98 RAM 2500 360 gas single converter. I need to get the converter replaced. I believe there is nothing left to it. Just hollow. The truck has 178k on it and it was probably the original converter.

My question is.. With the converter being hollow would I loose backpressure and horsepower? Or would I actually gain a few horses because it would basically be similar to a high flow cat?

Its also running very rich. (no visible smoke) just very rich smelling.
I would assume that to be the O2 sensors sending the wrong signal to the PCM because of the converter being junk, so in turn that is throwing off the air fuel ratio? Does that sound about right?

I do have a check engine light and its "catalyst below threshold", so I'm assuming the converter.

 

Welcome to the forums!

The air/fuel ratio will have nothing to do with the converter.

There are two sensors (unless its a California truck). The pre-cat or upstream sensor helps the PCM with air/fuel management. Nothing to do with the cat. The second sensor is behind the cat, the post-cat sensor or downstream sensor. All it does is tell the computer if the cat is functioning properly. That CEL looks like it was triggered by the downstream sensor. You can replace the front O2 sensor if you wish to try and fix what you think is a rich condition, but it will not effect the converter at all.

If it is hollow, if the CEL doesn't bother you, and if you don't have emissions testing in your area, I'd leave it. The whole backpressure thing doesn't really apply to these trucks (backpressure is the incorrect term for it anyway, but thats what everybody calls it) unless you get quite a bit larger than stock exhaust pipes.

If the CEL bugs you and/or you have emissions testing, I'd get a Magnaflow to replace it. All Magnaflows are high flow converters.