After experiencing some eye watering drives in a convertible behind classic cars, I've been wondering whether a catalytic converter would be a reasonable retrofit onto 50's & 60's cars, both domestic & foreign. For example a junkyard Miata cat onto an MG or modern Mustang cats onto a '67.
Not sure whether so many old cars are stinky because that's just the way it was, or they're all out of tune, over carbureted and/or down on compression. Any thoughts on the subject?
Only if you add fuel injection as well to keep it near stoich. Max nox which the cat will take care of.
Why not all of the above?
Adding a catalytic converter to a poorly tuned old car will kill it in a snap, and then there would be nothing but complaining about how awful and fragile the converter was.
Dashpot said:After experiencing some eye watering drives in a convertible behind classic cars, I've been wondering whether a catalytic converter would be a reasonable retrofit onto 50's & 60's cars, both domestic & foreign. For example a junkyard Miata cat onto an MG or modern Mustang cats onto a '67.
Not sure whether so many old cars are stinky because that's just the way it was, or they're all out of tune, over carbureted and/or down on compression. Any thoughts on the subject?
Out of tune is the worst of the worst when it comes to eye watering emissions. Carburetion in of itself isn't quite as bad- it's fault is the inability to maintain a consistent a/f across most ranges and conditions to keep a catalyst working and alive. Down on compression- depends on what that's caused by- but if it's wear, that's bad.
I'd not add a catalyst to a carbed car- just not worth it, really.
For old V8's, I'd find a decent EFI carb replacement, and add some catalysts, target 14.6 most of the time, and be done with it. Other cars need some more work- there may be some other carb replacement kits that are similar but for SU or Webers.
I'm still planning on adding EFI and a catalyst to my GTV (the one you see in my avatar)- probably Microsquirt, as it's verys simple and has all of the features I really need. But I'm starting with a mechanical injection set up- so it's a little more straight forward than a carb swap. One of these days.
There are a ton of people here on the board who would be helpful with the conversion. And at least one who is really, really familiar with making catalysts work really well.
Cats were on cars before EFI was the norm. So why all the pessimism?
I do agree that the mobile refinery fire thing does get old and is one of the reasons I have parked the GT. Not that is is stinking rich, just what old cars all smelled like back in the day; the smell of nostalgia.
Pete
NOHOME said:Cats were on cars before EFI was the norm. So why all the pessimism?
I do agree that the mobile refinery fire thing does get old and is one of the reasons I have parked the GT. Not that is is stinking rich, just what old cars all smelled like back in the day; the smell of nostalgia.
Pete
They sucked and failed very badly. Not to even mention how that set up also cost a lot of power.
Yes, you can put one on, but generally, it will take an air pump to be really robust, and the odds of it failing due to poor mixture control is quite high.
Given the cost of aftermarket EFI, and the effort for set up, it's the way to go. And the catalyst will be light years happier.
Agreed with pretty much everything alfadriver said.
Spend the time and effort to get your carb running as good as it can. Then spend the effort on EFI, if you want. _Then_ worry about a cat.
An oil burner will kill a cat, EFI or no.
You want smell? We were at a steam engine show this past weekend. A lot of the old timers swear by coal. The air over the fairground looked like the inside of a diner in the 1970's, before anywhere banned smoking inside. And it smelled like Pittsburgh during WWII in the middle of winter. If I ever buy an old steam engine, I'll run it on Hickory or something.
alfadriver said:NOHOME said:Cats were on cars before EFI was the norm. So why all the pessimism?
I do agree that the mobile refinery fire thing does get old and is one of the reasons I have parked the GT. Not that is is stinking rich, just what old cars all smelled like back in the day; the smell of nostalgia.
Pete
They sucked and failed very badly. Not to even mention how that set up also cost a lot of power.
To this day... The prevailing belief is that cats are still costing people power. I don't know how many mustangs I looked at with offroad pipes installed.. More power the owner said.. Sure.. I say.. Internally, I'm wondering what other poor decision making has clouded their minds about this vehicle.
