Downstream Cats: 100cell vs. 200cell. vs. 300cell?

[S4Gibbs]

Looking for any opinions/experiences on which downstream catalytic converters you're running. Especially any experiences with how much they reduced your rasp/sound, eliminated stank, and roughly how many miles you've run them for.

Any information greatly appreciated.

[RoofRails]

Looking for any opinions/experiences on which downstream catalytic converters you're running. Especially any experiences with how much they reduced your rasp/sound, eliminated stank, and roughly how many miles you've run them for.

Any information greatly appreciated.

I wouldn't bother putting anything less then a 300 cell in there. If I would have had the funds at the time, I would have sprung for the 400 cell GESI cats. The smaller cell counts will not catalyze as well which equals more stink and more Trumpet noise.

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[Fresh.S4]

I wouldn't bother putting anything less then a 300 cell in there. If I would have had the funds at the time, I would have sprung for the 400 cell GESI cats. The smaller cell counts will not catalyze as well which equals more stink and more Trumpet noise.

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200-300 cell works perfectly fine. dont over pay for gesi. its all metal substrate so any of the generic name brands (mf, flowmaster, etc) will work.

[ccssid]

200-300 cell works perfectly fine. dont over pay for gesi. its all metal substrate so any of the generic name brands (mf, flowmaster, etc) will work.

I wouldn't bother putting anything less then a 300 cell in there. If I would have had the funds at the time, I would have sprung for the 400 cell GESI cats. The smaller cell counts will not catalyze as well which equals more stink and more Trumpet noise.

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Those replies really hit the opposite ends of the spectrum. I tend to agree with RoofRails. It really depends on what goals you are trying to achieve. I look at it as you get what you pay for. It is the precious metals content that make up the intrinsic value of catalytic converters. Some have more than others. I sometimes wonder if the inexpensive units have any at all.

[RoofRails]

Those replies really hit the opposite ends of the spectrum. I tend to agree with RoofRails. It really depends on what goals you are trying to achieve. I look at it as you get what you pay for. It is the precious metals content that make up the intrinsic value of catalytic converters. Some have more than others. I sometimes wonder if the inexpensive units have any at all.

My 300 cell Non EPA have very little precious metal load in them, and the cost reflects that. They need to be good and hot to catalyze properly. If I'm sitting idling for an extended period of time, they will cool off, and the smell will get strong. A 100 or a 200 cell cat will cool off quicker and have even less surface area where the process takes place than a 300 or 400 cell cat. That isn't debatable. The same thing goes for the sound. The more dense the substrate the more the exhaust note will be tamed down. I like to give accurate information and try to answer the question presented instead of throwing out broad statements like " don't overpay for GESI."


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[Fresh.S4]

Those replies really hit the opposite ends of the spectrum. I tend to agree with RoofRails. It really depends on what goals you are trying to achieve. I look at it as you get what you pay for. It is the precious metals content that make up the intrinsic value of catalytic converters. Some have more than others. I sometimes wonder if the inexpensive units have any at all.

hes not wrong about his "300" cell because he has them.
i have "200cell". they both do exactly as intended, the biggest difference is the price point.
i also dont have smell issues in the cabin; maybe a small amount if i got down by the exhaust, but in no way does it smell like a straight pipe.
i dont know the science behind heat cycles but makes sense about cooling down, i guess.
i do agree about the noise filtering. more cells will help out much better.

in the end we all believe what we have is to be the best. you as the consumer take the information and formulate whats best for you. i am here to just inform the masses that you have options, many of which dont require the most biggest baddest most expensive things.

[S4Gibbs]

Thanks for the inputs y'all.

Bit of info for anyone lurking this thread that might not know: The terms "300cell" or "200cell" is actually car community shorthand for 300cpsi(cells-per-square-inch). So when trying to evaluate the total amount of restriction/filtering a cat provides, it may be beneficial to also consider the cross-sectional area of the catalyst body you're buying.

