Not a newbie to jeeps or the jeepforum.com, just a lurker and someone who knows how to use the search feature of forums.

TIA

Are we getting that bad on newbs that they need a disclaimer?:rofl:

Dont worry, you didn't ask about gas milage, BB's, Tire Sizes, etc.... youll be fine on this one

Edit: Look, he's been here 3 years and just mustered up the courage for post 1. Were not that scary :rofl: :cheers:

 

If the system is designed to use the cat, use it. By removing it you may have nice sound, but at the cost of possible power loss. People often remove everything they can from the exhaust, therefore trying to reduce the flow limits, but it's not that simple. Exhaust is extremely complicated thing, and it has to have proper length and capacity. By removing cat you are reducing it's volume, and changing torque curve. How? Hard to say.

 

Most of the restriction in the exhaust is from the main converter on your WJ, not the precats.

Removing the main converter will significantly add to tailpipe emissions. Not sure why you would want to do that when the environment needs all the help it can get. A high flow main converter has very little restriction. Also, the system is much louder and more resonant without the main converter, so you would need a larger muffler.

 

ras: Yup, learned my lesson the hard way on JU and pirate. I always do as much google/yahoo/forum searches b4 there is no possible way I could have missed it. Threre is always that little oops, and I feel dumb...

max: I'm not looking for niose, I'm looking for power. I may even go with a FM70 if it is a real concern. Also, I'm not reducing volume, I am increasing it over all with the 3" system. This system has a main cat (my XK does not)... but there is also a stock tire size, both were designed to have them, but it's looking like they both should go.

Kolak: I also don't believe that we are the cause of this "Greenhouse Effect" (even if it did win some stupid award). but that's MHO... if the main cat was to be "usefull" I believe they would have designed it with sensors.

I was misinformed about the pre-cats and the main cat is the culprit, so removing it would be beneficial, especially if "A high flow main converter has very little restriction".

I'm not trollin here, I just want to see if you get the CEL, but I've had a few PMs telling me to scrub it, it works great.

Thanx guys, see y'all again in 3 yrs :cheers2:

 

I removed my carsound cat and installed a E-cutout which i operate from inside the cab. Sounds great and defrinately a power increase. I will dyno the car again soon so then i can see if it really makes a difference. Get the numbers for the straight pipe and muffler.

 

ras: Yup, learned my lesson the hard way on JU and pirate. I always do as much google/yahoo/forum searches b4 there is no possible way I could have missed it. Threre is always that little oops, and I feel dumb...

max: I'm not looking for niose, I'm looking for power. I may even go with a FM70 if it is a real concern. Also, I'm not reducing volume, I am increasing it over all with the 3" system. This system has a main cat (my XK does not)... but there is also a stock tire size, both were designed to have them, but it's looking like they both should go.

Kolak: I also don't believe that we are the cause of this "Greenhouse Effect" (even if it did win some stupid award). but that's MHO... if the main cat was to be "usefull" I believe they would have designed it with sensors.

I was misinformed about the pre-cats and the main cat is the culprit, so removing it would be beneficial, especially if "A high flow main converter has very little restriction".

I'm not trollin here, I just want to see if you get the CEL, but I've had a few PMs telling me to scrub it, it works great.

Thanx guys, see y'all again in 3 yrs :cheers2:

I wasn't necessarily referring the the greenhouse effect, but rather to tailpipe emissions and air pollutants in general. Reducing tailpipe emissions surely has resulted in a very beneficial outcome in terms of improving air quality here in the US. A properly designed high performanace exhaust can be both clean and efficient, so I see no reason to remove the main converter entirely.

The main converter certainly does quite a lot -- just look at how large they had to make the precats on the late 2004 model WJs when they removed them. The sensors were moved closer to the manifolds to give improved mixture control, not because the main converter isn't "useful."

You will not get a CEL if you remove the main converter, but you won't pass a visual or a sniffer test if you have one in your area.

 

Thank you Nick, I have always respected and valued your experience. I go in Friday to see what these guys can do for me.

 

Simply removing the element, that was considered when counting all exhaust parameters will affect performance but not the way you desire it. Once I was learning a bit about the wave effects in the exhaust, and it is crucial to have properly tailored exhaust. Someone did a lot of mathematical work to count the proper length and capacity for the exhaust. He included the volume of cat. When you'll remove it you are going to decrease the exhaust capacity. Then the wave induction will change it's rpm range. In the worst case you would loose whole exhaust power. But I doubt it. I rather think you will move torque higher. But if you still want to try it- it's your rig. I wouldn't. Not because of saving the planet, not because of noise, but because of performance.

 

Simply removing the element, that was considered when counting all exhaust parameters will affect performance but not the way you desire it. Once I was learning a bit about the wave effects in the exhaust, and it is crucial to have properly tailored exhaust. Someone did a lot of mathematical work to count the proper length and capacity for the exhaust. He included the volume of cat. When you'll remove it you are going to decrease the exhaust capacity. Then the wave induction will change it's rpm range. In the worst case you would loose whole exhaust power. But I doubt it. I rather think you will move torque higher. But if you still want to try it- it's your rig. I wouldn't. Not because of saving the planet, not because of noise, but because of performance.

stock exhausts on non-high end sports cars are not designed with performance or max flow efficiency, they are designed to be quiet, pass emissions, and fit around all the other pieces of the undercarriage. performance doesn't even come in at a distant 4th.

all the mathematical work done on your stock exhaust was with emissions and sound levels in mind. which is why most cats and mufflers are massive.

 

Yes, but swanem said, that he has some custom 3" exhaust. If it was done properly, it was calculated with stock exhaust elements, that were supposed to stay there. Any change will change it's characteristics. And if this exhaust was made without these calculations, then I would simply throw it away.

 

Yes, but swanem said, that he has some custom 3" exhaust. If it was done properly, it was calculated with stock exhaust elements, that were supposed to stay there. Any change will change it's characteristics. And if this exhaust was made without these calculations, then I would simply throw it away.

I understand what you are trying to say Max, but if this were true, in must equal out... then the airbox and exhust would be tuned to get the max performance out of the engine right off the floor, however, dynos prove that changing the in and the out of a vehicle can significantly increase HP. I have already changed the in, now I am changing the out. Pick it up today...

 

You are mixing things. Whole system is designed to provide some benefits. In case of stock system it's fuel efficiency, emissions and quiet sound. Then you want to buy performance exhaust, to gain power. Someone had counted it with the things that are left from OEM type, I mean headers, pre-cats, pipes and main cat. It was whole designed to work together to give you maximum gain. If it would be needed, they would tell you to remove the cat.
Now- someone made a hybrid of OEM type and performance exhaust, calculating all crucial parameters. And whole work will be screwed up because of removing the original, important part. If you want that much to remove cat, put extra muffler there, that will have the same capacity as your cat is.