pop goes the 5.0

[19COBRA93]

The maf failed on my buddys Procharged '11 as well, and had a subsequent engine failure which we think is related.

What are your build plans?

Ouch, sorry man.

Stock MAF? Please don't say it was a BA-5000.

The maf's on coyotes are frequency based, the SCT maf's don't work with them.

 

[BruceH]

Interesting. I assume it's just the rich fuel tables typically used, that then causes the unburned fuel to catalyze and overheat the cat. In theory a "proper" AFR would never allow a cat to do that, although I'm certainly on board with the rich = safe mindset.

Stoich is the same na or boosted.

This is the first case of factory cats going I've seen. Almost always they are aftermarket ceramic cats that can't take the heat a custom tune with the rear o2 sensors turned off is capable of generating.

FWIW I still have the stock cats on my car. It's been boosted at least 3 years off and on.

 

[19COBRA93]

Cobras and GT500's are boosted with cats... Just sayin.

 

[klaw]

Stoich is the same na or boosted.

This is the first case of factory cats going I've seen. Almost always they are aftermarket ceramic cats that can't take the heat a custom tune with the rear o2 sensors turned off is capable of generating.

FWIW I still have the stock cats on my car. It's been boosted at least 3 years off and on.

Cobras and GT500's are boosted with cats... Just sayin.

In our group around here, we have several examples of both aftermarket and stock cats failing on high HP boosted cars.

 

[19COBRA93]

In our group around here, we have several examples of both aftermarket and stock cats failing on high HP boosted cars.

So it really has nothing to do with them being boosted. It's just the high HP part that is apparently wiping them out.

IMO, it likely has more to do with high exhaust temps than anything else. That can happen on any car, boosted or not. It's just more likely on a high hp car when the tune is being pushed to the limit.

 

[klaw]

So it really has nothing to do with them being boosted. It's just the high HP part that is apparently wiping them out.

IMO, it likely has more to do with high exhaust temps than anything else. That can happen on any car, boosted or not. It's just more likely on a high hp car when the tune is being pushed to the limit.

It's all part of the same equation, the airflow through most boosted engines is higher. The cats only have a certain amount of cross sectional area and under the higher airflows, the pressure drop across the catalyst increases. The forces created by the pressure differential start to break the catalyst up which then starts to plug the flowpath which increases the pressure drop which increases the forces etc etc etc. Excessive heat obviously can't be helpful either. We have several cars in our group over 700 HP and none of us run cats anymore.

 

[FAST3V]

Damn, hella sucks...

 

[Greg Hazlett]

Cobras and GT500's are boosted with cats... Just sayin.

Yes but we know how detuned and safe from the factory they are.

 

[19COBRA93]

It's all part of the same equation, the airflow through most boosted engines is higher. The cats only have a certain amount of cross sectional area and under the higher airflows, the pressure drop across the catalyst increases. The forces created by the pressure differential start to break the catalyst up which then starts to plug the flowpath which increases the pressure drop which increases the forces etc etc etc. Excessive heat obviously can't be helpful either. We have several cars in our group over 700 HP and none of us run cats anymore.

It's not the flow that wipes them out. It's excessive heat from a lean tune. You can melt down cats just as easily with a lean n/a setup as you can with a lean boosted setup.

Yes but we know how detuned and safe from the factory they are.

That's my point. It has nothing to do with the boost, it's all about the tune.

 

[Greg Hazlett]

But the a/f ratio changes NA to FI, would that cause a cat to let go?

There is something to be said about the trend of hi flo cats letting go vice stock cats.

Not sure what the actual temp difference is between NA and FI but common sense suggests the FI exhaust has to be hotter which should lead to the break down of the cat material, right?

 

[klaw]

It's not the flow that wipes them out. It's excessive heat from a lean tune. You can melt down cats just as easily with a lean n/a setup as you can with a lean boosted setup.



That's my point. It has nothing to do with the boost, it's all about the tune.

The O2 sensor in my Kooks hi-flow cats sits between the two catalyst packs. The O2 sensor head was actually bent from the force of the front cat pack hitting against it due to the airflow. Cat failure can be tune related but it can also be a function of the physical design - some cats just don't have enough flow area to accommodate the increased airflow of engine modifications N/A or boosted.

 

[19COBRA93]

But the a/f ratio changes NA to FI, would that cause a cat to let go?

There is something to be said about the trend of hi flo cats letting go vice stock cats.

Not sure what the actual temp difference is between NA and FI but common sense suggests the FI exhaust has to be hotter which should lead to the break down of the cat material, right?

It all depends on the n/a tune. With both setups properly tuned, exhaust temps should be similar.

However, unburned fuel can also greatly increase cat temps and burn them up as well. So an overly rich condition could cause cat failure, which is also tune related, and not aspiration related.

 

[klaw]

But the a/f ratio changes NA to FI, would that cause a cat to let go?

There is something to be said about the trend of hi flo cats letting go vice stock cats.

Not sure what the actual temp difference is between NA and FI but common sense suggests the FI exhaust has to be hotter which should lead to the break down of the cat material, right?

It's not just the temperature of the exhaust gases but the rate of energy transfer to the cat. The rate of energy transfer is a function of the heat capacity of the fluid (exhaust gas in this case), the temperature of the fluid (EGT), and the mass flow rate of the fluid (airflow). If the flowrate is really low, even very hot EGT's can't transfer that heat to the cats. The cat itself and the exhaust tubing can dissipate the energy faster than the engine can deliver it. As the mass flowrate increases, the energy arrives at the cat faster than the cat can dissipate it (at a given temp) and the cat heats up in order to dissipate the energy faster. Both EGT and flowrate are important factors in proper sizing of a cat.

 

[Greg Hazlett]

It all depends on the n/a tune. With both setups properly tuned, exhaust temps should be similar.

However, unburned fuel can also greatly increase cat temps and burn them up as well. So an overly rich condition could cause cat failure, which is also tune related, and not aspiration related.

Huh...guess I was wrong..I assumed the FI exhaust would be hotter than NA due to the compressed air.

 

[infinite_one]

Ouch


Sent from my iPhone, please disregard grammatical errors.

 

[Vapour Trails]

The question is whether the destroyed cat was a symptom or the cause of the low compression cylinder. I'm assuming there was detonation due to the faulty MAF reading, could that have damaged the cat?

 

[DILYSI Dave]

Stoich is the same na or boosted.

This is the first case of factory cats going I've seen. Almost always they are aftermarket ceramic cats that can't take the heat a custom tune with the rear o2 sensors turned off is capable of generating.

FWIW I still have the stock cats on my car. It's been boosted at least 3 years off and on.

Agreed - Stoich is the same either way. But the consequences for running lean are higher in boosted cars, so they generally cheat the tuning to the rich side. Do it too much, and you end up cooking the cat.

 

[stang8psi]

So what are you going to do for a maf since the stock one failed ?

 

[gimpy]

So what are you going to do for a maf since the stock one failed ?

replaced it with another stock maf already.

 

[gimpy]

The maf failed on my buddys Procharged '11 as well, and had a subsequent engine failure which we think is related.

What are your build plans?

Tear into the motor to see what condition the block and heads are in then decide on tossing forged internals in it or doing a short/long block. Either way i'm going to drop the compression down to 9.5:1 or 10:1 to make it a little more boost friendly.