My cat. conv. is rattleing on my 98 SSEi.
So, I stopped by my local exhaust guy and he told me that he recomends a direct replacement cat instead of a Magnaflow Hi-flow cat. (and he is a Magnaflow dealer.)
He says that in his experience with Magnaflows they tend to fail emissions test more than 50% because they do not have as much of the iridium or whatever in them. (I live and work in emission testing required counties in NC.)
Bad thing is that the cost of the direct repacement cat is about $450.
Has anyone here had any problems passing emissions with a Magnaflow cat??

From what I've read, no one here has failed an emissions test because of a Magnaflow. A friend of mine runs one, and though we don't require emissions testing in IN, I figured I might let you know. Anyway, the mechanic can go poop on a duck because the 3800 was designed with emissions first. One of the easiest ways to get this knowledge is here, and probably 4th or so in line is Wikipedia, which tells you that the original design was sold because it wasn't needed and was then bought back during the oil crisis.

You have the second latest 3800 design, and few thought Bonnevilles would run quarter miles, get new cams, and so on... at least in the design process. Though your emissions test might get a little bit closer to the NO side, it'll be far, far below other cars, even with the Magnaflow high flowing design.

If your car is running rich, though, or you know why the catalytic failed in the first place, please take care of that problem as well. That should help not only emissions, but the longevity of this new cat and the engine in general. If you get a used Magnaflow cat, know that it'* illegal for an exhaust place to install it, though you can... Well, good luck, and you'll probably get lots of replies about the ones people here are running. My last bit of advice is to stick with your exhaust pipe diameter.

His fears aren't proven true here. And the magnaflow cats simply have a larger core area, which means MORE catalyst. Larger grid to increase flow, but the grid is complete. It'* supposed to be 10% over stock.

Magnaflow cats will NOT cause you to fail emissions testing. I have one, and have beat the **** out of my car before I got my test, and my results were highly impressive. I was even told my car burns as clean as a ULEV Civic.

HC: My reading - 12.0, Limit is 123.0
CO: My reading - 0.01, Limit is 0.69
NO: My reading - 372.0, Limit is 878.0
CO2: My reading - 15.09, Limit is N/A
Gas Cap pressurization: My reading - 26.90, Minimum is 6.00

Enough proof right there.

Make your exhaust guy a wager...

If the Magnaflow fails emissions, you'll come back to him for an OEM.
If the Magnaflow passes, he pays you back for the labor and parts

Thanks for all the info...
i just might take your advice and offer him that wager!
i value the info and advice i see here on the BC.