Legend has it, “Let there be catalytic converters!” said GM’s Ed Cole, and »poof« the catalytic converter sprang into existence and evolved into the kind we now use. How it actually happened is a whole lot more complicated. Kind of amazing it happened at all, actually; it almost didn’t, several times over.
The idea of catalytic cleanup of exhaust dates back a lot further than many people realise. A top catalysis expert—probably the top expert for many years—was Eugene Houdry, who devised techniques for catalytic (rather than thermal) cracking of petroleum to turn it into better and more gasoline and other useful products, and then after WWII he applied his expertise to various kinds of exhaust. At first he worked to solve specialised, local problems like how to use engine-driven forklifts and machinery in warehouses, mines, and other enclosed spaces without gassing all the workers, and how to eliminate noxious odours from factory smokestacks. But it wasn’t long before he turned his sights on automobile exhaust.
Here’s an excellent article about his work (and exhaust catalysis in general) in Popular Science, June of 1955. “One of these days,” it starts out, “you are going to take a whiff of your car’s exhaust and get a surprise; the greasy smell will be gone.” That day was quite awhile in coming; it took about two decades’ time after this article was published.(click the pic for the whole article in a new browser tab):
For 1961 the road draft tube, which dumped hydrocarbon fumes and vapours from the engine crankcase into the atmosphere, was replaced in California by positive crankcase ventilation systems that routed crankcase fumes into the intake tract to be burned. Success with that first effort was followed by experimentation with all kinds of ideas for auto emissions control. Some of them moved things in a good direction, and while their R&D paid long-term dividends in knowledge of combustion dynamics and suchlike, at the time many of them degraded drivability, performance, and fuel economy, and none of them made car exhaust enough cleaner over enough miles to meet the increasingly obvious need.
From very early on there were musings about exhaust catalysis. Despite successful demonstrations of practical catalytic converters by outside suppliers, the idea was widely unpopular with automakers, so things moved slowly until 1970, when the U.S. Congress put the Clean Air Act on the books. It mandated that emissions of three major pollutants in exhaust—carbon monoxide, unburnt hydrocarbons, and oxides of nitrogen—be cut down by 90% by the 1975 model year (versus 1970-model cars, which the industry had straightfacedly argued were clean enough that no further regulation was necessary). The law had sharp teeth, too, requiring automakers to demonstrate not just a whack of money thrown at the problem, but actual, real, ongoing good-faith effort, subject to stringent audit. Suddenly there was very urgent interest in catalytic exhaust treatment. Yes, converters would be expensive, and yes, they might have to be bought rather than made in-house, and yes, there were lots of unknowns, but y’know, ninety percent cutdown or their vehicles wouldn’t be saleable!
That brings us to the start of the catalytic converter development timeline thoroughly and engagingly described in Doing The Impossible, a 2004 deep-dive article in the once defunct, now resurrected, highly worthy magazine “Invention & Technology”. If you’ll read only one of today’s links, please make it this one. Read it now; the rest of this post will make more sense afterward (alternate and better-formatted/more readable link here archived from their old website).
Y’back! Okeh, so if catalytic converters didn’t just appear on GM’s say-so, then what was GM’s role? Well…it’s complicated. GM, by dint of their employee Thomas Midgley Jr’s 1921 discovery and their 1923 joint venture with Esso (Ethyl Corporation) were largely responsible for the existence, proliferation, and persistence of leaded gasoline, which spoils exhaust catalysts. GM sold Ethyl in 1962, and so had likely been reluctant to do something that would degrade the value of the company they’d sold—such as develop and commercialise cars that couldn’t take leaded gasoline—but the Clean Air Act came along and put push to shove about it.
A quote attributed to GM’s Cole, to the effect of ~”give me unleaded fuel and I’ll put catalysts on the cars”, when taken out of context, has a spaketh-the-Lord sound about it, and that’s probably where the idea comes from that he was the go/no-go decider for the technology and industry as a whole. He wasn’t, but he did decide to go forward with catalytic converters on GM vehicles, and he overcame inertia and resistance to make that happen. Given GM’s market share at the time, his decision and effort surely went a very long way in terms of the percentage of catalyst-equipped ’75 cars on the road, and made it easier for the rest of the industry to do it. GM’s big market share probably amounted to a critical mass of the vehicle fleet; If an AMC or a Chrysler, a VW or a Toyota had decided in favour of catalytic converters but GM had gone with some other method, it would’ve been much harder (or likely impossible) to enact the mandate for universal nationwide availability of unleaded gasoline by July of 1974 in time for the first ’75 cars to hit the roads.
