I kinda of threw this in another post, where it quickly got buried. So I'm reposting it here, for further discussion. This thread was originally on another forum, in regards to comments from individuals on why the...
Mazda 3, Mazda 6, and Rx-8 had insanely high A/F ratios at WOT @ upper rpm's. How high? How's this AF look.
Actually dips below 10:1 stock, but most of the dynojets can't even read that low.
This is an issue that will begin affecting more and more new car's, as manufacturers try to match EPA2's new regulations for catalytic converter life, and there 5 min warmup cycle requirement.
Here's the original thread.
Here's some quotes and links as to why the 3,6,8,MPV...well every single 2004+ model car will now be running super rich.
Here's one of our earlier discussions on the problem.
http://forum.mazda6tech.com/viewtopic.php?t=644&start=0
And here's a quote from Canzoomer who developed the Stage 1 through Stage 3 ecu piggybacks for the rx8 (their fuel dilution was over 3%!!!!!) to help fix the rich problem.
quote:
--------------------------------------------------------------------------------
Hi there,
I followed your work with the RX-8 and was hoping that with your experience you could answer a more general question.
I seem to recall you saying that the RX-8 went lean at mid-RPMs to help heat the catalytic converters quickly, but rich at high RPMs to prevent them from overheating.
However, I thought the danger in overheating the catalytic converters was from running rich, where unburned fuel could ignite upon contact with the converter itself.
--------------------------------------------------------------------------------
There are a couple of factors at play here:
A catalytic converter actually burns some residual fuel left in the exhaust, to create the necessary amount of heat to support the chemical reaction. Ideally a small amount of fuel is needed, and the cat heats up to operating temperatures within around 10 minutes of startup.
However the EPA2 regulations which went into effect with the 2004 model year now require that the cat be at full operating efficiency within 5 minutes of startup. To promote this, the warmup cycle of the RX-8 is richer than what we would normally see, so as to heat the cat faster.
Now for the situation when warmed up:
A rotary engine makes higher exhaust gas temperatures than a piston engine, especially at higher rpm ranges. You are correct in saying that adding more fuel will cause the catalytic converter to burn more fuel and run hotter. At higher rpm the problem is compounded, as the incoming exhaust gases are quite hot. Typically, in second gear, at above 7,000rpm it is up to 1,640F BEFORE the cat.
Now, with the fuel in the mix, at an ideal AFR, we will see the cat rise above 1800F internally, which can cause some of the catalyst coatings to burn off the substrate. Typically this will result in the coatings lasting perhaps 50,000 miles or so.
Back to the new EPA2 regulations:
The cat must now be designed to last 120,000 miles, or the manufacturer will have to replace them, at pretty high cost, if they do not last.
So, Mazda was forced to do a rather nasty thing:
IF you add too much fuel to any oxidization reaction ( burning there will not be enough oxygen to support a full consumption of the fuel, and combustion temperatures will drop.
So, they run the engine VERY rich at higher rpm, and this effectively "quenches" the burning process inside the cat, thereby lowering the temperature.
The side effects are:
- Reduction in power at higher rpm, due to an overly rich mixture
- Increase of fuel consumption at higher rpm
- A lot of carbon, not fully burned, so you see a lot of soot on the tailpipes.
- A build up of carbon in the combustion chamber, and on the plug tips, causing some rough running, and some plug fouling.
We adjust the AFR back to a more ideal level for power, but in doing so, we cause the temperature inside the cat to rise higher than stock. This means that the cat is back to a shorter life due to higher internal temperatures. At a certain point, this effect becomes quite pronounced, and the cat may only last 5 to 10,000 miles.
With a tune causing an AFR in the range of 12.5:1 to 13.0:1 we see a cat life likely to be around 30,000 to 50,000 miles. Catalytic converter iternal temperatures are at around 1,800F
With a tune running up to 13.5:1 we see temperatures rising to as high as 1900F, and this will strip the coatings inside the cat within less than 10,000 miles.
quote:
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So with a leaner a/f ratio, are you really at MORE of a risk with destroying the catalytic converter?