In reply to Fueled by Caffeine :
In the days of yore, it did cost power- some from poor catalyst design (which would not be an issue today) and some from a poor tune that was required to make it work with a carb (still an issue).
Today, not so much, as tuning is light years more accurate, and the flow is quite good. +500hp on a ULEV70 or so vehicle is amazing. That's ~98% cleaner than the pre-carb days, and probably double the actual wheel power. So. yea, they don't cost power with the right set up/
alfadriver said:NOHOME said:Cats were on cars before EFI was the norm. So why all the pessimism?
I do agree that the mobile refinery fire thing does get old and is one of the reasons I have parked the GT. Not that is is stinking rich, just what old cars all smelled like back in the day; the smell of nostalgia.
Pete
They sucked and failed very badly. Not to even mention how that set up also cost a lot of power.
Yes, you can put one on, but generally, it will take an air pump to be really robust, and the odds of it failing due to poor mixture control is quite high.
Given the cost of aftermarket EFI, and the effort for set up, it's the way to go. And the catalyst will be light years happier.
Forgot about the air pump.
In addition to the air pump, getting all the vacuum acutated gizmos on an "emissions carb" was near impossible even when new.
Alfa, if you wouldn't mind sharing more of your knowledge and experience.
What are the chances of a cat surviving long behind a less efficient motor that is really only happy idling around 13.5?
My shelf of "when I have free time" projects includes a TBI setup I have been building for my mini and a catalytic converter has always been in the plans. The siamese ports have a habit of charge robbing so "conventional wisdom " says tune to around 13.5:1. I also have a cheap Amazon sourced "high flow" cat that I figured was better than nothing.
Am I just planning for future heartache?
Yeah, carbs tended to run rich and you had to have an air pump to make the cat work at all. As far as a serious odor goes, if the car is running a proper AFR and not misfiring or burning oil you probably won't have an odor serious enough to bother bystanders or people behind you in traffic, so i would call it mostly a tuning issue.
Jumper K Balls (Trent) said:Alfa, if you wouldn't mind sharing more of your knowledge and experience.
What are the chances of a cat surviving long behind a less efficient motor that is really only happy idling around 13.5?
My shelf of "when I have free time" projects includes a TBI setup I have been building for my mini and a catalytic converter has always been in the plans. The siamese ports have a habit of charge robbing so "conventional wisdom " says tune to around 13.5:1. I also have a cheap Amazon sourced "high flow" cat that I figured was better than nothing.
Am I just planning for future heartache?
I think your worry is that "rich kills catalysts" popular "common sense". But it's not running rich that kills cats- it's misfires. So as long as that 13.5:1 idle is not ever misfiring, you will be fine. And if the same engine is misfiring at 14.6, that would kill it. You will still have a CO problem that rich, but not nearly as bad as if you didn't have anything.
So, no, IMHO, properly set up, you are not planning a heartache.
Now, WRT the requirement to run 13.5:1, have you at all messed with the idle ignition timing? If you have spark control, may as well use it to the full benefit- there's no real factual reason to idle at 10 deg- other than the fact that pretty much every engine does. You can advance the spark all you want at idle, as long as it's smooth and robust firing. And in reasonable speed control, of course. But if that does not help- that's why you see port runner plates on cars- to up the turbulence so that leaner mixtures combust.
Just LS swap everything and keep the emissions controls. Boom solved. All those classics will actually be fast now too.
In reply to alfadriver :
Pulling the distributor and going with digital spark control is also part of the plan.
Thanks for the advice
Just wait until classics are forced to get EV conversions...
(runs and hides... 
)
I've had similar experiences and thoughts about my own classic cars. I would be very tempted to install a cat on my 1800ES assuming the D-Jet gets converted to a programmable system. I've thought about it on my Triumphs, but I don't have EFI plans for them at this time. My ex's Spitfire was fitted with an air pump, although I honestly have never seen a functional example (the one on her car was frozen solid). CARB spec'd Spitfires were fitted with a cat, but I can't only imagine how often they failed given how difficult it was to keep an emissions-era Zenith-Stromberg in tune.
