Vannin' Home Forums Dodge Performance (Dodge) Catalytic Converter Mini-Cat

Any of your B250 owners out there have the second smaller mini-cat (I think they also called it a mini-ox) right off of the driver's manifold?

Trying to figure out if we replace the big (main) cat do we cut this one out or leave it or try to find a replacement which has proven to be very difficult.

Neither my '88 with the 5.2, or the 94 with the 5.9 have that upper cat setup, Nicole. Both are California smog, and both are fuel injected. The B250 5.2 has an air pump, With the 5.9/Rochester, I'd wager to say exhaust tubing from your manifold flange to the exhaust merge is fine, and isn't going to harm the motor any.

Depending on your area of registration, you may or may no have a smog check. If so, I'd bet It will still pass with the main Cat only. They aren't going to pull a doghouse...
Your Van will love a free flowing exhaust with a decent flowing cat, and muffler.

The 454 Chevy setup with the rear pancake cat was ridiculous... God Bless Texas!

Thanks, Wedgy. We aren't sure if the mini-ox cat is clogged yet or not and the larger cat only shows problems when we get to grades out west so must get clogged as it tilts.

This morning before hitting the grade changes I drilled a hole in the pipe pre-big cat and am happy to report that I was able to not only maintain my speed up the grade but also increase speed while on the grade. That is so much better than the slow decline in speed we were getting as we climbed the mountains.

I am thrilled with the improvement but still feel like she is pushing against a wall (albeit a much smaller wall). So, Tomorrow a.m. before we hit the road I will drill the current hole before the big cat larger (or add another one - still deciding) and then also drill one before the mini just in case it is stopping flow from the driver's side.

Then we'll see what we get.

Since I have seen obvious improvement already and expect more with the additional holes I do believe that I will definitely replace the cat and it looks like eliminate the mini. I have yet to find any solid documentation on what it did or how it was constructed (honeycombed or not inside).

Since the state I am currently registered in as well as any state I may register it in the future requires emissions or any inspections for that matter I am not concerned so much with how it 'should' be set up so long as it improves the way she functions when climbing these mountain grades and takes any undue stress off the engine that backpressure is causing.

Well, we'll see what happens when I drill a few more holes tomorrow!

Modern highflow three-way catalytic converters flow better and catalyze better than the old 80s designs. Be sure to get a three way, though.

Reed, thanks. That brings up a great point. How would I know if I get a decent one? I mean I see anything from universal to direct fit and the price variants are ridiculous!

and.... most of them come with that tube that goes back to the air pump which I've deleted so I assume that tube comes with a cap too but am not sure.

If you have eliminated the air injection pump, then the chances are high the original catalytic converters have failed. You want a universal high-flow three-way catalytic converter that does not have an air injection tube. I am running exactly that on my 89 Ford van. A good one should be $100-$120. Summit racing sells them, you might be able to find one on rockauto using a part number from Summit.

Although I know the pump deletion would have brought on a faster failure the original actually failed long ago before the deletion of the pump. But wasn't causing problems on the eastern flat roads so we just left it as it was.

Not until we got back to the western mountains that we noticed a problem going up the grade. Guess there is some matter in there that makes its way to the bottom on flats but going up a grade somehow gets picked up and blown against the exit creating back-pressure.

I'll look for the one without the air injection tube. Other than the place where the tube would attach are they designed differently? Meaning, given my situation I may only have the option to pick one up in store as I do not have an address to ship one to. If all I can find is with tube do you know if it would matter if I just blocked that off or would it not work the same?

Thanks.

The catalyst material is different, as is the designed operating temperature. Before I had my current catalytic converter installed, my smog pump failed so I removed it and capped the line to the old catalytic converter until I could get to it. In that time the old catalytic converter overheated and cracked.

