To CAT or not to CAT, that is the question

[airjor13]

If you get a downpipe with a cat back, will it fail the emissions check?

If the down-pipe is cat-less, most likely yes you will fail emissions. If the down-pipe has an high-flow cat, most likely no you will not fail, but it all depends on the cell-count of the cat and/or the sensitivity of the emission test equipment.

I have seen people fail VA emissions with a high-flow cat, but I was not sure of the cell-count.

 

[joe@2j-racing]

Swapping the downpipe takes all of 15mins once you are running an aftermarket one. I'll ask Tim today @ Cobb about the rear 02. If I can work around an antifouler and not use it, then thats what we'll do!

 

[MrClean]

Plain and simple version for all those wondering:

Having an open (i.e. de-catted) downpipe will 9 times of out 10 fail your emissions test.

Having an semi-open (i.e. high-flow cat.) will allow you to pass emissions in some states, not in others. It boils down to how much of a nanny-state you reside in.

Having any sort of downpipe, whether it has a catalytic converter or not, in California, will automatically fail your emissions test.

Having a cat-back exhaust, will not fail your emissions.




Example combinations:
Stock cat + stock exhaust = pass!

Stock cat + aftermarket exhaust = pass!

High-flow downpipe + stock exhaust = sometimes pass! (check local laws)

High-flow downpipe + aftermarket exhaust = most likely going to fail

Open downpipe + stock exhaust = Fail!

Open downpipe + aftermarket exhaust = Fail! (But you will sound like one bad ass mo-fo rolling around city streets!!!)

 

[airjor13]

Plain and simple version for all those wondering:

Having an open (i.e. de-catted) downpipe will 9 times of out 10 fail your emissions test.

Having an semi-open (i.e. high-flow cat.) will allow you to pass emissions in some states, not in others. It boils down to how much of a nanny-state you reside in.

Having any sort of downpipe, whether it has a catalytic converter or not, in California, will automatically fail your emissions test.

Having a cat-back exhaust, will not fail your emissions.

Good summary!

 

[the duke]

No CAT for the win, cat-less DP is the best bang for the buck power mod you can do. Tree hugger's be damned. VA has emissions testing too......but not for every county

Or don't be a jerk and buy a cat. You will see ZERO difference in sound or power with a high-flow cat while still being (somewhat) legal and emission compliant.


I imagine the "NOT CAT IS BEST" crowd are the same that think we need 3'' straight-pipe for maximum flow.

 

[pwnall1337]

Or don't be a jerk and buy a cat. You will see ZERO difference in sound or power with a high-flow cat while still being (somewhat) legal and emission compliant.


I imagine the "NOT CAT IS BEST" crowd are the same that think we need 3'' straight-pipe for maximum flow.

No emmissions testing In Bexar County, San Antonio,TX

 

[joe@2j-racing]

Or don't be a jerk and buy a cat. You will see ZERO difference in sound or power with a high-flow cat while still being (somewhat) legal and emission compliant.


I imagine the "NOT CAT IS BEST" crowd are the same that think we need 3'' straight-pipe for maximum flow.

Both are incorrect, esp regarding the Fiesta.

 

[the duke]

Both are incorrect, esp regarding the Fiesta.

You're telling me my larger mass flow, higher flowing, IHI VF39 (which see almost no gain Cat vs. Catless OR 3 inch piping) ii less affected by smaller diameter piping or restrictions than the unit in the ecoboost? How did you come to that conclusion?

 

[joe@2j-racing]

We've tested catted, high flow catted, race catted, 2.25, 2.5 and 3.0 and 3.0 with a merge. You can do that when you have a dyno in the next room.

 

[airjor13]

Or don't be a jerk and buy a cat. You will see ZERO difference in sound or power with a high-flow cat while still being (somewhat) legal and emission compliant.

I imagine the "NOT CAT IS BEST" crowd are the same that think we need 3'' straight-pipe for maximum flow.

 

[airjor13]

We've tested catted, high flow catted, race catted, 2.25, 2.5 and 3.0 and 3.0 with a merge. You can do that when you have a dyno in the next room.

 

[pwnall1337]

Or don't be a jerk and buy a cat. You will see ZERO difference in sound or power with a high-flow cat while still being (somewhat) legal and emission compliant.

I imagine the "NOT CAT IS BEST" crowd are the same that think we need 3'' straight-pipe for maximum flow.

Both are incorrect, esp regarding the Fiesta.

You're telling me my larger mass flow, higher flowing, IHI VF39 (which see almost no gain Cat vs. Catless OR 3 inch piping) ii less affected by smaller diameter piping or restrictions than the unit in the ecoboost? How did you come to that conclusion?

