Benefits of Removing Cat and Running Straight Pipe?

[WRXGUY02]

Unless you have a forced induction vehicle don't even think about removing or gutting the cat. It will do nothing but hurt the enviroment and possibly make you lose hp or torque. Your engine is designed and tuned from the factory to have a certain amount of exhaust backpressure. If you change that it affects everything from how exhaust pulses exit the cylinder to combustion in the chamber. You need a certain amount of backpressure for the car to run correctly. Lets face it. If you bought a Yaris you didn't plan on having a fast car. That is unless you are planning on adding some form of forced induction. Even then.. It probably won't be really that fast. Faster than it was but without some kind of major engine overhaul and engine management you're not gonna beat too many things these days. Don't get me wrong. I respect the idea of modding a car. My Subaru has over 350AWHP and I love it. But you buy cars for what they are good at. The WRX is a AWD Performance Car. The Yaris is a FWD Economy car and there is nothing wrong with that. I am on this forum because I am about to buy a Yaris for my daily driver. I think they are great cars for what they were made for. Without a crap load of money invested there probably won't be too many fast Yaris's out there. Now.. onto the emissions lesson.

Gasoline Engines only produce a few harmful emmisions that are tested for.

HC- Hydrocarbons aka non completely combusted fuel
CO- Carbon Monoxide
NOx- Nitrogen Oxides- It is not Noxious Emissions as stated by another one of your users.. NOx is a deadly gas produced above 2500degrees F. Your EGR system in most vehicles is designed to help combat NOx. It would be a whole different lesson on how the EGR works.
CO2- Carbon dioxide- A properly working exhaust system will produce about 14% CO2.

Your Catalytic Convertor combats these emmisions.There are several chemical compounds and materials in the Cat that make is work. If anyone has ever had a cheap narrow band air/fuel sensor they see how your ratio is constantly going from rich to lean to rich very quickly. It actually switches about 10 times faster than the gauge shows. When you go to WOT the ECU automatically goes to rich. Your Cat fights emissions differently during different conditions. When the engine is rich the cat battles one emission and when the engine is lean it battles another. The target average between the two sides is 14.7 AFR. That is the ideal ratio to battle all the emmisions properly.

Bottom line is I felt I had to write this because I see a constant amount of bad information being written. I had to give people some proper direction. If you are trying pick up a few HP from removing the cat on a NA Yaris then you really are wasting your time. The money and time involved won't gain you any real results. Now if you are going forced induction it may help to remove the factory cat but I would replace it with a high flow. Just remember that no matter what you do that altering a working emmisions system is a Felony. The last time I checked it was like a $10,000 fine plus possible jail time. Remember I am not bashing Yaris's or their owners what so ever. I think they are great little cars and I look forward to owning one. If anyone has any other questions feel free to ask.

[largeorangefont]

Originally Posted by WRXGUY02

Unless you have a forced induction vehicle don't even think about removing or gutting the cat. It will do nothing but hurt the enviroment and possibly make you lose hp or torque. Your engine is designed and tuned from the factory to have a certain amount of exhaust backpressure. If you change that it affects everything from how exhaust pulses exit the cylinder to combustion in the chamber. You need a certain amount of backpressure for the car to run correctly. Lets face it. If you bought a Yaris you didn't plan on having a fast car. That is unless you are planning on adding some form of forced induction. Even then.. It probably won't be really that fast. Faster than it was but without some kind of major engine overhaul and engine management you're not gonna beat too many things these days. Don't get me wrong. I respect the idea of modding a car. My Subaru has over 350AWHP and I love it. But you buy cars for what they are good at. The WRX is a AWD Performance Car. The Yaris is a FWD Economy car and there is nothing wrong with that. I am on this forum because I am about to buy a Yaris for my daily driver. I think they are great cars for what they were made for. Without a crap load of money invested there probably won't be too many fast Yaris's out there. Now.. onto the emissions lesson.

Gasoline Engines only produce a few harmful emmisions that are tested for.

HC- Hydrocarbons aka non completely combusted fuel
CO- Carbon Monoxide
NOx- Nitrogen Oxides- It is not Noxious Emissions as stated by another one of your users.. NOx is a deadly gas produced above 2500degrees F. Your EGR system in most vehicles is designed to help combat NOx. It would be a whole different lesson on how the EGR works.
CO2- Carbon dioxide- A properly working exhaust system will produce about 14% CO2.

Your Catalytic Convertor combats these emmisions.There are several chemical compounds and materials in the Cat that make is work. If anyone has ever had a cheap narrow band air/fuel sensor they see how your ratio is constantly going from rich to lean to rich very quickly. It actually switches about 10 times faster than the gauge shows. When you go to WOT the ECU automatically goes to rich. Your Cat fights emissions differently during different conditions. When the engine is rich the cat battles one emission and when the engine is lean it battles another. The target average between the two sides is 14.7 AFR. That is the ideal ratio to battle all the emmisions properly.

