Today, emissions standards are both well-defined and strictly enforced. Cut back to the 1970s, though, and restricting automotive emissions was still a new art that automakers were getting to grips with. That led to all kinds of inventive solutions, and a particularly cheeky one from Ford.
The story comes to us from Rare Classic Cars and Automotive History, a YouTube channel which covers the car stories of yesteryear. A new video covers the oddball solution Ford found to meet 1975’s emission standards on a budget.
As covered by the New York Times in 1975, Ford had just decided to roll out catalytic converters across all its models. Its big full-sized vehicles with V8 engines all got dual catalytic converters, just like today’s vehicles. However, for the 1975 Ford Thunderbird and Lincoln Continental Mark IV, the Michigan automaker found a sneaky little workaround.
Why Not Just One?
There were two main solutions for putting cats on big V8 vehicles in this era. GM decided it could go with just one big pancake-shaped unit. It combined the exhaust headers from both banks of the engine into a single pipe which fed a single big catalytic converter. Ford, on the other hand, used a more modern solution on the LTD, Grand Marquis, and the Lincoln Town car. Each bank of cylinders had its own cat up near the headers. This made perfect sense for cars with dual exhausts.
Of course, this was expensive, as it required Ford to fit two cats, which didn’t come cheap. The 1975 Ford Thunderbird and the Lincoln Continental Mark IV would make do with one cat instead, a decision that surely saved a lot of money. However, the cheeky part was this. Ford only attached it to the driver’s side cylinder bank. The passenger-side bank simply went without one!
If you’re familiar with modern cars, you’ll be used to seeing dual cats on cars with V-engines and dual exhausts. The entire exhaust stream needs to pass through a catalytic converter in order to pass modern emissions. Apparently, though, that wasn’t the case in 1975. Ford was able to skate by with these models, still meeting emissions standards while only running half of the exhaust output through a catalytic converter!
Notably, there was an H-pipe that connected both sides of the exhaust. However, this was after the cat, not before. Thus, the exhaust from an entire bank of cylinders was largely going entirely untreated by the cat.
This choice had some pros and cons. On the one hand, it saved Ford quite a bit of money. Catalytic converters have never been cheap, so using one instead of two is naturally much more cost-effective. On the other hand, though, the cars still suffered one major drawback. They still needed unleaded petrol to avoid poisoning the single existing catalytic converter.
Ultimately, you’d never get away with this today. Modern emissions standards wouldn’t even let you run a single cylinder of an engine without passing it through a cat. Emissions of carbon monoxide and nitrous oxides from an untreated exhaust stream are simply too high. But back in 1975, you could skate by just cleaning up half the output from a V8.
It truly was a different era back then. Today, we’re blessed with cleaner-running vehicles and nicer air as a result. Still, it’s amusing to see what Ford was willing to try to get by in the bad ol’ days of the 1970s.
Image credits: Rare Classic Cars & Automotive History via YouTube screenshot
Most carbureted V8s used a thermal valve on the RH exhaust manifold to force exhaust thru the heat riser in the cylinder head, under the carb, and out the LH pipe. So the cat was getting 100% of the exhaust when the engine was in its warm-up cycle (aka pig rich). When warm, the engine ran so lean that a cat would only help a little.
“Ford was able to skate by with these models, still meeting emissions standards while only running half of the exhaust output through a catalytic converter!”
So did they pass by making sure only the catalyzed pipe was tested or were (what I presume) 49 state standards just that lax?
Volkswagen actually gutted it’s cats. The 75 Rabbit was originally fitted with a catalytic converter, but later on VW revised the carb settings and passed without it. VW issued a tech bulletin to reset the 75-76 carb and knock out the catalytic converter guts. It’s in the John Muir book and probably the early A1 manual from Robert Bentley.
VW, messing around with emissions? Unglaublich!
I ran headers and true dual exhaust on my 77 Mark V
Ford probably thought that whole “EPA” thing was just a fad. Sadly, they might have been right…
You know else sucked ass with these types of cars? The HUGE 2 doors on them even though they could sit 6 people with the gigantic bench seats. The car would be parked at the curb and you would open the 4 foot long door. Everyone would get in, the car would lower, and now the door is stuck in the grass next to the curb.
Now began the dance. If you had a good co-pilot, they would pull the door towards them while you crept the car forward. Still ended up with a bunch of dirt, but it was better than asking everyone to get out and reposition the car so they could get back in without the door dragging again.
