S2 stock cat and HJS cat questions - Page 2 - RX8Club.com



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Old 08-25-2017, 06:41 PM   #26
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I am trying a more logical approach, maybe some guesses, but since I am not with my car right now, I am just searching the possible failure points and try to test them. With slow but smooth revving, the troubleshooting procedures I have seen point to some kind of restriction in airflow, or a O2 sensor fault.

Coil failures tend to lead to failures that involve some kind of roughness, like misfiring or stumbling. Not that it's impossible for me to have ignition failure, but I just think it's also unlikely since the symptoms I have don't match up.
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Old 08-25-2017, 07:58 PM   #27
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No, I'm trying to tell you that's not always the case from my own personal experience. That doesn't mean they're either bad or good, but you can't be sure without being sure.
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Old 08-25-2017, 08:01 PM   #28
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Old 08-26-2017, 03:25 PM   #29
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No, I'm trying to tell you that's not always the case from my own personal experience. That doesn't mean they're either bad or good, but you can't be sure without being sure.
I actually read your thread about the ignition testing, which I will try next.

Will hopefully have an exhaust back pressure test done as well, just to be certain that there is nothing wrong with the portion in the back.

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Old 08-28-2017, 08:21 PM   #30
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Small update:

I was able to tighten 2 of the 3 studs on the front of the cat, so my car has a tiny bit of exhaust leak. One of the studs is stripped, so I will have a muffler shop try to remove it(the stud's seized onto the cat).

Despite this, it drove fairly well. I went out and bought an inline ignition spark tester. All 4 coils fire very normally and consistently, so the ignition components are out of the question.
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Old 08-29-2017, 02:23 PM   #31
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Checked the AFR yet?
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Old 08-29-2017, 02:46 PM   #32
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One of the studs is stripped, so I will have a muffler shop try to remove it(the stud's seized onto the cat).
The exhaust studs are knurled into the flange, so they simply need to be pounded out and the hardware replaced.
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Old 08-29-2017, 08:08 PM   #33
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Checked the AFR yet?
I will once I fix the exhaust.

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The exhaust studs are knurled into the flange, so they simply need to be pounded out and the hardware replaced.
I was able to pound one of them out(the one that snapped in half), but I just can't pound the stripped one out.
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Old 08-29-2017, 09:28 PM   #34
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Sometimes it takes a torch to heat it up before it can be pounded out because on a street car with that kind of mileage the combined long term effect of heat and corrosion becomes an issue. The factory doesnt use anti-seize on anything.
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Old 09-13-2017, 09:50 AM   #35
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Just saw this thread. Have this to add to the discussion on page 1.

The cat I bought was recommended to me by the rep at HJS NA, after I sent him a chart of my rear O2 sensor temps on track. He said it would stand up to that abuse, and is the same cat used by Porsche in the 911 Turbo as OE. Supposedly has 3 winding centers instead of 2, like their motorsports cats.

So far, it has held up to about 10 track days and 5,000 miles of street driving. NO CEL and no signs of clogging. As for performance, my lap times stayed the same or improved after installation, so I don't think it cost me anything. In any case, life smells a lot better now, and it is nice to not have to swap midpipes every year to pass inspection.
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Old 09-13-2017, 03:38 PM   #36
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I think whoever said that is mistaken because the high end Motorsport cats have always had the three-winding core since I first became aware of them in 2005. This is what keeps them from telescoping out like the cheap single-winding cats. Plenty of pics of that happening on here for the people that tried to get by for $150, heh.
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Old 09-14-2017, 07:20 AM   #37
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Let me restate that. The cat he sold me supposedly has a 3 winding core like their motorsports cats do.
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Old 09-14-2017, 04:15 PM   #38
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Let me restate that. The cat he sold me supposedly has a 3 winding core like their motorsports cats do.
Which model HJS cat was that (even if not available now)?
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Old 09-14-2017, 04:24 PM   #39
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Which model HJS cat was that (even if not available now)?
Steve uses the 90 95 0182 HJS Tuning cat, which is also the one I ordered.