--------------------------------------------------------------------------------
Yes, as per above.
quote:
--------------------------------------------------------------------------------
(I am currently working to tune a Mazda6, which runs south of a 10:1 a/f ratio stock- ouch- and has precats on the headers. If you're interested, I've posed this question in a thread, here: http://forum.mazda6tech.com/viewtopic.php?t=644)
Thanks for your insight, and keep up the outstanding work!
--------------------------------------------------------------------------------
Welcome.
The practice of running the top end too rich is not confined to the RX-8. Many cars from Mazda, Honda, Nissan, etc. are being tuned this way now, so as to make the cats last longer. Basically, the higher rpm ranges are the problem for them.
quote:
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To think that a Manufacturer would intentionally increase fuel consumption is ridiculous.
--------------------------------------------------------------------------------
So there you go. There is your explanation as to why the 3, 6, 8, MPV, and Tribute...will now all be soot covered and carboned all to **** . Because of EPA2. Its mazda's solution to the new regulations. Its also why the rx8's hp was dipped from 250 to 238...and people got buy back options. The EPA regulations were slapped on right at the last second...much to every manufacturers angst.
So what can you do? It won't matter what car you go with now, because EPA2 effects all US branded models (Starting with the 2004 model years). The only solution is aftermarket. (A/F tuning/High Flow cats)
This is also the reason why the intakes are giving absolutely rediculous gains...like 25 peak WHP gain on the CP-E system...lean out the ratio from 10:1 and you get a hella lotta power...but your cat's won't last no 120k .
Here's the EPA link on the new "Tier 2" regulations being enacted on all 04 models.
http://www.epa.gov/otaq/regs/ld-hwy/tier-2/index.htm
quote:
--------------------------------------------------------------------------------
The Tier 2 Vehicle and Gasoline Sulfur Program is a landmark program that affects every new passenger vehicle and every gallon of gasoline sold in the U.S. By designing cleaner cars that run on cleaner fuels the result is cleaner air. The program is a series of "firsts." For the first time:
SUVs, pickups, vans, and even the largest personal passenger vehicles are subject to the same national emission standards as cars;
vehicles and the fuels they use are treated as a system, so the cleaner vehicles will have the low-sulfur gasoline they need to run their cleanest;
new emission standards apply to all light vehicles, regardless of whether they run on gasoline, diesel fuel, or alternative fuels.
The Tier 2 Vehicle and Gasoline Sulfur program is part of a series of major initiatives that will reduce emissions from passenger vehicles, highway trucks and buses, and nonroad diesel equipment. The result will be reduced emissions, cleaner air, and improved human health.
On EPA's Green Vehicle Guide Web site you can research which cars, SUVs and trucks meet the new standards.
--------------------------------------------------------------------------------
http://www.epa.gov/otaq/regs/ld-hwy/tier-2/basicinfo.htm
quote:
--------------------------------------------------------------------------------
The key to meeting the stringent Tier 2 emission standards in such a short time has been the large reduction in sulfur levels in gasoline. Sulfur in the fuel impairs the effectiveness of vehicle emission control systems. By removing most of the sulfur from gasoline, oil refiners are helping the new emission controls work longer and more efficiently. Average national gasoline sulfur levels are already declining, and by 2006 will be 90% lower than before the program. Sulfur in gasoline has no fuel value, in fact it can damage sensitive components such as onboard diagnostics systems and fuel injection systems. As a result, even vehicles manufactured prior to the 2004 Model Year will benefit from using low-sulfur fuel.
--------------------------------------------------------------------------------
There is more on their site...you can also check the rules yourself which require cat's to last 120,000 miles.
Its my belief that products such as LC, FP, and Auto-RX will greatly increase in value as more and more manufacturers are forced to followed EPA2 regulations for cat warmup and longevity, requiring the use of overrich A/F mixtures, just for the sake of "environmental cash backs"
Mazda 3, Mazda 6, and Rx-8 had insanely high A/F ratios at WOT @ upper rpm's. How high? How's this AF look.
