Third-Reef

I am looking for some high flow yet functional Cats to retrofit to my stock exhaust. I want the quite no-drone sound of the stock exhaust but would like to reduce the back pressure of the dual stage Cats on the stock exhaust. would something like this work?

https://www.summitracing.com/parts/mpe-59959/overview/

Any recommendations would be appreciated.

powdrhound

$100?? My guess is that's going to be garbage. High quality Catalysts are going to be much more expensive. I think this is one of those items where you get what you pay for. I'm running HJS 100cell Motorsport 153mm cats which are efficient at flowing up to 900hp. After 3 hard track seasons they are still in perfect shape and pass emissions with flying colors. I've never had a check engine light. They are not cheap however at $1000 each (just for the core)...

http://www.hjs-motorsport.de/product...catalysts.html

T10Chris

I came in here to recommend exactly what powdrhound said. If I were to run cats, that's the right way to do it.

Third-Reef

Thanks for the info, that is kind of what i had expected. Anybody else make "Good Cats? Like the ones that come on the kline exhausts? Mine have numbers on them but i cannot find any reference to them.

I would rather not spend $2K on thes project.

powdrhound

Keep in mind that not all cats are the same even if listed as 100 or 200. A large diameter 100 will always have less restriction than a smaller 100 and thus will flow better. You want the largest diameter cats you can get (which currently are the HJS 153mm race versions) because they will flow the best and provide effective scrubbing due to the large amount of material present. The large HJS Motorsport catalysts are 95% efficient in flow at their rated power. That's pretty astonishing. I will be doing a comparison on the Dyno with my set up with the race cars versus 3.5" cat bypass pipes. I'll post the results.

manimal

Good info. I need these for my other car.

my04996tt

I installed the Kline Exhaust, with 200cell HJS cats.

powdrhound

Those are great cats that you will never have any problems with as far as passing emission. The HJS 200 cell are called "tuning" cats by HJS and they are street legal. Their Motorsport 100 cell cats are not but the large ones probably have just as much (if not more) platinum as the smaller 200s so they pass emissions without any issues. Many aftermarket exhaust manufacturers will use the HJS 200 cell cats (usually 100-130mm large) because they are reasonably cheap (about $300 each), high quality, and will work for 99% of end users out there where the end use is street with some track work.

Keep in mind however that the 200cell cats will not stand up to continual hard track use. They just do not have the ability to flow and dissipate heat like the race catalysts. As such they overheat and the substrate eventually break down. We have a number of people in my area, couple of GT3s and a Cayman that are run hard at the track and they have both burned up the HJS 200 cats through hard track use. The catalyst substrate failed and clogged the exhaust bogging the car down. Upon disassembly the HJS 200 cell cores looked like this. The left cat had the center basically charred and plugged up. It was loose within the body of the catalyst. The right cat was staring to fail also with partial blockage. These came out of an FVD exhaust.



Here is what the HJS Motorsport 100 cell catalyst cores look like in my exhaust after 60 hard track hours where cat temps continually reach +1000F. Perfect condition.... The voids on the race cats are large which allow the exhaust gasses to flow freely through the core thus keeping the temperatures at a manageable level. These cores are made for HJS by Emitec.

"02996ttx50

what is always with this constant litany of "track bias suitability" vis a vis "performance" of aftermarket parts(?)

the man asked this:

this does not suggest he needs or requires anything more than he seeks! a good hi flow cat that he can retrofit given the stupidly restrictive cell "number" of the oem cats.

i also ( live with? ) am "ok" with the 200 cats the kline 2.5 came with also, but prefer the car without them. i'd go with some tuv certified 200's to replace the stockers. hjs 200's are probably ( as recommended ) the best aftermarket bet bet. i would never buy some "internet specials".

Third-Reef

Thanks all, this is exactly what I was looking for. I was worried when I posted it would turn into a why use cats at all, personal choice discussion.

F1CrazyDriver

If you track the car solely, i tell people no for cats. It's not IF it's a matter of WHEN.

If you want to get HJC cats, and track - swap every season (to play it safe). Last thing you want is broken catalytic converter material banging against turbo turbine or getting sucked into engine.

If you're in California (this is track only) and you would like to keep car registration up to date. California only performs obd2 check. No longer sniffer test. You will pass with no cats, if no check engine light..
If track AND street. Swap every season if you track a lot. I have seen OEM GT3 catalytic converters fail with cars that otherwise 100% stock but used as intended / marketed.

powdrhound

Because I figure on a crazy off chance that someone OTHER than the OP may read this thread and may have a different goal in mind (i.e more track use) hence my comparison of the various options. There are plenty of guys on this forum that track their cars, many that don't. I'm not sure why it rubs you the wrong way about discussing what's available? It's all about having knowledge of the available choices and then people can make up their mind what is the best choice for them. Most people don't know much about the differences on the various cat options besides 100/200 or what makes one better than the other. It's a largely misunderstood topic. Maybe the OP would prefer the highest flowing cat money can buy, maybe a cheaper alternative is all he needs. Who knows? Nobody is twisting anyones arm, it's up to him or other potential readers to decide what is best for their use. Cheers...

"02996ttx50

it doesn't "rub" me at all and i am a frequent adherent to your advice! as you are no doubt aware. but, it also just seems that many often offer recommendation's, and advice, that are not particularly germane or relevant to the op's "intended usage" of the car relative to the "part" in question. but you explained that you are addressing a wider audience. i get that, and it's terrific you also ( or have ) mentioned the options.

you sell great parts and have great advise, and also have your 40/60 street to track 'bias". clearly. hey! i also want to ( if necessary? ) re-build some day, so i have a 3.8 street driven 996t also, but hey.

you know what works ( for you ) others possibly don't require the same parts, for their intended usage. my point ( if there is one ?) is that some here focus on parts that are better suited to tracking vs pure "street" driving. so, while my comment was not directed to you, per se? your recommendations do often reflect your "track bias" vis a vis "parts"? and i read them with interest. nothing wrong at all with posts re "parts" ( and favoritism for, and of ) that tend to reflect your primary usage of the car, by proportional degree. i get that. was only pointing out, the OP was seeking a "near" oem replacement with a bit less restriction.. hjs 200, should meet that requirement well as you've said. so, with that in mind..cheers!

powdrhound

Roger that...

"02996ttx50

thx for that. unrelatedly 100 cell cats can have "smog pass" issues here. 200 i would think you'd agree? is the number for a street car given the oems are, what? 600!? i guess that why some have drilled holes lol

either way, rather than buy new cats? i'd probably just get a new exhaust. like a catted kline.