Cats Exploded. Suggestions?
 

Took the car out for a short drive. Accelerated onto Freeway (WOT), at the top of 2nd car lost all power and struggled to rev, exhaust note immediately changed, went super deep and rumbly. Was blowing a bit of dust coloured smoke out the rear. Smell was very unusual, definitely not fuel or oil, sorta like breaking in a new exhaust system. Was getting check engine light flash when attempting to rev during those few seconds, but very oddly no error code actually stuck/stored when I checked a little later.

Pulled over and shut it off. Waited 5 minutes, started it up again, struggled to start the first time. Got it fired up and idled a little rough. Shut it off, waited 30 mins, fired it up again and it started almost completely normal, was able to rev resonably well but still very slight dust coloured smoke out the rear. Turned it off.

Got out and looked into the exhaust pipes and saw very fine dust-like sediment in the tips. Catalytic Temp Sensor used to give me 400-600c, now it's stuck on 28-32c. Got it towed home to be safe, dropped it off on the street in front of my house, fired it up and drove it into garage like nothing ever happened.

TL: DR = Fairly confident I've blown my stock Cats. Have OEM Cats. Need new Cats for Vortech SC setup. What are people going with? Heard HFC are just as worse as the Stock Cats. What about Test Pipes, what's the noise like with them? Rough prices or good suppliers? Any info appreciated.

Stilen SC @ ~10psi
Stock Headers
Stock Cats
Motordyne CBE

Come on! Over 200 views in the Forced Induction Sub-group and no one is willing to share their FI & Cat setup or experiences?

Many have already shared that info. Search is your friend. If the site's search isn't working for you, try any of the big web search engines and add "site:the370z.com" to your search string.

With the stock Stillen setup, test pipes may cost you power. Maybe another set of OEM cats?

My A2A kit should be there already no? It will make more power by freeing up the exhaust system. You will be making even more power now so any and all cats are a no go for you, unless you want to replace them again and again. If you want to reduce rasp/noise as much as possible then Motordyne ART pipes are your best option as they sound exactly the same as HFC's.

Are test pipes out of the question?

I thought that cats helped build/maintain pressure in s/c systems, and are more or less a mandatory item? I understand the need for their removal in turbo applications.

Perhaps with the lower torque curve of s/c systems, we need to stick to a "theoretical" redline of maybe 6 grand or so -- anything higher than that is asking for trouble.

I am, by no means, an expert in this stuff.. but I always thought the benefit of back-pressure wasn't really the pressure itself, but the increase in exhaust gas velocity in the lower rev range (which you want for scavenging purposes)... this is why you lose low-end torque if you go way oversized on your exhaust pipes. I think keeping the velocity in a good place is important for both NA and SC, but you have to factor in the big increase in exhaust volume when you go SC.

No matter how you slice it, the OEM cats are an enormous restriction and are not beneficial to making power. Otherwise, few people would buy HFCs or test pipes.

You might see more boost with OEM cats, that is only because flow through the motor is being restricted... without them, boost pressure likely reduces and power will absolutely increase. Often times this is a misunderstood concept and you will see people wonder why their car makes less power at the same boost pressure compared to another with a different setup.

Moving on, I have read many times that the heat, pressure, and volume of exhaust associated with going FI will destroy your OEM cats.. but there are plenty of HFC options for factory turbo charged cars. I have read on Subaru forums of folks having good success with some of the magnaflow universal cats... I would probably start by getting a cheap or second hand pair of test pipes and having a shop weld in a couple of those.. they aren't terribly expensive... I considered the same when I thought about keeping cats.. but I have test pipes now and am perfectly happy with them.

If you simply MUST have cats then dont put them way up high by the exhaust manifold, they will get too hot there. The best thing is to put them downstream where they will keep cooled from air passing by them and not being bolted to a red hot manifold.

Mil.spec have been holding up the best.

Mil.Spec :: Universal

Thanks for the good explanation!

This was kind of my thought as well. With test pipes you may get lower boost, but total air flowing through the system could be higher.

I've got the stillen kit and resonated berk test pipes and love it. Just know that you'll want to get retuned with whatever you switch to.

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I have had the Stillen HFC's that are connected to my Stillen headers for over a year now with the stock Stillen SC setup. I have also done a track day with this setup and so far no issues. Now that I have recently gone A to A setup I will be monitoring this more closely. :eekdance:

A2A kit hasn't arrived, but both boxes have apparently landed in Australia. Might get them by the end of the week if I'm lucky.

And I reckon your idea is by far the best solution, moving the Cats further down. Can't be coincidence that on the Z32 TT platform I had before the Cats were also in the middle of the vehicle and not right after the dumps.

Currently have the Motordyne E370 CBE, and just so happens there's an ideal section for them, complete with OEM Heatsheats hah. Shouldn't be hard to undo a couple of V-band clamps, take those pipes to a nearby exhaust shop and get them welded in place. Photo attached.

Can't get Mil.Spec local, but Magnaflow gear which I've used before is also a great easily sourced local brand. Can't imagine each 100CPSI 3" IN/OUT Cat would cost more than 100-120 AUD each.

What I will need to get shipped is a decent pair of Test Pipes now... or Long Tube Headers if I wasn't scared at the thought of trying to undo the stock Headers in that tight arse space.

