Benefits of Removing Cat and Running Straight Pipe? - Toyota Yaris Forums

WRXGUY02 · 10-19-2008, 02:13 PM

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.

10-19-2008, 02:13 PM	#18
WRXGUY02 I've made a post! Drives: 02 WRX Impreza Join Date: Oct 2008 Location: Fort Myers, Florida Posts: 1	Catalytic Convertor Removal... 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.