The Stovebolt Site Forums The Shop Area Engine Shop catalytic converter installation

Has anyone experimented with the installation of a catalytic converter. Like others I would like to reduce the smell, it would seem the hotrodders are doing it mainly for that reason. I have a 1954 235 stock engine and would like to hear suggestions on such an application. Also any ideas on how to figure the right one to use, thanks

I have very little knowledge about converters, my thought is that it wouldn't last very long due to the "dirty" exhaust. Rich fuel mixtures and oil in the exhaust would probably kill the catalyst. If you try it, I would think the bigger the better, less restriction and more surface area.

For catalyst to work correctly the air/fuel ratio must be accurately controlled (the main reason that auto manufactures went to electronic fuel injection) and very close to stoichiometry which is probably a lot leaner than any engine calibration prior to the mid-70s. I suspect with a stock 235 a catalyst would become extremely hot as it burned all the excess hydrocarbons until it melted down and either plugged the exhaust or became a through pipe. I have seen exhaust systems run so hot that the steel is virtually transparent (well past red hot).

I had the same thoughts of installing one on my 250 engine. After talking with a few shops, they all said the same thing, the engine must be kept in tune very close to perfect or you will melt it down.
My solution was to install a AIR / FUEL ratio gauge. It uses a O2s in the exhaust to read the ratio. After a few weeks of tuning and a handful of different metering rods, I was able to eliminate 90% of the smelly exhaust, increase fuel mileage, and make for much better driving truck. I went from 14 - 15 mpg to 20-21 out on the highway, and that's at 65 mph! I will bet money, your running rich and needs more timing.
Joe

I was behind a friend of mine at night (we were double dating) and I saw a red glow under his car - (Olds 98 ~ 1988).

I pulled up close and saw the red molten metal dripping off in globs onto the street. It looked like lava!

Of course we all piled into my '68 Camaro and AAA came to get his Olds. The catalytic converter had plugged up and the exhaust system turned to molten metal.

Would solve the A/F ratio issue.....if only it were GM friendly.

https://www.holley.com/blog/post/up...te_1100_carb_with_modern_fuel_injection/

Wrangler, Go take a look at the HiPo forum and see the thread about Fuel Injected 216.

Someone has already adapted the Ford throttle body to a Chevy intake.

A fuel injection system doesn't know (or care) what vehicle it's installed on- - - -sort of like me using Ford 223 six pistons in a "235" engine rebuild that ends up with a 270 cubic inch engine. Whether or not it's an advantage over a properly built carburetor is still up for discussion.
Jerry

Guys, let’s get back on the PO’s question about catalytic converters.

A carbureted engine without sophisticated electronic mixture controls capable of adjusting the fuel mixture in a VERY narrow band of operating range (0.5 volts +/- 0.2 volt on an O2 sensor) several times a second CANNOT run a catalytic converter. The converter will experience a catastrophic meltdown within a very short time span.

Is that beck on topic sufficiently?
Jerry

The OP lives in Vancouver. There has been a rash of catalytic converter thefts there. They are literally ripped out causing all sorts of damage. I wouldn't want one.

That's a problem everywhere. Here in Atlanta they cut them off with cordless sawzalls and sell them for scrap.

Another good reason to drive antique vehicles.

Whether or not it is an "advantage" depends on what you are looking for in an induction system. Both have advantages and disadvantages, which ones are more valuable to any given person is up to their needs/desires.

I would echo the sentiment of several people above and recommend looking through the HiPo forum if you are actually interested. It has been discussed extensively with valid perspectives on both sides. I particularly recommend D B Cooper's build as a real world example with a lot of good info/discussion.

What about all of the carbed vehicles from the 70s and 80s that ran cats from the factory? We never had a catastrophic cat failure on our 84 C15 with the I6 in 150k miles. I can't say how effective it was after that much time, but it did not fail.

You can't get away with as rich of a mixture if you have a cat or it will cause the cat to fail, but a carb in good working order that is tuned to run close to stoich will work just fine with a cat.

