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Old 05-11-2015, 04:27 PM
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YJ Straight Pipe Questions

I've been looking to do a straight pipe on my '93 Wrangler YJ. I went to Advance Auto the other day and one of the workers, who suprisingly did a straight pipe on a YJ, came outside and looked at my jeep. He said there was two cats on it and that confused me. For a cat back on jeep would I go from the first cat or the second one? I just dont want toup the back pressure and ruin my engine in some way. By the way I have a 4.0L I6 engine. All help will be appreciated!

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Old 05-11-2015, 04:50 PM   #2
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I ran a true straight pipe, 2.25" from the header back for about a year on my 4.0. No bad things happened to the engine, and I actually got like 1-2mpgs better and had a crisper throttle response. So you won't mess anything up. But take into account the legality of removing any cats, and the fact that a straight pipe is somewhat obnoxious, though not near as bad as all the straight pipe V8s and ricers running around.

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Old 05-11-2015, 05:01 PM   #3
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You are breaking federal law, not a little thing. Will anyone notice? With the sound of a straight pipe, I would say yes. The bigger question is for what purpose? If you're building a street racing YJ, I guess it's s place to start. Most of us are looking for low end torque, something a straight pipe will hurt because of no back pressure. If you're only looking at throttle response for drag racing, go ahead and remove both cats and hope you don't get towed.

Btw, another issue may be the readings from the sensors such as the O2 without a cat. Our year YJ's run smoothly by readings from the multiple sensors.
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Old 05-11-2015, 06:47 PM   #4
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Quote:
Originally Posted by reno92 View Post
Btw, another issue may be the readings from the sensors such as the O2 without a cat. Our year YJ's run smoothly by readings from the multiple sensors.
I agree with the first part. But this a straight up completely false information. Last time I changed any OBDi Jeep there was no sensor after the headers. The cat is after the O2 sensor, which means the computer will have no idea if it's there or not. OBDii is a different story.
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Old 05-11-2015, 07:03 PM   #5
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Yj's never came with 2 cats the parts guy is a idiot. Also if you want to remove the cat replace it with a hiflow cat so you remain legal
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Old 05-11-2015, 08:56 PM   #6
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Yj's never came with 2 cats the parts guy is a idiot. Also if you want to remove the cat replace it with a hiflow cat so you remain legal
Yeah, if you run the hi flow cat and no muffler, it usually sounds real tough without being abrasive and obnoxious.
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Old 05-12-2015, 05:33 AM   #7
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Yj's never came with 2 cats the parts guy is a idiot. Also if you want to remove the cat replace it with a hiflow cat so you remain legal
Agree. You should go see the guy again, and ask him to give you a price on both replacement cats. Fun to watch him fumble around the computer while the line builds up behind you. "Those who can't do, sell parts"
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Old 05-12-2015, 08:06 AM   #8
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Yeah, if you run the hi flow cat and no muffler, it usually sounds real tough without being abrasive and obnoxious.
That's what my cherokee is imo that's the way to go if you're going to do it. I've had the cat ripped off offroad and as said above the back pressure does matter on these 4.0s
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Old 05-12-2015, 11:58 AM   #9
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It is against the law to remove emission control equipment from vehicles in America. To prevent discussion of illegal activities, this thread is now closed.

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