By the late 1950s, it was grossly and painfully apparent that “traffic smog” was a real and really bad thing. Dutch-born scientist Dr. Arie Jan Haagen-Smit figured out unburnt hydrocarbons and nitrogen oxides—noxious in their own right—react with sunlight to form a toxic stew of ozone; peroxyacetyl nitrate; nitrogen dioxide, and aldehydes.
And automobiles, more and ever more of them as the postwar boom boomed along, were the main source of atmospheric unburnt hydrocarbons and nitrogen oxides. Add sunshine and unfavourable valley- or bowl-shaped topography, and the result was poisonous air so thick it could almost be shovelled. Los Angeles was the American poster child…
…but far from the only affected locale; Denver—300+ sunny days a year; bowled in by the Rocky Mountains, and up at high altitude so rich-running cars chuffed out enormous amounts of unburned hydrocarbons—had its persistent “brown cloud”:
Smog was ugly and smelly and eye-burning and far, far worse. Car reviewers of the day added colour to their stories by resignedly describing the need to hurry and get all the brake testing (or whatever) done before noon when breathing outside became too painful. People got really sick. People died. Crops withered. Its severity cannot be properly understood by first-worlders who didn’t live through the worst of it back then, and who’ve never been someplace like Beijing or Delhi or Mexico City.
A first whack at the lowest-hanging fruit was ducting engine blowby into the intake tract rather than out to the atmosphere; PCV (positive crankcase ventilation) became mandatory on 1961 cars in California, 1962 cars in New York, and by 1964 it was standard equipment—more or less; hold that thought—throughout North America. That helped, because those crankcase fumes and vapours were very high in unburnt hydrocarbons. And despite a bit of initial turbulence—some early PCV valve designs made a maintenance hassle of themselves, especially at the hands of the uneducated or skeptical—positive crankcase ventilation made life better. The wretched odour of crankcase fumes was much reduced for those behind (and inside) the car; the engine oil stayed a lot cleaner, and here’s Gus Wilson to describe a less obvious advantage; click the pic for the episode as a PDF:
Subsequent whacks were going to be a lot trickier, because tackling tailpipe emissions meant automakers suddenly had to figure out how to make engines run as well as buyers had come to expect, but with much sweeter breath, and without costing significantly more. The technology, technique, and knowledge of engine emissions and combustion dynamics were primitive, and for years the standard fix for any driveability faults had been to fatten up the fuel mixture. Balky cold starts? Add more fuel; richen the choke. Stumble on acceleration? Add more fuel, bigger accelerator pump shot. Surge at cruise? Add more fuel, put in a bigger jet. Hesitation on flooring the accelerator to pass another car? Add more fuel, loosen up the power valve. This was easy, cheap, and effective, but the resultant exhaust was filthy (and fuel mileage was stinkin’ to match). Once emissions started mattering, that method was right out.
As they bumped and bottomed along the rocky learning curve, under tight deadlines and budget constraints, automakers flailed around with a variety of tweaks and twiddles, gadgets and widgets, thoughts and prayers—mostly to no viable, commercially-acceptable effect. Chrysler’s engineers wanted to avoid afterburners, air pumps, and other costly, problematic hang-on devices other automakers were kludging around with; instead to improve combustion so less unburnt fuel would wind up in the exhaust.
Groping around for the beginnings of an understanding of the factors at work, they found that tailpipe emissions were especially dirty at idle and while decelerating. The common factor between those two conditions: the throttle was damn near completely closed.
Idle cleanup was relatively easy. Curb idle speeds at that time were very slow—500 rpm was pretty normal—and so at closed throttle there was very little air admitted to the engine.
A wider throttle opening admitted more air, but raised the idle speed too high. Retarding the basic ignition timing by as much as 10 degrees slowed the idle back down despite the wider throttle opening; now they had their market-acceptable idle speeds with much cleaner exhaust.
But retarding the spark and just leaving it like that would do a real job on driveability, performance, and economy. Ripping off all those extra-fuel band-aids was an obvious and necessary first step to clean exhaust, but then how to provide acceptable driveability? Engines run poorly with retarded timing and lean carburetor jettings and settings; they have no power and they guzzle gasoline. That was where pretty much the whole rest of the auto industry was stuck.