So GM certainly deserve substantial credit for getting catcons onto the roads. But as to those converters themselves, well…yeah…about that. GM didn’t participate in the monolithic honeycomb converter R&D described in the linked I&T article, or avail themselves of its fruits; they wanted their own AC Spark Plug division to make their converters, and they weren’t going to use a monolithic design. GM had spent a mountain of dollars in the ’60s and early ’70s trying to develop a practical catalytic converter, and it seems some chunk of that expenditure went into flailing and failing. John DeLorean’s scathing memoir “On a Clear Day You Can See General Motors” makes a tantalising, cryptic, one-line reference: “monolithic converter—$millions wasted”. I hope someday to find an access point for that particular rabbit hole.
Here’s what you see if you peer into one end of a monolithic converter—a gazillion tiny straight-through tunnels. Hold such a converter up and you can see light coming through from end to end:
And here’s a cutaway showing how the exhaust has a relatively easy, straight flow path from inlet to outlet in such a converter:
That’s the kind GM decided against. Instead of a cordierite honeycomb for exhaust to flow through, GM went with a bed of alumina pellets or beads for exhaust to be forced through. And “force” is quite an apt word. Here’s the inlet of a GM converter; exhaust hits this wall and has to turn two sharp corners, then enter the bead bed through slotted louvers. Look closely and you can see individual beads in some of the louvers:
And at the other end of the converter, here’s the outlet—more tight corners and flow restriction. Some might remember the prominent hissing sound from the exhaust of a converter-equipped GM vehicle at high engine RPM, as when the driver would floor the accelerator. Hissing is caused by gas turbulence resulting from flow restriction. H’mm…y’think?
The beads were packed in pretty tightly, but there had to be a little wiggle room or else there’d be no flow possible. But that also meant the beads would tend to bounce around and abrade one another with gas flow and road vibration. Gradually the beads would attrit, accrete, and plug up the bead bed outlet plate, causing severe exhaust restriction. And the louvered plates containing the beads eventually tended to soften and distort, letting beads out of the bed (so much for GM’s claims that this design was superior because it allowed for replacement of just the catalyst rather than the whole assembly). Some of those freed beads were caught by the muffler downstream of the converter, but sometimes a red-hot bead managed to make it through the muffler and was ejected at high speed out the tailpipe. So heavy-duty GM vehicles—station wagons, trucks, and vans—came with a spark arrestor at the end of the tailpipe. Here’s such a one, photographed recently on a decrepit RV factory-lettered “454 SG” on the side and obviously on a Chev/GMC chassis. Someone has punched three larger holes in the outer screen, revealing the inner screen:
By and by, when enough beads plugged enough holes in the spark arrestor, the hiss grew more prominent and occurred at lower engine speeds.
Now, any kind of catalytic converter will overheat and melt down if too much raw fuel hits it. That’s why automakers installed them only in conjunction with high-power ignition systems—GM’s was especially good—and other catalyst-protection measures. But carburetors, particularly non-feedback ones, and catalytic converters were a bad marriage from the start; there were going to be rich conditions sooner and later, and the catalyst would suffer—especially at high altitude.
One morning in the mid-1980s my mother, in turn to drive the carpool, pulled her 1978 Caprice Classic into the driveway of one of my elementary schoolmate’s house to pick him up. He opened the door and we heard an alarming sound coming from under the car, like BvvFFFft!……bvvFFFft!……bvvFFFft! An exhaust leak, that much was obvious, but it didn’t sound like your ordinary everyday faulty muffler—my mother was quite adamant about that (“Shut up about the car, Daniel! I’ve had a broken muffler before! I know what they sound like, and that’s not it!”). The muffler got replaced, but the car’s original converter stayed—and wheezed—on.
In retrospect, what we were hearing was exhaust backing up behind a severely clogged catalytic converter and eventually forcing its way out, once enough pressure built up. That would also explain the eyewatering stink of its half-catalysed exhaust, which smells worse than uncatalysed or fully catalysed because it’s a fœtid mix of both. Dad’s ’77 Cutlass Supreme had the same ailment up there at 5,500 feet near Denver. It ran poorly, too, but this was the early 1980s and “clogged catalyst” just wasn’t much on the radar at that time, at least not the radar of the service stations my folks patronised. Those cars would have run a lot better with monolithic replacement converters.
But those bad ol’ bead beds were gone by 1981 and GM went to monolithic converters like everyone else, right? Actually, no. While they did begin phasing in monolithic converters in the early-mid 1980s, GM kept putting pellet-bed type converters in trucks and vans clear on up through the mid-1990s. When oxidation + reduction “3-way” converters came in for ’81, GM put two bead beds, one above the other, in the one housing. That’s twice the baffle plates, for those keeping score at home. (Sorry, what were we talking about? Oh yes: flow restriction and turbulence.)
