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removing the two catalysts converters under the JK

 
Old 09-19-2009, 05:09 PM
  #11  
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Originally Posted by drumnatural View Post

From what I see it looks like the second two are just resonators. The first o2 sensors(before the cats) dictate A/F ratio. The second o2 sensors(after cats) just monitor emissions.
So putting test pipes in way of the resonators won't be a problem at all. I'd want to hear the sound though. Resonators often take the raspiness out of exhaust notes. I've had friends take resonators out of stock exhausts before and it's sounded like ass.

To jump on what Redneck was saying about actually replacing the cats with test pipes is easier said then done. A o2 simulator could easily be used on the "after cat sensors" to "trick" the OBDII system into thinking the cats are still there.

My question would to worry about how much removing the cats would "lean" out the A/F when in Open Loop.
It is true the upstream O2 sensors feed data to the computer for air/fuel ratio.
However, the downstream O2 sensors don't simply monitor emmissions. They keep track of how much O2 makes it through the catalyst as a way of tracking the age/effectiveness of the catalyst, based on the fact that when a catalyst ages, it loses some of its oxygen storage capacity.

In your last sentence, did you mean closed loop? Open Loop is before things warm up. Closed Loop is when everything is functioning, and the computer is using info from all the sensors. It is then a closed system.
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Old 09-19-2009, 05:17 PM
  #12  
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Open loop is also at WOT.
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Old 09-19-2009, 05:24 PM
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Originally Posted by ronjenx View Post
It is true the upstream O2 sensors feed data to the computer for air/fuel ratio.
However, the downstream O2 sensors don't simply monitor emissions. They keep track of how much O2 makes it through the catalyst as a way of tracking the age/effectiveness of the catalyst, based on the fact that when a catalyst ages, it loses some of its oxygen storage capacity.
Never heard that before. Regardless they can be tricked electronically or mechanically to make them think the catalyst is still there/working.

Originally Posted by ronjenx View Post
In your last sentence, did you mean closed loop? Open Loop is before things warm up. Closed Loop is when everything is functioning, and the computer is using info from all the sensors. It is then a closed system.
It's Open Loop I'm concerned with. In an OBDII system Open Loop is pre-determined by the ECU to add "x" amount of fuel. Open Loop occurs when you give it a certain amount of throttle. Closed Loop is when your giving it part throttle. The ECU will switch from Closed Loop to Open Loop based on throttle position.

At Closed Loop the ECU will tune the A/F to 14.7 or stoich. Modifying exhaust componets don't really effect Closed Loop performance since the ECU will compensate.

Last edited by drumnatural; 09-19-2009 at 05:27 PM.
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Old 09-19-2009, 05:28 PM
  #14  
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Originally Posted by drumnatural View Post
Never heard that before. Regardless they can be tricked electronically or mechanically to make them think the catalyst is still there/working.



It's Open Loop I'm concerned with. In an OBDII system Open Loop is pre-determined by the ECU to add "x" amount of fuel. Open Loop occurs when you give it a certain amount of throttle. Closed Loop is when your giving it part throttle. The ECU will switch from Closed Loop to Open Loop based on throttle position.
I think I see what you meant now. Less back pressure when in open loop would mean the predetermined A/F ratio would not be correct, but closed loop would be fine due to the "electronic foolery".
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Old 09-19-2009, 05:39 PM
  #15  
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Originally Posted by ronjenx View Post
I think I see what you meant now. Less back pressure when in open loop would mean the predetermined A/F ratio would not be correct, but closed loop would be fine due to the "electronic foolery".
Kind of. If you open up an exhaust system it will "lean" out the Open Loop map.

Thats not always a bad thing though. Most ECU's run the motors very "rich" from the factory.

You will actually gain power from leaning out. But there is a balance. Run too lean and the motor goes BOOM

Most vehicles can have long tube headers, no cats, and a larger diameter exhaust and not run dangerously lean though.

But I don't know how finicky the JK's are.
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Old 09-19-2009, 05:49 PM
  #16  
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Originally Posted by drumnatural View Post
Kind of. If you open up an exhaust system it will "lean" out the Open Loop map.

Thats not always a bad thing though. Most ECU's run the motors very "rich" from the factory.
You will actually gain power from leaning out. But there is a balance. Run too lean and the motor goes BOOM

Most vehicles can have long tube headers, no cats, and a larger diameter exhaust and not run dangerously lean though.

But I don't know how finicky the JK's are.
I was thinking they try to maintain stoichiometric A/F ratio, (not rich and not lean), which would result in the least pollution.
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Old 09-19-2009, 05:56 PM
  #17  
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Originally Posted by ronjenx View Post
I was thinking they try to maintain stoichiometric A/F ratio, (not rich and not lean), which would result in the least pollution.
The Open Loop map is rich. Your dead on about stoich being the best for pollution. It's 14.7:1 for gasoline motors.

So in Closed Loop the ECU will try to keep the A/F ratio around 14.7

What we need are dyno graphs with the A/F ratios taken.
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Old 04-14-2011, 05:16 PM
  #18  
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Damn never thought this was gonna be so hard! I was just thinking on removing them in order to have a better sound.
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Old 04-14-2011, 05:33 PM
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Originally Posted by drumnatural View Post
The Open Loop map is rich. Your dead on about stoich being the best for pollution. It's 14.7:1 for gasoline motors.

So in Closed Loop the ECU will try to keep the A/F ratio around 14.7

What we need are dyno graphs with the A/F ratios taken.
Is it true that as far as performance the A/F ratio would be 12.5 (something around there), I say that cause in tuning GSXR 1000's we seen 12.5or 12.7 to be great performance????? just askin where the best performance for a gas motor is, roughly.
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Old 04-14-2011, 08:56 PM
  #20  
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Does anybody know the dia. of the piping the stock cats are on? I have two 2.5 inch race cats laying around I wanted to put on the jk.
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Quick Reply: removing the two catalysts converters under the JK


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