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Thread: exhaust removal question

  1. #1
    Junior Member up4it1023's Avatar
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    Default exhaust removal question

    so i wanted to upgrade my muffler so i can get that rumble but didn't want anything too loud. anyway took off everything past the cat on my '06 LJ. just for shits and giggles i started it up to see how it sounds with it all off past my cat. it sounds pretty much exactly how i wanted it to. my question is - is there any negative impacts on the engine with keeping it off e.i. back pressure, yaddy, yaddy - thanks guys
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    MODERATOR warrior's Avatar
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    If you like the sound....is good
    But you need to add tail pipes to it.(Without muffler)
    Also you can buy high flow cats.
    Last edited by warrior; 10-30-2010 at 20:14.
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    Senior Member CutterN55's Avatar
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    You won't have any torque. You'll wind up quick but that's about it. I ran my Waggy open headers for a couple days until I got the exhaust done. It was fun for about 30 minutes. Then again, I was running a mild built AMC 360.

    As said above throw a pipe on it (2 1/2") and a chamber. It's gonna sound ratty when you goose it though. you may throw a cheap glass pack on it or a cherry-bomb and call it a day.
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    Senior Member jeepdreamer's Avatar
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    I would advise against the Cherry bomb/Glass pack idea. They ARE junk and won't last very long before the packing material (fiberglass batts) breaks down and either goes through the pipe or gets stuck causing an issue. A better option is hang out near the scrap carts at the auto center on post. When someone is putting on an entirely new exhaust kit they will usually throw away the factory stuff. If its a new vehicle that stuff is usually good quality. What you want to find is a resonator from this pile. It looks like a swollen chunk of pipe or a weird cat/muffler looking thing. That will help "tune" the brashness of an open exhaust a little without giving up any real flow...I did it on my FSJ with a 258 and it sounded like an old duece and a half.
    The other thing to consider is will they give you any flak when its time for vehicle inspections...? They don't to me but my jeep is a heep...

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    Zombie Slayer MetViper's Avatar
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    If your Jeep is registered in Texas, it won't pass inspection.
    Prepared for the Zombies

    91 XJ, 4.5" RC Long Arm Suspension, 35" BFG KM's on black steelies, Ford 8.8 rear, D30 w/Aussie, AA SYE, Custom bumpers, JCR Rock Sliders, Rusty's gas tank skid


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    Junior Member up4it1023's Avatar
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    lose my torque? that doesn't make sense to me. cutterNn55 explain that a little more if ya could. my jeep is registered in ohio so i'm worried about the inspection thing. i'm putting a tail pipe on it today.
    '06 unlimited
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    Senior Member jackhammer's Avatar
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    My buddy welded a flat flange with 4bolt holes on each side of muffler. Then made the same with a straight pipe. He would simply unbolt the straight pipe section and bolt in the muffler when it came to emiisions. Alot of work but it did what he wanted

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    Senior Member CutterN55's Avatar
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    I don't know the science behind it, but I know it just is by experience and have read numerous times. You need to have enough back pressure to make things work right. If not you will also burn valves prematurely so I've heard from the Jeep Guru's on Pirate and IFSJA. Also why you never see anybody running anything bigger than 3" pipes on big built motors.
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  9. #9
    Senior Member SavageSun4x4's Avatar
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    Well you don't really lose the torque, what happens is the torque gets moved around on the torque curve. That said its possible to move it so far as for it to disappear. You its possible to burn valves but this normally occurs due to uneven pipe lengths which causes uneven exhaust flows. You will see on a lot of Hi Perf engines that use dual exhaust a connector pipe, this is to even out the pressures on both sides.

    Generally speaking, shorter exhaust will push the torque curve higher and longer is lower...BUT exhaust is a VERY complex business.

    Auto engines unlike motorcycle engines do not really depend upon back pressure to function properly. You want a degree of pressure inside the pipe. Exhaust gases are heavy and when they move they take or extract gas with them...generally referred to as 'scavenging process'.

    Take a garden hose turn water on high. Holding it level with the ground see how far the water squirts past the opening. Now add an adjustable nozzle. All things being equal the smaller the opening the faster and further the water squirts out. However you can and most likely will lose volume in the process. So the challenge becomes max volume vs max PSI, or the chart that looks for the 'X' (where the lines cross).

    Take away: Shorten you exhaust pipe and move your torque curve. Maybe to your advantage or maybe not.

    Since you most likely do not have access to a Dyno then its going to have to be seat of the pants.

    In addition if you INCREASE the exhaust flow you NEED to increase the intake flow. Failure to do so will result in no gains and just more noise.

    Here is my suggestion and I have done a lot of experimentation on this. Go to a tested (by Chrysler-Jeep) Hi Perf exhaust system AND remove the 'Air Horn' as found on the front of your air box on your LJ. Install a 'Power Cone' that ALLOW more air into the system. Then lower your air intake temp. This will provide a denser air charge. The results are a 'seat of pants' improvement across the board and improved mpg by about 1 - 1.5 mpg at highway speeds.

    I also recommend the cheapest air filters Wal Mart sells and toss at every oil change.

    FAQ:
    1) Should I buy one of the fancy 'cold air systems'? Yes if you want added bling and little if any USABLE gains in performance. For less than $10 bucks you can go with a Power Cone system and 'Trash air'. Remove your headlight chrome rings will do more than the $400 buck Bling-Aire systems.

    2) What about 'headers'. Again, do not waste your bucks unless you just need the decal and also believe it will go faster, jump higher with the decal on it. Fancy headers will add nothing, the Jeep OEM system works fine if not better.

    3) What about the claims by all the Cold Air and header folks, are they just lying to us? NO, they are telling the truth, just NOT all of it. Most of those systems provide as stated improvements under very controlled parameters and its WHERE they provide it! Almost always at the very top end of the power bands and the result they do nothing for your off road or even on road performance. For a excellent exhaust system, but near OEM quite the Borla system for he LJ has been tested by Jeep and will provide some performance gains.

    Jeep OEM replacement Borla cat-back system install: http://www.savagesun4x4.com/enter/fa...mance_cat.html

    Jeep TJ Trash Air and Power Cone install: http://www.savagesun4x4.com/enter/fa...d_install.html
    Don

    '15 Jeep Unlimited Rubicon Hard Rock...OLD SCHOOL 6 Spd Manual Trans
    17 Oaks Ranch Companies LLC

    www.savagesun4x4.com

  10. #10
    U.S. Paratrooper GOVT1911's Avatar
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    SavageSun,

    Thanks for the info. I appreciate all of the experience and knowledge you toss our direction, especially without the "I know everything and you new guys know crap" that I have found on alot of other sites. Yeah, I'm talking about Pirate as well as a couple others. Pirate has a TON of great info, I just get tired of them bashing new guys with questions. Everyone's gotta start someplace and if you belittle the new guys, they may just say "screw these guys AND this hobby!"

    Once again, thanks for the knowledge and helpful attitude!

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