Here’s a very detailed 1979 analysis of nine catalytic converters after what passed for high miles at that time. As today’s clickbait headlines are wont to say, Photos 10 and 19 will shock you! (Click Photo 10 here, of meltdown in a ’75 Dodge converter, to get the analysis in the background as a pdf):
Now, I’ve been plenty critical of GM here, but they’re hardly the only automaker to have faffed around with half-melted half-baked catalytic converter systems. Ford used monolithic converters, thus avoiding the bead badness, but in many cases the inlet was at 90° to the flow axis; the exhaust hit a wall on entering the converter and had to turn a sharp, restricted corner to get into the main body. But wait, there’s more: for 1975 Ford put a catalytic converter on just one leg of the headpipe on many V8 models, thus treating the exhaust from one but not the other bank of cylinders. On learning this really happened, I was reminded of a ’75 LTD that lived in our high school auto shop’s fenced yard. We figured the single cat meant someone had repaired half of the exhaust system without bothering to replace the “other” cat, which actually wasn’t ever there to begin with. This meant different backpressure for each half of the engine even when new, let alone after some miles—small wonder cars of that time developed a reputation for running poorly.
These kinds of monkeyshines, amongst many others, paint a plausible picture of automakers indulging in a cynical effort to kill vehicle emissions and safety regulation, which many of their SAE papers of the time reveal they viewed as a needless, pointless, passing fad. And they resented being told how to make cars. They invested enormous money and effort into fighting and delaying almost each and every provision of each and every regulation. Maybe if that money and effort had been put into the cars instead, results might’ve been much nicer. But as it was, cheap and nasty compliance was one of their primary tools in the war against regulation: “Oh, gosh, Mr. and Mrs. Carbuyer, you say your new car has ugly bumpers and runs poorly and gets lousy gas mileage and won’t stay fixed and buzzes angrily at you until you put on the uncomfortable seat belts? Gee, »tsk« what an awful pity. Not our fault; the government made us do it. Guess you’d best run get busy writing to Congress!”.
It didn’t work. The catalytic converter is still with us. It’s not without baggage or tradeoffs, and here’s a biggie: most of the noble metals used in catalytic converters come from South Africa. The sudden surge in demand for platinum and palladium and eventually rhodium came at the depths of the Apartheid era, which means we got to breathe cleaner air over here by dint of vicious, brutal racial enslavement over there, ugh. But the cat does a terrific job of cleaning up engine exhaust, and is now in virtually universal use on petrol-powered road vehicles all over the world.
Worthy further reading:
• New: A Catalytic Converter That Really Cleans Up Auto Exhaust (Popular Science, December 1970)
• Detroit Promises Clean-Air ’75s…But Ups the Sticker Another $300 (Popular Mechanics, September 1973—AMC, Chrysler, Ford, and GM emissions bigwigs scorn the law, ruefully resign themselves to using catalytic converters, and predict big troubles and costs)
• Mining Platinum, Palladium, Rhodium From Street Dust (Pity this wasn’t around in the ’70s and ’80s when GM’s bead converters were chuffing out catalyst dust!)
• Moving Violations: Automobiles, Experts, and Regulations in the United States (a graphic look at how the sausage was made. Includes direct accounts of some of the dramatics and disingenuous ploys the automakers tried to get the standards loosened. Relevant sample pages available online here)
• A Review And Analysis Of The Good Faith Of The Automobile Industry In Attempting To Comply With The Statutory NOx Standard (A very deep mid-’70s look at the complex matter of whether automakers were really doing their best—and if not, whether appropriate remedies were legally available)
Very interesting and well written article Daniel. One name I did not see in your piece or the Doing The Impossible side was Dr. Richard Klimisch. ( It’s possible I missed it.) GM actually had a magazine ad describing his work with catalysts. The name of that ad campaign was “Interesting People Doing Interesting Things”. I believe Bob Stempel was also involved in the development.
Another thing I always wondered about was the spark arrestor at the end of the tailpipe. What determined whether a vehicle got a spark arrestor? It looks to me like a horizontal discharge got one while a tailpipe with a turn-down at the end did not. Correct?
GM also had different fill plugs in the pellet converter housing to replace the pellets. As near as I can tell, 1975 to 1977 vehicles used a plug with a large screw-in hex fitting while 1978 and later used a pressed-in plug you had to deform with pliers to remove. I have a factory service manual for my 1978 Camaro Z28 that shows all the tools needed and the process to replace the catalyst.
You could also buy a new bottom cover for the GM pellet converter in case the cover got damaged by road debris.
Years ago, when faced with an aging, clogged GM converter, my buddies used to remove this big access plug, empty out all the beads from the GM converter and install a new bolt-in plug….. without the beads, for a reduction in back-pressure. We never had smog tests but visual checks were a thing, so it helped to have the appearance of a converter, even if it didn’t function.
But we all have to breathe so replacing the horrible GM converter with a new universal monolithic converter was the better choice.
Thanks, Glenn.
The answer to which cars got the spark arrestors is there in the article; it was station wagons (maybe only the bigger ones), trucks, and vans. Those all had side-discharge tailpipes, but so did the Nova/Omega/Apollo/Phoenix, and those didn’t have spark arrestors.