THIS was basically with every 2 door car from the 1970s. They really really really sucked. If you asked anyone that drove in the 1970s which was worse: exhaust pollution or the dreaded super long 2 door design. I’d bet folding money on 2 door winning that poll.
Plus savage door dings from trying to get through a 12″ wide door opening situated three feet behind the driver’s seat.
My shins still have scars and dents from these doors slamming on them. Do not miss a bit.
I had a ’72 Buick Limited 2 door. On a hill, if that door swung shut with any momentum and your body parts were in the way, broken bones were about guaranteed, and amputation was a real possibility.
My 03 Mustang had 4 cats!
Same with most modern GM vehicles with and LS. Pre and post cats.
My 03 WRX had 3 and not because of it being a boxer, one pre turbo (up pipe), one post turbo (down pipe) and one between the downpipe and muffler
Did we ever ultimately find out the number of cats in a Jeep Grand Cherokee?
I once knew a girl with 12 frickin cats…Then she got married and eventually they have all taken the big dirt nap. But one hangs on still.
The husband?
He bailed after 2 years…
Aston Martin’s V12 Vantage has 4 as well. Two of them basically integrated into the exhaust manifolds up top, which can be a problem as they start to deteriorate and the engine can actually pull some of the material backwards into the cylinders in the right circumstances.
You are forgetting the benefit of the H-Pipe which is to better scavenge the exhaust. engines run far cleaner and smoother if the vaccum of the one bank helps to pull spent exhaust out of the cylinder so you get a smoother running motor. those Pancake things in GM exhaust were so restrictive they actually did more harm than good. same with spread bore 4 barrels versus a big 2 barrel and over-retarded ignitions.
You could pry out the plug and dump the catalyst pellets, the GMs weren’t honeycomb inside like all the cats are today. GM even sold a service replacement plug. Then we made a hardened steel mandrel tool to expand the filler neck size to allow a leaded gas pump to insert (which was quite a bit cheaper back in the early days of cats).
Or get the black plastic adapter to put on the leaded gas nozzle to fit in smaller hole vs trying to punch out bigger hole and risk metal pcs in tank.
Our expander tool was built by a journeyman toolmaker and was quite elegant, and it only took about a tenth of an inch in diameter expansion IIRC.
I’m just going to say that I am old enough to remember when you could taste the air. Modern emissions standards are a good thing. And wow was that half-assed.
It almost shocks me now when an old car goes by and you can taste the gasoline. Every car was like that when I was a 70s kid.
Lived in Salt Lake City for a few years and I remember tasting the metallic air in the winter. That city can have some of the worst air quality in the world due to the inversion.
I spent the 70’s in LA’s smog bowl. Not only could you taste the air, it burned your eyes and lungs. First degree smog alerts in the summer were common and with them everyone had to stay inside. As a bonus that was mostly leaded gas fumes.
As an extra special bonus one of our neighbors was biggest lead acid battery recycler in the country:
https://www.dailynews.com/2022/12/14/quemetco-battery-recycler-in-city-of-industry-to-pay-2-3m-fine-fix-problems/
(if you think they’re bad now hoo boy, you should have seen them then!)
For anyone who feels like they missed out on the fun you too can experience an accurate recreation if what it was like! Just wait for a major wildfire and breathe deep a few miles downwind. Its as close as you can get but without the lead.
Did they use the Torchinsky Method :tm: of battery disposal?
It was a notorious commercial lead smelter in the 1970s so I expect Torch and his chainsaw would have been preferred by OSHA, the EPA and anyone else within the plume.
Big Chinese cities were like that until a few years ago. I’m told it’s much better now. Air in Beijing used to taste like metal.
I had a 1975 Ford Thunderbird from 2002-2005 (Yeah, I know, best time ever to have a land yacht that got 5-10mpg, it’s the only car I ever replaced the factory carburetor with a Holley double-pumper and INCREASED the fuel economy on.)
The first time I lifted it up and saw that exhaust, I thought someone had replaced a clogged cat on one side. It was so weird. Mine also had a secondary cat downstream, also just one the one side. It also had an H-pipe, and all of it appeared original.
I miss that car, but the 13-14mpg highway and 8-9mpg city (yeah, the Holley 750cfm double-pumper improved the fuel economy that much, and improved performance over the Motorcraft carb) got old when the Iraq war pushed gas prices past $4 a gallon. I sold it for a loss and drove a Saturn until gas prices came back down.
Too bad you don’t still have it. That’d be an ideal candidate for an EV conversion.