Actually dips below 10:1 stock, but most of the dynojets can't even read that low.
This is an issue that will begin affecting more and more new car's, as manufacturers try to match EPA2's new regulations for catalytic converter life, and there 5 min warmup cycle requirement.
Here's the original thread.
Here's some quotes and links as to why the 3,6,8,MPV...well every single 2004+ model car will now be running super rich.
Here's one of our earlier discussions on the problem.
http://forum.mazda6tech.com/viewtopic.php?t=644&start=0
And here's a quote from Canzoomer who developed the Stage 1 through Stage 3 ecu piggybacks for the rx8 (their fuel dilution was over 3%!!!!!) to help fix the rich problem.
quote:
--------------------------------------------------------------------------------
Hi there,
I followed your work with the RX-8 and was hoping that with your experience you could answer a more general question.
I seem to recall you saying that the RX-8 went lean at mid-RPMs to help heat the catalytic converters quickly, but rich at high RPMs to prevent them from overheating.
However, I thought the danger in overheating the catalytic converters was from running rich, where unburned fuel could ignite upon contact with the converter itself.
--------------------------------------------------------------------------------
There are a couple of factors at play here:
A catalytic converter actually burns some residual fuel left in the exhaust, to create the necessary amount of heat to support the chemical reaction. Ideally a small amount of fuel is needed, and the cat heats up to operating temperatures within around 10 minutes of startup.
However the EPA2 regulations which went into effect with the 2004 model year now require that the cat be at full operating efficiency within 5 minutes of startup. To promote this, the warmup cycle of the RX-8 is richer than what we would normally see, so as to heat the cat faster.
Now for the situation when warmed up:
A rotary engine makes higher exhaust gas temperatures than a piston engine, especially at higher rpm ranges. You are correct in saying that adding more fuel will cause the catalytic converter to burn more fuel and run hotter. At higher rpm the problem is compounded, as the incoming exhaust gases are quite hot. Typically, in second gear, at above 7,000rpm it is up to 1,640F BEFORE the cat.
Now, with the fuel in the mix, at an ideal AFR, we will see the cat rise above 1800F internally, which can cause some of the catalyst coatings to burn off the substrate. Typically this will result in the coatings lasting perhaps 50,000 miles or so.
Back to the new EPA2 regulations:
The cat must now be designed to last 120,000 miles, or the manufacturer will have to replace them, at pretty high cost, if they do not last.
So, Mazda was forced to do a rather nasty thing:
IF you add too much fuel to any oxidization reaction ( burning there will not be enough oxygen to support a full consumption of the fuel, and combustion temperatures will drop.
So, they run the engine VERY rich at higher rpm, and this effectively "quenches" the burning process inside the cat, thereby lowering the temperature.
The side effects are:
- Reduction in power at higher rpm, due to an overly rich mixture
- Increase of fuel consumption at higher rpm
- A lot of carbon, not fully burned, so you see a lot of soot on the tailpipes.
- A build up of carbon in the combustion chamber, and on the plug tips, causing some rough running, and some plug fouling.
We adjust the AFR back to a more ideal level for power, but in doing so, we cause the temperature inside the cat to rise higher than stock. This means that the cat is back to a shorter life due to higher internal temperatures. At a certain point, this effect becomes quite pronounced, and the cat may only last 5 to 10,000 miles.
With a tune causing an AFR in the range of 12.5:1 to 13.0:1 we see a cat life likely to be around 30,000 to 50,000 miles. Catalytic converter iternal temperatures are at around 1,800F
With a tune running up to 13.5:1 we see temperatures rising to as high as 1900F, and this will strip the coatings inside the cat within less than 10,000 miles.
quote:
--------------------------------------------------------------------------------
So with a leaner a/f ratio, are you really at MORE of a risk with destroying the catalytic converter?