There were both pressed-in and threaded plugs. I don’t know if there was rhyme, reason, or consistency to which was used. It’s tempting to believe it was a model year split, but GM used spherical beads or cylindrical pellets in converters on different cars in the same model year, and installed transmissions on a seemingly random basis (TH200 behind a 350 in a wagon, much stronger TH350 behind a 305 in a same-year sedan, both as standard equipment, for example), so…!
As to GM’s promotional efforts: yes, once they decided to go with catalytic converters they mounted a big PR campaign about it. They talked up the fuel economy benefits, and there was some substance to that—rather than detuning to squeak past the new-vehicle emissions type approval tests as before, they could come closer to optimal tune and let the converter clean up the exhaust. They were on perhaps thinner ice boasting as though they’d come up with this great new device all by themselves and ahead of everyone else.
I wonder why automakers never did this–putting ozone generators in cars to reduce emissions. The free oxygen would react with pollutants, neutralizing them:
Ozone generators used to scrub NOx for fixed power installations parasitically reduce efficiencies by between 3-10 percent, and that is with highly efficient turbogenerators, as opposed to a pulley-driven alternator. Also, ozone is a pollutant too.
also, ozone generators – high voltages – automotive electrical systems – bleah.
Er…you’re kidding, Poindexter, yes? I hope? By all appearances of this clip you’re showing us, it’s baseless babble written by a crackpot who didn’t know a damn thing about what he was talking about. (“Unborn hydrocarbons”? Quick, call Right to Life. Sheesh.) Where’s this from, please?
Oh, didn’t read that clip closely, because ozone generators were part of the early Clean Air Act engineering toolkit for scrubbing fixed installation flue gas. The energetics and stoichiometry do not work for pre-combustion ozone injection at all, but it seemed plausible into the exhaust stream, briefly, without working out the exact math.
Here’s the book:
I’m not making any value judgments; I’m just saying, “This is what the book says.”
How fun! So yeah, pop pseudoscience from a huckster with no qualifications to be pontificating about exhaust emission control (or “therapy”). I’ll file that with this (remember the cesspool that was Usenet?).
Take away the huckster’s ignorant handwaving about ozone generators and all that piffle, and you’re left with a sound idea: make sure there’s sufficient oxygen for combustion as complete as possible. That’s a basic principle, and one that’s been centrally in mind since the beginning of the emission control era.
Hey, are you suggesting that “Mr. Oxygen” is something less than a genuine scientist? I’m sure his fellow scientists peer-reviewed it, and then gave him that title for his scientific breakthroughs.
I only drink this ever. I want to make sure there’s the right amount of oxygen along with the hydrogen in the water I drink. 🙂
Isn’t water (H2O) with and extra Oxygen atom Hydrogen Peroxide (H2O2)? – I don’t think I’d want to drink that, Paul. 🙂
you jest, but dissolved oxygen is not akin to “gluing” another oxygen atom onto a molecule.
Let’s not forget this type of water.
Right up there with the 100 MPG carburetor.
Great article Daniel, I spent 5 years instructing technicians on emissions repair, and it’s hard to tell this story in a compelling way.
Also, while you stated this in the article, I’d like to emphasize that the US Government NEVER mandated catalysts.
Manufacturers could meet tailpipe regulations with alternative choices such as electric vehicles or hydrogen powered IC engines, and Honda famously avoided cats for a time using CVCC technology. But over time exhaust catalysts became the clear choice.
Also, excessive fuel melts catalysts, but the reaction also requires oxygen which typically isn’t present in the exhaust. However, early tech cars often melted cats when the air injection control valves stuck open and fed air in the exhaust during rich operation. When this occurred, techs often replaced the cat without repairing the AIR system, and a couple months later the car came back with another melted cat…
That also explains why misfire is a cat killer- Nothing fans the flames of a catalyst inferno like a dead cylinder dumping raw fuel and air fuel straight into the cat.
Thanks! Yeah, that’s an important point: catalytic converters were never mandated. Neither were ugly bumpers or uncomfortable seatbelts. What was put in place was a performance standard, not an equipment standard.
As to melted cats: one day in the ’90s I was walking down the street at dusk when a late-’80s Escort audibly running on fewer than four cylinders came along. From underneath came a prominent orange glow that grew brighter as the car struggled up the hill: a severely overheating catalytic converter. I’m surprised the car didn’t blow up right then and there.
If it weren’t for those GM pellet/bead converters, there’d be no need for an asterisk after saying “Dead catalytic converters are always murder victims”.
“Neither were ugly bumpers”
case in point- nearly everything Chrysler made in 1974 looked better than the competition, because for the most part when they fully implemented the 5 mph standards they spent the effort and re-styled the front and rear ends as well. As opposed to Ford and a lot of the European and Japanese companies, who just slapped jutting battering rams on their existing vehicles- worst of them being the Mercury Comet, Thunderbird rear bumper, the BMW 2002 and the Mazda RX-4.