Bottom line is I felt I had to write this because I see a constant amount of bad information being written. I had to give people some proper direction. If you are trying pick up a few HP from removing the cat on a NA Yaris then you really are wasting your time. The money and time involved won't gain you any real results. Now if you are going forced induction it may help to remove the factory cat but I would replace it with a high flow. Just remember that no matter what you do that altering a working emmisions system is a Felony. The last time I checked it was like a $10,000 fine plus possible jail time. Remember I am not bashing Yaris's or their owners what so ever. I think they are great little cars and I look forward to owning one. If anyone has any other questions feel free to ask.

So its ok to remove all cats on a WRX but not on a Yaris? That makes no sense. A catless Yaris will pollute about half or less of what a catless WRX will.

You lesson is about half correct. Keeping the AFR at 14.7:1 is not some "emission balance", it is chemistry, specifically it is Stoichiometry. It is the point at which 100% of fuel and air is used in a given reaction. In this case that reaction is the combustion process. Because byproducts of combustion such as heat are created, cars need to be run richer than 14.7:1 under load to keep the engine from destroying itself.

Your cat works better the hotter it is. Above 1600 degrees the cat can melt or burn up, which is bad. If your car is tuned to rich, the cat won't get hot enough to work properly, and could become clogged.

Your narrowband example in not valid. The car is not actually making wild swings in fueling. The narrowband gauge does that because it is taking a reading from a vary narrow voltage window. Anything below is rich, anything above is lean. That is why you use wideband sensors for tuning.

Removing the cats on a Yaris WILL get you 1-2 HP. Every engine mod you do to a Yaris except FI gets you a couple HP. If the car is catless, it will smell and stoplights, and you may not like that. Hi flow cats are a good alternative, and you will still keep the HP gain, and most likely pass a smog test. Contrary to what you said, removing the cats does not remove all back pressure and make the car lose power.

If you installed a 3 inch catless exhaust system on the car, then yes, you would lose too much backpressure and feel a loss in low end power, but no one is doing that.

[Jeepman28]

wow I just traveling the interwebs and ran across this I know it is a bit old but I just have to laugh at all of you,

One: you all own a f'ing Yaris, really who own those pieces of crap!
Two: The guy that started this thread hit it on the head when he said that Global Warming is BS. It is made up to do this shit, make us buy shit for our cars and homes that don't need to be there, or go out and buy a new car because it is "Cleaner"
Three: A Motor is like a big Air pump that more air up push though it the faster and stronger she will be, "remember the muscle car races from the big Three bigger motors that sucked as much air as possible and pushed it out just as fast. I got rid of My Cat. when I got my ZJ and shorten my pipe and put on a 3.5in upgrade, plus I ripped out all the computer crap and put a crab in replace of the EFI I haven't been happier, And to top it off I drive over yaris's and other shitty Toyota's on the weekend.

[3cyltrbo]

Originally Posted by Jeepman28

wow I just traveling the interwebs and ran across this I know it is a bit old but I just have to laugh at all of you,

One: you all own a f'ing Yaris, really who own those pieces of crap!
Two: The guy that started this thread hit it on the head when he said that Global Warming is BS. It is made up to do this shit, make us buy shit for our cars and homes that don't need to be there, or go out and buy a new car because it is "Cleaner"
Three: A Motor is like a big Air pump that more air up push though it the faster and stronger she will be, "remember the muscle car races from the big Three bigger motors that sucked as much air as possible and pushed it out just as fast. I got rid of My Cat. when I got my ZJ and shorten my pipe and put on a 3.5in upgrade, plus I ripped out all the computer crap and put a crab in replace of the EFI I haven't been happier, And to top it off I drive over yaris's and other shitty Toyota's on the weekend.

ROFLMAO.

This right here (post above), is reason enough for higher education.

Will

[MadMax]

Originally Posted by Jeepman28

wow I just traveling the interwebs and ran across this I know it is a bit old but I just have to laugh at all of you,

One: you all own a f'ing Yaris, really who own those pieces of crap!
Two: The guy that started this thread hit it on the head when he said that Global Warming is BS. It is made up to do this shit, make us buy shit for our cars and homes that don't need to be there, or go out and buy a new car because it is "Cleaner"
Three: A Motor is like a big Air pump that more air up push though it the faster and stronger she will be, "remember the muscle car races from the big Three bigger motors that sucked as much air as possible and pushed it out just as fast. I got rid of My Cat. when I got my ZJ and shorten my pipe and put on a 3.5in upgrade, plus I ripped out all the computer crap and put a crab in replace of the EFI I haven't been happier, And to top it off I drive over yaris's and other shitty Toyota's on the weekend.

What is even more hilarious is someone who owns a Grand Cherokee and thinks it is a fucking Jeep!

Get a REAL Jeep, that would be one that resembles the original Willys; and ditch that POS ZJ you have. It's for pussies...and I'd rather drive a Yaris than that joke!

(Damn, just noticed he's already gone! And here I am awaiting his witty response! )