Meanwhile, exhaust is dirty under deceleration because at road speeds with the driver’s foot off the accelerator, the vehicle motorises the engine and creates very deep manifold vacuum, but the nearly-closed throttle limits the amount of mixture drawn into the cylinder. The density of the mixture is thus low, and so combustion is uneven and incomplete. Camshaft overlap aggravates the problem; the exhaust valve opens before the piston reaches the bottom of the power stroke, so some exhaust is pulled into the cylinder, which dilutes the cylinder charge and further interferes with combustion.And with the retarded basic ignition timing there isn’t enough time to burn this raggedy mixture. Net result: a great deal of unburnt gasoline flies out the tailpipe.
The wider throttle opening at idle helped some, but not enough. The core problem was that under deceleration when a lot of spark advance was needed to give a complete burn in the cylinders, there wasn’t any advance provided. The engine wasn’t typically spinning fast enough for much centrifugal advance, and because the vacuum advance was tapped in above the throttle plate, there was no vacuum there when the throttle was mostly or fully closed. But if they hooked up the distributor to manifold rather than ported vacuum (below rather than above the throttle plate), it caused other emissions and driveability problems: two steps forward, two steps back.
Advanced timing under deceleration would start the fire earlier, giving more burn time, and so what was needed was to somehow provide retarded timing at idle but advanced timing under deceleration—two closed-throttle conditions differing only in engine speed, driven in turn by whether the car was moving or still.
Chrysler’s emissions boffins leveraged the strong manifold vacuum that was sucking unaerated fuel into the intake manifold under deceleration. Their solution was to send either ported (above throttle) or manifold (below throttle) vacuum to the distributor, depending on driving conditions. This was achieved with what was called a distributor vacuum control valve:
The control valve has three vacuum nipples: one to manifold vacuum, one to the vacuum advance port on the carburetor, and one to the distributor vacuum advance. The spring has a tension adjuster screw running through the centre of its keeper cap.
This is a pneumatic logic gate—really, the first engine control module. It advances the timing under closed-throttle, high-vacuum situations: deceleration or coasting with foot off accelerator. When manifold vacuum (below the throttle) is equal or less than ported vacuum (above the throttle), the distributor receives an ordinary ported vacuum signal as though the valve weren’t there. When the throttle is closed and there’s no ported vacuum, the strong manifold vacuum under the closed throttle at higher-than-idle engine speed overcomes the control valve’s preload spring, opening the valve and sending manifold vacuum to the distributor, which advances the spark.
This handily resolved the timing conflict, and so Chrysler were first with an emission control system that met all the targets: it radically cut emissions without spoiling driveability, performance, or fuel economy.
The system comprised this control valve, a carburetor with leaner and more precise calibration, and a distributor with a modified centrifugal advance curve to provide normal levels of spark advance for acceleration and cruising despite the retarded basic timing.
It was called CAP, the Clean Air Package, and was first launched on a trial basis in California in 1963. That trial was a grand success; equipped cars ran well, with good driveability and fuel economy and much cleaner exhaust. Here are two tests of the time (again, click the pic for the article as a PDF); a Popular Mechanics article from November of 1963…
…and one from Car Life, September ’63:
These 1963 installs show the valve with spring exposed; a snap-on plastic cover was added for volume production to attenuate valve rattle and discourage errant screwdrivers. The distributor vacuum control valve wasn’t a service nightmare, but it did add some check-and-adjust points at tune-up time. With insufficient spring tension it would give vacuum advance action at idle, which would interfere with setting the idle mixture and speed for a smooth, stable, clean idle. With excessive spring tension it was as though the valve weren’t present. It didn’t tend to go out of adjustment; as with many such things, it worked fine and best when left alone.
Starting in 1966, CAP became standard equipment on all Chrysler Corporation vehicles sold in California, and Chrysler even offered “UCCAP” (Used Car Clean Air Packages) at dealer parts counters, for retrofit to any 1955 or newer Chrysler vehicle.
