I feel this warrants its own thread. Perhaps this can become a sticky or Tech Info article in the future. I do not believe we have readily-available information on properly choosing a catalytic converter for our cars, and it would benefit myself and others to have a healthy conversation where we can discuss what we know about converter size in relation to engine displacement/output.
I just got off the phone with a Magnaflow tech adviser. I asked him which cat converter would be appropriate for a '97 Bonneville application, and he recommended a 94000 series that is rated for up to a 378 CID motor. I thought this was a bit unusual, because a 3800 only displaces 231 cubic inches, and there are smaller Magnaflows that are rated for less displacement.
I asked, "Wouldn't a larger body restrict my exhaust more than necessary? I'm only running a 231 CID engine." His reply was that there is a negligible difference in flow between larger and smaller models, and that a smaller one "would get too hot" on my car. His opinion was that the Bonneville needs a 94000 series.
Example: Here is the information on the Magnaflow 94000 series converters
...and here are the stats for the 91000 series converters
As you can plainly see, the 91000 series should be able to handle our engine displacement. However, the weight rating could become an issue. It would be quite easy to exceed 4500 lbs. with a full load. Perhaps this is why the larger 94000 series was recommended?
The only troubling factor is that CarSound'* website (when the server is actually up
) recommends a 91000 series cat for a '97 Bonneville, which is contrary to the Magnaflow tech'* advice. I'm not sure what to believe, whether a larger cat actually flows the same or not. My fear is that a large converter would be overkill, and would keep things from flowing efficiently. I would like to understand more about catalytic converter selection.
Another topic that should be addressed is O2 sensor placement. Magnaflow does not recommend a converter with an O2 sensor bung for our application, because the stock O2 installation is in the exhaust pipe. Is this valid advice, or is it easier to order a converter with a bung?
Let'* talk about this kind of information and decide what it means for us in choosing a high flow catalytic converter. I want my exhaust to flow optimally, to maintain legal emissions standards while allowing the most power in a given setup. I want to spend my money on the right product the first time around, so that I'm not forced to buy another unit when I discover that I purchased the wrong item initially.
I'm eager to see what we can find out about this topic!