You can still get it, just harder since HJS North America is no more. You will have to buy one from Germany.

Bought it from Turbo Zentrum here. They seem to have the best price, but you have to wait for a little bit since they are special ordered.
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Old 09-15-2017, 06:30 PM   #40
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From earlier in the thread; Motorsports are the serious race cats and Tuning is for for stricter emission standard street cats. If you gave a 3" midpipe I'd recommend the next larger size.

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Old 09-15-2017, 06:50 PM   #41
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From earlier in the thread; Motorsports are the serious race cats and Tuning is for for stricter emission standard street cats. If you gave a 3" midpipe I'd recommend the next larger size.
So for the lesser informed...may I use a race cats for mostly hard street use in a state w/o emissions? Which is best for no test situations relative to engine performance / cat longevity?

Curious minds want to know.
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Old 09-15-2017, 07:31 PM   #42
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They're only 100 cpis compared to 200 cpis for the street cats. So the street cats will provide more catalyst surface area with slightly less flow. Most of those street cats meet fairly strict european standards as listed on the website. However, I ran the 400 hp PE race cat on mine here in the US without any cel issues and passed local emissions tests without any trickery, but it wasn't driven much on the street so I can't vouch for long term street mileage use. I could smell some light fumes from cold startup, but otherwise it ran clean once it started to warm up.





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Old 09-15-2017, 09:42 PM   #43
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Motorsport cats are also a bit more expensive than Tuning ones from what I have seen on the Turbo Zentrum website.

HJS also carries the Motorsport UL series, which is a bit lighter than the other Motorsport and Tuning cats.

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They're only 100 cpis compared to 200 cpis for the street cats. So the street cats will provide more catalyst surface area with slightly less flow. Most of those street cats meet fairly strict european standards as listed on the website. However, I ran the 400 hp PE race cat on mine here in the US without any cel issues and passed local emissions tests without any trickery, but it wasn't driven much on the street so I can't vouch for long term street mileage use. I could smell some light fumes from cold startup, but otherwise it ran clean once it started to warm up.
As long as you are not in Commiefornia, emission tests shouldn't be an issue. I have heard some places in the States pretty much just check if you have a CEL on; if you don't, you pass the emission test.

I would imagine even the cheapest cat can get the RX-8 to pass emissions in most places; it will just melt and blow out quickly.

And every single car will have gas fumes on cold startups. The cat is not up to temperature yet, so it's not at its maximum efficiency. Most cars will also run rich when cold, so it's pretty normal to have piston cars that are bone stock to smell bad on cold startups.
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Old 09-16-2017, 09:30 AM   #44
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I went with a heavy duty tuning cat, because HJS NA could not tell me if one of their motorsports cats would pass emissions in the US. I wanted to be able to stop swapping midpipes every year, get rid of the stench (so people would actually ride with me), and get rid of the CEL with that purchase. So far, so good.

A 200 CPSI cat is still high flow, compared to the usual 400 CPSI cats, just not high-est flow. And a cat that will flow exhaust for >100 BHP than the engine is capable of producing adds to that. I did not notice any loss of performance after having my cat installed. Butt dyno and lap times confirm it is not a significant enough restriction to make a difference.

For comparison, my 137 WHP Miata does not even run a high flow cat. It has a Magnaflow universal federal cat rated for 6.2L. The fact that my engine is 1.8L makes it high flow. That car actually produced 2 WHP less with a test pipe, as the engine seemed to like the exhaust frequency with the cat installed better. I have that dyno somewhere...
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Old 09-16-2017, 01:38 PM   #45
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2 hp is smaller than the dyno repeatability error ...

Just remember that a rotary engine generates a much higher exhaust flow for it's displacement than a reciprocating engine with a much higher velocity and temperature. I'd generally warn people to avoid making wide sweeping assumptions and generalizations and instead focus on what specific requirements need to be accounted for.