All in all, CAP gave a much better result than other automakers could come up with for awhile, as these Popular Mechanics “Detroit Listening Post” excerpts show:
The distributor vacuum control valve was used on some CAP-equipped engines from 1963—those prototype CAP cars—through 1969. CAP became standard equipment on all US-market cars for ’68, and in ’69 Chrysler renamed it CAS, for Cleaner Air System. A few years after Chrysler, Ford and AMC began using more or less similar valves. Other emission control strategies supplanted the valve by 1970.
This seminal work on the original CAP poured a foundation for Chrysler’s later Electronic Lean Burn system, which also controlled ignition timing in unusual ways to allow for nonstandard carburetion. As emissions regulations grew tighter, Chrysler did eventually use such add-ons as the air pump and catalytic converter, just like everyone else, at least on some models. But for awhile there at the start, Chrysler were the only automaker putting out cars that ran well and put out exhaust clean enough to find favour with California’s air guardians.
Ironically, Dr. Haagen-Smit died aged 77 of lung cancer. While he was busily working to clean up everyone else’s air, he was just as busily toxifying his own as a heavy cigarette smoker.
Very interesting. I was uninformed about these early emission systems, but thanks to this, you’ve filled in some blanks.
My father’s ’68 Dart exhibited the symptom of poor engine braking described in the article. I knew ’68 was the first year for nationwide emission controls and that it was thus a consequence of that, but did not know the precise reason for it.
A ’68 Dart with a 170 and manual transmission definitely had this setup with the vacuum control valve. Greater freewheeling under coast/deceleration would’ve been due to the wider throttle opening at idle and more complete burn due to the newly advanced spark; the engine was actually running, not just sputtering along and mostly providing frictional and pumping resistance. With the underspecified brakes of that time—I sort of doubt your father paid extra for the 10″ drums over the basic 9-inchers, let alone the discs—I can imagine how less engine braking would have been somewhat alarming.
Thanx Daniel ;
There’s a valve like this plumbed into my brother’s 1979 Dodge D299 W/ 360 V8 & 4V carby .
Is there a test procedure you can share ? .
“Is there a test procedure you can share ?”
You could tee into the line running to the vacuum advance and attach a long hose to a vacuum gauge. This setup lets you observe advance vacuum during vehicle operation.
If you see vacuum advance during steady cruise anf high manifold vacuum conditions (closed throttle deceleration), the valve is functioning correctly.
It’s not quite that simple; see link ⬇︎
That’s interesting. Are you quite sure it’s a valve just like this? There were several other kinds of widgets installed in distributor vacuum advance hoses in the ’70s—one was an OSAC, which just delayed the vacuum signal to the distributor for a set number of seconds—but as far as I know, this first kind of distributor advance control valve was not used after 1969. I’m not as closely conversant with the heavier-duty truck emissions equipment, though, and a valve like this is very easy to retrofit—I did so myself on several occasions, to pick up a bit of gas mileage and a more freewheeling closed-throttle coast.
Check-and-adjust procedure starts about halfway down the right column of this page and continues on subsequent pages.
Fascinating history and another feather in the cap of Chrysler engineering, which was a major part of their branding in the 60s.
Fascinating. My ’68 Fury VIP has a sticker on the passenger fender well I need to take a closer look at about the Cleaner Air Package. If that’s what it’s referring to, someone has deleted the distributor vacuum control valve from it a long time ago as I don’t remember ever seeing it in all the years the VIP has been in the family. A quick check of Rock Auto doesn’t show a new part listed. I was hoping it would, I think based on the description of how it works, I’d like to add that back if it came with it originally. Looks like I might be searching for an NOS part if no one is making new replacements.
Chrysler V6 in 1965? Could they have been contemplating an LA based V6 that early?