If I still had it, I’d drop a diesel in it.
Had mine in 1981. 460 engine and slim wallet for me then. Sat all summer.
Then one day the city towed it away for blocking the sidewalk and expired plates.
It was in a 9 out of 10 for condition overall. Wish I had it now, just for comedic effect at times.
Then there’s the smog pump. Pump clean air into the exhaust to dilute the pollutants, so while your total pollution stays the same, your parts-per-million goes down. And that’s what’s measured.
They still do this. At least on Motorcycles. It actually serves to reignited unburnt fuel as it come out of the exhaust while also helping to scavenge when flow is diminished. It is also why non stock exhaust on some metric Motorcycles sound like the jetting is completely off as the things cackle and pop unhealthily .
JDE is correct, the air pump improves emissions. Besides reigniting unburnt fuel the extra O2 converts CO to CO2. The emissions standards are in grams per mile, not ppm, so you really can’t cheat with dilution.
Hardly see any air pumps on cars and trucks anymore and that’s a good thing. My old F-250 has one but all the plumbing is rusty/crusty/leaking so it’s probably not doing anything at this point.
CO and HC standards are in g/mi so the air pump does not reduce those by dilution. NOx standards are stated in PPM so the air pump dilution can help. When injected in to the exhaust ports of a vehicle with late ignition timing it can help reduce emissions by providing O2 to complete the combustion of some of those HCs that were going to go out the exhaust. The other reason is that for the Cat to turn CO into CO2 and HCs into CO2 and H2O there needs to be additional O2 introduced upstream (2 way cat) or mid bed (3 way cat)
Now with the O2 sensor and modern engine controls they just vary the mixture between slightly rich and slightly lean to provide that extra O2 and keep the cat at optimum operating temps.
https://www.walkerexhaust.com/support/tech-tips/evolution-of-the-catalytic-converter.html
Thermal reactors! The bane of every late 70s big BMW.
And pre-’81 Mazda Rotaries! Fitting one with headers was like bolting in a whole new motor, as well as losing about 25lbs from an already light vehicle. Then they ran so dirty that you could max out one of those old-school smog machines, though – ask me how I know.
I don’t know about you, but I feel exhausted after reading this story and am hopeful that Ford will feel so much shame that this article could be the catalyst for change! 😉
I completely agree! I’m glad you piped up about this!!!
Thank you. I make it my emission to point out whenever there is shoddy engineering going on! 😉
Speaking of asymmetry, that Mustang exhaust system from Flexx Motorsport in the illustration seems like a complicated solution to some sort of a problem, but what?
I presume you are talking about the multi-piece nature of one of the headers? My first thought would be engine bay obstructions and ease of install.
Following the letter of the law, not the spirit. A corporate tradition.
It’s technically compliant, which we all know is the best type of compliant.
Unless you like clean air…
Its cleaner than a Thunderbird with no catalytic converters, slightly better is still better
For the 1968 model year SAAB got around the new US emissions standards for their two-strokes by reducing the engine bore to bring the total displacement down from 850 to 820cc, just small enough to be exempt. This also reduced the output from 46 to 44hp but at least the smaller engine came with a lifetime warranty:
https://www.autopaper.com/images/40103/photo/img2865_182937.jpg
I guess this saved some money, but the Thunderbird and Mark IV were already the most expensive cars in their divisions, and I think the Mark IV was easily outselling the Eldorado throughout the ’70s. The margins on those things had to be close to the margins on high-option F150s now.
If you’ve ever been to the Mutter Museum (of medical oddities) in Philadelphia you will appreciate the likeness to the worlds largest impacted colon.
Sounds like something you can never un-see
Tell us about the gift shop…
They sell a life sized stuffed colon plush toy. No kidding. The place is amazing
Soap lady soap!
It’s full of old shit.
Btw the colon itself is probably 5 times bigger than the catalyst in this story. It captured a lot of pollutants!
Swear to god you could roll a volleyball through that thing.
Sounds like a case for: Super Colon Blow!
https://m.youtube.com/watch?v=Ku42Iszh9KM
Number one in recalls for 3 years running. The half-assness isn’t just a recent management decision, its a tradition.
Pick your evil, recalls for things they messed up or the Stellantis Way® of not recalling the things they messed up.
Had one of these. Went to change oil, and my 22 year old self saw this crap.
And thought WTF Ford?
Is this one of “your better ideas?”
America, what a country…
it was half measure to be sure. I doubt it made it past 1976 if that.