This also means that replacing old style pellet converters with new style high flow ones can keep exhaust factory clean AND increase horsepower. It was nice in the 90s to read lots of articles in magazines like Hot Rod telling guys how to keep the car 50 state legal and gain horsepower.
There was also an article…lemme see if I can find it…yep, here it is, where they used a dynamometer to demonstrate the utter lack of any significant difference in engine output with vs. without a reasonably modern catalytic converter in good condition.
Yes what I meant was the guys who try to find an excuse to remove catalytic converters lost all excuses when the modern high flow models hit the market. I’ve got a 50 year old car and I would seriously consider installing new aftermarket cats once I get a TBI system installed.
If you do this, shop carefully. Most aftermarket cats have a much lower catalyst content than OE cats to begin with, and many-to-most “performance” catalytic converters are especially minimal in their exhaust cleanup capabilities and are pretty much a waste of money and effort: cheaply-made weaklings, warranted only for 25,000 miles and barely able to clean up the exhaust of even a clean-running fuel-injected vehicle.
The trick for a good-working, durable setup is to get a California-spec converter suitable for an engine larger than yours. They’re type-approved to much stricter durability and performance standards, so while they cost a bit more up front, you won’t have to spend more money later because they won’t fail or melt in response to the dirty exhaust being put through them. I’ve used this kind on three vehicles and been enduringly happy with the results.
Remember the further the cat is from the engine, the harder time it’ll have reaching and staying at operating temperature. Easy solution is to wrap the headpipe (from manifold to cat inlet) with this stuff, which keeps the heat inside the pipe.
Intriguing stuff. I remember the beginnings of “low lead” and unleaded gas around 1971 but it was more expensive and the cars seemed to run no better than on regular. The catalysts made unleaded mandatory, and thus begun the “test pipe” phenomenon. Yes, use this pipe in place of the catalyst to see if the car runs better, so you will know if your catalyst is plugged. “Be sure to replace your converter when the test is complete. . . . hello? Anyone still here? OK, never mind.”
For those of us in areas where there were no emissions checks it was a win-win for a few years – substantially less exhaust restriction and the ability to use cheaper regular gas. And before someone jumps on me for the environmental consequences, remember that there were still a bazillion pre-catalyst cars on the road, so a few more wasn’t going to have any real effect.
I put a test pipe on my 77 New Yorker and had forgotten all about it when I traded it on a new car in 1985. The next day the salesman called me and informed me that I was financially responsible for the cost of the new converter they had to put on my trade-in. I (being a new lawyer and all) asked for some legal authority that made a seller responsible for working emissions equipment in a trade-in (because I genuinely had no idea). I never heard from them again. And from then on I joined the rest of the world in moving on from 1965 in terms of emissions and fuel requirements on my cars.
The operational benefits of unleaded gasoline (longer spark plug life, longer engine oil and engine life, longer exhaust system life) were a later/long-run thing. The price at the forecourt (typically five or ten cents more per gallon of unleaded) was a right-now thing. That was later identified as a major mistake in the American phaseout of leaded gasoline; it encouraged vehicle tampering and misfuelling and significantly prolonged the emissions cleanup. If taxes had been more thoughtfully reworked to eliminate or reverse the price difference between leaded and unleaded gasoline, things would’ve been cleaner quicker and there’d’ve been considerably less misfuelling (or as the EPA labelled it in an almost comically unhip way, “fuel switching”).
Test pipes from J.C. Witless or other back-of-the-magazine vendors were ancient history by the time I bought a much-used 10-year-old ex-police ’91 Chev Crapiece. It had a crack almost the whole length of its catalytic converter. I lived in Michigan at the time, where there will likely never be any vehicle inspections (regarded as a sort of war-on-cars affront to the local industry), so I paged through the Walker exhaust parts cattledog, jotted down the critical dimensions of the direct-fit replacement converter, went to a local exhaust shop and told them I needed a short piece of pipe for a generator shed installation: so-and-so long, ball expansion and 2-bolt flange at one end, etc. The twenty-something dollar result found its way under the car, then once I disabled the air injection the exhaust lost its furnace odour (and reverted to, as you say, a 1965 odour).
I have other stories of catalytic converter mayhem, but they’re probably best saved for the apposite COAL entries.
I race radio control boats, and I can’t believe the idiots who insist they have to use leaded Avgas in these stupid 8:1 compression chainsaw engines because they “run so much better on it.”