Here’s the relevant page from the factory parts cattledog; assuming your car had this valve from the factory (only on manual-transmission cars in ’68) you aren’t going to find it at RockAuto. These valves were serviced in the aftermarket, but long ago discontinued. A fairly steady trickle of them goes by on eBay as new old stock, and there’s a reproduction valve as well (unknown which base bracket it has and unknown quality/function; black cover is the giveaway). As mentioned elsewhere in this comment thread, I’ve retrofitted these valves to cars not originally equipped, including my ’65 D’Valiant with automatic transmission. It’s easy; takes about six minutes.
Thanks for the info. If it was only on manual transmission cars in 1968, my car didn’t leave the factory with it as it has an automatic.
From reading your posts over the years, the retrofit must have genuine benefit if you put them on your own cars. All the more incentive to add one to mine.
Here’s the ’67 FPC page—as you can see, same valves used as on manual-trans ’68 models.
Thanks, the parts catalogue page was very helpful. I’ve got a NOS part on my watch list on eBay. Waiting for the budget to free up so I can buy it. Shouldn’t be long.
Fascinating stuff. What is interesting is that I don’t recall any unusual parts/systems on either my 68 Chrysler or my 71 Scamp. With no emissions testing hereabouts, it was not at all uncommon for midwestern garages/owners to remove extraneous parts to get the cars back to pre-emissions tune, so it is possible that what might have been there had been removed long before I got the cars.
The ’71 would not have had a valve like this, but it did have another interesting early emission control system—one I might write about another time. The ’68 Chrysler wouldn’t’ve had one, either, unless it had a manual transmission.
Wow. I’ve always been puzzled why I recalled my 66 Ford as not having a PCV (it had a breather cap, iirc) and I often have chalked it up to years and beers! What a silly thing to drop the PCV…did that actually happen or am I misremembering?
Looks like it actually happened. Ford really didn’t start taking emissions control seriously until the late ’60s; before then they treated it as a passing fad amongst a bunch of dumb hippies in California.
Great history! Thanks.
The nicest looking piece of emissions equipment I have ever seen. Thought it was a
Certainly the right colours!
It’s too bad these are so hard to find and expensive; my Dart (manual transmission) is a little jerky under low-speed deceleration, and it would be fun to tinker with one of these to see if it helps.
They’re not all that hard to find or expensive, but…is your carburetor missing its throttle dashpot?
Thanks, Daniel – this is an excellent write-up on early anti-pollution technology. I learned a lot. Once again I’m impressed by the Chrysler engineers of the past. I don’t recall hearing of Chrysler’s CAP before today. It sounds like a cost-effective and very effective system. I wonder if it wasn’t used here on Canadian cars, which would explain my ignorance.
I’d thought PCV valves were pretty much universal by about 1960. Perhaps that was the case here in Canada. (I think our safety laws tended to be nationwide here, rather than under provincial jurisdiction – front lap belts for ’63, front lap and shoulder belts and rear lap belts for ’68, side-marker lights for ’68 [yeah, I know Ford did rear side reflectors for ’68], 3-point belts for all outboard positions at some point, the evolution of airbags, neutral safety switches, etc. – I was surprised to read how the seatbelts, at least, came in state-by-state in the US.) I remember later on that cars were often specified “49 state” or “California” emission-wise.
In my mind, replacing the crankcase draft tube with a PCV system plucked much of the low-hanging fruit, reducing emissions significantly – by 50% or better. And after that, I thought there were only incremental changes (charcoal canisters, cumbersome belt-driven air pumps, anti-dieseling solenoids, etc.) that often affected driveability and fuel consumption adversely, until the next great leap – unleaded fuel and the catalytic converter (although honourable mention goes to Honda’s CVCC technology), and later on variable-venturi carburetors, throttle-body FI, MPFI, and now GDI. When OBD II came in (1996 MY?), someone claimed that a modern car being driven was cleaner than a 1966 car sitting. A similar claim was that in a large urban area, an OBD II car’s exhaust was cleaner than the intake air.
Anyway, kudos to Chrysler for taking automotive pollution seriously back in the day, and to you for this fine article. I thought I’d read through all of the Gus archives perhaps 15 years ago, but this one was new to me. Enjoyable story, and it tied in perfectly.
You’re welcome and thanks!
