Strategies to keep cats from melting

[engineermike]

Also, the two thermocouples are maybe 6” apart in the exhaust system. It’s amazing how different they are.

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[sjmurphy34]

Eek!

That’s 1650-1740 Fahrenheit.

So depending on how accurate the PID is and the actual temp...

Can’t remember, but I’m pretty sure I’ve seen that.

Just keep in mind what you're seeing is inferred temperatures unless you have actual thermocouple readings. Since this is a non-boosted engine from the factory, the model probably wasn't calibrated to accurately model temperatures for boosted applications. It probably was calibrated to be safe and overpredict at the higher ends to protect the cats under high speed or high load conditions.

So while your inferred temps might be showing really high, you may or may not actually be in trouble unless you are stock.

 

[WildHorse]

Eek!

That’s 1650-1740 Fahrenheit.

So depending on how accurate the PID is and the actual temp...

Can’t remember, but I’m pretty sure I’ve seen that.

Do they do smog tests in Ontario ? Here in Manitoba it's just a visual. They don't care what may/may not be inside the cats if you catch my drift. If you go gutted/catless/whatever flavor you choose retain the fully functional rear o2, & just move them out of the exhaust stream w/ spacers. If you retain them boosted.. go with GSI cats.. spendy, but well worth the price of admission. Cheers bud.

 

[engineermike]

@sjmurphy34 I have access to modify the exhaust temp model as a function of load, speed, and cam timing. I can’t change the calculated effects of lambda or spark timing. The Whipple model does account for boost but I believe it underestimates the temp by a few hundred degrees. I started with the Whipple egt model but made some pretty big changes to it, borrowing heavily from the gt500 model.

 

[Torinate]

Do they do smog tests in Ontario ? Here in Manitoba it's just a visual. They don't care what may/may not be inside the cats if you catch my drift. If you go gutted/catless/whatever flavor you choose retain the fully functional rear o2, & just move them out of the exhaust stream w/ spacers. If you retain them boosted.. go with GSI cats.. spendy, but well worth the price of admission. Cheers bud.

No smog tests anymore. It’s been a couple years now. But the cops like to crack down on noise etc. and they don’t mess around and hand out fines. I do have deletes that I change out when I’m going to track etc. I have a convertible and when cruising with my wife, she’s not a fan of the extra noise and smells when running without them. So, they stay on the car most of the time. Even though they’re fairly quick to change out, it’s usually a pain to do it unless I know I’m going to the track or going to be running it really hard. Even then, I found I’ve left them on the last few times. I guess I need to log the catemp PID and see where the temps fall.

GESI is local (well couple hours I guess) and likely the way to go for aftermarket.

Funny though, at least around where I live, catalytic converters seem to be a hot item for thieves to steal.

 

[WildHorse]

Funny though, at least around where I live, catalytic converters seem to be a hot item for thieves to steal.

huge problem here as well. But then again, what isn't a problem in Winnipeg ? Murder capitol, violent crime capitol, theft capitol, Slurpee capitol...

 

[Torinate]

huge problem here as well. But then again, what isn't a problem in Winnipeg ? Murder capitol, violent crime capitol, theft capitol, Slurpee capitol...

Lol that’s funny. I was unaware of the slurpees there...

Hottest spicy food there as well. Was at a stag 30+ years ago at a restaurant downtown. Ordered the Kung Pao Chicken with 3 peppers (5 was hottest) and that was and still is the spiciest meal I’ve ever eaten. You guys are nuts!

 

[engineermike]

Got some great data this morning. Made a WOT pull for approximately 8 seconds. This is a Whipple Stage 2 on a 4" pulley, running the XDI GDI pump and modified exhaust that enabled 21-21.5 deg of timing. So, this should be about the best case you could expect for EGT on a supercharged Gen3 Coyote on pump gas.

In the bottom graph, orange is collector EGT just upstream of the cat, red is just behind the 1st cat element, and yellow/white are PCM calculated cat temps. The cursor is placed at the moment when cat protect kicked in, in this case 1680 deg F (OEM usually sets this at 1650).

Notes:
- Max collector EGT was 1496 deg F. My calibration predicts exhaust temp to be 1990 at that load/speed. GT500 calls is 2040 and Roush says 1860.
- Max downstream of cat EGT was 1580 deg F. IF this is indicative of the actual cat element temp, then it's in a safe range with this tune.
- All 4 temps dropped when COT kicked in. COT enrichment backs off once it achieves its goal and you can see all temps rise after then initial fall.
- Both the predicted cat temp and the downstream EGT have a 2nd "hump" after letting off the throttle. I presume this is the effect of after-burning off the extra fuel dumped in due to PE and COT. But here's the problem. Predicted EGT peaks 3-4 seconds after letting off. The downstream EGT doesn't peak until a solid 30 seconds after letting off, and at that time is showing 250 deg F higher than the inferred cat temp! I can adjust the EGT model as a function of speed, load, and cam timing, but I cannot change the way it calculates the cat temp as a function of time, thermal capacitance, or anything else.

 

[Torinate]

Interesting. Question about the GT500 cats. Are they the same or different? Wonder if they accept more heat before failing? Same as for the Hellcat and ZL1 cats...

Nice to see that the CAT protection actually helps preserve the cats at the cost of some performance albeit.

 

[engineermike]

My guess is that the elements in the gt500 cats are the same but a little larger diameter. I think they share with the gt350 that came out years before. Same with the hellcat; they share the same cats as the srt392 na motor. I believe them all to be ceramic substrate which withstands heat (but not thermal shock)better than aftermarket metal substrate cats.

gt500 goes into cot about 2 seconds after going wot, so the main difference between them and na is how soon cot kicks in. Wildhorse iirc tells me that his na car didn’t go into cot at all during an entire quarter mile pass.

 

[Torinate]

On the GESI site, the G Sport says stainless substrate I believe. Proprietary metal in the higher end ones...

https://gsportbygesi.com/high-perfo...rters/g-sport-catalytic-converter-technology/

 

[WildHorse]

Wildhorse iirc tells me that his na car didn’t go into cot at all during an entire quarter mile pass.

That's correct.

 

[Grimreaper]

That seems a bit lengthy. Cooler ambient temps maybe? I would hit cot by middle of 3rd with a frpp2 tune and they use the gt350 temp tables which said the exhaust was colder than the stock tables did.

Great info though. I'm wondering if the lack of restriction behind the cats is why they are infered a bit hotter. Iirc whipple/ roush use stock catback to model. Although I'd put more stock in roush to model this to a higher degree.

Surprised no aftermarket has created finned attachments to increase heat dissipation.

 

[jojo4711]

Is it possible to have some of the cat come loose and get into the muffler and cause a rattle?

 

[engineermike]

Is it believable that the exhaust gas enters the cat at 1450 and exits at 1550, just a few inches downstream?

What about entering at 1100 and exiting at 1500?

What would you suppose is the temp of the catalyst itself in the above scenarios?

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