cat?
No, it won't stress the catalyst. Unless it misfires. Trucks with trailers run very rich going up passes for as long as the pass is, and it won't damage anything.

This sort of skirts around my primary issue: high-power turbo engines. Obviously with the current proliferation of OEM turbo engines, running a cat on a moderate-power turbo car is possible without any major drawbacks. My concern is with a much elevated power level over stock. Under boost and power and with proper tuning I wouldn't be too concerned, since the richness is basically unburned HC which the cat is designed to deal with, but the "misfires" and such are what concern me. I have to run a slightly rich tune to protect the engine on pump gas, and when running track events the exhaust heat/richness/etc is enough to get pops/firespit between shifts after a few laps even with a recirculated BPV. It is my suspicion that this would fry a high-flow cat in short order. Any thoughts?

Also, medium-term plans (i.e. spare time during house-move prep and job-search) include plans to install my Aquamist setup; theoretically this should help by dropping temps a bit, especially on track, and leaning out the tailpipe mixture a bit. Is this an accurate assumption?

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/22/15 8:02 a.m.

In reply to jsquared:

A lot of your concern is covered, to me, by who calibrated it. And OEM application that is intended to pull heavy trailers up a long hill on a hot day is calibrated to not misfire and still be able to go up the hill. One thing is may do is reduce power to keep the system from breaking, but exhaust wise, the rich limit will run and not misfire. Besides, OEM systems have full range misfire monitors. Lots of testing, quite a few cars, many studies to do that.

Some aftermarket calibrators are good, but I don't have a very high opinion of all of them. Can't really comment how much work they do to make sure not to go too rich to prevent misfires.

I assume you mean a mist system for water injection in the engine. For that, the primary benefit is knock reduction, which greatly improves exhaust temps, which, as you think, leans out the need to keep the fuel mixture at best richness for power.

Again, how well that is figured out on an aftermarket side is not known- one has to do a lot of work to figure out what the knock limit is, and understand the amount of richness that is used to keep temps down, etc- not sure what kind of tools and experiments they do to figure that out. It can be done- OEM's spend a lot of time and effort on that.

Spoolpigeon
Spoolpigeon UberDork
8/22/15 9:50 a.m.

Great article, especially since I'm looking at replacing the current one on my S2000. Were all of these cats similar cell count? The rules for ST* have a minimum 100 cell count, and that is what I'm leaning towards, just curious what count these were.

Shaun
Shaun HalfDork
8/27/15 11:44 a.m.

Thanks Alfadriver!

jsquared
jsquared Reader
8/27/15 8:51 p.m.
alfadriver wrote: In reply to jsquared: A lot of your concern is covered, to me, by who calibrated it. [...] Some aftermarket calibrators are good, but I don't have a very high opinion of all of them. Can't really comment how much work they do to make sure not to go too rich to prevent misfires.

It's going to be a guy who builds and tunes race engines, somewhat known in the Subaru world, wins Time Trials and has huge-HP Time Attack cars, so relatively speaking it should be a pretty good calibration once it's done (and given Subaru's issues with the OEM tune, probably better than a stock tune on a stock engine). I'm wondering about the difference, though, between the temps from a between-shift mini-fireball out the tailpipe from the momentary over-richness and the temps from a combustion-chamber misfire under load. Is the unburnt fuel igniting in the exhaust pipe on it's way out going to be at a heat that could hurt the cat, or is the EGT spike from a misfire in the combustion chamber going to be way higher? I don't have an EGT gauge on the car or else I probably wouldn't have to ask that question

alfadriver wrote: I assume you mean a mist system for water injection in the engine. For that, the primary benefit is knock reduction, which greatly improves exhaust temps, which, as you think, leans out the need to keep the fuel mixture at best richness for power.

Yep, the Aquamist is a brand name for a water-injection system (uses a pulse-width-modulated valve rather than pump speed to control injection as well, and my particular model can be operated off of an additional map in my standalone, so in effect I have a 3D map control over a single injector in the intake manifold... if I ever get around to installing it, that is! hahaha)

Big thanks, BTW, for dropping the knowledge on us Always nice to have a pro's viewpoint.

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/28/15 8:43 a.m.

In reply to jsquared:

Quick misfires from shifts should be ok (but I'll suggest doing fuel off shifts- engine speed will drop faster). Decel misfires- even slowing from 60mph- can destroy a cat. Again- lots of time is spent making sure that misfires don't happen on tip outs, to the point of being really aggressive turning the fuel off.

As for the aftermarket tuner- spark is still hard to calibrate. Takes a lot of time if one wants to do it really well- harder if the engine is knock limited, as the knock on effects (see what I did there....) are numerous. Mostly in exhaust temp effects and keeping that in a safe range not to break something.

Coupefan
Coupefan Reader
9/1/15 12:19 p.m.

Having added a modern cat to a 34 year old car, I can say it made an extraordinary difference. Now likely the old cat was slowly dying and plugging up, but the addition of the new cat allowed the car to breath at higher RPMs. Additionally, from a numbers perspective during emissions testing, the car ran numbers comparable to a late 90s/early 2000s car. Win-win, as they say.

