Running lean overheats cat?

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I wish I were so lucky to have unrusted flanges as seen 3 min into that video.

Cats do two or three different things and you need to vary the air mix going into them to light off the different processes. This is why narrowband o2 sensors that wiffle waffle around the right air/fuel mix have been so successful.
 
It's a sort of a no, and a no to your presumptions.

A lean misfire will dump unburned fuel with oxygen into the catalyst, and the catalyst WILL get them to burn, and with no power stroke between combustion and exhaust, the temperatures will skyrocket.

The extra fuel to burn off needs oxygen...it can't burn itself.
 
Originally Posted By: eljefino
I wish I were so lucky to have unrusted flanges as seen 3 min into that video.



Yeah. It don't work like that. Saw and reweld.
 
Many hi performance tunes will actually dump extra fuel into the cats during high load/long duration runs.

The mfgrs say it's for cooling...
 
If it is so lean that it doesn't burn in the cylinders, it is going to burn in the cat. The cat doesn't care why it is getting unburned fuel.....It just does what it does.
 
Originally Posted By: Miller88
https://www.youtube.com/watch?v=q5VaQ0wLOLw

I always thought running lean would cause them to not get up to temperature as they use extra fuel to "burn off".

Too much extra fuel definitely causes them to overheat ....


Too little fuel makes the overall EGT high even before it hits the cat, throw in a "lean misfire" that then adds some unburned A/F mix to the exhaust flow, and its a recipe for a red-hot catcon. Too rich (with air injection) will overheat the cat itself even though the pre-cat EGT is lower. Too much fuel without sufficient air will cool the cat- its not quite as simple as running too rich or too lean will overheat it.
 
The new car cal's that I have seen all have Catalyst Overtemp Protection functions. They richen the mixture well in excess of what is required to make best power in the engine. Most of the time, most cars on the road are running in closed loop with the O2 sensor controlling the air-fuel ratio at stoichiometric. Over about 75% throttle, the mixture is richened to best power, and at higher engine speeds, COP kicks in. The goal is to keep EGT from exceeding ~1650F to protect the cat.
 
With properly functioning fuel and ignition systems you don't even need a cat, emissions should be low enough to pass anyways..

Open carbs and straight pipes and I score 1.37% CO (pass is 4.5) and 401 ppm HC (pass is 1200)

And I put it down to accurate fuelling and good ignition components. No doubt a cat would get my numbers even lower but the extra cost and extra weight and reduction in ground clearance make it a pointless exercise when I pass the annual inspection with such a large margin.

Do any of you guys know your pre-cat emissions and wether they would pass or not?
 
I don't know of any states that had emissions inspections before cars got cats. Cats went on pretty much every passenger car in 1975. Pickup trucks didn't get cats until later.
 
We Oz had depending on states emissions inspections before cats, which came on in 1987.

They inspected for the removal of the ADR 27A abortions that were extant at the time, EGR, no vacuum advance in lower gears, only top...features that sapped about 30% of the effective displacement,and substituted fuel burn for PPM...could get lesser parts per mile travelled, but the standards were express concentration limits.

When Cat Cons came to Oz, they were pushing mandatory annual tailpipe emissions, and the garages were gearing up...but a pre cat vehicle could be made compliant with a basic tune-up, while a post cat vehicle needed $500 (1990 dollars) to be made compliant.

Cat Cons were a great boon to performance and economy, letting the engines have their displacement back, but were seriously early 70s in their emissions with a cat not functioning.
 
Originally Posted By: A_Harman
The new car cal's that I have seen all have Catalyst Overtemp Protection functions. They richen the mixture well in excess of what is required to make best power in the engine.


Originally Posted By: SteveSRT8
Many hi performance tunes will actually dump extra fuel into the cats during high load/long duration runs.

The mfgrs say it's for cooling...



The key here is that when extra fuel is used to cool the catalyst, it has to be done WITHOUT sufficient oxygen in the exhaust stream. In vehicles with air injection, it is shut off during catalyst protection. I'm sure it jacks up the HC emissions downstream of the catcon, but by saving the cat it lowers total life-cycle emissions.
 
Originally Posted By: Olas
With properly functioning fuel and ignition systems you don't even need a cat, emissions should be low enough to pass anyways..

Open carbs and straight pipes and I score 1.37% CO (pass is 4.5) and 401 ppm HC (pass is 1200)

And I put it down to accurate fuelling and good ignition components. No doubt a cat would get my numbers even lower but the extra cost and extra weight and reduction in ground clearance make it a pointless exercise when I pass the annual inspection with such a large margin.