Great article! Everything has a cat now. They have water cooled ones for boats even. When I was in R&D for a portable generator line, I hand built the first cat-in-muffler prototype for the upcoming 2400W EFI we were devloping. Not only was emissions way down, but a added bonus was with the cat inside the muffler it acted like a pre-muffler and reduced the decibels by quite a bit. Machine is now in production, and they adopted my muffler design across the rest of the line (patting myself on the back)
Hey, how cool! That has got to be one of the finest perqs of R&D work: seeing the results working out there in the world. Last I checked a fair number of years ago, the American small engine industry (i.e., Briggs & Stratton) were working dilligently to kill or delay any regulatory interest in catalytic converters. “Technically impossible”, “too expensive”, “impracticable at this time”, “further research warranted”, “wouldn’t address any actual need”, and all the rest of the crapola the automakers came up with on the same subject in the early ’70s.
And that is one of the reasons electric law mowers are becoming common.
Excellent article Daniel! I have been looking forward to this since you first made mention of it some time ago. 1975 is an interesting year with many North American cars seeing the introduction of the catalytic converter. This resulted in a significant horsepower drop between 1974 to 1975. Without actually doing the math, I’d put money on 1975 being on average the worst year for horsepower per cubic inch in modern times (at least for GM and Ford).
As poorly executed as these early converters were, they were a good idea overall. It’s too bad GM did the bead style converter, but as you pointed out FoMoCo’s alternative execution wasn’t much better in the real world. It just seemed to be the flavor of the era for the Big Three, do what’s required with as little cost as possible and little regard for real world performance. Regardless of how restrictive these converters were, they did for the most part improve the driveability of cars, compared to the ultra leaned out carbs form 1974 and the many rudimentary emission controls of this time. Our 1976 Chevrolet 350 for example only required a EGR valve, heat riser valve and the cat as its emissions controls. It’s too bad GM half-assed the engineering, but I wonder what the cost comparison would be between the two styles of converter.
In my younger years I was well aware of how restrictive these bead style converters were. I must confess in more than one of my past cars I removed the cat to install a straight pipe, since we had no emission checks. They did improve the performance a bit, but those smog era engines didn’t really perform well no matter what. I also recall a family member’s ’78 Olds Delta 88 blowing out the plug on the bottom of the cat one morning. You could hear the beads flying out followed by the exhaust leak. The exhaust shop just welded a cap over the hole and no one was the wiser. It did run a bit better after that too! The big bead style converters were used on the GM B-body sedans long past the early 80s too. I recall seeing them even on late 80’s cars.
“The big bead style converters were used on the GM B-body sedans long past the early 80s too. I recall seeing them even on late 80’s cars.”
Bead type converters had a number of issues, but they contained more (reactive) surface area than the monolithic cats. Because of this, GM used them on larger displacement engines (think greater exhaust volume) through the 80s, particularly on the truck side.
I have some difficulty with this idea that the bead-type converters had more surface area than the monolithic converters. To me it doesn’t pass the sniff (har har) test: Ford and Chrysler managed to put monolithic converters on engines up to 460 cubic inches, and packaging solutions were available for adequate surface area right from the start (double-biscuit monolithic converters, for example).
Both types of substrate present enormous available surface area; Tenneco (Walker) cite about 20,000 square metres (215,000 square feet), or about two football fields’ worth, for a monolithic converter, while GM cited similar figures for the volume of pellets in one of their converters.
The obvious exception would be the miniature cheap aftermarket universal converters, which will get past a visual inspection and are marginally adequate for passing a couple years’ emissions tests as long as nothing else is wrong.
LOL-
I’m confident I recall that statement accurately, but the source may have been a GM publication and thus a bit biased…
Thanks, Vince—I had you in mind while I was writing this, as I recall our exchange of comments on the subject in the HEI article.
I don’t know whether or what logic was applied in GM’s gradual migration to monolithic converters. The ’78 Caprice I mentioned was replaced by an ’84 that came with a monolithic converter ex-factory.
Do you suppose ’75 was the worst for engine output vs. displacement? I would guess a year earlier: the strictest emissions standards before converters came in, so the engines had to be severely detuned. GM made a lot of noise, backed up by independent testing, that their ’75s got better mileage than comparable ’74s because the engines could be tuned to run better and the resultant dirtier exhaust was cleaned up by the cat.
I don’t know whether or what logic was applied in GM’s gradual migration to monolithic converters.
You can say that again. We had a ’84 Parisienne with a 305, which is a rebadged ’84 Caprice, and it had the bead style converter. I remember ripping the rotten cover off the converter after years of salty winters corroded severely. It’s been a long time, but I am pretty sure the old ’87 Custom Cruiser (307-4bbl) I had used a bead style converter, but my 1990 Caprice (305 TBI) sedan had the monolithic.
I wonder if the Canadian emission cars were more likely to use the old bead style converter, maybe even the 2-way units if there was a surplus? They didn’t bring Canadian emissions in line with US standards until 1988, and they stayed at around the 1975ish levels until then. This is why Canadian cars used fully mechanical carbs up until that time.
