Bringing the Cat back...enough is enough.

SquareRoot said:

Magnoflo. I did a LOT of research when I put this together. See post 41. I'll try to dig up the part number for that cat. It was slightly different from the rest in that it is CA rated. All that means is it has more catalyst and cleans the exhaust better than the same non CA version. Still a high flow unit.

Some pitfalls to avoid. It needs to be hot to work. The hotter the better. The closer you can get it to the Y-pipe flange the better. My first Y-pipe was 2-1/2" diameter. Big mistake. It shed heat way to fast, I remade it with 2" and the difference was noticeable. Ceramic coating or wrapping the Y-pipe would also help. Since I shi*t canned the headers and used the Holley Manifolds (ceramic coated) it solved the issue.

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bucket said:

I understand the small y-pipe and single converter, it makes sense for heat. What confuses me is why GM went this route on a lot of trucks/vans, but on others, they had large (like 2.75") pipes into dual converters, sometimes with one of the converters mounted all the way back by the muffler. Any idea on that?

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SquareRoot said:

Air injection played a role in some of the configuration as well as engine size. I'm sure a BB exhaust had more capacity to produce heat. They have electric heated convertors but I don't know when those started. Also the type of catalyst (ceramic vs metallic). But with what's available today in the aftermarket it's limited. Most new cars put smaller, single convertors on EACH manifold outlet flange. That's my best guess to your question.

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bucket said:

I guess I didn't go into enough detail, so here's this as an example. There were late 90's vortec 350 pickups with the little y-pipe and a single converter, but the very same engine in an Express van got dual 3" exhaust, and two converters that fed into a single muffler.

Same engines, same time period, but completely different setups.

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