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Andy Hollis
Andy Hollis
8/13/15 2:50 p.m.

Are catalytic converters just a cork in the system? Many enthusiasts think so, and we can’t say we’re surprised. After all, these components were born out of federally mandated emissions regulations, an origin story that doesn’t exactly scream “performance boost.” In fact, issues with cats have been fueling performance woes since their introduction more than 30 years ago.

Those first …

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alfadriver
alfadriver GRM+ Memberand UltimaDork
8/13/15 2:53 p.m.

I'm glad this article has finally been posted.

flatlander937
flatlander937 Reader
8/13/15 6:41 p.m.

So the Magnaflow cat is 0.5lbs lighter than the test pipe?

Hungary Bill
Hungary Bill GRM+ Memberand SuperDork
8/13/15 7:06 p.m.

Impressive results and great article.

I wonder what the test would be like with something older. Say mid-80's ish?

KyAllroad
KyAllroad Dork
8/13/15 7:15 p.m.

Makes me feel better about keeping the cat on the race car. It'd be interesting to repeat the test (circa 2008) on something turbo and something bigger.

irish44j
irish44j PowerDork
8/13/15 7:37 p.m.
Hungary Bill wrote: Impressive results and great article. I wonder what the test would be like with something older. Say mid-80's ish?

ditto.

I just keep the cat in the e30 because without it, the M42 exhaust sounds like complete raspy garbage.

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/13/15 7:39 p.m.
irish44j wrote:
Hungary Bill wrote: Impressive results and great article. I wonder what the test would be like with something older. Say mid-80's ish?
ditto. I just keep the cat in the e30 because without it, the M42 exhaust sounds like complete raspy garbage.

Something of that era, you'd be better off with a modern HP cat. Flow better, lighter, and even though I'm not a fan of aftermarket cats (not good info), it will still be better than the original hardware.

Advan046
Advan046 SuperDork
8/13/15 8:24 p.m.

This was a refreshing article. I learned that my impressions were some what accurate about cat delete and high flow cat impact on modern-ish cars.

novaderrik
novaderrik UltimaDork
8/14/15 2:11 a.m.

now do the same test on a late 70's/early 80's GM car with the stock pellet style converter... those things were restrictions on engines that only made just over 100hp..

Tyler H
Tyler H GRM+ Memberand SuperDork
8/14/15 7:13 a.m.

Great article. We don't have emissions tests here and I find myself huffing Hondabro (or new Silverado with dual straight pipes)exhaust every time I get stuck at a light. WHY? A Magnaflow cat is $150 and does nothing to hurt performance.

Roll by and they inevitably have that glowing check engine light. That would drive me crazy.

foxtrapper
foxtrapper UltimaDork
8/14/15 7:22 a.m.

The results don't surprise me.

BUT... this isn't the whole picture.

1, these were all matrix or honeycomb type converters. Those flow great! Throw in the a pellet type, and the results will be different, very much to the worse. Yes, I know pellet types are old, but they are still around. Especially on older GM vehicles.

2, none of this dealt with a damaged cat, particularly an overheated and melted. This isn't always as obvious. Get into home-tuning and get the mixture overly rich, and it's not to hard to get the cat partially melted, killing flow through it.

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/14/15 7:40 a.m.
foxtrapper wrote: The results don't surprise me. BUT... this isn't the whole picture. 1, these were all matrix or honeycomb type converters. Those flow great! Throw in the a pellet type, and the results will be different, very much to the worse. Yes, I know pellet types are old, but they are still around. Especially on older GM vehicles. 2, none of this dealt with a damaged cat, particularly an overheated and melted. This isn't always as obvious. Get into home-tuning and get the mixture overly rich, and it's not to hard to get the cat partially melted, killing flow through it.

Why would they want to test technology that's over 30 years old? What's the point of that? This article was to illustrate how things have progressed. Nobody in the aftermarket does pellet cats, and I'm not even sure one can get them from an OEM. That would be pointless.

As for 2- this does somewhat illustrate that- as it's a cat swap. So if you damage the catalyst- instead of just putting a straight pipe in, here's the performance impact of various choices VS. a pipe. The damaging of catalysts could be fit into a sidebar.

Basically, this is the picture a couple of years ago. And it's not changed much since then.

pushrod36
pushrod36 Reader
8/14/15 8:12 a.m.

I would be interested to see the same test on a turbo engine making over 500hp. Even if the results were teh same (test pipe isn't gaining you anything) I think it would add resolution to the test results (5-10HP changes instead of 1-2HP changes).

Power curves and backpressure measurements would be good information, too.

dean1484
dean1484 GRM+ Memberand MegaDork
8/14/15 8:24 a.m.