You’re probably right, though I guess it was more deliberate specification and less using up surplus parts. The lagging Canadian emission standards gave rise to some interesting effects. Early on there were snide, smug Ford ads like this one (hit the zoom-out button and scroll up), calling Canada’s dirtier exhaust “more reasonable” than the US standards.
Chrysler Canada were crowing about their catless K-cars’ ability to take cheaper regular gas even as late as ’82 (never mind that running leaded gas was more expensive in the long run—shorter spark plug, exhaust system, oil, and engine life).
Canadians could buy Volvo 240 cars with the B21A engine (single sidedraught carburetor with manual choke, no cat) up through ’84.
And I’m sure there were others, too.
Its still legal to remove cats here up to year model 2010 or near that date, I have a feeling the particulate trap on my diesel may be clogged by now so it will be going some time in the near future, I’ll leave the mufflers alone as the car is very quiet though with the window down you can hear the boost dump when changing up.
It’s still legal up…where?
Up there.
You know, the place that isn’t here.
Duh!
Years ago a neighbour said to me “GM must be making lots of money.”, how come? I asked. “Well, every car on the road has to have a Cadillac part on it.”. What are you talking about I asked. “Even my Ford has a Cadillac converter on it.” NOT kidding! No joke! He really was that stupid.
Yes, well. What did the airport gate agent say to the overpacked vulture?
“Sorry, sir; you’re allowed only one piece of carrion baggage.”
When I was running a fleet of taxis, we converted all our cars to LPG. Normally, this would mean about a 10% drop in horsepower and the same in fuel consumption
Except we actually found the fuel consumption on the LPG cars was actually better. The reason was simple-beaded catcon. When the exhausts were unplugged, it made the car have more power, less fuel consumption and excellent throttle response.
Back then, regular was 5-10 cents cheaper, which meant $2 more per tank for unleaded – when minimum wage was $3 an hour. There were a manner of ways to get around the cat – and get rid of things like the EGR valve and the air pump also. Test pipes, cut outs in the exhaust pipe, little funnel adapters you put over the end of the regular gas nozzle that let you put gas into a car with the smaller unleaded opening, the sky was the limit. That the cars of the time ran no worse and with some judicious bodging and replacing of parts like carbs and distributors sometimes ran better without the orange-hot tube under your car melting away and setting the grass on fire made this fairly commonplace. There were even strategies to put all the equipment back on to pass the test and then remove it again until next year.
I did not know Invention and Technology restarted…. I actually own every issue from the premier until it went defunct…it really was wonderful. Great well written stories about innovation and technical things…similar to many of the best pieces here. Glad to hear it is back.
I’m with you on all counts! Tickled it’s back. I’m considering a donation to the cause.
The most interesting bit was several automakers managed to do without catalytic converters until 1980. VW actually released a service bulletin for rejetting 74-75 cars and gutting the converter and the 77-79 cars with fuel injection never had cats and ran fine on leaded regular. After 1980 emissions regs were .tighter so VW added both a catalytic converter and an oxygen sensor. This was also the era where some manufacturers were still clinging to carburetors and comparing the vacuum lines in my 84 Jetta to my mom’s 84 Accord was instructive.
Further to that, BMW’s thermal reactor setup didn’t work well and they had catalytic converters by 76 or 77.
I’d surely like to see that VW TSB; got a link?
Not the real thing but the Robert Bentley manual for the early Rabbit and Scirocco does have the procedure and so does the John Muir book. As i recall there was an official parts kit for the carburetor to retune it.
The 1975 Opel I owned did not have a catalyst, apparently the electronic fuel injection did a good enough job of metering fuel is was not needed. I still had to run it on unleaded gas though.
Lol!!! That 1975 Dodge Charger melted converter looks just like a tumor cross section. All kidding aside I have a strange fascination with laminar flow. Monolithic converters appear to be extruded just like pasta albeit much more precisely and cut with a hot wire (I think). 100% automated process due to tolerences. Not only does it maximize surface area for heating but also turns exhaust flow from turbid into laminar.
I remember working under cars on a hoist. We’d always whack the muffler with our fist; if it sounded like a Maraca; we’d try to sell exhaust work (New converter, new muffler, pipes as-needed. MOST folks didn’t give a rat’s ass about the emission controls; so it was a tough job getting permission to do the work.
Wasn’t unusual to see (GM) vehicles spitting converter beads out the tailpipe.
I remember the early ones having an engine mounted air pump pushing air into the converter. IIRC that went away with three-way catalysts since the added free oxygen would prevent the reduction catalyst from cleaning up NOx.
(I also remember that those air pumps usually had laughably skinny V-belts driving them because they were prone to seizing and a thin belt would snap without making too much noise first.)