We've tested catted, high flow catted, race catted, 2.25, 2.5 and 3.0 and 3.0 with a merge. You can do that when you have a dyno in the next room.

 

[the duke]

We've tested catted, high flow catted, race catted, 2.25, 2.5 and 3.0 and 3.0 with a merge. You can do that when you have a dyno in the next room.

How was the test completed? In succession? Same days? Multiple runs? What parameters were measured, exhaust gas temperature, exhaust velocity, pressure drop, etc? What were the measured deltas between configurations? How was the testing compiled (what order and what configurations)

Dynos are not an absolute measuring device. There are way too many variables to account for to perform a proper DOE.

Bring the tech.



EDIT - let me clarify. Now I want to understand the mechanism of change. Its entirely possible there is a change, but the mechanism of change doesn't directly point to one specific variable.

 

[RAAMaudio]

I decided to cat because I believe we should do what we can for the environment so I do, I can give up a little power for that.

I just hope it gets hot enough to do the job, 5" diameter, 100 cell count, least restrictive cat I have ever seen.

If it does not do a decent job I will have to put a 4" 200 cell cat on and try again.

The DP should be done today, exhaust tomorrow, still intake or tune, big IC on the way, GT....turbo when ready.......

 

[joe@2j-racing]

How was the test completed? In succession? Same days? Multiple runs? What parameters were measured, exhaust gas temperature, exhaust velocity, pressure drop, etc? What were the measured deltas between configurations? How was the testing compiled (what order and what configurations)

Dynos are not an absolute measuring device. There are way too many variables to account for to perform a proper DOE.

Bring the tech.



EDIT - let me clarify. Now I want to understand the mechanism of change. Its entirely possible there is a change, but the mechanism of change doesn't directly point to one specific variable.

SMH We're a cobb protuner. The PIDs tell you everything you need to know.

 

[airjor13]

How was the test completed? In succession? Same days? Multiple runs? What parameters were measured, exhaust gas temperature, exhaust velocity, pressure drop, etc? What were the measured deltas between configurations? How was the testing compiled (what order and what configurations)

Dynos are not an absolute measuring device. There are way too many variables to account for to perform a proper DOE.

Bring the tech.

EDIT - let me clarify. Now I want to understand the mechanism of change. Its entirely possible there is a change, but the mechanism of change doesn't directly point to one specific variable.

Duke, why are you hatting on people to go cat-less? I respect your decision to keep the cat and your opinion on the positives of the cat and environment and blah blah, but DO bring it down a notch and keep it respectful.

 

[the duke]

Duke, why are you hatting on people to go cat-less? I respect your decision to keep the cat and your opinion on the positives of the cat and environment and blah blah, but DO bring it down a notch and keep it respectful.

Its unnecessary. Same thing happens with Subaru people who want the most power for all the bragging rights.

And this is not hostile. I asked for data and got a simple "trust us". Engines are highly complex machines in constant feedback loops. Lack of control of variables invalidates any and all data. Yes, a dynomometer is nice tool to have, but they have high variability between runs and are a single tool to test changes. Sure, you can get match a mass flow rate by simply increasing velocity or decreasing pressure, but there is a point where the velocity drops too much and your mass flow drops. Same as adding too large an intercooler, the air slows too much. Given the displacement of the engine and the compression ratio or the turbine, it is significantly less than the unit in my Subaru both in flow rate and displacement. Exhaust energy could be greater due to higher limits of DI, but I don't know what they measured them at. I don't know what their inlet/ out pressure was, turbine rpm, or exhaust gas velocity. All these things affect the energy content, flow, and thus performance. And that's assuming the car doesn't correct itself. I suppose the best outlet would be a divergent nozzle design (think De Lavel nozzle) would separate the exhaust flow best, but this isn't formula one. Thus we're left with tubing. Without data this is mostly speculation but drawing upon my previous experience, there should not be a significant difference.


Maybe I'm too used to my controlled environments at work, but I'm not attacking them, I want to know what they did, what was measured, and what the results were. If its a simple 4hp peak delta, that's variability on a dyno (run your car 3 times and see what the results are. Then run it 10 days later). What else was changed, was it bolt on/off or did they tweak other parameters.), etc. This is no different than my cold spray research. We played with many different nozzle designs and some were better than others. We had a problem with the computer logic adjusting parameters to meet specific pressure and temperature sets before initiating the test, which some we could not align.