But yeah... go to a classic car show and then follow along in an open air car... it'll make you appreciate how much better things are now.
There is also a serious packaging issue on some old cars. I have no idea where I would even put a cat on a late Corvair. You might be able to tuck on up in the fender in an early, but it would be pretty funky. I am not sure where they put the cats on later Beetles (tucked up into the fender?).
My Corvair is super stinky at idle (I am told the modified hi-squish heads result in un-burnt fuel), but I don't it's too bad at cruise.
In reply to alfadriver :
agreed.. but a 10 or 15 year old mustang... no need to remove cats unless race car pushing 3x stock horse.. or so
+1 for switching to EFI first, a decently-tuned EFI'd engine won't have any noticeable exhaust smell even without a cat, and then you can add a cat to make the car more environmentally friendly.
In reply to aircooled :
Placement is definitely a concern with the 1800. There is "some" room under the car for a cat where the first resonator sits (and could be removed), but I would also need to fabricate some sort of OEM-style heat shield so it doesn't bake the passenger foot well.
With a Spitfire it'd be damn near impossible as there's barely room for the exhaust as-is, which is tucked up in between the frame rails under the drive shaft. I don't think a cat there would be a good idea...
Fueled by Caffeine said:In reply to alfadriver :
agreed.. but a 10 or 15 year old mustang... no need to remove cats unless race car pushing 3x stock horse.. or so
LOL- a 2004-2009 Mustang is hardly a classic that has a carb... 
For the "don't waste your time with the catalyst removal" thing, I'd go back to at least 1995. In that era, fuel control was really getting figured out, and catalysts became both a lot less restrictive and more efficient (better metal combinations)- so things changed in a big way in that time. Which would be a ~25 year old Mustang.
aircooled said:There is also a serious packaging issue on some old cars. I have no idea where I would even put a cat on a late Corvair. You might be able to tuck on up in the fender in an early, but it would be pretty funky. I am not sure where they put the cats on later Beetles (tucked up into the fender?).
My Corvair is super stinky at idle (I am told the modified hi-squish heads result in un-burnt fuel), but I don't it's too bad at cruise.
For a car like that, find as late of a water cooled 911 you can, and just mimic it's layout as best you can. The real hard part is figuring out what EFI you could even run to make it worth the effort.
OK Random thoughts
So my dual sport Beta 520RS is carburetted (Keihin flat slide) and the exhaust also has some type of catalyst (not sure exactly what) but the throttle response is flawless throughout the entire range and the mileage equal to EFI bikes. So the combo is possible.
So carbs do not have to suck. Honda's CVCC motors burn very clean (yeah I know you can't install a pre-chamber to an existing head)
Sadly most people do not tune carbs properly; I am semi guilty of this on my 1200, I use the aforementioned Keihin carbs and while the 1/4 to full throttle is spot on I've not really spent the time on the idle mixture screws that I would if it where a street car. The idle is close but I know it's rich, not horribly so but still richer than it truly needs to be.
With all that said I think putting a modern FI set up and a cat on a classic is a great idea for a street car. If you drive the car car across a broad range of altitudes and weather conditions then FI is worth the switch. If you are going to redo the exhaust why not put a modern high flow cat on as polluting less is a good thing.
Now as for FI and a cat on a vintage race car; nothing wrong with it other then it violates the rules for many cars.
Back to the regularly scheduled program.........................................
alfadriver said:aircooled said:There is also a serious packaging issue on some old cars. I have no idea where I would even put a cat on a late Corvair. You might be able to tuck on up in the fender in an early, but it would be pretty funky. I am not sure where they put the cats on later Beetles (tucked up into the fender?).
My Corvair is super stinky at idle (I am told the modified hi-squish heads result in un-burnt fuel), but I don't it's too bad at cruise.
For a car like that, find as late of a water cooled 911 you can, and just mimic it's layout as best you can. The real hard part is figuring out what EFI you could even run to make it worth the effort.
Small "race" cats right off the manifolds should be workable. Agreed on the hardware aspects though, it's likely not a popular combo to easily source fuel rails, tb, etc for.
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