The system you have in mind is called Secondary Air Injection, and its application is more complicated than you recall. It first appeared in the mid-late 1960s, before catalytic converters, and its use continued well into the 3-way catalyst era. The problem you envision didn’t exist, because the air was injected into the catalytic converter between the first (reduction) biscuit or bed and the second (oxidation) biscuit or bed. There’s a pretty good article about it on Wikipedia.
The air pumps were not particularly prone to seizing, and they used ordinary V-belts, not unusually thin ones.
Thanks very much for this article. I was fascinated from beginning to end.
You’re welcome!
Really rather late to the party here, but gotta say, Mr S, hats off. A great effort indeed, and especial kudos for the link to that article.
A tiny burst of politics now: f** me, but that mean old Republican Nixon signed off on the laws that led to this?! The world has indeed changed. Apart from anything else, in acceptance that there was a problem, and then that there was faith that science could help answer it.
Can’t help but add that as now, there were big players whose profit would be affected who denied the problem and who lobbied accordingly, who then tried cheap-arse self-solutions for it, and finally had to give in to reality.
Anyway, you’ve done a sterling job here sir, and deserve many thankful plaudits such those as I now offer.
»bows, doffs cap«
Thank you kindly, good sir! This is the first of what I hope will be a fair good number of articles, long percolating, which had to wait while most of 2019 was elsewise (and unpleasantly) occupied.
And I agree with you completely; the structural political difference in the US between then and now is just astounding.
I posted elsewhere recently mentioning the EPA was formed under Nixon’s administration, and the response I got was “Nixon was hardly a conservative.”
And I was like, “so what?”
Many of today’s conservatives have a very poor understanding of what conservative truly means so no surprise you got that response.
I worked at a GM store , there was a recall in the early 80′ s involving replacement of the pellets in the Catalytic converters. I kept my distance from this procedure as it produced a lot of dust that was likely poisonous. There was one post 1975 GM engine that was sold in the US without a catcon, the 1976 one barrel vega 140, it still had a restrictor for unleaded. I had one of these hatchbacks with a 4 speed. I ran regular leaded and took advantage of the higher ( 89) octane by advancing the timing by about 10 degrees and other modifications that resulted in much better performance and fuel mileage. On the other side of the coin, I left my 84 Z28 H.O. 5 speed stock . it had a wider free flow exhaust pipes and cat than the base V8 and I was satisfied with the performance.
This is why I love CC; it’s as much about human nature as engineering. The malicious compliance on the part of manufacturers, the clinging to carbs because they’d been burned before on mechanical FI and EFI was Not Invented Here, the apparent evaporation of political will on the last hurdle of structuring gas taxes to prevent leaded gas being cheaper, allowing a financial incentive towards more malicious compliance from car owners.
By the time I was the 16-year-old owner of a 10-year-old car in salt country in 1990 this led to repair shops having War on Drugs-style posters warning of the dire penalties for cat removal. “Just Say No” to straight pipes!
The government tried to clean up the air, human nature was what put the malaise in the Malaise Era.
I haven’t looked into the squabbles that must’ve gone into the fuel taxation question; all I know is they got it wrong on a really simple,straightforward question. Sounds like you’ve seen more about it than I have; whatchya got?
Thanks for the interesting article! I owned a ’79 Fiat Strada which used the GM pellet converter. At one point it started to run very sluggish and almost no power. I limped to a Fiat dealer (about 40 miles). They brought the car in, took off the air cleaner and started the car up. The pellets blew out of the converter and plugged the muffler so badly some of the exhaust was coming out of the carburetor! This was right at their closing time and they just swept up the shop for the day. To get me by until a new converter and muffler were ordered ($) they cut a hole in the exhaust pipe just before the muffler, started the car up and revved the engine. Pellets blew all over the shop! The service guys were really pissed and had to sweep out the whole shop floor again just as they were getting ready to leave! I for one am really glad those pellet converters went away!
I initially read this when posted but didn’t read “Doing the Impossible” link posted by Daniel at the time. I did today and as always enjoyed the pure science and engineering behind it. Just go with the facts, Jack, and you’ll be fine.
I know that I’m late to the party, but I just HAD to comment to let you know how great this article was! I learned things that I have been trying to find out for 40 years.
Same here. I had no idea the tailpipe screen was a spark arrestor. I thought it was a guard to keep critters from making a home in there. Or guys like Axel Foley from shoving bananas up there.
All my old GMs always rusted out right at the rear converter flange. I would just cut out the whole mess and replace it with a spun stainless converter for like $30-$50. And every time I’d catch hell from the guys at work, saying why don’t I just straight pipe it? Well without a cat it stinks that’s why.
Yeah, it’s really noticeable these days that a single old car’s exhaust stinks, even a well-tuned one. I remember how the roads and parkades and tunnels used to be full of cars that all stank even worse (dirty-burning old gasoline; slack maintenance on needy carburetors and ignition systems, etc). I don’t miss it!