Cats with Superchargers

bcfromfl

Thanks both of you for the input. While researching this a bit more, I came up with this interesting tidbit I'd never heard of before:

How to Break in Your Cat

A replacement catalytic converter needs to undergo a proper break-in procedure to ensure that it will continue to work as it should, and deliver the required emissions reliability and long service life. If the converter is not warmed-up properly (broken-in), the substrate inside could be adversely affected and eventually cause the converter to fail prematurely.

A problem typically occurs when a shop installs the converter and immediately returns the vehicle to the customer without breaking in the cat. The customer drives away and runs the car for a long distance or lets the vehicle idle for an extended period of time. Under these conditions, the matting, which is intended to secure the substrate, will not expand properly and hold it in place.

Converter matting is made from a mineral called vermiculite, which is held together by a fiber mat and an organic binder. This matting is wrapped around the converter’s ceramic brick. The matting is installed in the converter in an unexpanded state. During the first heat up, the fiber mat and binder burn off, and the matting actually gets looser before it expands to fill the converter cavity and hold the ceramic brick in place. If that warm-up is not done properly, the brick can come loose and get damaged. That rattle you might hear inside the converter shell is a sure telltale sign of this problem.

Warm Up That Cat First

The best way to avoid this service issue and potential warranty problems is to include the warm-up period as a key part of your overall converter installation procedure. This heating cycle will allow for correct matting expansion.

Here are suggested steps for a proper break-in or warm-up:
• Start the engine but do not touch the accelerator pedal.
• Idle the engine and allow it to warm up slowly.
• After five minutes, increase engine speed to 2,500 rpm.
• Hold engine speed at 2,500 rpm for two minutes.
• Allow the engine to cool down.
• Road-test the vehicle to confirm correct installation.

Hmmm. Could it be possible that folks upgrading didn't properly break-in the HFCs after replacing?

bcfromfl

Here's more info I just found on a Mopar forum, that corroborates what Topz says:

That's refreshing to hear; as it's been an ongoing poor excuse to remove CATs as opposed to properly tune for them.

CATs don’t commit suicide on their own, they get murdered by incorrect A/F ratios that are either too lean to too rich. Too lean, and the platinum-enhanced element overheats and melts the nickel that is used to furnace-braze the rolled up element to itself...and before you know it the element separates under exhaust pressure and breaks up causing some of its parts to exit the exhaust system. Or worse, get stuck further downstream causing a major blockage. Too rich simply puts too much unburned fuel into the element itself, and because they are designed to operate so hot they glow, they then catch on fire and melt. Again, blockage becomes a real concern. These are tune issues…not CAT issues.

The other thing that gets swept under the rug is that increases in engine output means there is significantly more latent heat produced by making that extra HP / TQ. Catalytic convertors have thermal ratings, in other words, they all have a maximum rating to process exhaust gases. So the solution when increasing horsepower and torque...is to increase the thermal handling capabilities of the catalytic convertors.

It's real simple...you buy bigger CATs to deal with bigger engines / more thermal output.

KOOKs (manufactured by Global Emissions Systems Inc. here in Canada) offers quality CATs and are thermally viable up to ~700HP, their GREEN version is good to upwards of 900HP (both are 300 cell/inch). They are not the only supplier, Vibrant btw is another good example manufacturer that offers high-performance CATs of various thermal capabilities - right over the counter. FWIW, I would not touch any of Magnaflow's CATs with a ten foot pole.

This is a link to a manufacturer of "racing" cats: HJS FIA-Approved Motorsport Catalysts but I bet it would be a major job to rework one of these to a Z undercarriage.