Chunks fell out of muffler inlet

[Stainless]

When I removed my stock muffler, a pile of chunks fell out. I'm assuming these all came from the cat. What does this mean? Is my cat toast? Time for a cat delete? Is this the excuse I need to go aftermarket? For reference, my car has around 53k miles.

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[TTait]

That was the interior of your Cat, unless its the remnants of a previous cat. if you remove the cat you can put a small light bulb in through the outlet and look through the inlet, you will likely be able to see the core all chewed up and fragmented, and some more chunks may fall out, however the exhaust gas pressure is probably pretty good about blowing smaller chunks into your muffler. If the cat does appear pristine and there is a reasonable chance that you are finding remnants from a previous failure, then maybe you do nothing. That's probably not the case though.

Get the chunks out of the muffler if you can - they are causing restrictions.

Environmentally Speaking, you should replace the Cat, of course.

Until then, you can use a metal bar to break up the remaining core inside the cat and remove all the chunks and you will have free flow and no more chance of damage. Technically a new pipe would give cleaner flow, but that would fail a visual inspection if the car went to a state with visual inspections but no actual tailpipe test in the future.

Have no illusions that a cat delete will add raw unbridled power to your Delorean - In fact your car was designed to have some back pressure in the exhaust, so you may see little or no improvement at all. Without going political there are good reasons to have a cat as well. Regardless of your opinion as to how much your exhaust might contribute to climate change - nobody is going to argue that the raw exhaust is better for us to breathe or potentially a cure for cancer. If you can afford a Delorean you can at least afford a 49 state catalytic converter.

I've driven my Delorean for short months with a hollow cat, and also a test pipe for a while on my taller cammed car, but I had to come up with a working ones again to pass my next California Smog tests and I can tell you the hollow cat didn't provide any noticeable increase in power or fuel economy. I had no motivation to put the hollow cat back on after passing smog - it didn't seem to buy me anything.

Again - I mean nothing political here - if anything I'm trying to be apolitical and just say in my experience only having a test pipe etc. didn't seem to make any noticeable improvement to me. switching out the cams made a difference (granted the idle was pretty awful on Steger cams) and then later adding a dual cat DP! gen1 exhaust helped even more - but a hollow cat didn't make enough of a blip for me to detect it. For goodness sakes don't gut a perfectly good cat just to try to gain power - it won't do enough to feel IMO.

BTW - its possible somebody wants those chunks - there is good metal in them - that's why cats get stolen.

[dn010]

When I had no converters, my biggest complaint was how much I smelled like exhaust after a drive.

[David T]

It's also louder without a cat and harder to tune. The stock motor was designed to work with it. The cat probably failed because at some point in the past the motor was running WAY too rich.

[Helirich]

In fact your car was designed to have some back pressure in the exhaust, so you may see little or no improvement at all.

TTait has a lot of good info in this post, but this statement is false. No engine is designed to have back pressure and there is no benefit to back pressure. This is a myth that has no backing in science. I think it got started by people confused about terms. Savaging is negative back pressure. So you could say negative back pressure is a good thing. I don't like the term "negative back pressure". Why not say "vacuum" is a good thing?

I suggest you watch this video.

https://www.roadandtrack.com/new-cars/car-technology/a14530205/what-is-exhaust-backpressure-and-why-is-it-bad-for-horsepower/

I'm not suggesting that removing your cat adds power. It may or may not, because it may or may not add to back pressure, but you never want more positive back pressure.

[Ron]

TTait has a lot of good info in this post, but this statement is false. No engine is designed to have back pressure and there is no benefit to back pressure. This is a myth that has no backing in science.
* I can think of at least two counter examples WRT benefit:
1. If you run open headers, you may loose a significant amount of low end torque.
2. If you run with no headers (or manifolds), when the exhaust exits into the much cooler ambient area, the exhaust valves will be heated and cooled (by a waive which I'm not going to get into) at such extremes that they suffer from fatigue. Pronto.


I think it got started by people confused about terms.
Jargon! -- Even back in the day, "back pressure" referred to restriction throughout the exhaust system, where "back" has nothing to do with direction -- It is referring to the back side of the exhaust valve... Pressure has no direction, only magnitude -- It's a scalar quantity. (Flow has both magnitude and direction, a vector quantity.)


Savaging is negative back pressure.
Savaging is tuning the exhaust where one port's pressure assists the flow of another.




So you could say negative back pressure is a good thing. I don't like the term "negative back pressure". Why not say "vacuum" is a good thing? I agree, it's like a screwed up double negative. If we're going to be scientific (picky;-), vacuum is devoid of matter, which exhaust is not. ...just call it what it is here, "less pressure".



I suggest you watch this video.
https://www.roadandtrack.com/new-cars/car-technology/a14530205/what-is-exhaust-backpressure-and-why-is-it-bad-for-horsepower/

I'm not suggesting that removing your cat adds power. It may or may not, because it may or may not add to back pressure, but you never want more positive back pressure.An excellent explanation! But he is focusing on why back pressure [restriction in exhaust system] is bad for horse power, never claiming or even implying you never want any...*

Removing a cat will definitely lessen the engines load. But the affect on the other systems, all working in conjunction with each other (emission=>fuel delivery=>...), may not result with more power. When designing the D's exhaust, the tune had to keep emission restrictions in mind, so I would say that removing the cat would, at best, add power, but not enough to appreciate.