Prior to the 1961 California mandate, PCV was used only as special equipment on a very small number of vehicles. Canada was behind [any of] the States, not ahead; PCV systems didn’t begin to appear in significant volume in Canada until the 1963 model year.
As to there being only incremental changes after PCV and before the catalytic converter, consider this what Chrysler said in a 1967 technical pamphlet: Even without CAP our engines are both clean and efficient under most normal operating conditions. A typical late-model car, in normal city driving, emits only 500 to 1,000 parts per million of unburned hydrocarbons (…) the new federal law requires that this be reduced to 275 parts per million. 500 ppm HC is very dirty; a car putting out 1,000 ppm is a severely gross polluter, based not only on iteratively tightened standards, but on the evolving state of knowledge.
The regulatory structures are very similar in the US and Canada, though here again, Canada was a little delayed; the Motor Vehicle Safety Act came in for ’71. Most cars in Canada got more-or-less US-spec safety equipment by default, because with the market commonised by the Auto Pact of 1965, it was generally less expensive to just go ahead and put the side markers, for example, on ’68-’70 Canadian cars even though they weren’t yet required by law, than it would have been to delete them (and produce and manage different sheetmetal or blockoff plates, etc).
And the same was even true to a large degree before the Auto Pact. Sealed beam headlamps were standardised in the US by consensus among the automakers, lamp suppliers, and state administrators. They weren’t legally required in Canada, but the overwhelming majority of Canadian cars got them anyhow. Seat belt anchorages at all outboard seating positions were likewise standardised by consensus in the US for ’62, and spilled into Canada the same way.
By the time 3-point belts for all outboard positions (including the rear ones) came along on this continent, it was a matter of severely tardy, decades-overdue regulation delayed by disingenuous automaker footdragging, and the US and Canadian national safety standards took effect at the same time.
Component-level specifications were more likely to be different, particularly in the emissions realm. Canadian emissions standards weren’t brought up to US stringency levels until 1988 or so; prior to that there were vehicles available in Canada that would not come close to being legal in the States: ’82 Chrysler K-cars that took leaded gasoline; ’83 GM B-bodies with nonfeedback carburetors and 2-way catalytic converters; ’84 Volvo 240s with a single carburetor, manual choke, and no catalyst…probably just about every Lada ever sold up here; likely the Hyundai Pony, and I’m sure there are more.
As a child growing up in Southern California in the 50’s, 60’s and 70’s, I vividly recall “smog days” when kids weren’t allowed outside for recess due to burning eyes and lungs. Chrysler’s CAP seems like an innovative and effective answer to early smog controls – a pretty dramatic reduction! I’m not aware of Ford or GM’s efforts being nearly as easy to live with.
Thanks for the detailed information, and I’ll echo the “kudos to Chrysler” for doing something without being dragged kicking and screaming to make a difference.
An interesting piece of corporate behaviour, isn’t it! I don’t know that it can be attributed to altruism; I think it’s at least as likely that Chrysler early perceived business or PR opportunities. In any event, yes, at that time they had a well-deserved reputation as an engineering company—much like pre-McDonnel-Douglas Boeing.
Imagine my surprise upon moving from Maryland to the San Fernando Valley in June 1966. In Maryland one could run around the track, or the neighborhood, without a problem. However, in 7th grade PE class in September 1966, there were days just running outside made my lungs sear. From clean air in May to filthy air in September was my first big take away concerning the move. Second big take away was bikinis at Santa Monica Beach but that is another story.
I moved to California from the Mid-Atlantic in 1986, and I recently scanned all the slides I took when I first arrived. Every picture has an orange haze on the horizon, even sunny days on San Francisco Bay, let alone in San Diego. And I have no idea how anyone lived in the Inland Empire then. Now you get just a very little orange only on days with offshore winds (Santa Ana conditions). And I’m sure it was much worse in the 50s/60s/70s.
I guess this explains why the last US spec Series III Landrovers had vacuum retard valves on their distributors. I thought that was odd when I first encountered that since vacuum advance was the norm.
