Exhaust question for off road only xjs

[sjstar]

So i was wondering what you guys where doing with your exhaust when you use the cherokees only off road. Do you take the cat out and run just a muffler? what do you do with the o2 sensor after the cat? Any input would be great. Thank you

 

[xj dreamin]

i don't know why people run straight pipe, that's stupid in my opinion. Just run a muffler before the rear axle and dump it or bring it through the side, a couple of good quality hangers in the right spot and you're set. I got a 44 series right before the rear axle with a dumped tip. tied the muffle with two good hangers and it's solid as a rock.

 

[zachhooters]

I have the same set up for my Jeep works great.

 

[sjstar]

well my cat is gone and i wanted to dump the exhaust out the side in front of the tire cause i always smell exhaust inside from it dumping underneath. But anyways i only drive it offroad green stickered so legality isnt an issue. In order to put the exhaust out the side i need to put my muffler where the cat is. I am wondering what to do with the o2 sensor.

 

[cruiser54]

well my cat is gone and i wanted to dump the exhaust out the side in front of the tire cause i always smell exhaust inside from it dumping underneath. But anyways i only drive it offroad green stickered so legality isnt an issue. In order to put the exhaust out the side i need to put my muffler where the cat is. I am wondering what to do with the o2 sensor.

Ever think of leaving the cat and eliminating the muffler?

 

[simsfamxj]

do not straight pipe it will cause you problems . your engine needs back pressure for the head design to work right . you will loose all you low and mid range and only gain 1-2 horse flat out . keeping the cat and dumping will not cause any problems but when the internals of the cat brake your ride will sound like crap. get a shorty muffler from any of the GOOD manufactures ex. flow master , magnaflow . Dino wise a magnaflow creates more hp on a stock motor . just my 2 cents

 

[XJRunner]

borla header, full 2.5 mandrel bent tubing, high flow cat, flowmaster 50 to a direct dump. sounds tits and doesnt drone. super loud. I set off every car alarm lol

 

[Johnnie Walker]

Straight pipe ALL THE WAY back, would do just fine with a cat. Maybe even just to about the axle.

 

[techno1154]

I would think you need to keep the cat in the system. Federal law. For offroad, you do need some form of spark aresstor,...a good muffler come to mind. That is to prevent sparks if the engine should back fire or other hot metal/material from exiting the exhaust pipe and cause a fire.

A few years ago a malfunctioning vehicle that did not have proper exhaust (parts of the exhaust was intentionally removed) started a fire in the Florida Everglades. It took the park service and the fire fighters more than a week to put it out. That unfortunate incident have been etched permanently in my brain.

Maybe it is because I have never tried it but I fail to see any gains to the performance of a street vehicle by removing the or parts of the exhaust system.

 

[ktm racer 419]

for the sake of keeping the tree huggers out of our ass a little less. run a cat.

you can get a small highflow for around $40.

i actually made 20 bucks by scrapping my old bad cat and going to a highflow.

 

[NorCalChris]

Why dont you have a cat?

 

[FunkRider]

do not straight pipe it will cause you problems . your engine needs back pressure for the head design to work right . you will loose all you low and mid range and only gain 1-2 horse flat out . keeping the cat and dumping will not cause any problems but when the internals of the cat brake your ride will sound like crap. get a shorty muffler from any of the GOOD manufactures ex. flow master , magnaflow . Dino wise a magnaflow creates more hp on a stock motor . just my 2 cents

No engine NEEDS back pressure. Exhaust gas velocity is a result of pulse tuning/scavenging and back pressure which is a result of the CFM a system is capable of flowing. The two are not married. You can have a system with no back pressure that is tuned to the operating range of an engine. It is not easy or even realistic to design a system like that due to available pipe diameters and packaging constraints but it can be done.

The reason people complain about loosing low and mid range torque is because they have installed an exhaust setup that is too big for the operating range the engine is making power in. They end up with a system tuned for a peak of 6000rpm and the engine peaks at 4700. All they see is a small gain outside of the peak power output and huge losses everywhere else. They likely have no back pressure at lower rpm but the power loss is not the fault of the lack of back pressure.

 

[FlexdXJ]

No engine NEEDS back pressure. Exhaust gas velocity is a result of pulse tuning/scavenging and back pressure which is a result of the CFM a system is capable of flowing. The two are not married. You can have a system with no back pressure that is tuned to the operating range of an engine. It is not easy or even realistic to design a system like that due to available pipe diameters and packaging constraints but it can be done.

The reason people complain about loosing low and mid range torque is because they have installed an exhaust setup that is too big for the operating range the engine is making power in. They end up with a system tuned for a peak of 6000rpm and the engine peaks at 4700. All they see is a small gain outside of the peak power output and huge losses everywhere else. They likely have no back pressure at lower rpm but the power loss is not the fault of the lack of back pressure.

Drive a stock civic with a stock muffler and then drive a stock civic with a muffler that fell off and tell us that again. I call BS on not needing back pressure.

