In reply to alfadriver :
man you can't swing a dead cat around here without hitting a new edge with a offroad X pipe installed..
In reply to alfadriver :
man you can't swing a dead cat around here without hitting a new edge with a offroad X pipe installed..
Paul_VR6 said: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.
There is a TBI kit for dual carb Corvairs, uses TB's from a 90's Cavalier IIRC. I know the guy who developed it, he runs it in his '69 Corvair convertible that is his daily driver. Knocks down mid-20's MPG behind a powerglide. No cats, though.
Fueled by Caffeine said:In reply to alfadriver :
man you can't swing a dead cat around here without hitting a new edge with a offroad X pipe installed..
A lot of Fox and SN95 owners are hypersensitive to the idea of plugged cats since the Foxes tended to clog them by 50k.
GCrites80s said:Fueled by Caffeine said:In reply to alfadriver :
man you can't swing a dead cat around here without hitting a new edge with a offroad X pipe installed..
A lot of Fox and SN95 owners are hypersensitive to the idea of plugged cats since the Foxes tended to clog them by 50k.
That may be true for the pre SN95 Fox Mustangs, but not for the SN95. Control and catalysts had gotten quite good by then. Funny how one thing in the 80s has been extrapolated all the way into the 2000's vehicles. Waste of time and money, and just really makes the car less liveable on a daily basis.
I have to interject.
Cats on carbs aren't an issue... if you have the million-dollar R&D that the OEMs used to calibrate carbs ad infinitum. It doesn't take long running rich to completely ruin the catalyst.
You can even spoil a good cat with a haphazard tune on EFI. Cats work in a very narrow range of mixtures immediately above and below stoich. Too lean and they don't get hot enough to do anything. Too rich, they get too hot and clog quickly... and when I say quickly, I mean a few thousand miles if you're running rich enough that it's making your eyes water.
I had an S10 that someone stuffed an LS1 with a carb and MSD ignition box. They figured they would do the "right" thing and put cats on it. They lasted 5200 miles. They got so hot from the Holley running on the rich side that they partially clogged, got screaming hot, cracked the honeycomb which fell sideways, and the truck wouldn't run.
Getting catalysts to work right takes really intense R&D. I would love to put cats on my 67 LeMans once I get the LS6 in it, but with a 234/244 cam, full head porting, 11.3:1 compression, and bigger injectors, it is a complete no-go.
In reply to Curtis :
Funny thing about catalyst, we cool them off by running rich. Like down to 10:1 rich. They very much don’t overheat when rich, it’s the misfire that does it.
volvoclearinghouse said:Paul_VR6 said: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.
There is a TBI kit for dual carb Corvairs, uses TB's from a 90's Cavalier IIRC. I know the guy who developed it, he runs it in his '69 Corvair convertible that is his daily driver. Knocks down mid-20's MPG behind a powerglide. No cats, though.
EFI is not an issue. With 3 barrel Weber manifolds, you can run a 911 3 barrel TB. I have some custom Corvair carb tops with bungs built into them... I just have to install the system... some day.
Regarding the cat placement. 911’s hang their mufflers off the back of the motor. Corvairs don’t have as much overhang and that would result in the cat being exposed under the bumper.
The best solution would likely involve putting a muffler on one side and the cat on the other and connecting them. Lots of pluming since one side would have to cross over, then come back across again and very little clearance (over the top of the transaxle would likely need to be done).
alfadriver said:GCrites80s said:Fueled by Caffeine said:In reply to alfadriver :
man you can't swing a dead cat around here without hitting a new edge with a offroad X pipe installed..
A lot of Fox and SN95 owners are hypersensitive to the idea of plugged cats since the Foxes tended to clog them by 50k.
That may be true for the pre SN95 Fox Mustangs, but not for the SN95. Control and catalysts had gotten quite good by then. Funny how one thing in the 80s has been extrapolated all the way into the 2000's vehicles. Waste of time and money, and just really makes the car less liveable on a daily basis.
It doesn't just bleed over to SN95, pretty soon your Fox buddies were telling you that's what was wrong with your Camaro or Firebird... then everyone is taking off their cats or gutting them when really what was making them run poorly was intake gaskets, ignition timing or a dirty MAF sensor.
