Catalytic Converters

[Guest dapy]

Not sure when the government mandated them but my 1982 Avanti II has one and my 1989 convertible HAD one.

As a product of new mufflers in the '89 there is now an exhaust smell when the car is stopped with the windows open. The exhaust repairer pointed out that at some point the original catalytic converter had been removed and the fumes that it absorbed was what I was smelling. The solution is a new converter, but that will reduce engine performance.

So the question is...will I notice a difference? The new converter installed price is modest. The fumes are tolerable.

Edited March 14, 2013 by dapy

[billy]

Not sure when the government mandated them but my 1982 Avanti II has one and my 1989 convertible HAD one.

As a product of new mufflers in the '89 there is now an exhaust smell when the car is stopped with the windows open. The exhaust repairer pointed out that at some point the original catalytic converter had been removed and the fumes that it absorbed was what I was smelling. The solution is a new converter, but that will reduce engine performance.

The 1989 catalytic converter has been removed but you still smell it ? Maybe the mechanic put it in the trunk. When mine smelled I switched to a different gas station, try gas without methanol. bill

[Gunslinger]

Most, if not all American cars got catalytic converters starting in 1975...some imports didn't for several years as they were still within emissions limits at the time. I can't say for sure Avanti Motors started installing them in 1975 but since GM did, I would think Avanti Motors did as they piggybacked on GM's certifications. That also assumes Avanti didn't receive a waiver for a period of time like they did on some items previously.

I don't understand how you can be smelling accumulated fumes from a removed converter. Maybe you have an exhaust leak somewhere in the system. New mufflers and pipes are often coated with a preservative as a rust preventative...this burns off when they're installed and as they heat up and they will smell until the coating completely burns off. Your problem may be as simple as that.

You can buy performance catalytic converters that are very free flowing compared to earlier designs...they're not too hateful in cost either. Look at Summit Racing...they carry them. As long as your state doesn't require them on older cars you're ok with not replacing them.

[Guest dapy]

My exhaust guru said that if I had a catalytic converter I would not smell exhaust fumes because the converter "cleans" those emission fumes. We have rechecked and there are no leaks anywhere in the system.

To keep this simple...Would I notice a performance difference if I installed a new (cheap) converter?

P.S. How do I find gas without ethanol?

[Gunslinger]

That's a new one on me...that the cats will clean the exhaust odor! I'm not gonna say there may not be truth to that but I've never heard that claim. I remember the days when converters were first installed and unleaded gas was mandated that the result was a putrid smell like rotten eggs from the exhaust. That doesn't seem to be a problem now but whether that's due to changes in fuel formulations or improved converter technology is an open question.

I doubt if you'll notice any difference in performance if you use a performance catalytic converter like Magnaflow sells.

For finding non-ethanol gasoline try this website http://pure-gas.org/. It will give you a list for such gas stations in the US and Canada.

[Skip Lackie]

I think your exhaust guru may be partially correct. The catalysts in the converter serve to convert unburned hydrocarbons and carbon monoxide into water and carbon dioxide. That's why modern cars have an oxygen sensor(s) to keep track of the amount of free O2 in the exhaust, as plenty of that is needed to combine with the HCs and CO. CO is odorless, so you're not smelling that -- but most HCs do smell, as do some of the unburned additives that the oil companies add to improve performance. So I suspect that installing a modern catalytic converter will reduce some of the stink.

The earliest cats really only worked on the unburned HCs, but the modern ones also complete the oxidation of CO and do some magic with the oxides of nitrogen as well. And the modern fuels contain less phosphorous, which results in a reduction in the rotten-egg SO2 smell.

Just so you know: you are technically in violation of the Clean Air Act and EPA regs, which require a functioning catalytic converter on the vehicles as described by Gunslinger. Not suggesting that you are likely to get caught (or that you even care), but cars built with cats are required to remain equipped with them. In many states, cars with antique/historic plates are exempt from inspection, but they still are supposed to maintain all original emissions equipment in operating condition. (Lecture is now over.)

[Guest dapy]

Skip,

I get it. Question remains whether one might notice a performance difference with and w/o a cat.

Related question...is there a quick visual clue to whether my 1989 Avanti (with Caprice frame and engine) is a 305, or 350 Police Special?

[Avanti83]

Skip,

I get it. Question remains whether one might notice a performance difference with and w/o a cat.

Related question...is there a quick visual clue to whether my 1989 Avanti (with Caprice frame and engine) is a 305, or 350 Police Special?

I don't recall the years but look at the top of the block on the left rear of the engine just behind the heads. They had a 5.0 or 5.7 cast into them.

Bob

[Gunslinger]

You can identify exactly what engine is in your car by copying down the ID stampings in the machined pad just forward of the passenger side cylinder head. You can look it up online or post it here and we can find it for you...engine size, where it was cast, what car it was intended for, etc.

As far as the performance differences between with and without a cat, I doubt if your "seat of the pants" dyno will be able to tell the difference even if it could be measured on a dyno. Modern cats are quite free-flowing...especially those designed with performance in mind. It's when one gets plugged from miles and age that performance lags.

[Skip Lackie]

Agree with both of Gunslinger's points. A modern catalytic converter has to be pretty well plugged before you would notice much change in performance. We had one fail on a 350-equipped Chevy Tahoe on the Jersey Turnpike. It first manifested itself as poor acceleration, but within 50 miles, it was so constricted that the truck was unable to get over 50 mph on the flat. I note, however, that the Tahoe had 160K on it at the time -- well beyond the warranty on emissions equipment.

I think the early cats were much more prone to both failure and a reduction in horsepower, and this reputation has become an urban legend. Several years ago, I bought a used 78 El Camino from which the previous owner had removed the cat. In order to pass inspection, I bought a low backpressure rebuilt cat. No change in performance, but a definite reduction in emissions.