The Best free flow cats

[Trumpkin]

About 4 years ago I replaced my two lower cats with Magna flow after market cats. They performed excellent, but they are puttting out a nasty smell. The kind of smell you get when you run no cats. I am assuming they are toast, melted, aka no longer working as intended. Those of you who are running high flows, can you give me some feed back on your experience with your choice? BTW, front cats-punched.

[Trumpkin]

Maybe this wasn't the right forum for this question. I may be better off at a performance site. Either way, thoughts welcome if any.

[MinisterofDOOM]

I'm not sure what brand I have, I'll have to crawl under the car and have a look. I had Rex put them on before I bought it. I, like you, have high-flow main cats and removed precats. The ones I have are adequate to pass emissions with the stock ECU, but will not pass with a NICO ECU.

[Q45tech]

4 years is extremely good life for aftermarket replacement or so called performance cats. Most barely make it thru 1 or 2 year.

People have a hard time understanding that the higher the performance [lowest back pressure and resistance to flow] the lower the catalytic efficency and the shorter is its life.

OEM are required by law to last at least 8 years and most last 10+ years and 150k + miles.

The 90-93Q cats were way over designed even for the above and most will last 20+ year and 300K miles and still meet Fed Emission standards.

Why replacing them costs thousands of dollars.

Even the 94-95 cats are significantly less robust and can be made to fit.

Engineers might find this oldy but goody interesting concerning design size and shape:

"For a fixed catalyst volume, the increase of length decreases CO and HC emissions but increases NO emissions. The increase of cross-sectional area for fixed catalyst volume (achieved by reducing length), however, increases CO and HC emissions, and does not have much influence on NO emissions. The results show that a short catalyst with a large cross-sectional area is generally not as effective in pollutant conversion as a catalyst of similar volume but of larger length and smaller cross-sectional area.• The increase of cell density and decrease of wall thickness have favorable effect on catalyst conversion performance. The combination of high cell density and thin wall results in an increase in substrate geometric surface area and has favorable effect on the catalyst emission conversion performance."http://amseweb.org/Documents/Dr.%20Tareq.pdf

Look up the 18 references the paper quotes to become a cat expert.

It appears California is getting tougher on aftermarket junk cats:http://www.arb.ca.gov/regact/2...2.pdf

Here is a less technical article specifically about type and results of Magnaflow:http://www.importtuner.com/fea....html

[lino]

OEM are required by law to last at least 8 years and most last 10+ years and 150k + miles.

The 90-93Q cats were way over designed even for the above and most will last 20+ year and 300K miles and still meet Fed Emission standards.

Is there any other part of the exhaust system that was over engineered or also might last just as long?

[Q45tech]

In 1994 I replace oem with a Stromung custom exhaust it lasted [100k]until 1999 before it rotted away. I found a 28K 1994 system [at our muffler shop] which I installed [had to weld in a short jumper pipe/flange to match the different cat lengths between 90-93 aand 94+] and still have today.... 190K + 28k later.

Hopefully you understand why I have a low opinion of after market exhaust system after paying $1,000 for one and it's internal rot.5 years vs 10 years.

My 10 year old USED oem looks very very good today as do most of the 20 year old early Q's we see today!

[paranoidjack]

Tech, no chance of grabbing a g50 Cat and putting them on a fgy33 instead of replacing with OEM fgy33?

[Q45tech]

Unfortunately the emission standards got more severe and thus the cats designs changed each time: Cats must match year series to achieve longevity and match emission tests:

90-93 series, 94-95 series, 96 series, 97-99 series and 2000-2001 series.

[Trumpkin]

I thank all of you for your input. However, it is a little off the question. Long life is really not my concern. Considering my exhaust, and nos module and hard driving, I could care less how long they last. My concern is more performance to my particular set up. If they last one year I'm happy!

[Q45tech]

Why have cats at all other than smell which should not bother you if performance is your #1 Goal.

As the magazine article pointed out a test pipe increased power from 147 rwhp to 152 rwhp................with N2O you might get 15 HP more with 2 test pipes.

[Trumpkin]

I have run test pipes. Quite frankly the sound is nasty. It sounds like two coffee cans refracting! And the smell with no cats will literally choke you. I can't stand it at a standstill! When I installed my magna flows no smell and a glorious exhaust tone! Thanks for your input. Test pipes I am sure would max my performance, however choking folks behind me is not nice.

[Q45tech]

So performance is NOT your #1 goal?

[Trumpkin]

I would rather gain more hp through other means then sacrifice exhaust tone/odor. #1 yes, but I don't track it. So outward impression is still high.