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Catalytic Converter Mini-Cat

Posted By: nikothenomad

Catalytic Converter Mini-Cat - April 27th 2019 3:29 pm

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.
Posted By: Wedgy

Re: Catalytic Converter Mini-Cat - April 27th 2019 4:12 pm

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... grin God Bless Texas!
Posted By: nikothenomad

Re: Catalytic Converter Mini-Cat - April 28th 2019 12:28 am

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!
Posted By: Reed

Re: Catalytic Converter Mini-Cat - April 28th 2019 2:29 am

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

Re: Catalytic Converter Mini-Cat - April 28th 2019 2:32 am

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!
Posted By: nikothenomad

Re: Catalytic Converter Mini-Cat - April 28th 2019 2:35 am

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.
Posted By: Reed

Re: Catalytic Converter Mini-Cat - April 28th 2019 5:36 am

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.
Posted By: nikothenomad

Re: Catalytic Converter Mini-Cat - April 28th 2019 2:33 pm

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.
Posted By: Reed

Re: Catalytic Converter Mini-Cat - April 28th 2019 4:51 pm

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.
Posted By: nikothenomad

Re: Catalytic Converter Mini-Cat - April 28th 2019 8:43 pm

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