Do any of you guys know your pre-cat emissions and wether they would pass or not?


My 1992 alfa 155 had a cat, but doesn't require one to pass MOT. CO emissions are below 0.5% even without the cat, PPM is extremely low (but not tested).
 
Hmm interesting. I didn't give thought to the fact that it could still be injecting fuel, but not enough to ignite and dumping that into the catalyst.

Lack of oxygen + extra fuel does make sense to me for cooling.
 
Originally Posted By: Miller88
Hmm interesting. I didn't give thought to the fact that it could still be injecting fuel, but not enough to ignite and dumping that into the catalyst.

Lack of oxygen + extra fuel does make sense to me for cooling.


The engine is acting as an air pump then. Outside air is much cooler than that of regular exhaust.

Cylinder misfires will burn up a cat too from the unburnt fuel.
 
Originally Posted By: lexus114
my rx 350 stinks like sulfur when i floor it. i hate that.


That's very much a Toyota thing, at least in recent years. Something unique to their catalyst protection algorithm. Back in the 70s, it was a very common smell behind carbureted cars with catcons, of all brands both because mixture control was a lot cruder and because there was more sulfur in gasolines. After fuel injection and computerized powertrain controls, it pretty much went away... then re-appeared mostly with Toyotas starting in the early 2000s, maybe late 1990s.

I drive my wife nuts because she'll be cruising along and I'll be looking down reading or something, catch a whiff of that smell and say, 'Toyota or Lexus ahead, accelerating or climbing a hill.' And I'm usually right- probably 80-90% of the time. She thinks I'm about half machine and can speak the machine language, I guess doing stuff like that to her doesn't help prove her wrong.. :p
 
Originally Posted By: Miller88
Hmm interesting. I didn't give thought to the fact that it could still be injecting fuel, but not enough to ignite and dumping that into the catalyst.

Lack of oxygen + extra fuel does make sense to me for cooling.


And when the engine is running fuel-rich there's lots of CO2 to to lower the speed and temperature of any burning that might happen downstream in the convertors as well.

There's also a use of "cool" exhaust gas in the gas-generator cycle rockets like the Saturn V first-stage engine. The turbopump exhaust isn't super fuel-rich, but at ~1200-1500F degrees F its a heckuva lot cooler than the main engine exhaust at 5800F. So its injected into the rocket bell extension around the circumference, where it acts like a "cool" boundary layer to protect the rocket bell extension (the upper part of the bell is cooled by liquid oxygen in a grid of tubes). The turbopump exhaust is the dark band you see coming out of the rocket bell on slow-motion video, before the 5800F gas mixes through the cooler gas film further away from the end of the rocket bell. See 2:13 thru 2:30 in this:

https://www.youtube.com/watch?v=DKtVpvzUF1Y&spfreload=10


When it comes to catalytic converters and rocket bells, "cool" is a relative term... ;-)
 
Originally Posted By: Olas
With properly functioning fuel and ignition systems you don't even need a cat, emissions should be low enough to pass anyways..

Open carbs and straight pipes and I score 1.37% CO (pass is 4.5) and 401 ppm HC (pass is 1200)

And I put it down to accurate fuelling and good ignition components. No doubt a cat would get my numbers even lower but the extra cost and extra weight and reduction in ground clearance make it a pointless exercise when I pass the annual inspection with such a large margin.

Do any of you guys know your pre-cat emissions and wether they would pass or not?


I took a quick look, and I would have to look later. I can find epa limits in grams per mile; but I cannot find ppm limits.
 
Originally Posted By: 440Magnum
Originally Posted By: lexus114
my rx 350 stinks like sulfur when i floor it. i hate that.


That's very much a Toyota thing, at least in recent years. Something unique to their catalyst protection algorithm. Back in the 70s, it was a very common smell behind carbureted cars with catcons, of all brands both because mixture control was a lot cruder and because there was more sulfur in gasolines. After fuel injection and computerized powertrain controls, it pretty much went away... then re-appeared mostly with Toyotas starting in the early 2000s, maybe late 1990s.

I drive my wife nuts because she'll be cruising along and I'll be looking down reading or something, catch a whiff of that smell and say, 'Toyota or Lexus ahead, accelerating or climbing a hill.' And I'm usually right- probably 80-90% of the time. She thinks I'm about half machine and can speak the machine language, I guess doing stuff like that to her doesn't help prove her wrong.. :p


hahaha, your right! funny thing is, if i use sunoco fuel (cause its a low sulpher fuel) or an 89 octane fuel instead of 87 (which it calls for) it doesnt do it.
 
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