(Ignoring the thickness of the shell/tubing)
3.0" body = 7.07sq-in
3.5" body = 9.62sq-in (36% more surface area than 3")
4.0" body = 12.57sq-in (78% more surface area than 3", 31% more than 3.5")
(OEM 3.0T Cats)5.0" body = 19.63sq-in (178% more surface area than 3", 104% more than 3.5", 56% more than 4")

In terms of longevity, has anyone ever had a 200cpsi, 300cpsi, or any downstream cat for that matter, fail on our platform? If not, sharing how long you've successfully been running your downstream cats + brand would be awesome.

More importantly, some real math for today: a 14" pizza has 1/3rd more pizza than a 12"

[Nillious]

I’ve always wondered if you could locate stock cats downstream. Wouldn’t be any louder and should still pass emission testing but also would not meltdown.

[S4Gibbs]

EDIT: Sorry, misread your post Nillious. Not a bad idea about relocating the stock cats downstream. As long as there's enough clearance, it would just take some nice fab work to install and get rid of the nasty bends the stock cats have.

However, nothing makes a cat thief happier than being able to quickly steal a German performance car's OEM cats.

[JRYtheS4]

EDIT: Sorry, misread your post Nillious. Not a bad idea about relocating the stock cats downstream. As long as there's enough clearance, it would just take some nice fab work to install and get rid of the nasty bends the stock cats have.

However, nothing makes a cat thief happier than being able to quickly steal a German performance car's OEM cats.

Good point, except I'm not sure how you could fit under an S4 to steal them!

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[S4Gibbs]

Good point, except I'm not sure how you could fit under an S4 to steal them!

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True. Who needs those expensive cat theft cages if you just slam it and park with frame on the ground!

[ccssid]

True. Who needs those expensive cat theft cages if you just slam it and park with frame on the ground!

Let the cats get stolen.....less work to install the test pipes.

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[f4m0u5]

i had a set of "MagnaFlow Universal Catalytic Converter Standard Grade Federal/EPA Compliant 59955" down stream in my dp a6.

one of them failed and clogged the exhaust and amlost blew my engine.




as of now im not runing cats because im scared this will happen again.

i may give those gesi non epa 300 cells a try. ( can get a pair as low as $350 shipped)

[S4Gibbs]

i had a set of "MagnaFlow Universal Catalytic Converter Standard Grade Federal/EPA Compliant 59955" down stream in my dp a6.

one of them failed and clogged the exhaust and amlost blew my engine.

as of now im not runing cats because im scared this will happen again.

i may give those gesi non epa 300 cells a try. ( can get a pair as low as $350 shipped)

Wow you got lucky man. What symptoms made you look inside your cats to see if they clogged? Also where downstream did you install these cats?

[f4m0u5]

Wow you got lucky man. What symptoms made you look inside your cats to see if they clogged? Also where downstream did you install these cats?

Thwy were installed roighly where the stock resonators are but in cuatom made downpipes.


I was runing into an issue where thencar would loose power and cel for random misfires. and in logs it showed 1 banks o2s to be way different then the other banks o2.


i belive roof rails helped with seeing that in log.

[Fresh.S4]

how long did they last?

do you have a crackle tune?

how are you shifts? like up to and past redline?

[f4m0u5]

how long did they last?

do you have a crackle tune?

how are you shifts? like up to and past redline?

no crackle tune, lasted about a year. i did bring car to the drag strip 2 times( maybe 5 runs). redlines set at 7.2k rpm but i dont see that high rpm that often

[Twi7ch]

I currently have 200cell Flowmaster cats in custom downpipes. I've had them in for about 2k kms. I might need to inspect them to see how they are doing.

They definitely reduced the stink and helped maybe a smidge with rasp. I have a Borla ProXS to try and reduce rasp.

This is on a EPL stage 2 single pulley tune (no crackle since that'll definitely destroy the cats)PXL_20221130_005010223.jpg