That’s a different emissions control strategy, aimed at lowering NOx emissions. Many vehicles from a wide variety of makers had vacuum retard (or, more commonly, dual-chamber vacuum advance/retard) pods on the distributor.
Thank you for another great article Daniel. The time and effort you put in to these is appreciated.
You’re welcome and thank you!
A example of really good engineering… simple, effective and very clever.
When I moved from San Francisco to Los Angeles in July 1977, I immediately noticed that the sky wasn’t blue, but it didn’t seem too bad other than that. And then one day I was riding my bicycle near Griffith Park, and my eyes started to sting.
And it’s not like SF was all that clean then either. As noted above, my 1986 pictures of SF all have that distinctive orange haze on the horizon.
I experienced two long family car trip vacations from East coast to West in 1962 and 1964. The smog In Pittsburgh was unbelievable in center city. Literally difficult to see across the street. Smokestack mills likely more to blame than autos there. Denver and LA were quite the bad haze.
My father’s new 1963.5 Galaxie (not Cal.) had a PCV valve, perhaps the first for Ford? Perhaps the first application for the 289 ci vs. 260. Seatbelts became standard. The alternator may have been a first for Ford on that car as well. I recall that being replaced under warranty and otherwise several times.
The explanation of how dirty deceleration is tells me why my car’s mpg readout pegs to 99mpg when I let off the gas. I thought it was just some mpg savings programming. Now I know.
If your car is new enough to have a fuel economy readout, it’s far too new to be running dirty on deceleration. That 99 mpg figure might not be too far off reality!
I think every vehicle I’ve encountered from the EFI era forward, will cut fuel completely on closed throttle deceleration while in gear. Admittedly, I’ve been “out of the loop” on stuff produced in the last 20 years, but would guess that this is still the case with modern cars… as it’s probably easiest to control emissions under these specific conditions by just removing combustion from the equation altogether.
DFCO or Deceleration Fuel Cut Off is a common strategy but didn’t pick up steam until a few years into the EFI era and was originally on MT vehicles, and was typically only active at higher rpms. On our 90 Ranger you could feel the fuel come back it at about 1500 rpm if you payed close attention.
As others have said, EFI cars aren’t generally dirty under deceleration because the computer can and does completely shut off fuel, unless a few conditions arise. One such condition is low engine temperature, another is low catalyst temperature… coasting down a miles-long mountain pass can cause engine and catalyst temps to drop out of the favorable range such that when power is needed, the engine would be nearly as dirty as on a cold start. Re-fueling (and cracking open the electronic throttle or idle air control solenoid) as needed while decelerating keeps enough heat in the engine and catalyst to make sure it’s clean if power is suddenly needed. I have a 2008 pickup truck with an aftermarket exhaust (more melodic than “loud”), and you can actually hear the system de-fuel, re-fuel, then de-fuel again on long downgrades. I’m convinced it actually manages things specifically to keep the catalysts hot, there’s a particular regime where it’s clearly dumping a burnable mixture right past the engine (extremely late timing? Spark deactivated? I don’t really know) because you can hear a burbling in-exhaust combustion and watch the catalyst temps rise on an OBD-II monitor.
The increase in idle speed used to be pretty hard-wired to road speed in earlier systems. I had a 1993 vehicle and if you let the car roll forward in neutral, the idle speed would kick up to about 1000-1200 rpm… just based on the speedometer input. That really had a negative effect on engine braking, and actually made one ride the brake in parking-lot maneuvering. Newer cars are quite a bit more sophisticated in how they manage this.
Well thank you for the lecture, Dr Stern. I now feel as if I know new things today, instead of my now-usual knowing no new things, and though I’m sure those new things were known before my knowing them today by those who knew them, their not being known by me before today makes them of course new things that I now know where once I did not, and they say one should try to do that every day, don’t they?
Clever types, engineers. They go applying logic and stuff to problems in order to solve them in a rational manner, doubtless making them an unpopular class in our alchemical times.
To have explained their works in terms this lazy person, sorry, lay person, could fathom, is an achievement to be lauded.
Math is hard.
Let’s go shopping!