Your C15 had an electronic controlled carburetor that used a computer to adjust the fuel mixture 10 times per second, probably a Rochester Monojet. It also had an O2 sensor that provided feedback to the computer once the sensor reached 600 degrees F. and started generating a signal.
Jerry

The final generation of Quadrajets were also electronically controlled in order to work in sync with the emission control systems.

Learn something new every day.

Your description of the operation of a catalytic converter is correct for reducing emissions. However, speaking about GM specifically (seems appropriate for this site), the first vehicles with catalytic converters were built in 1975. The first vehicles with an electronic carb (Rochester) didn't show up until 1981. So, six years of traditional carb/catalytic converter vehicles. I don't know the specifics for Chrysler and Ford. All the car companies had to have converters in '75.

You're absolutely correct that converters will melt down if given enough fuel and oxygen. Everyone has a story about having a converter get too hot. Running consistently a little rich or lean isn't too big a deal from a heat standpoint. But, if you cycle the two from one extreme to another things do heat up. For example, something like consistent cylinder misfires that dump unburned fuel and O2 down the exhaust pipe.

You certainly can install a converter on an older vehicle. Regardless of the potential emissions benefits, it'll definitely burn off any excess fuel that might be causing a bad exhaust smell. However, you'll also want to make sure it's installed in an area reasonably close to the engine but away from anything that can't handle some heat (like fuel lines). It would probably be worth adding some sheet metal heat shields to the floorboard to protect it from getting too hot as well.

"Your description of the operation of a catalytic converter is correct for reducing emissions. However, speaking about GM specifically (seems appropriate for this site), the first vehicles with catalytic converters were built in 1975."

I spent 30+ years teaching auto mechanics, including catalytic converter theory and operation, and the chemistry involved in the process. Of course I'm correct. The 72 Mazda RX-2 I bought brand new had a cat- - - -for about three weeks until I broke it in half during a hill climb on Okinawa.
Jerry

Getting the carb and ignition in order, so you don't run rich during a parade would be my first thought.

I don't do this as a business, but some of my friends with older vehicles often ask me to dial in their cars, cause I have a big ole Sun tester and some other fancy equipment.
Most of them are idling with way to less advance, and a carb that is already on the transfer circuit. Also the jetting is all over the place.
If you test drive them with an AFR gauge they run with 13:1 at cruising speed, which is insane in my book.

Frank

Like I said early in the thread, and what Frank is telling you, get an Air Fuel ratio gauge and tune the engine so it doesn't stink. I cleaned mine up, it doesn't smell any worse then my '03 Toyota I drive everyday. Mine cruises at highway speed with a ratio in 15 to 16-1 range and around town in the 14 to 1 range. Before adding the gauge, it ran great and I thought all was good till I add the 02s and the gauge. I very quickly figured out it was in the 12-1 range most of the time, that explained why it smelled. I run dual Carter W-1 carburetors and still manage to get over 20 miles per gallon at 65 miles per hour. I could run a converter with no problems and probably would if I came across one for a decent price.

As far as the older '75 and up GM cars not melting converters down, I would guess the pellet type of converters used back then could handle way more abuse than the modern honeycomb type. I live up on a summit about 20 miles from down town Kansas City, I can still picture the yellow/brown fog that was over the city from all the smog so the addition of a converter doesn't bother me one bit.

To be clear, you were incorrect about everything I quoted in my reply except the general description of how fuel control is performed with an O2 sensor to optimize catalytic converter performance for emissions reduction. You even came up with another example of a traditional carb/converter application from 1972 that didn't have this type of fuel control. If you just don't like the idea of putting a CC on a Stovebolt, that's fine. However, we shouldn't be making things up to influence someone else's decision. Stick with the facts and let people decide for themselves.


I'd agree with the general consensus that you want the engine and components tuned as well as possible to see if you can mitigate the smelly exhaust first. As mentioned earlier, if things are way out of whack with your fuel delivery and combustion, the converter not only won't help but will likely cause more problems.

