Now that Ive commited myself to running a cat, Ive been thinking of a way of improving how the AFRs are handled.

What Id like to do is have the short term fueling be closer to where the engine makes peak power, but then have the fueling richen over time to around 11:1 to shut down the cat during extended throttle. I was thinking of a two stage system. The engine would start off with around 12.5:1 AFR across the board to improve the passing power. If I stay on it, the AFRs in the midrange would richen up. Finally after awhile, it would go to full rich at all rpms to protect the cat.

Few questions I have are:

1) How long can a cat be safely run at around 12-13:1 AFR before I risk melting it?

2) Whats the best way to transition over to richer AFRs? Have them decay to the long term values?

3) Should I have some timer that restricts how fast the system can reset. IOW, not allow the leaner AFRS to be run right away if PE is engaged again.

Finally, is there a calibration I can see that already does something similar?

 

I'm not 100% sure on this, but I think the $A1 mask for the 730 does this (60 degree V6 stuff).

 

Do you plan on towing, or road-racing? If not, I wouldn't get tooooo worried about the cat. Input temperature, catalyst conversion rate, and ambient airflow are the main factors in catalyst temperature. The conversion rate drops quite rapidly when richer than 14.7. NOx conversion efficiency is high when rich, but not much NOx is produced, due to the lack of leftover O2 INSIDE the combustion chamber to even form NOx. CO and HC conversion is next to nothing when rich for longer than a second (due to lack of O2 post combustion - air pump diverted to atmosphere of course).

If I were you, I'd stick an EGT/thermocouple mid brick of both bricks (front one is most critical), and look for temps above 800 C. Short Stints to 1000 C are OK, keeping in mind at those temperatures, washcoats melt and recrystalize when cooled and are less and less efficient as time above this temperature increases (Thermal Aging). Long enough, and the substrate will begin to melt.

A little empiracle testing in your application would probably show you what you need better than several guesses. Cats hate misfire most. Anything that sends large quantities of air AND fuel into a hot cat is catasrophic (punny, ain't it). Transitioning from combustion to fuel cut will also give a brief spike in temps (there's always a bit of misfire while the manifold cleans out).

Maybe another thing to measure would be cylinder head temps.

 

I didnt really give that much thought that the catalyst coating on the ceramic can change over time with reheating. With that in mind I wonder if just running rich all the time in PE is better overall. I just ordered a nice 3" cat for my exhaust system and I dont want to jepardize it.

I know some of the other manufacturers seem to do it like this. Some of those newer cars blow black smoke like its nobodies buisness when theyre under high loads.

 

It is also done to cool the engine. Some masks just drop the AFR after a set time in PE (say 1 AFR after 20 seconds).

RBob.

 

Arrrrgh........

The rest however, was excellent.

 

there is a new Catalyst in the market called a metal cat by brand name i belive its an arvine/meritor product. there are sevral versions avaiable from other manufacturers. there a by product of the japense turbo tuner car wars and have been in use by mitsubishi for sevral years. . there doing things with the brick to make it more resistant to learner calibrations and rich spikes and more abuse. there specifically designed for performance applications and when we last tested one it produced no noticeable or measureable rise in exhuast system back pressure when place 10-14 inchs downstream of the collector. it also provided a side benfit to canceling standing waves/reflected pulsation in the exhuast system and helped fatten up midrange Tq oddly enough! again the idea with the egts is good. although some cheaper cats will melt down well before 800*c.

Best of luck got emissions testing.

post thought

the most concerning thing youll have is avioding ignition missfires at high loads. that will quikly destroy a hot cat with to much fuel in the brick under heavy load. instant oxidation

 

1) All day if you aren't running a high flow rate through it. AFR's don't kill the cat, high flow rate and AFR's (like RednGold pointed out) are what kill the cat. Or if your cat isn't friendly and walks up to ME and scratchs me out of nowhere then I'd kill the cat!

2) The time in PE AFR modifier would work well but you'd want to find out the cat temps to be sure of a, you're actually putting out the cat, and b, that the cat needed to be cooled down. Else you're wasting more fuel and making yourself slower.

3) That's a really good question. I don't know what they do with the newer stuff other than that they calculate the cat temps based on the MAF, baro, commanded AFR, and air pump status. I bet you could do the same seeing as you're MAF. Just get a k-type thermocouple installed and I'll provide you with a thermocouple linear 0-5v circuit. I've got a few of em sitting here and am only using 1 so you can borrow it if you need it. I think there is an SAE paper that goes into great detail but it's pointless if you don't know the cat's specs .

 

Engineering without spec sheets is a blast. It's like engineering by sight of the part, or maybe by hours/days wasted. Gotta love it, hehe. "It should be OK" gets you so far. Working with these Chinese Copyneers is painful sometimes.

I like cats. They're fun to torture.

 

i agree and the info for the arvin/mreitor cats youll have to directly contact arvin/meritor. i couldnt find a damn thing online but do a google and see what ya get. they have some limited info on there website.

 

The idea of what would happen with an ignition misfire is enough to deter me. I have the worlds crappiest ignition system so misfires and other such malfunctions are common.

I might just have it go pig rich in PE instead like it does now and just avoid the issue altogether rather then risk melting the damn thing. I hate cats. Emissions equipment is a pain in the ***.

 

yes cats are a pita. and yes a missfire will kill it quick if you have enough of them. upgrade the ignition system make sure its rock solid and you shouldnt have any problems if the AFR's are haf decent.