The insides of the cat on my 924s came apart and I removed them as they clogged up my exhaust to the point that it would not run over 4,000 rpm. I immediately found that the downside was that it stunk. Stand behind it and your eyes water. It also made the car much louder and it had a horrible drone at highway speeds. I actually got a magnaflow cat based on that article and put it in. Huge improvement in day-to-day drivability of the car. No more eye-wattering exhaust and you could have a conversation on the highway with your passenger. I don't know if performances changed but it made the car much better to live with.

Driven5
Driven5 Dork
8/14/15 9:32 a.m.
foxtrapper wrote: BUT... this isn't the whole picture.

I beg to differ. If you have an old technology or damaged cat on your car and are worried about performance, get a new modern replacement instead of a test pipe. If you already have a test pipe on your car, installing a cat will greatly lower your "d-bag coefficient". It is my longstanding belief that there are no good reasons to run totally catless on most any EFI car that is registered for street use, and have yet to see a decent argument to the contrary.

foxtrapper
foxtrapper UltimaDork
8/14/15 10:13 a.m.
alfadriver wrote: Why would they want to test technology that's over 30 years old?

Because the pellet type cats are still around and were on the cars favored by American muscle hot rodders, GM.

I'm not anti-cat, and the matrix type has always been around. It's not a new technology by any means.

bmwbav
bmwbav Reader
8/14/15 10:30 a.m.

This is relevant to my interests. I'd love to add cats to my BMW project car to reduce drone and not choke on it's exhaust all the time. My worries are in three areas. How close do they need to be to the engine? Is my backyard tuned megasquirt going to ruin them in two weeks? How much extra heat is this going to generate?

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/14/15 11:31 a.m.
foxtrapper wrote:
alfadriver wrote: Why would they want to test technology that's over 30 years old?
Because the pellet type cats are still around and were on the cars favored by American muscle hot rodders, GM. I'm not anti-cat, and the matrix type has always been around. It's not a new technology by any means.

Where? As in the last 20 years, who sold a pellet style catalyst?

If hot rodders use them, it's because they are either lazy or just don't know things have changed a lot.

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/14/15 1:35 p.m.
bmwbav wrote: This is relevant to my interests. I'd love to add cats to my BMW project car to reduce drone and not choke on it's exhaust all the time. My worries are in three areas. How close do they need to be to the engine? Is my backyard tuned megasquirt going to ruin them in two weeks? How much extra heat is this going to generate?

Now that I'm back at a real keyboard....

Start with ruining a cat- so what you are trying to make sure is that the calibration does not over temp the cat- and the way it will, so badly that you damage anything, is misfires. Lean or rich misfires will hurt- the rich ones being really painful- with plenty of fuel to go with the air. Ignition problems that cause misfires are equally as bad.

So if you can prevent all of those now, you should be fine. And if you notice a misfire, stop and fix the problem quickly, and you should be ok,too.

Can you tune it in a weekend to work well? Sure. If you are using a narrow band O2 sensor, just keep that going back and forth around stoich, it should work. Keep that oscillation small enough that you don't feel it, even better. For a WB system, I'm not that familiar with the MS fuel control, but stick it at stoich all the time- it will work fine. There will be enough noise in the system to keep it from being perfectly constant- and that helps.

How close? At the end of headers will work well. If you do any active work to get the cats hot, that will help, but unless you are being tested, you probably are not so worried about the starting emissions. On my Alfa, I was planning where the headers end below my feet- which ends up being about 2 1/2 feet. OEM's have them super close to get lit off quickly. But at the longer distance, it will light off reasonably well, and it also reduces the risk of overheating just from aggressive driving.

As for extra heat- your headers will be hotter. Catalyst construction really makes the outer skin of those cooler than the metal exhaust part. Under normal conditions- you'll see about 100F increase across it. When running rich for power, that will go down to below 50F. As a matter of fact, we go rich to keep the exhaust components cool. So shoot for 12:1 at peak power.

rcutclif
rcutclif GRM+ Memberand Dork
8/14/15 1:52 p.m.

how can you tell if a cat is clogged or ruined?

Trackmouse
Trackmouse HalfDork
8/14/15 1:56 p.m.

You guys must be retired to have this much time to argue about crap that doesn't matter.

bmwbav
bmwbav Reader
8/14/15 1:56 p.m.

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?

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 ignition 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.

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?

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/14/15 1:56 p.m.

Clogged is pretty easy- engine performance will drop considerably- since there's a nice blockage in it.

Over temped so the metal is sintered, but the substrate is still ok? Outside of gas measurement, you need to have a second O2 sensor to compare to the first one.

If it rattles- it's shot (not including the heat shield).

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/14/15 2:02 p.m.
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.

alfadriver
alfadriver GRM+ Memberand UltimaDork
8/14/15 2:03 p.m.
Trackmouse wrote: You guys must be retired to have this much time to argue about crap that doesn't matter.

I have to retire to STOP worrying about catalysts.

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