High performance catalytic converters

[CarlC]

Let's discuss cats.

For the new project I have seriously considered using catalytic converters. It would be nice to have an exhaust system that is free flowing, sounds great, and helps keep the stink down. In the big scheme of things they are not that pricey.

The two that seem to be options are Dynatech and Magnaflow. I have not yet talked to Dynatech. When I talked to Mangnaflow they said the cats needed to be 24" past the collector. That does not seem right to me unless there is a restriction due to supercharging. A 3" i/o with a 9" body/13" OAL/4" round seem pretty popular.

So, has anyone done something like this? What did you do for fitment? Heat shields? Floor insulation? Placement? Back-to-back testing? Limitations?

Some basic tech might be helpful as well (two-way, three-way types, metallic, etc.)

[zbugger]

The only thing I know that would tell them that distance off the collector is for light off. Part of it is a timing thing, part of it is a temperature thing. If it is too close, it'll run too hot and burn out prematurely. If it's too far away, there's the chance it won't light off at all. That would make it useless. Three way is better than two way as it's what all late models use. My '77 would have originally come with a two way. You will want to insulate the floor a little better, and a heat shield bolted under the floor would probably be a good idea.

[chicane67]

Yup... having a 68 in California sure does suck.

I have always used Random Technologies. This here link >> yeah, this one right here << should be of some help in explaination.

My question to them would be... " what part of the collector, if it doesnt have flanges ?? From the merge or the end of the can ??"

Ya know... one day we'll quit playing phone tag and get to the discussion of months ago...

[CarlC]

One day Tom, one day... I'll be your way on Nov. 1

'68 is still smog testing exempt, so the cat deal for me is voluntary unless The Man makes me pop the hood. I'd rather fly under the radar no matter what resides under the hood.

OK, looking at the Random site. Round vs. oval. Ceramic vs. metal matrix. Advantages, disadvantages?

[68Formula]

[quote=CarlC]One day Tom, one day... I'll be your way on Nov. 1

'68 is still smog testing exempt, so the cat deal for me is voluntary unless The Man makes me pop the hood. I'd rather fly under the radar no matter what resides under the hood.
quote]

If you use a late model engine in an old car that previously didn't have a cat you have to install one? That blows. I imagine even without the cat, just with the modern fuel system and a few other goodies, it's probably twice as clean as original.

[CarlC]

State of California mandates that if an engine swap (newer engine into older chassis only) is performed that the emissions systems be transferred as well and that it pass the emission requirements for said engine in the chassis that it came out of. In other words, legally mine would have to pass the emission requirements, both visual and sniffer, for a 2002 Z28. Stupid law made by people without a clue.

Random says no problem with mounting their cats on the collector flange. Heat shields are a good idea but do not attach anything to the body. Metallic is the way to go for us. It is a more modern stainless steel construction type that is more robust than brittle ceramic cores.

The tech also said that basically the two primary methods to damage their cats is by a too rich AFR or by something mechanical hitting the interior. His suggestion was to build the engine, tune it, then install the cats. He did not know how cats would affect the tuned length of the collector.

So, how do cats that are mounted near the end of the collector affect the tuned length?

[68Formula]

They discourage the use of modern engines... brilliant!

So what consitutes a "newer engine swap?" What if I use a '75 block for a rebuild, do I also need a Cat? Or if it's out of a truck for the same year I don't?

[CarlC]

You can install an LS1 into a 68 Camaro but not the other way around. CARB will not allow putting a L78 into a newer WS6.

Engine family has a lot to do with swaps. If you are installing a rebuilt stock '79 shortblock into a '76 car with the same SBC family they are not going to bother you as long as the correct emissions equipment for your year car is installed. If the inspector wants to get really technical they can go after the cylinder head and intake manifolds, but most just make sure that the emissions equipment is in place and that it passes the sniffer. But adding an LS1 to an older car will bring out the red flags.

[redhead]

you are right on with the spun metallic over the conventional ceramic cat. Not only do the metal types take more heat abuse but they radiate less heat so many do not even include heat shields. I personally like magnaflows line of cats. I just can't figure out what makes the random cats so pricey. checkout www.performancepeddler.com - they are having a sale.

da.

[CarlC]

Agreed. The Magnaflow parts are much less excpensive.

Another booth to visit at SEMA....

[MonzaRacer]

what makes them expensive, actual certification for replacements(buddy had only 2 comapnies that he was told he could use(forget which state but it uses same specs as CA) and Randome was the top of the list.
Why they are expensive? Platinum,Paladium,Rhodium and a few "-iums" that i forget.
Have you heard, stock cats are getting stolen off cars for recycling.HeckI know of one used car lot that had every cat stolen one night,,,43 cars, no cats.
someone brought a lot of sawsall blades and batteries i guess!

[ehummelman]

This peaked my curiosity so I have been researching this some. It seems that the primary reason for not adding cats to older cars is because of their inability to run a stable stoichiometric air-to-fuel ratio. This is only an issue with carbureted engines; fuel injection with 02 sensors and computers can self-regulate. With a carb though, you will get raw and partially unburned fuel into your exhaust depending on the tune of the carb and even to load on it at times. This then combusts in the cat, causing it to melt the substrate and clog up, even causing a potential fire hazard. So on the surface it seems that unless you're running EFI with a computer and 02 sensors, it's a bad idea to add cats.
Re the comment from Random about the spun metal cats being more resistant to heat, I wonder if they are saying that this in effect overcomes the limitation I'm talking about or if they're just trying to sell cats. My primary concern of course is safety, with unnecessary replacement of these things when they burn up periodically.
I'd love to hear more from you guys about this, as I really would love to feel good about putting some on my car.

[SLO_Z28]

This peaked my curiosity so I have been researching this some. It seems that the primary reason for not adding cats to older cars is because of their inability to run a stable stoichiometric air-to-fuel ratio. This is only an issue with carbureted engines; fuel injection with 02 sensors and computers can self-regulate. With a carb though, you will get raw and partially unburned fuel into your exhaust depending on the tune of the carb and even to load on it at times. This then combusts in the cat, causing it to melt the substrate and clog up, even causing a potential fire hazard. So on the surface it seems that unless you're running EFI with a computer and 02 sensors, it's a bad idea to add cats.

^ Dead on right.


Price/quality you're not going to beat the magnaflow cats. You still need to mount them about 24-36 inches from the collectors.


I say don't do this swap, you're inviting trouble where there isn't any now. You're also creating a fire hazard that isn't on your car now. You're still not compliant with California Vehicle Code 27156(b) even with the cats.

[68Formula]

Also, 3-way cats without A.I.R. are most effective at stoich. Without an O2 feedback system, you'd really need to keep up with the tune, and you'd need a very accurate wide band O2 sensor to measure if you have it correct.

[Lance-W]

Carl,

Heads up last time I tried to buy an aftermarket Cat in California I discovered there was a recently passed law that made all aftermarket Cats illegal in CA. I got around it by having a friend in Washington state but buying or having a Cat shipped to California was not possible.

Lance