catalytic converter question?

Can I just add a cat to a car that already has one to make a car more clean for emissions? I'm guessing it would need to be close to the engine to warm up properly, but otherwise is this correct?

Andrew

Why not replace the one that isn't working?

Catco converters do not count. Those rarely pass NOx even when new.

It depends on where you put it and how you drive.

If you mostly drive on the highway, then you can put it pretty far back and it will still do a lot of good. If your drive is mostly short distances, in town, then you are better off keeping them close.

And, as knurled metiond- quality does count- cheap means less precious metals (generally). Oh, one "counter" argument to that- if you are putting it downstream of your main catalyst- you don't need much to do a lot. So as long as you are getting good parts, you don't have to spend a fortune.

What were you thinking of doing?

Eric

One guy on the mercedes forum bought a very rare 560sel AMG to save from the scrap yard. He said it took 3 catalysts to pass smog, probably one on each down pipe then one on middle.

For my car passing the NOx test is all about tune, the car failed even with a new catalyst.

well the car is a 87 civic wagon with classic 80's solutions to clean the air if you know what I mean, I was thinking about devacing, losing about 3/4 of the random hoses, but I found that weber makes a kit to drop one of their downdraft carbs on it. I wouldn't be able to likely pass smog, I'm wondering if I add a couple more catalytic converters to the car if I had a chance to get closer to passing. Then again the car does only have 2 more years before becoming a classic, and its alot easier then to get away with alot more, classic tags and all, lol.

Andrew

a well tuned carb with the original cat should still pass.

i've been there and done that.

Remember Cats need to be placed close enough to the engine where they get hot enough to "light" off and do their jobs.

Indeed - as long as the ignition timing isn't out of whack, and it's not running heinously rich or lean, you should be able to pass with little difficulty.

If I can make an RX-7 pass with locked ignition timing, a tweaked carburetor, a half-plugged Catco converter, and no air pump or air control valve (*), you can get a Civic to pass.

(*) I stuck a Ford A.I.R. checkvalve on the ACV blockoff plate, and just let it breathe atmosphere. I have pictures, too.

In reply to digdug18:

If you are adding a second cat to a carbed car, then the benefit would probably be very limited. You are far better off spending the money tuning it to the limit of the limit, and go with that.

Carbs and catalysts are an interesting combination- to make them work, the best set up I've ever seen was ever so slightly rich + an air source for the exahust. Too rich and too much air, and those catalysts don't last too long. Interesting side note- Alfa did the mechanical injection + air pump from '75-'81, and on the dash of all the cars was a "slow down" light, that was connected to a thermister placed in the catalyst. Crude, but it worked.

If you were ever considering a MS install, then you could really take advantage of that kind of set up.

Anyway- before parting with all of the vacuum hoses, make sure you know what you are cutting off. While most of them wil be for fuel control and the carbs (which I'm sure you'll part with), some may be to power various things on the car- which you'll want to keep.

BTW, if you need a new cat- you can do a more modern "unversal fit' one, and it should work a lot better than the original.

Eric

Well the OEM cat is about 2" from the exhaust ports, and considering the age of the car and it having 180k or so on it, I'm guessing its either clogged or is getting there, and since they do NOT sell a replacement, I was thinking an aftermarket one, and either replacing the stock, or more likely, installing a 2nd cat someplace in the exhaust system.

I do know what lines go where and do what, as well that red pepper racing has some excellent write ups with multiple members willing to trouble shoot problems from half the country away. Then again the factory service manual I grabbed off ebay for $9, is worth its weight in gold, or maybe silver in today's market.

I would like to go with a weber carb, but it is lower mpg, though I think I can go from 44mpg to the 30's without too much or a problem. I do have a mpfi system that I could bolt on, but it would be more of a hassle then just getting a weber carb, though the fuel injection I'm sure is a bit cleaner and less work in the long run.

Andrew

that is for a 2wd one. not california legal now though

yeah mine is a 4wd, completely different design

i checked walker exhaust's site, the one they list for my car is not even a oem location for the cat, i only have one on the car, and its like the one above, but a different angle coming off the exhaust manifold, whatever, i'll figure it out

I don't know if this still works, but, in the '80s and '90s when emissions was such a pain, we ALWAYS, regardless of time of year, dumped at least one can of winter fuel de-icer/preventr in the gas. Cost all of $1.00-$1,50, the isopropyle type--not the cheapy(?) red plastic bottled variety. I had a car buring oil pass smog with two cans of that in the fuel. Floored me when the tech came back and said, "passed." And, one more thing, does PA allow you to modify the exhaust so you can add another CAT? Some states want everything to be OEM, no changes.

Some guy on the mercedes forum mentioned dumping alcohol in the fuel to pass smog so maybe there is something to that as Triumph said.

Some of the mid 70s model US mercedes have what are called thermal reactors on the downpipes under the hood. These are the predecessor of the modern catalytic converter. They get real hot like a catalyst and lucky for you they are put right under the hood where they cook all the vacuum lines. I don't think you can upgrade to a modern cat in california; you have to keep a flawed design to keep the state happy.

In reply to digdug18:

I guess I am lucky, I don't have to pass smog on cars that are not OBDII. There is just a visual inspection to make sure the emissions equipment is still installed.

I notice you're in PA. You should be able to adapt another piece of hardware into the system without running afoul of any laws.