Catalytic converters are not what prevents smelly exhaust. More generally, they're not a good idea on non-EFI cars.
The one car I ever had with a carburetor and a catalytic converter did slag the cat. It was a 4-cylinder Fox Mustang.
I didn't buy into that explanation and addressed basically everything else first. Rebuilt the carb, converted it from "Thick Film Ignition" to Duraspark, set the cam timing, checked compression... I can't remember what finally inspired me to Dremel a big hole into the downpipe, but that was what finally got her running again.
Around the same time, I had a '77 Cutlass with a "test pipe" that was pretty well-tuned. It did not smell bad, at all.
FWIW, that Fox body never misfired in the 10+ years I drove it. Merely running rich for a while was sufficient to toast the EPA's little box of gold.
Quite some time ago I Remember GRM doing an article where they tested a bunch of aftermarket cats. That would be a good read and reference for this thread.
alfadriver said:In reply to Curtis :
Funny thing about catalyst, we cool them off by running rich. Like down to 10:1 rich. They very much don’t overheat when rich, it’s the misfire that does it.
Truth. Peak egt is at stoich.
In reply to Ian F :
You could do like later Spitfires where the cat was attached to the manifold (which would eventually cause the manifold to crack).
Paul_VR6 said:alfadriver said:In reply to Curtis :
Funny thing about catalyst, we cool them off by running rich. Like down to 10:1 rich. They very much don’t overheat when rich, it’s the misfire that does it.
Truth. Peak egt is at stoich.
I do have to edit one thing- if you are running rich AND have some kind of source of air going into the exhaust- big leak, air pump, etc- that will burn out the catalyst too, Not as fast as a misfire, but it will do it.
But a sealed, rich exhaust with good burning combustion will not hurt the catalyst, it actually cools it down.
So many people say that rich kills catalysts- I'm starting to think there are other factors involved in their issue.... so back to the basics- O2 + fuel = combustion. Without one of them, you won't have combustion- so lean, where there's almost no fuel is cooler, and rich where there's almost no O2 is cooler, too. But in either case, if you give it fuel when lean or air when rich- you will get combustion in the catalyst.
And here I thought I wanted to but a cat on the Renault when I swap in a Zetec... but now I am confused.
RossD said:And here I thought I wanted to but a cat on the Renault when I swap in a Zetec... but now I am confused.
That would be a pretty straightforward thing to do, if you want to. What would be confusing? Many here can help! :)
alfadriver said:In reply to Curtis :
Funny thing about catalyst, we cool them off by running rich. Like down to 10:1 rich. They very much don’t overheat when rich, it’s the misfire that does it.
As a rotary owner (and tuner!), I second this motion!
triumph7 said:In reply to Ian F :
You could do like later Spitfires where the cat was attached to the manifold (which would eventually cause the manifold to crack).
Except I will be using the Euro exhaust which has a 4-2 cast iron manifold with a 2-1 collector pipe that comes together under the transmission. Even a small race cat would be the lowest part of an already low car.
I have one of the CARB manifolds with an original cat. Yep - the manifold is cracked. And because those manifolds were designed around the single Z-S intake, they are really restrictive compared to the Euro system, which is essentially a good 4-2-1 header, but it requires either a dual carb set-up (and I'm hoping will work with a quad carb set-up... 
)
I've been planning on adding a cat to my TR6 with EFI project. There's room, and with proper heat shielding it shouldn't melt the plastic tunnel cover. My plan is to get the car running and tuned without the cat, then drop the mid-pipe and weld it in.
Thinking longer term, I'm concerned about how running a zinc-rich oil for an older flat tappet engine will effect the cat, especially with the poorer oil control (e.g., lack of valve stem seals) on older engines. I would assume some shortening of the cat's lifespan, but will it be significant?
Ian F said:triumph7 said:In reply to Ian F :
You could do like later Spitfires where the cat was attached to the manifold (which would eventually cause the manifold to crack).
Except I will be using the Euro exhaust which has a 4-2 cast iron manifold with a 2-1 collector pipe that comes together under the transmission. Even a small race cat would be the lowest part of an already low car.