Im sorry if I came off as harsh. I'm an engineer at a stressful job. I want to know the tech and reason behind anything even if I'm proven wrong. I just want to be proven wrong correctly, not just " us vs. Him". Prove me wrong. I hate mis-information but until I have better evidence, I don't see cat vs. Catless having a significant enough difference. And if there is a measured difference, we can start to argue configurations, distances, materials, etc. Its a never ending cycle

 

[airjor13]

Its unnecessary. Same thing happens with Subaru people who want the most power for all the bragging rights.

And this is not hostile. I asked for data and got a simple "trust us". Engines are highly complex machines in constant feedback loops. Lack of control of variables invalidates any and all data. Yes, a dynomometer is nice tool to have, but they have high variability between runs and are a single tool to test changes. Sure, you can get match a mass flow rate by simply increasing velocity or decreasing pressure, but there is a point where the velocity drops too much and your mass flow drops. Same as adding too large an intercooler, the air slows too much. Given the displacement of the engine and the compression ratio or the turbine, it is significantly less than the unit in my Subaru both in flow rate and displacement. Exhaust energy could be greater due to higher limits of DI, but I don't know what they measured them at. I don't know what their inlet/ out pressure was, turbine rpm, or exhaust gas velocity. All these things affect the energy content, flow, and thus performance. And that's assuming the car doesn't correct itself. I suppose the best outlet would be a divergent nozzle design (think De Lavel nozzle) would separate the exhaust flow best, but this isn't formula one. Thus we're left with tubing. Without data this is mostly speculation but drawing upon my previous experience, there should not be a significant difference.

Maybe I'm too used to my controlled environments at work, but I'm not attacking them, I want to know what they did, what was measured, and what the results were. If its a simple 4hp peak delta, that's variability on a dyno (run your car 3 times and see what the results are. Then run it 10 days later). What else was changed, was it bolt on/off or did they tweak other parameters.), etc. This is no different than my cold spray research. We played with many different nozzle designs and some were better than others. We had a problem with the computer logic adjusting parameters to meet specific pressure and temperature sets before initiating the test, which some we could not align.

Im sorry if I came off as harsh. I'm an engineer at a stressful job. I want to know the tech and reason behind anything even if I'm proven wrong. I just want to be proven wrong correctly, not just " us vs. Him". Prove me wrong. I hate mis-information but until I have better evidence, I don't see cat vs. Catless having a significant enough difference. And if there is a measured difference, we can start to argue configurations, distances, materials, etc. Its a never ending cycle

First off, nobody is bragging about anything, it's just a discussion. I would like to know what would you suggesting then? Stock DP is best? If a dynometer is not the best way to measure power gains, then what is?

Remember we are talking about <$30K sub-compact hot hatches, not F1, what do you recommend to use to measure any gains?

You said it yourself you are purely drawing this up on speculation, how about this, if a CAT doesn't make a difference, why are the new V6T F1 engines not running one?

They should be because it doesn't make a difference in power and its better for the environment??

 

[the duke]

First off, nobody is bragging about anything, it's just a discussion. I would like to know what would you suggesting then? Stock DP is best? If a dynometer is not the best way to measure power gains, then what is?

Remember we are talking about <$30K sub-compact hot hatches, not F1, what do you recommend to use to measure any gains?

You said it yourself you are purely drawing this up on speculation, how about this, if a CAT doesn't make a difference, why are the new V6T F1 engines not running one?

They should be because it doesn't make a difference in power and its better for the environment??

I'm not saying stock is best, OEM cats are the big restriction on any car due to emission regs (both us and EU. The point is a high flow cat (low density unit) should be able to flow as much as Catless, and until I see evidence, 3" piping is not an optimal cross-sectional area. From what I have seen there simply isn't enough air to warrant that size of tubing. I've asked for proof, but I admit what I'm looking for I don't really expect many to have. Other factors are likely at work beyond just " we swapped a part therefore its the reason". On a closed system with controls, yes. On a massively complex and feedback looped machine, not so much.

The dyno is a tool. Dont rely on one tool. Its a great tool, but it is not (and shouldn't) be a definitive answer. Its used to measure changes that in conjunction with other data can draw a conclusion.

And yes, let's compare a fiesta to a formula 1 car that is in no way completely misguided. I was only using f1 as an example to illustrate the optimal outlet of a turbine (which would likely still apply to the fiesta), not to be taken literally in a wild comparison at face value. Besides, current turbo f1 cars do get better mileage and lower emissions thanks to forced induction, hotter temps, and smaller engines. Other race series have cats though.

 

[baldtaco]

Back to the point at hand, I always run catless on forced induction cars so I have no chance of melting it and causing a lean condition.