Modern catalytic converters have the catalyst matrix in a honeycomb structure. If the catalyst overheats the honeycomb can collapse and cause a blockage. The problem you will have is the fact that your engine still uses a carburetor. The fact is that carbs don't control the fuel mixture tight enough and allow the exhaust gasses to have too many unburned hydrocarbons. This leads to reduced lifespan of the catalytic converter. Having a functioning air injection system helps with longevity of the cat, but it won't last long behind a carbed engine.

More info than you ever knew existed about catalytic converters:

https://en.wikipedia.org/wiki/Catalytic_converter

What you can do to get a good, cost-effective, durable cat(s) is to order (or tell the mechanic to put in) a "California-legal" converter. Those are the good ones that last, and they can be ordered in any state. The catalog of Eastern Catalytic, a reputable maker, is HERE, and they show listings for your van. They have universal and direct fit, with and without the air injection tube. The rear direct fit cat for your van is part no. 645332.

I don't know what diameter exhaust you are running, but CLICK HERE for a pre-filtered list of the catalytic converters offered by Summit. You can further filter by diameter and inlet size, cost, etc... I would stick to Wlker or Catco for brands.

Thanks Reed! I'll look into all of that.

The latest update...

Finally managed to get the main cat (we've got a mini-ox and a big cat) cut out and explored.

Link to a photo of what I found in that...

https://photos.app.goo.gl/QCQwMcCegFj5Lywx8

With some pieces missing I decided to shine a light down into the exhaust and... there they were!

https://photos.app.goo.gl/m1wmjotyKcJeY8w96

All pieces have been recovered.

https://photos.app.goo.gl/kPHJNXo711isErbX9

The ones that had spent some time in the exhaust were a little worse for wear. The ones out of the cat you could actually still see through them but there were lots of deposits on one side of them.

I was surprised to only find one catalyst block inside our cat though. I thought most had two at the minimum even back in 88.

Hope the pictures work. First time trying this!

Now I am trying to decide if I should keep the original exhaust. 32 years old stamped with mopar symbol. Been working just fine.

Thoughts?

The mini converter has a low precious metal load and don't hold up well to a heavier gross vehicle weight, if going dual they work ok for a while but smell to high heaven when hot..

Astro... so then I should check that the mini is not also broken up and possibly blocking flow?

The mini/ cat is prone to melting and fragmenting into rear converter blocking exhaust flow. The pre should be removed and replace both with just one high capacity converter. AP part# 602006 will work, what I was saying if you dual it out you can use 2 mini converters one on each side. Thunderbolt part# 410225

That front pre converter was a stupid design being it was on left side only and the y pipe goes in the top of this dinky converter and out the rear in a tight L 90 degree bend. Depending on the state you live in that pre needs to go.

Interesting, Astro.

I always wondered about the mini and why it was located where it was. Have also seen the set up where there are just two mini's one on each side like you say.

Tomorrow should be drier so I'll probably try to see if I can get a rod of some kind and gently send it up the pipe to see if I hit 'anything' in the mini-ox or if it is empty at this point.

If it is empty, I will leave it as it doesn't leak and seems small enough to not be harming anything if the exhaust just blows through it. Then work from that point on to determine my set up.

Been debating keeping the original muffler. I think that I will. After all it still works just fine and keeps things plenty quiet.

Well, finally had time to get to the mini-ox and yes, indeed it is empty! So, after I get the brake master back on I'll get to start her up and enjoy NO PIPED ANNIE for a few days before getting the exhaust all back together!

No piped Annie! Y'all are scaring the wildlife .....

https://www.youtube.com/watch?v=9d_7pJS19xw

Couple of grown kids ........

Yeeeehaw..she is loud and proud..and slightly illegal.lol

Ha Ha! Thanks for adding that CatFish! You must have heard us all the way up in your part of the state. LOL! Boy did we enjoy that for the short time we were able to.

What did you say? Huhh?

Astro... LOL! When I got her off of the slow speed back roads and onto the highway I had to wear my earplugs!

Like riding a loud bike without a helmet. Hey doc what's this ringing in my brain???