Pretty much spot on. Only thing I would add is to reinforce the fact that PSI does not directly equal power. PSI is a measure of pressure, or specifically resistance to flow. It does not measure flow. I see this mistake way too often. If you have a shitty flowing system, you're going to see higher PSI, but not necessarily more power.

Anytime you go Forced Inducted, you want to prioritize a good flowing exhaust, and yeah can't imagine Stock Cats designed for an NA application would help with that. The goal is to get more air in, and just as quickly get more air out.

I don't care if I lose a pound or two of boost, I care about what it'll do to the response and power curve if I free up the exhaust, and do it in a safe reliable manner for my application/circumstance, hence my plan above.

Yeah that would be a perfect place to put them and your right, almost like it was designed for some there. I'd imagine any cat would live very long in that location. Glad you have an easy solution.

Now with your test pipe problem. If it were me I would just gut those cats and keep them on there. Hell, they are pretty much gutted already from the sounds of it..lol..

TopgunZ has a point. The only benefit to switching to test pipes would be if you went with resonated test pipes. Should mellow the sound a tiny bit

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Test pipes can be had so inexpensively it may not even be worth the effort to gut them. Any slight fitment issues will get resolved when the X-pipe is cut to add cats.

Yeah for us they can. He lives in Australia where he would need to pay for shipping and import taxes.

I wouldnt worry about resonated test pipes as the mid pipe cats will take out the rasp.

Exactly topgunZ! Just gut those cats. I know In some areas they use a mirror to check for the catalytic converter for emissions so test pipes are not a option for everyone.

Oh yeah =) Good point.

forced induction can kill cats, especially if the tune isnt spot on. i would just ditch the cats and do resonated test pipes if you can get away with it in your area.

if the boost goes down a little with test pipes, thats how you know they are doing their job. thats the good type of boost loss.

Had a ~550rwhp capable Z32, and was part of the Z32 crowd for many years before moving onto Z34. Can probably count on one hand all the cases of exploded cats due directly to the F.I. fact, as opposed to Z34 platform where it seems to be way more common. Which like said earlier makes sense, can't have Cats so close to an F.I. motor.

Ended up, ordering these:

https://conceptzperformance.com/mega...z34_p_7318.php

They looked alright, and value was good. Can't for the life of me justify some 250+ USD just for some short test pipes because of a brand name.

Where I live though, Cats are crucial, and even if they do almost jack sh*t, at least they're there when the cops peek under, plus those TP's I picked up give the appearance of Cats with that 'resonated' chamber (which looking at it I know it can't do much). So, also picked up two 3" IN/OUT Cats. Should be able to take the Vortech @ 10 PSI + TG's A2A kit happily all day.

Any chance you can do a dyno before and after the cat installation? I'd love to see how these impact the performance...

Yes, I would expect the factory cats on a factory turbo car to hold up to being turbo better! After-all, they have to warranty that. Cat failures on turbo converted vehicles is much less of a surprise.

Actually, not a bad idea... chances of getting pinged without Cats for a week or two is tiny. I'll wait till these TP's show up, which is like 6-10 days I was told, whack them on, Dyno, then get the 3" Cats welded in and Dyno after.

Awesome!! Really looking forward to the results.

Cats are in. Just waiting on TPs, should be here tomorrow or Thursday. :tup:

Test Pipes are in. Going in this weekend.

Nice looking test pipes. I have been thinking I need to get a set with flex sections.

Which cats did you end up going with? Magnaflows?

Sub'd for sound clips once those Megans are on :tup:

Naively sold my ART pipes and want to grab a cheap set of resonated pipes for the time being. Probably these or the 1320, which are probably exactly the same except for $10 1320 comes with O2 extensions.

BAD IDEA. TEST PIPES + MOTORDYNE WERE A BAD IDEA!!! CHRIST THE NOISE! It's loud before you even lay into it. When you plant your foot down, you could wake the dead. First cop to hear me and I'm done. I'm not convinced my pair of 100cpsi Cats are gonna do sh*t to combat this. =/

Video! :pics:

Did you consider getting ART pipes? They are quieter.

Video will be coming.

And doesn't matter how large a resonance chamber you hang off a Test Pipe, it's still gonna be LOUD. Not to mention 4 times the price lol. :icon17:

You can go stock exhaust and be mistaken for a hybrid car 24/7 like I was all last year :eekdance:

It makes a massive difference.

ART pipes are light years beyond any other. And depending on the air moving through can actually be very quiet too. This from personal experience.

My god I couldn't stand the stock exhaust. Barely had it off the dealer lot and had the motordyne setup ordered!

Sorry, I've heard various clips of ART Pipes and I disagree. The only major difference was the level of rasp. Noise level still went up.

That's why I qualified it by saying it depends in the air going through. When I was NA I had Art+Motordyne with both Injen and Stillen CAI's. With the Injen it was loud and raunchy and could hear it blocks away whether you were WOT or not. With the G3 it was as quiet as Motordyne + factory cats, which is not loud whatsoever.

Internet doesn't trump real life experience.

So MoulaZ are you keeping the TPs or are going to get CATs on soon?

Keeping TPs, waiting to find a buyer for my current Motordyne then going Invidia.

By the way, for those curious for what the Cats actually looked like after exploding, here's a before & after.

When it happened, got the CEL flashing at me every time I tried to rev and it struggled... but strangely it didn't generate a code.