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Old 02-14-2014, 03:19 PM   #1
qdeezie
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Who makes high flow (stock replacement) cats for our cars and what classifies it as high flow?

So, I have given up on trying to replace the crankshaft sensor on my car without removing the cat, so I'll be pulling the cat off this weekend and reinstalling it with anti-seize compound on the threads of every bolt, the O2 sensor fittings and the EGR fitting so that I will be able to easily remove it again in a couple of years whenever the cat goes bad.

With this being said, I have seen people mention high flow cats for our cars.

My question here is who makes them?

I assume the regular stock replacement Magnaflow is a high flow. That assumption is just off of reputation alone. I have done nothing to confirm this.

How would I know if a cat is high flow or a regular aftermarket (stock) replacement? Would one telltale sign be mandrel bends vs compression bends?

Are all stock replacement converters for our cars classified as high flow because the stock ones at the time the car was built were just that restrictive?

I'm comparing apples and oranges here, but on my 1990 F150, pretty much anything flows better than the stock unit, so my definition there is anything other than stock. Is that the case here?

Are there any high flow cats that turn the CEL on due to it and the downstream O2 sensor not seeing eye to eye?

I don't plan on buying a new cat soon because my car runs well, but I'd just like some clarification around exactly what is considered a high flow cat for our cars.


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Last edited by qdeezie; 02-14-2014 at 03:32 PM. Reason: clarification
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Old 02-14-2014, 03:41 PM   #2
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It is surely a misleading term and under-explained.
Basically 'high flow' is a higher cell count than stock. It should also be larger inlet and outlet, but that isn't the case for direct stock replacement.

Lets say the factory catalytic converter is a 180 cell count. A high flow version should be something like a 220 cell count.



So the holes through the media (cell), there are more of them.
Now you see the catch 22 here I'd bet. Well is the cat physically larger? No. the holes are smaller and the wall thickness is reduced.
That also means the cat is more susceptible to heat and impact. If the cat gets too hot (and I'm talking a couple thousand degrees F) it can break apart. If it's hit hard it can also break apart.

IMO, if you keep the cat and want better flow, you shouldn't skimp and avoid ebay at all costs. Don't expect to get one cheap. But revel in that it will be quality and work as intended.
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Old 02-14-2014, 03:48 PM   #3
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[QUOTE=iminhell;5477249]It is surely a misleading term and under-explained.
Lets say the factory catalytic converter is a 180 cell count. A high flow version should be something like a 220 cell count

Mayee it's just me, but I believe that is a 42 cell count differential!
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Old 02-14-2014, 04:13 PM   #4
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(I think the cell count was more for illustration than "specification".)

High Flow, like "High Performance" can be in the eye of the advertiser using the words, so if you want something that works well iminhell's suggestion of name brands makes sense. Cheapo's could be anything....

At a glance, CFM offers the magnaflow "high flow" unit for the Zetec the OP is inquiring about. That should function like stock & flow a bit better.

Looking a bit further, they offer both "Race" & "stock replacement" types for the SVT. So if an SVT header is installed on the Zetec, there are a couple choices of type. Choosing between those would be more of a debate since the race version is less likely to "pass" as a stock replacement and would differ quite a bit more in function.

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Old 02-16-2014, 08:34 PM   #5
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I doubt the FSWerks part necessarily counts as a cat but it goes where the stock cat was. On their site I think they say it's a muffler, and that's essentially what it looks like, it's a straight through pipe with a can around it. But if you want a high flow cat replacement I don't think you could get much higher flow than that lol
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Old 02-16-2014, 09:00 PM   #6
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factory cats since like the 90's have had the capability of about 150% flow... meaning everything is "high flow".

sorry I don't recall the exact details... been awhile.
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Old 02-16-2014, 09:25 PM   #7
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It is actually the reverse of what iminhell said. Advertised high flow cats are typically 100 or 200 cpi cats. OEM would be 400 or more. The more cells the more restriction.
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Old 02-16-2014, 10:23 PM   #8
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I got mine made all stainless with a stainless vibrant 200 cell high flow cat. For Svt headers. The guy who built it for me also made an elbow for the second o2 sensor so it wouldn't be in the main stream of the exhaust and it wouldn't throw a code.
If you still have the stock zx3 header even if you get a high flow cat you wouldn't see much of a difference in power maybe a couple HP's. But I've seen a couple around i know magnaflow has one. But if i was you I'd get an Svt header and then a high flow cat for more noticeable gains.
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Old 02-16-2014, 10:25 PM   #9
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