If you still want to try something, Rockauto shows a replacement CC for 1978 250ci truck (Walker PN :15501) that doesn't appear to have any flanges. Looks like it could be clamped in place just like a muffler. Again, you'd want to locate this closer to the engine and have some heat shielding installed. Otherwise, it looks like it would be the least intrusive to try and easiest to uninstall if it didn't work out?

81tta, I’m not trying to start a fight but you have accused a member of spreading false information. It is very important that Stovebolt provides the correct information whenever possible. We are all aware of Hotrod Lincoln’s credentials as he posts them regularly. However we don’t know your credentials. It is only fair if you’re going to make such accusations that you provide the membership with your credentials so that good decisions can be made. Thank you.

No problem, Martin- - - - -I consider the source. I'm glad the forum has an "ignore" option.
Jerry

Hi Martin!

I don't want to start anything, either. I've tried to keep these replies respectful and without personal attacks with no name-calling or use of inflammatory terms. Although, I realize especially in this day, telling someone they were wrong, incorrect or mistaken can be seen as a horrendous personal attack that requires immediate cancellation regardless of whether they are correct or not. I don't think this is a place like that! I'm also aware of some of Hotrod Lincoln's history and abilities from reading posts on this site over the last few years. I'm very impressed with his work and knowledge.

I also don't want to make any more of this than necessary. I cringe a bit thinking anyone who called out something like this would be considered "accusing someone of spreading misinformation". I think it can be better termed as "telling someone they made a mistake". Or, maybe more precisely in this particular case "telling someone they exaggerated a bit by using a fact mixed in with some fictional hyperbole". Only after this is pointed out can we determine whether they really meant to say a catalytic converter added to a non-computer-controlled vehicle will "meltdown" because catalytic converters were only ever installed on computer-controlled cars. Or, that there were no trucks made with non-computer controlled engines/carbs and catalytic converters.

To that end, I'm happy to discuss further anything I stated if someone disagrees. I've tried to supply my own "evidence" of any corrections in my replies. If I'm wrong/incorrect, I'm usually happy to learn something new. Although, I'll freely admit I have an initial reaction of "I am NOT wrong/incorrect" when first presented with new information.

Now, to finally get around to answering your question.... I'm an electrical engineer (BS, MS with some PhD work) working at General Motors for the last 23 years. I'm currently working in the autonomous vehicle area. But, for my first 17 years at GM, I was responsible for developing engine controls and software for systems including gasoline engine torque estimation and control, fuel/spark delivery and exhaust after-treatment. The exhaust after-treatment work was done on "conventional" exhaust systems along with lean-burn/stratified charge engines. Here is a link to a patent our team received involving after-treatment for the lean-burn engine after-treatment system : https://patents.google.com/patent/US9714625B2/en . If you click on my name (Donovan) on that page, you can see the entire patent list for everything where I was involved. Since GM keeps a tight seal on their intellectual property, I don't have anything beyond the patents I can share for more detail.

While this list feels nice to document here, none of it inherently makes me immune to making mistakes. Regardless of education or experience, I get things wrong. Probably more often than I care to admit. Once of the nice things about forums like this is that information can be shared and discussed so we can learn more.

Finally, as I eluded to in my previous reply, I don't think Hotrod was specifically "spreading misinformation". I do think he was exaggerating when saying installing a converter on a vehicle without computer-based fuel control would cause a "meltdown". We know, and he confirmed with his own example, he was factually incorrect about catalytic converters only being used on vehicles with computer-based fuel control.

OK guys, you both made your points, it time to move on. Don’t force me to lock the thread.

81tta, thank you.

I have found all the comments interesting and they certainly give food for thought. Most informative.

Yes its true that they are being stolen from cars and trucks everywhere however to Gord and Fran that is not the topic of this conversation. Tell me something I don't know. Once again people are doing more hijacking on this thread, start your own