DAVEG
DAVEG New Reader
9/18/15 1:04 p.m.

Good article...I have both CAT which I reinstall when not racing and bypass pipe. I have not had the car checked with the CAT to see HP difference. I know that a revised chip made a big difference in HP and according to the chip maker a big difference in emissions with a leaner air fuel ratio.

Ian F
Ian F MegaDork
2/27/18 8:23 a.m.

While it tends to be an unpopular opinion, I've wondered about adding one of these high-flow cats to an older car that never had one to reduce exhaust smelliness. 

alfadriver
alfadriver GRM+ Memberand MegaDork
2/27/18 8:29 a.m.
Ian F said:

While it tends to be an unpopular opinion, I've wondered about adding one of these high-flow cats to an older car that never had one to reduce exhaust smelliness. 

While a catalyst will be reasonably effective with a carb, you would be far better off with a programmable EFI system for effectiveness and durability.  The dawn of EFI and exhaust sensors really was a turning point in vehicle emissions.

Ian F
Ian F MegaDork
2/27/18 8:35 a.m.

In reply to alfadriver :

That is sort of my plan - add a high flow cat to the exhaust of my 1800ES which will get a closed loop EFI system.  Still on the fence on the two Triumphs, but I suspect they'll get EFI eventually, given my general dislike for carburetors. 

rslifkin
rslifkin SuperDork
2/27/18 8:43 a.m.

Being that decel misfires have been mentioned, does that mean anything that gives off some crackles and pops on decel is probably beating up the cat?  

Any chance of getting a quick run-down of what's safe for a cat and what will damage it from a tuning perspective?  (for those of us who are tuning our own stuff)

alfadriver
alfadriver GRM+ Memberand MegaDork
2/27/18 8:51 a.m.
Ian F said:

In reply to alfadriver :

That is sort of my plan - add a high flow cat to the exhaust of my 1800ES which will get a closed loop EFI system.  Still on the fence on the two Triumphs, but I suspect they'll get EFI eventually, given my general dislike for carburetors. 

I, too, have plans to convert my GTV to EFI and add a catalyst.  Even have the catalyst in hand.  Not sure if I will ever do it, though.

rslifkin
rslifkin SuperDork
2/27/18 8:53 a.m.

As an additional thought / question on cats: I know a standard 3 way catalyst won't do much to reduce NOx when running lean burn.  But what's out there for catalysts that would?  Maybe running a diesel catalyst behind the standard one?  

RossD
RossD MegaDork
2/27/18 8:58 a.m.

I plan on adding a cat to the Renault 8 while I add MS2 and a turbo. I hate smelly exhaust. It smells.

alfadriver
alfadriver GRM+ Memberand MegaDork
2/27/18 8:59 a.m.
rslifkin said:

Being that decel misfires have been mentioned, does that mean anything that gives off some crackles and pops on decel is probably beating up the cat?  

Any chance of getting a quick run-down of what's safe for a cat and what will damage it from a tuning perspective?  (for those of us who are tuning our own stuff)

Depends on how bad they are.  Seems to me that many of the current OEM's that are doing it are likely to be doing tricks to make it sound like you are getting pops and crackles in the exhaust without hurting the cat- and that is possible.

But, generally, *some* should be ok, a lot will burn the catalyst up in short order.  Basically- all the energy that is used to move the car forward would end up in the catalyst to burn.  The hard part for tuners is that the only real way to know what is "safe" is to measure the cat temp.  Which isn't exactly an easy thing to do without some decent resources (which then makes it really easy).  In that regard, I would just suggest that instead of leaving the fuel on during decelerations longer than 2 seconds or so- just turn it off.  That actually saves fuel, too.

For everyone here, if you are adding a cat, the issue that OEM's face about recovering the cat for performance isn't an issue- the big issue for you would be to make sure there's enough fuel to re-start the engine.

Now if you can measure gas temps (which is easier for most fabricators than cat temp- just due to drilling the catalyst material)- I would suggest keeping the cat inlet temps below 1600F, and that should keep the cat temps below 1700-1750F- which is where most cats get damaged.  If you get close to that temp, run a little richer.  But since it's not common for people here to have that kind of instrumentation- a "safe" cal would be to run about 11 to 11.5:1 (relative to gas of 14.6:1) which should keep the cat temps down, and not result in a big loss in power from best fuel of 12.5:1 or so.

And below WOT, just run closed loop around stoich.  It will work great.

The0retical
The0retical UltraDork
2/27/18 9:20 a.m.

I feel like this article needs to be posted once a year. It's such a great showing of how far the tech has come and the comments have so much info from people who do this for a living.

It gets tiring to hear about "ripping out all that emissions crap" from other people when you can build quite a bit of power with catalysts and not smell like a gas station when you get to work.

I worked in aviation long enough to get tired of smelling like gas all the time and now that I work at a desk I don't want to reek when I get there.

Stanger2000
Stanger2000 New Reader
2/27/18 10:03 a.m.

Not sure if this has been mentioned but most aftermarket cats last nowhere near as long as OEM, especially most high flow cats.  

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