When I read the headline, my first thought was that they made the car with a GVW as high as an F150, which was the workaround for the then typical 1/2 ton pickup. Those ‘Birds were heavyweights.
Shenanigans!
I would think this would cause massive problems, with one bank blowing free and the other all choked up. It would make for a very unhappy engine.
1970s Detroit wasn’t concerned with such things. Back then, if you could get your new car just to crank over on a cold morning, and not stall out at the first stop sign on the way to work, you could consider it a win
I’m still grateful that the intersection nearest my house has a yield sign so that most days I don’t need to run the risk of stopping before the engine has had a bit more of a chance to warm up.
I have uphill traffic lights…. I dread the red…
Those old cats were restrictive. Did this lead to running problems between the banks of the engine?
Also, those GM cats got very hot. You knew exactly where that thing was installed.
GM’s idea of “dual exhaust” on my brother’s Trans Am was to merge both banks into one catalytic converter, then split it out back to two exhaust pipes.
Yup. One pipe in, two pipes out of that muffler behind the cargo well.
Is that fundamentally any different than an X-pipe?
Doesn’t an x-pipe usually help with exhaust scavenging?
X Pipe setups are usually two separate exhausts manifold to tailpipe except for the x merge.
F-Body exhaust would merge basically under the hood, run a single pipe from there to the cat and single to the rear axle. Behind the axle the single pipe would go into a single muffler with two exhaust tips hanging on opposite sides of the car.
My buddy had a late 70s Sunfire. The cat was mostly clogged from the copious amounts of oil that didn’t get burned and made it into the exhaust system. The cat would glow a rich orange and would cause anything that came in contact with it to combust. Especially sucked because the car would often stop working and need to sit on the side of a country road to cool down, get refilled (with any number of fluids) or simply take a break.
The only reason my buddy didn’t just let it burn up in the ditch was that it was his only way to get to work.
Eventually he stabbed the cat many times with a screwdriver, thus relieving the pressure and lowering the temp by a good 1000 degrees. Strangely it didn’t change the noise (loud), power (low to nill) or anything else (sucking donkey balls at level 9).
“My buddy had a late 70s Sunfire. “
Wouldn’t it have been a SunBIRD?
Probably was a Sunbird. It didn’t have any emblems left on it, nor trim pieces.
Subconsciously I guess “fire” stuck with me since many memories was of it setting stuff on fire. Itself, roadsides, small woodland creatures, etc.
Well, the Sunbird started in ’75 but there was also the Olds Starfire from 75-80…it could have been either one anyway; just thought it was interesting and I’ve always enjoyed both model names. I have seen one of these 70’s Starfires a long time ago, and also used to have an 86 Sunbird
This is why so many older car models that got retrofitted with cats in the ’70s had those “Floor Heat” warning lights on the dash, things could literally set the carpet on fire under certain circumstances, especially in small British roadsters where the cat was directly against the opposite side of the thin sheet metal floor pan
Better solution than the Explorer, where the exhaust is routed into the cabin. /s
Humans are cheaper than precious metals, but you need one in each seat to clean the air to today’s standards..
The human respiratory system is remarkably efficient at capturing particulate matter.
It’s okay, the cigarette filters cleaned it up.
Did they do sniff tests back in the day? Did they just instruct inspection stations to only test the drivers side tailpipe?
Maybe they had to average the emissions per tailpipe, i.e. if one runs clean and the other is filthy it averages out to acceptable.
That’s what I’d figure, average of results from both.
I wonder how it works in my state though, where all vehicles model years 1975 and up are required to have a catalytic converter in addition to passing the curb idle test, having one half the exhaust non catalytized looks sus as hell and I’ll bet most of the staff doing the inspections aren’t well versed in OEM specs on 50 year old Fords. Imagine you’d have to keep some documentation handy and be ready for an argument every 2 years
Article said it had an H pipe which should average out the emissions. Still a half assed solution.
An H-pipe doesn’t really do a substantial amount of mixing. They mostly are there for sound purposes, but since the pressure is fairly equal on both sides, there’s not a ton of mixing of gasses between the two sides. Some mixing for sure, but nowhere close to enough to expect equal emissions from both sides.
There were sniffer tests, but I’m pretty sure they only had a single probe.
It’s been a long time since I’ve seen that testing setup, though. We had the sniffer, then the dymo and sniffer. Now we just do OBDII port testing and let OBDI slide unless it’s smoking out of the exhaust.