 

[cruiser54]

Drive a stock civic with a stock muffler and then drive a stock civic with a muffler that fell off and tell us that again. I call BS on not needing back pressure.

I can see your point on some of the higher tech motors. But on a 4.0 it's probably not a big difference.

 

[FunkRider]

Drive a stock civic with a stock muffler and then drive a stock civic with a muffler that fell off and tell us that again. I call BS on not needing back pressure.

Got anything to back up with what you just said?


Sure, it IS possible that particular civic in question lost torque when the muffler "fell off" but tell us why the loss in back pressure was the cause of the loss?

So what you are saying is if you take the stock exhaust, take a pressure reading on it. Then cut the muffler off and weld a cap on the end of the pipe and drill a hole in the pipe that produces the exhaust same back pressure reading as the stock muffler the power will be un changed from the factory exhaust?

 

[tbburg]

I wouldn't recommend a side dump exhaust on a trail rig. The problem is the pipe has to run under the frame rail, and becomes the lowest point to hit/crush shut if you slide over a rock.
The side-dump works on the race rigs because they never see rocks or obstacles. It's basically trail running: Fast trail running, but trail running non-the-less. We have a side-dump on the 7118 Comanche, here's a pic, (thumbnail is a link to full size photo)

The dents you can see in the pipe are caused by rocks being thrown up from the front tires. We've beat this truck so hard the anti-sway bar links got pushed through the inner fenders, and that side pipe never got touched. On the other hand, looking at the frame rails on my XJ, anything hanging down that far would have been crushed flat or ripped off.

I'd say keep a cat in the system, and a decent muffler if it's at all road legal. Saying"it's a trail rig only", doesn't mean squat when it's licensed, registered, and insured for street use.

On back pressure: No motor NEEDS back pressure, but all automotive motors are tuned to run with a certain amount of back pressure. due to emissions, sound levels, etc. equipment required from the factory creates back pressure. The motor is tuned to run as efficiently as possible with it. Things like cam lift/overlap, port size/design, are speced to match.
Radically reducing exhaust back pressure while making no other changes may(OK, probably will) cause a loss of power at lower RPM. Yeah if you're building a high reving motor, big cam, lot of custom/aftermarket internals, an open exhaust is going to help, at which point I have to ask: for a "trail rig"? I don't think I've ever seen 4Krpm in my XJ off highway, and I don't think even the 7118 truck has gotten above 5500.

 

[FlexdXJ]

Got anything to back up with what you just said?


Sure, it IS possible that particular civic in question lost torque when the muffler "fell off" but tell us why the loss in back pressure was the cause of the loss?

So what you are saying is if you take the stock exhaust, take a pressure reading on it. Then cut the muffler off and weld a cap on the end of the pipe and drill a hole in the pipe that produces the exhaust same back pressure reading as the stock muffler the power will be un changed from the factory exhaust?

Nothing was changed except the car gaining a muffler and it drove like a completely different vehicle. An OEM muffler no doubt adds back pressure. I'd say that had a lot to do with it. Now, can you back up what you've said?

 

[FunkRider]

Read up on it from a reputable source if you like, maybe they can better explain it than I can.

 

[FlexdXJ]

I have been let me rephrase that a little. On a stock vehicle it can make a difference. Now obviously in High performance vehicles you don't want that but i can tell you that it made a big difference in a civic. What I said before was not exactly correct so I apologize. Not saying you were wrong or anything.

 

[simsfamxj]

No engine NEEDS back pressure. Exhaust gas velocity is a result of pulse tuning/scavenging and back pressure which is a result of the CFM a system is capable of flowing. The two are not married. You can have a system with no back pressure that is tuned to the operating range of an engine. It is not easy or even realistic to design a system like that due to available pipe diameters and packaging constraints but it can be done.

The reason people complain about loosing low and mid range torque is because they have installed an exhaust setup that is too big for the operating range the engine is making power in. They end up with a system tuned for a peak of 6000rpm and the engine peaks at 4700. All they see is a small gain outside of the peak power output and huge losses everywhere else. They likely have no back pressure at lower rpm but the power loss is not the fault of the lack of back pressure.

Not trying too start a pissing contest on who is right or wrong .If an engine that was designed with back pressure ,doesn't need back pressure then why did you contradict your self with this

"The reason people complain about loosing low and mid range torque is because they have installed an exhaust setup that is too big for the operating range the engine is making power in. They end up with a system tuned for a peak of 6000rpm and the engine peaks at 4700"

is this not loss of back press? and we are talking a bought an in line 6 cylinder no a v12 in a Indy car . Jeep engineered this engine with back pressure involved so if you take it away what do you gain?

pressure is created by flow through restriction ex. catalytic converter,exhaust tubing bends,muffler . so if you take that away you get crap except attention from your buddies saying that sound like ass and THAY WILL ALL LAPH AT YOU .