Bringing the Cat back...enough is enough.

[bucket]

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.

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?

 

[SquareRoot]

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?

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.

 

[bucket]

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.

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.

 

[dd1990]

On a side note if anyone is looking to reduce emission exposure from their vehicle a working PCV system is key. Engine blow-by can be worse than anything coming out of tail pipe, even catless.

 

[SquareRoot]

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.

Mongo not that smart.

 

[brooksman9]

I think I have a 2 1/4" y pipe that goes to 2 1/2" pipe to the muffler ans out the back driver side. Someone probably cut the exhaust in front of the cat and replaced the rest. I'll have to measure it all and see but plan is to add cat right behind the y pipe and leave the rest. Saw a couple of magnaflows right at $100. The smaller 8" version and the larger 13" one. Probably choose one of those and see how it goes.

 

[SquareRoot]

Go as large as you can fit.