--------------------------------------------------------------------------------
Yes, as per above.
quote:
--------------------------------------------------------------------------------
(I am currently working to tune a Mazda6, which runs south of a 10:1 a/f ratio stock- ouch- and has precats on the headers. If you're interested, I've posed this question in a thread, here: http://forum.mazda6tech.com/viewtopic.php?t=644)
Thanks for your insight, and keep up the outstanding work!
--------------------------------------------------------------------------------
Welcome.
The practice of running the top end too rich is not confined to the RX-8. Many cars from Mazda, Honda, Nissan, etc. are being tuned this way now, so as to make the cats last longer. Basically, the higher rpm ranges are the problem for them.
quote:
--------------------------------------------------------------------------------
To think that a Manufacturer would intentionally increase fuel consumption is ridiculous.
--------------------------------------------------------------------------------
So there you go. There is your explanation as to why the 3, 6, 8, MPV, and Tribute...will now all be soot covered and carboned all to **** . Because of EPA2. Its mazda's solution to the new regulations. Its also why the rx8's hp was dipped from 250 to 238...and people got buy back options. The EPA regulations were slapped on right at the last second...much to every manufacturers angst.
So what can you do? It won't matter what car you go with now, because EPA2 effects all US branded models (Starting with the 2004 model years). The only solution is aftermarket. (A/F tuning/High Flow cats)
This is also the reason why the intakes are giving absolutely rediculous gains...like 25 peak WHP gain on the CP-E system...lean out the ratio from 10:1 and you get a hella lotta power...but your cat's won't last no 120k .
Here's the EPA link on the new "Tier 2" regulations being enacted on all 04 models.
http://www.epa.gov/otaq/regs/ld-hwy/tier-2/index.htm
quote:
--------------------------------------------------------------------------------
The Tier 2 Vehicle and Gasoline Sulfur Program is a landmark program that affects every new passenger vehicle and every gallon of gasoline sold in the U.S. By designing cleaner cars that run on cleaner fuels the result is cleaner air. The program is a series of "firsts." For the first time:
SUVs, pickups, vans, and even the largest personal passenger vehicles are subject to the same national emission standards as cars;
vehicles and the fuels they use are treated as a system, so the cleaner vehicles will have the low-sulfur gasoline they need to run their cleanest;
new emission standards apply to all light vehicles, regardless of whether they run on gasoline, diesel fuel, or alternative fuels.
The Tier 2 Vehicle and Gasoline Sulfur program is part of a series of major initiatives that will reduce emissions from passenger vehicles, highway trucks and buses, and nonroad diesel equipment. The result will be reduced emissions, cleaner air, and improved human health.
On EPA's Green Vehicle Guide Web site you can research which cars, SUVs and trucks meet the new standards.
--------------------------------------------------------------------------------
http://www.epa.gov/otaq/regs/ld-hwy/tier-2/basicinfo.htm
quote:
--------------------------------------------------------------------------------
The key to meeting the stringent Tier 2 emission standards in such a short time has been the large reduction in sulfur levels in gasoline. Sulfur in the fuel impairs the effectiveness of vehicle emission control systems. By removing most of the sulfur from gasoline, oil refiners are helping the new emission controls work longer and more efficiently. Average national gasoline sulfur levels are already declining, and by 2006 will be 90% lower than before the program. Sulfur in gasoline has no fuel value, in fact it can damage sensitive components such as onboard diagnostics systems and fuel injection systems. As a result, even vehicles manufactured prior to the 2004 Model Year will benefit from using low-sulfur fuel.
--------------------------------------------------------------------------------
There is more on their site...you can also check the rules yourself which require cat's to last 120,000 miles.
Its my belief that products such as LC, FP, and Auto-RX will greatly increase in value as more and more manufacturers are forced to followed EPA2 regulations for cat warmup and longevity, requiring the use of overrich A/F mixtures, just for the sake of "environmental cash backs"