»bows, doffs cap«
The air was still pretty bad in L.A. in the early 1980’s. I worked in Downtown L.A. in ’83 and ’84 and Stage One and Two smog alerts were still quite common in the Summer. I recall that an intersection just a couple of blocks away would look pretty hazy. Go to L.A. today ( I go there frequently) and it’s blue skies most of the time. It’s taken a concerted effort by not only the automotive industry but other manufacturing and energy producing industries to being about this improvement. I don’t know that this would have happened without the imposition of government standards, but the pay off is better air quality for everyone. Now the work is in carbon reduction.
The air was frequently awful in Denver-metro well into the ’90s, too, especially in winter when temperature inversions trapped the garbage down near ground level.
Today’s massively cleaner air is such a monumental achievement that its magnitude is difficult to wrap a mind around. Enormously more people driving enormously more miles in enormously more vehicles, and yet.
(…and yet, there are still people who babble and bleat about how much better everything was back in the good old days…)
Chicago didn’t have the same bowl-valley-geographical issues as LA or Denver but I do remember coming back from college in 1995, the first time I had been away from Chicago for any length of time, and being able to see the skyline from my parents’ apartment, which was a very rare treat in the 80s. Not that it suddenly got better over a semester in Champaign, but taking the frog out of the cooling water has its effects.
Daniel, as always, thank you for the article. Definitely a lot of new knowledge for me.
This x 10
Superb article! I had little knowledge of how much work had been done on pollution control prior to about 1973, aside from the EGR valve and PCV valve. Like the disputed start of the Brougham Era, Malaise Era and Pollution Control Era, it seems you’ll have people tell you that either 1973 or 1974 was the magical year that cars ran crappy due to new pollution control tech.
And, I became aware of it at the time as that was discussed quite a bit then by the adults around me, and my father had to deal with occasional dealer visits with his 1974 Olds Delta Royale 455 company car when on the road.
Ultimately, that car ended up his favorite among the many Oldsmobiles he was assigned, and he considered bidding on it when the company was ready to sell it. Eventually, they must have been able to make that car a satisfactory ride considering both its popularity with employees as well as it running for a zillion miles into the 1980s with its second owner. It finally succumbed to massive fatal skin and bone cancer.
Well, there were some real stumbles along the way—yes, even by Chrysler, sometimes especially by Chrysler—between 1963 and 1973. I’m sorry to tease, but there’s posts in them thar hills, so…I’m adding the stumbles to the list.
But there’s a sturdy case to be made for 1974 being particularly bad. That was the last year, with the tightenedest of standards, without catalytic converters. However clean the exhaust was at the manifold outlet, that’s all the cleaner it was going to get, so engines had to be strangled and detuned and gadgetted almost to death to squeak the new cars past their emissions type-approval tests so they’d be legal to offer for sale.
Daniel, I hope there’s a forthcoming post about Chrysler’s Lean-Burn system!
MMmmmmmmmaybe. I feel like it would be prudent to have somebody qualified cast a protection spell over me before I attempt that.
A great explanation, so logical and easy to follow.
We had that green device on my ’66 California Dodge A-100 (273/Loadflite). I understood basically how it worked from the plumbing, but your explanation of the details is excellent. I did not understand why Ford and GM used that expensive air pump system, except maybe to “trick” the test by adding air to the exhaust stream when they measured ppm instead of grams/mile. I never fully bought into the idea of “after combustion” in the manifold without catylist.
The ’71 Chevy (250ci six/stick shift) had an electric vacuum advance relay that I assumed was for NOx, that only allowed advance in high gear.
I took my ’67 VW (imports were not subject to California emissions requirements) to the automotive lab at my engineering school and discovered just how much spark advance had to do with hydrocarbon emissions. By reducing idle advance a few degrees, I cut HC in half, 1200ppm to under 600ppm.
Great article Dan. If you want to see something interesting, take a look at the Skinner oil rectifier as used on the 20’s and later Willys-Knight engines. PCV from the factory in the 20’s.
Thanks, Erik, I’ll go look.
Another interesting read from Dan!