What's the newest/best hi-flo catalytic converter for a supercharged LS6, making over 700hp at crank, that'll still trigger the OBD II cat monitor?

I was running two C6 Z06 cats that have apparently disintegrated.

 

 

If you disintegrated C6 Z06 Cats, you probably need to look at the tune, not the cat. You are almost certainly allowing them to get beyond a safe temperature (roughly 950* C) during either WOT or on transition to decel fuel cut. Both of these can be managed through the ECU calibration.

 

Thanks. Andy's recalibrating the tune. The car never ran hotter than 185° though. The cats were used, so it's possible they'd been banged around and, from what I understand, once a piece breaks off, it cascades from there. I don't run the card hard either, so it was very weird that this happened. We're going to get the C6 Z06 cats made by Magnaflow. They're tougher, flow better and are CARB certified. So let's see.

 

more info !
Can these withstand a rich afr ?

 

I'm not sure about the rich AFR but they are designed to flow 500-800HP through the 3" cat. I have one I'm getting ready to weld into my circuit Subaru.

 

I've had good luck with the metallic spun high flow cats from Magnaflow. I want to say they are 200 cell. This was in turbocharged 4 cylinders making less power, but 400-500hp thru a single cat. In theory should be similar heat/flow/conditions. Haven't used Vibrant, but every single one of the things I've used of their has been top notch.

 

The company who manufactures these for vibrant is Gesi , and its local to me, I emailed them yesterday wether they would stand up to a rich FI , here is there reply:
Thank you for the inquiry. Your interest in our product line is appreciated. In response to your email, a rich air fuel ratio will negatively affect any converter. It typically results in temperature fluctuations that could exceed the material’s capabilities. Our converters are definitely a more robust solution for the high performance market, they are capable of handling tremendous horsepower, but they do need to operate under the right settings. Our units will typically flow more than our competitors, and will keep check engine lights off… we just can’t guarantee their longevity in a rich fuel environment.
And I think they have a high cell count, like 300-400 cell.

 

Thanks Greg!

As so often, Cat Overtemp is disabled in the tune, at least during tuning, and for a good reasons.

Anyway, since there is no temp sensor in the cat itself, I guess these values - and actions based on them - are because of some internal PCM calculation logic which is not visible in the tune.

So how to tune these?

 

Well, so rich afr affects catalysator negatively?

But isn't that exactly what Cat Overtemp protection is doing with C5 PCM stock tune...

Interesting indeed.

 

Yes, there is an exhaust temp (and catalyst temp) model within the ECU. It is roughly based on engine speed, total air/fuel flow, spark advance, and air-fuel ratio. You can often log the result of the factory calculation as "catalyst temp" in many scanners, but this is not necessarily accurate with modified engines.

When I do development programs with aftermarket companies, I like to install an actual thermocouple in the catalyst so I can log the temperature along with all the normal ECU data. I follow the same strategy in the aftermarket as I do in OEM applications when working to keep that temperature in a reliable range. YES, this means running rich at full load. The cat manufacturers are typically worried about rich operation at normal temps, not necessarily at full load. When you start making big power, with high flow rates and knock limited spark timing, you MUST run richer to control the cat temp or risk instantaneous failure. Their concern about "running rich" is usually skewed toward poisoning of the brick over time, which is a lower priority than avoiding an immediate meltdown (or burning the washcoat off) at high load/flow.

 

Just out of curiosity, I checked some aftermarket tunes so that I could learn something. I compared those tunes with stock ones.

And here are the results:

- 2006 Z06 with Vortech kit vs. stock 2006 Z06: Max enrichment under cat overtemp protection changed from stock 1.21 to a 1.35
- 2007 LS2 vith Edelbrock E-force vs. stock 2006 LS2: no changes for cat overtemp protection
- 2011 Corvette Grand Sport with Vortech kit vs. stock Grand Sport: no changes for cat overtemp protection
- 2012 Camaro with Edelbrock E-force vs. stock LS3 Camaro: no changes for cat overtemp protection

Interesting indeed.

 

I've had some problems with the older stainless steel bullet cats

the work ok but durability just isn''t there and if you do a lot of racing and dyno work, take them off

they tend to blow out the centers with a reasonable tune

factory goes a bit rich (like 12.5 to 1) on na

if you lean er out for power expect to have troubles after a few years

 

I thought I replied to this thread after starting it, but I think it didn't update. Either way, Andy replaced my old C6 ZO6 cats with C7 Z06 Cats and now, nearly 5 years later (driven twice a week for a total of 60 miles/week, but with some spirit, especially during the no-traffic COVID days), the OBD II Cat monitor is showing incomplete for cats. It passed SMOG in May 2022. O2 sensors are fluctuating fine; no codes; no rotten egg stench; no wet or thick soot in the tailpipes; and no sand in the exhaust pipe sounds like last time. So, I don't know.

Anyone experience this. Could it still be the cats? I'm in CA, so I need the stupid monitor to run in order to pass SMOG and we only have that crappy 91 octane fuel here.Andy isn't really working on cars anymore, so he's kind of scratching his head.

 

Have you recently reset the PCM? Sometimes they can take quite some time after a reset to show ready again.

 

I had and as I was driving today, I plugged in the tool at a red light and accidentally did it again like a moron because the light changed and I hit the wrong button.

 

Oof! So there's an actual procedure that you can do in an attempt to set the monitors, but it's not 100% reliable unfortunately. Many people have posted that it helped and others (including myself), not so much. Depending on what kind of roads you have available, it can be difficult to even be able to execute properly. I went through the ringer almost 4 yrs ago now with this too and Andy said he actually had to put mine on the dyno to get them to set because he wasn't having any luck doing it on the street. My best guess is it's the PCM, not the cats. Do the procedure multiple times and see if it helps. If not, maybe double check with Andy to see if they can throw it on the dyno. With how much time it may take, it may be a very expensive option though if they'll do it.

General Motors OBD-II driving cycle

• Cold Start. In order to be classified as a cold start, the engine coolant temperature must be below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at start-up. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.

• Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.

• Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.

• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.

• Decelerate. Let off the accelerator pedal. Do not shift or touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.

• Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same diagnostics as in step 3.

• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.

• Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.

 

Thank you. It seems to set the all monitors rather quickly without me really trying save for the cats, which it says are "inc." meaning incomplete I guess. Andy said that if the cats are on their way out or not terrible, but not perfect, it could cause this problem, but he's not sure either. I'll drive it more often and try the step 4 you noted. What a hassle.

 

Unfortunately, it's not an uncommon problem :/ Countless posts in the archives of people struggling to get it to reset even on stock cars. Might be worth keeping an eye out for a used OEM midpipe to keep around for smog time if you can find one for a decent price. Most people want an arm and leg for them since cat scrap value skyrocketed again a few years ago, but you can still come across them at decent prices every once in a while. Unfortunately the C7Z cats aren't smog legal on a C5 if they ever get called out by an overzealous smog tech or if you get sent to the state ref for any reason, so definitely worth having an OEM midpipe handy for multiple reasons just in case.

 

If I get sent to ref, I'll have a lot more problems. The only reason I have them is to trigger the OBD monitors and stay legal. It's such a stupid law with zero practical application - hence VW cheating it for so many years. At least with the tailpipe probe, they could see whether the car was polluting.