Jared, it sounds like a perfect excuse to me! :deviltail:

[Rich]

Savaging is tuning the exhaust where one port's pressure assists the flow of another.


Most of us know what's being discussed regarding this bit of engine jargon. However, there is no term such as that.

Without getting into the description the correct term is scavenging. Exhaust scavenging, as noted in the R&T article Helirich posted.

The correction may help if this thread continues in that direction.

[Jason]

Years ago, when I had my car at a local shop to fix an exhaust manifold leak they found the same thing with my cat. At the time they hollowed it out and put it back with the plan that I would source a new one later. I forgot, took the car in for PA inspection... and it passed. Even with the sniffer test.

I ran it like that for a few years. No noticeable increase in power, but no issues either. The next time the exhaust had to come apart a working cat was installed.

[Mark D]

If you end up replacing that cat, please be sure to recycle the old one along with those chunks as they most likely still contain precious metals like platinum, palladium, and unobtanium. We don't need to be needlessly destroying the lives of indigenous people on other planets just to harvest their resources.

I actually watched a really great documentary on it the other day that James Cameron produced, and it was covered in great detail. Check that out if you're looking to learn more about how some of those rare metals are sourced to produce catalytic converters.

EDIT:

I just looked it up, and the name of the documentary is Avitar: The Last Air Bender. The most interesting part of the film besides the mineral mining aspect was how certain people can manipulate one of the four elements—water, earth, fire, or air—with telekinetic variants of the Chinese martial arts known as "bending". The most famous of these benders, of course, is Bending Unit 22 or simply "Bender" who is the assistant manager of sales on the interplanetary delivery ship, the Planet Express.

[Ron]

Most of us know what's being discussed regarding this bit of engine jargon. However, there is no term such as that.

Without getting into the description the correct term is scavenging. Exhaust scavenging, as noted in the R&T article Helirich posted.

The correction may help if this thread continues in that direction.Thx! My mistake -- I blindly went with the flow. :smile:

[Helirich]

2. If you run with no headers (or manifolds), when the exhaust exits into the much cooler ambient area, the exhaust valves will be heated and cooled (by a waive which I'm not going to get into) at such extremes that they suffer from fatigue. Pronto.

Not sure about this statement. I've seen aircraft exhaust stacks so short that I could see the exhaust valve. This was on WWII aircraft that fly at high altitude. It can be -50 at altitude. I had a discussion on this very subject with an old coot at an air show. He said there is so much hot air coming out that no cold air gets in. He did say it was a worry when they shut down an aircraft in freezing weather. (Cold breeze)

[David T]

Not sure about this statement. I've seen aircraft exhaust stacks so short that I could see the exhaust valve. This was on WWII aircraft that fly at high altitude. It can be -50 at altitude. I had a discussion on this very subject with an old coot at an air show. He said there is so much hot air coming out that no cold air gets in. He did say it was a worry when they shut down an aircraft in freezing weather. (Cold breeze)

You make a lot of references between cars and aircraft. While they do have things in common, there are too many differences to compare them directly. For example cars get to coast most of the time and rarely run at full power. Most internal combustion engines will run better with a tuned exhaust. BUT you can only tune it for a very narrow range of HP or RPM or torque.

[Ron]

Not sure about this statement. I've seen aircraft exhaust stacks so short that I could see the exhaust valve. This was on WWII aircraft that fly at high altitude. It can be -50 at altitude. I had a discussion on this very subject with an old coot at an air show. He said there is so much hot air coming out that no cold air gets in. He did say it was a worry when they shut down an aircraft in freezing weather. (Cold breeze)
First I shouldn't have said "pronto", especially on a non-performance engine.

Anyway, it will be significantly much hotter right behind the valve when there is a manifold. Heat is still being produced (and held) until combustion completes there. I'd bet if you ask the old coot, he will tell you that they used to cut the pipes (or open collectors) off right where the discoloration ends to tune them...time to turn it loose.

Never, say never. :smile:

[Helirich]

I think when you guys say "tuned", you are perpetuating the myth that "some back pressure" is good. When they tune an exhaust, they are trying to have negative back pressure (vacuum) at a certain RPM. They actually would like this negative back pressure at all RPMs, but that is impossible. So they pick a useful RPM for what they are trying to do. Ron mentioned that headers help in low end torque. This is often true, but it is not the only "tune" there is.

David T is correct in some things on aircraft are unique. Like their engines are tuned to run in a very tight RPM range at the expense of all the rest. That's why they idle so bad. The differnce between cruise power and max power might be less than 400 RPMs. In the case of helicopters and constant speed props, there is no differnce.

Ron, I will say, I agree with you on the short stacks have to be bad for temp fatigue and I was arguing that to the old mechanic. One thing he told me was the TBO (time before overhaul) was as low as 250 hours on those aircraft. He said that most got shot down before reaching that. (Not a perticular comforting thought) So maybe breaking valve heads is not a concern.

I'm not trying to start an argument here. I'm just saying that I've not heard of any "good back pressure" unless you are defining "negative back pressure" as back pressure.

[Stainless]

Well, after pulling the motor, I removed the crossover pipe and cat and was surprised at how good the cat looked on the inlet side. It was hard to get a good picture of the outlet side due to the curving of the pipe, but I could see that place where some of the internals were missing. I'm currently considering going aftermarket with my exhaust, so I'll noodle on it for a bit to see what route I decide to go.
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[TTait]

Might be time to buy a boroscope/endoscope inspection camera for your phone or laptop...