I have one of the CARB manifolds with an original cat. Yep - the manifold is cracked. And because those manifolds were designed around the single Z-S intake, they are really restrictive compared to the Euro system, which is essentially a good 4-2-1 header, but it requires either a dual carb set-up (and I'm hoping will work with a quad carb set-up...
So there's no mid system resonator? Any kind of device in the middle of the car? There are some pretty small catalyst designs out there that are pretty flat.
Yea, a system like that will take forever to light off, but we are not trying to make a brand new car that has to be SULEV30, you are just trying to make a car that is easier to live with on a personal basis.
JoeTR6 said:I've been planning on adding a cat to my TR6 with EFI project. There's room, and with proper heat shielding it shouldn't melt the plastic tunnel cover. My plan is to get the car running and tuned without the cat, then drop the mid-pipe and weld it in.
Thinking longer term, I'm concerned about how running a zinc-rich oil for an older flat tappet engine will effect the cat, especially with the poorer oil control (e.g., lack of valve stem seals) on older engines. I would assume some shortening of the cat's lifespan, but will it be significant?
yes, it will lower the life span of the catalyst. And relative to it's brand new emissions, it will be significant. But in the context of things, it will still be very, very efficient and quite useful in the position it will be in. So put it in. If you are worried about the lifespan of it, then find a system that has two O2 sensor inputs, where you can occasionally look at it's signal to the front one- which should tell you very quickly that it's poisoned beyond usefulness.
Thanks for clarifying my post.
The point I was trying to make is that cats work in a narrow range of conditions, and OEMs have craploads of money to engineer and test systems that make it work. Just slapping a cat behind a carb on your classic won't really help emissions, and could simply cause problems.
I will also echo b13990's comment... the eye-watering exhaust won't be cured by a cat. The problem is that the engine is running rich. Both of my carbed cars are tuned to the Nth degree and you don't smell anything other than a regular exhaust smell. I do have to slow the squirt of the accelerator pump on my one 2jet because it sometimes gives a wee grey puff when I floor it, but otherwise they smell like plain exhaust.
RE: the "eye watering smell"- yea, a poorly tuned running rich engine will be horrible and miserable to live with in the long term.
But to say that a catalyst will not cure the smell issue also discounts what it does- a good running engine will put out 3000-5000ppm HC, 2000-5000 ppm NOx, and 3000-10000ppm CO. Of that you mostly smell the HC, and some of the NO's produced.
A catalyst will reduce that to under 100ppm for all three, and if it's running really well it will be under 10ppm (we can get it to ~1ppm). So to think that it will do nothing to the smell is not really correct- even when everything is right, the catalyst still does a huge amount of reduction in smell, and increase in liveabilty. I've smelt plenty of "perfect" engine out exhaust- it still stinks and still gives me a headache pretty quickly. The catalyst solves that.
alfadriver said:So many people say that rich kills catalysts- I'm starting to think there are other factors involved in their issue....
I think it's just that running *really* rich and massive misfires smell about the same. So to someone less experienced, likely watering, eyes they are equal.
Also the "narrow" range the cat works is decently wide. Maybe not wide enough for really bad tuning, but wide enough for my 95 GTI on MS1 to get through MD state dyno emissions with flying colors without any significant tuning.
alfadriver said:so back to the basics- O2 + fuel = combustion. Without one of them, you won't have combustion- so lean, where there's almost no fuel is cooler, and rich where there's almost no O2 is cooler, too. But in either case, if you give it fuel when lean or air when rich- you will get combustion in the catalyst.
In an attempt to keep the education and clarification thing going, I know I've associated lean with hot, but perhaps that's just all about slow combustion and heating exhaust valves?
And to make sure I understand your last sentence, you're talking about a misfire dumping unburned fuel into a lean environment in the catalyst, or a leak adding oxygen to a rich environment, either of these causing cat-destroying combustion?
I would definitely install one of the modern metal core 300 cell cats in an old car to clean up the nasty stench. You’ll definitely get some good life out of it
I successfully used one in my FD RX7 running around 10.9-11.2 afr and premixed when on track for a good 5 years and about 35k miles and it was still functioning and not clogged when I removed it for a mid pipe with both a metal cat and muffler to quiet the car.
Here is an example of what I used:
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