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Old 09-17-2017, 12:57 PM   #46
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It's cute that you think I and the dyno operator didn't know that. That's why we logged multiple pulls and averaged the results, while accounting for changes in atmospheric conditions.

Anyway, I'm happy with the performance of my inferior cat so far, and that is what matters to me.
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Old 09-17-2017, 08:12 PM   #47
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I recognize that you're splitting RCHs and then trying to generalize it over to a completely unrelated subject; a zero port timing overlap rotary engine compared to a reciprocating engine with cam timing overlap. Whether or not either of us like your cat converter or not is completely irrelevant.
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Old 09-18-2017, 08:22 PM   #48
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I tried to get HJS to give me a definitive answer. Their recommendation from the German HQ was this:

Dear Wannawankel,

thank you for your request.

For the requested vehicle, we do not have a TÜV approved engine sport / tuning catalytic converter in the program.

HJS offers universal tuning catalysts with 200 cpsi for such applications. These are designed according to the displacement, the performance and the exhaust gas standard, replace the serial catalytic converter and can also be used with vehicles with EOBD control.

The universal tuning catalytic converter suitable for your vehicle is HJS article 90950166-HD.
Net price per piece: 440,00 € plus 19% VAT
Drawing and further information can be found here HJS Universal 200cpsi Tuning Katalysatoren - HJS Motorsport & Tuning and HJS Vertriebspartner für Tuning Produkte - HJS Motorsport & Tuning
So far we have only received positive feedback with the HJS catalyst 90950166 in the Mazda RX8.
With Wankelmotoren we assume no guarantee for the durability of the catalysts!

HJS Universal Tuning Catalysts
Catalyst components for building exhaust systems. HJS universal tuning catalysts have been developed on the basis of our motorsport catalysts. Our 200 cpsi catalysts are the right component for self-designed exhaust systems. You will achieve higher horsepower with less backpressure without having problems with your EOBD or MOT inspection. The specially designed HJS cones provide an ideal exhaust gas flow into the catalyst, which contributes to optimal power performance. HJS generic catalysts must be approved by your Department of Transportation prior to initial use.
The vehicle exhaust emission characteristic will be influenced from different factors like engine performance, capacity, power range, exhaust temperatures and vehicle weight. For any installation of exhaust systems out of the applicable range please note that the indicated Euro norms are to be understood as a recommendation and help for system lay out only.
In this context HJS cannot guarantee that the required Euro standards will be achieved.


Mit freundlichen Grüßen / Regards

Sven Kampmann


HJS Emission Technology GmbH & Co. KG
Motorsport & Tuning
Dieselweg 12
D-58706 Menden/Sauerland
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Old 09-18-2017, 08:48 PM   #49
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^I'd ask about the maximum operating temperature just to be sure. Our exhaust temperature is a lot higher than most piston cars with similar power.

Btw, the AFR is correct as far as I know(LTFT and STFT are pretty normal), but my cat would still glow after a while if I keep it around 5k RPM. No obstruction in my exhaust system, either.

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Old 09-19-2017, 08:10 AM   #50
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He said wankelmotoren.

The cat he recommended is smaller than mine in every dimension save cone size, which means the core has to be smaller in diameter at least. No idea if that means anything significant. It is interesting that they don't list capacities on their web site for the ECE line of cats.

Speaking of cone size, the cones diameters on mine are a little on the small side. The HJS guy told me to have the shop cut them to the correct diameters. They flared them instead, and it worked.

I sent the North America rep a chart of my EGTs and told him the engine is a 2.3L putting out 250BHP (ha!). The cat he recommended is rated for 5L and 340BHP and will supposedly survive 1700F EGTs.



Anyway, I can't guarantee that what I chose to do will work for anyone else, and I have limited time on mine. I have abused it more in a short period of time than most people would, and it has stood up to that abuse, but the data set is very limited.

Also, don't use my methodology, because Team says it's flawed (with no explanation of how or why, of course).

Relative size:

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