Least obnoxious cat back/muffler?

Sorry Gary, I beg to differ. DAA- I've tested my exhaust a fair amount in all forms with the removal of the factory muffler, removal of the 3rd cat, install of spintech muffler, ran both with and without the 3rd muffler with that. Also with clogged front upper cat, and full replacement with both new cats, new 3rd cat and spintech. I'm currently running all 3 cats and the spintech now.

Having done so with the changes all on MY rig with no other changes at the time, I will say this-the biggest increase you'll see in power, performance and yes, Mileage-will come from pulling the factory muffler and swapping in a high-flow setup like the spintech or other high flow setup, and the removal of the 3rd cat. That will be your biggest gain in performance/power/mileage overall, BUT at the expense of added noise. I'm guessing this will be TOO loud for you. It's as loud as I will tolerate myself. I also like a quiet rig through all the ranges and especially at slow-crawl on the trail.

My exhaust guy here in town did say that if it was too noisey for me, he could install either a second high-flow muffler in front of my main muffler (where the 3rd cat is now) or another small chamber device to help isolate the sound a little and said it would make a noticeable difference in sound (quieter) without the drawback of decreased performance. I never did have this done, although I wish I would have tried it just for kicks. When my upper front cat clogged, I got a full replacement from Eastern Catalytic, which included the 3rd cat. I installed this all myself and welded it in, to the existing spintech. My exhaust guy had made 3 prior attempts years ago to relocate the exhaust tip due to hitting it off-road a lot. It took 3 attempts as each change he'd make, I'd go wheel it and find where my suspension would make contact and in what situations, so I'd go back and explain that to him, he'd re-route it again and I'd test again. After the 3rd time, we found a setup that would work for me without any suspension contact, or contact off-road. He did this all at no charge to me, just said to come back with some "real" work. I took him a case of beer and a crisp bill as a Thank You which he was grateful for. I've been recommending him ever since and sending him lots of business. He's about the best in town and is GREAT at what he does. It's worked well for both of us. I kept his rear tailpipe section in place as it works well with my current setup.

Now, with the setup I currently have in place-the new Eastern Cat full replacement setup including 3rd cat and spintech, I WILL be removing the 3rd again as I did see both a drop in mileage and power/performance with the addition of the 3rd again. I'm not happy with that with the towing and wheeling I'm doing and want that slight added performance/mileage back. I think this time I WILL try that addition of the second high-flow muffler or other chamber to see if it effects power at all and what it does to the sound levels.

One other test I did do was a decible sound test running my rig using a hand-held decible reader with a few of the mods. To my surprise, the spintech setup and removal of 3rd cat actually came in a decible or two quieter than the stock setup at various points around the rig and inside the cab. Not sure why that was, I tried several tests with and without using the same meter. I'm not a sound guy so I can't explain it. It seems louder to the ear, but the meter said otherwise. Perhaps it's the deeper, throatier note you hear, I don't know. Regardless, there was no "droning" with any of the above setups. I've heard that before in other rigs and in some friends Jeeps and it drove me crazy! What I might do as the Eastern setup uses ceramic in their cats rather than steel like the factory does, I MIGHT just pull my cat and clean it out or remove the insides and see how that does as the second "chamber" of sorts just for kicks. Haven't had the time lately or physical ability to do much of that type of work just yet. Working on it.

Here's my disclaimer-if you even consider removal of the 3rd cat, as far as the computer issues are concerned, the two upper cats are monitored with O2 sensors. The third cat is not and makes no difference to the computer or running conditions if it's there or not-the computer doesn't know its there so it won't know if it's gone. I never tripped any codes for it's removal for the entire time it was out. There ARE however various laws against modification or removal of stock/factory cats and equipment for emissions reasons. Check your state laws if you do consider this as it may not be a "legal" mod where you're located. I'm not advocating you do this or telling you to do it, just what I've found in my testing.

Now for performance-the best increase I had made a noticeable difference in town. This was the second biggest performance increase and mileage increase compared to the gear swap. It made a big difference, even my wife commented many times on how much more "fun" to drive it was as it just flat up and went much quicker, responded much quicker, shifting the 6 speed changed as well as I could pull hills in town easily in 4th now where I'd need 3rd before at high rpms. Slight differences like that were what I noticed the most. Towing the trailer was easier as well in many areas of the state, for instance on the way up to our ranch, I'd drop to 4th and have trouble maintaining speeds depending on how loaded the trailer was. With the changes, I could run 5th and have power to spare, maintaining higher speeds. Now for fuel economy-with the total removal of 3rd and spintech, I forget the exact numbers but want to say it was a 2-3mpg increase in mileage. It was much bigger than I expected to get and for a while, I was edging on 19mpg out of my heavy rig. 18 was an easy average, 19's were there on the low end and I was working towards trying to get a solid 19 average. Unfortunately never happened as I started getting my OPDG issues and poor running conditions with the #2 misfire. To date, I've been unable to repair that issue and consequently, my mileage is in the toilet. I'm bouncing between 12-15 now with the current engine troubles. One of my maintenance guys at work gave me a couple ideas last night that I will try for kicks as it won't be too much money involved. If that doesn't work, I fear the lifter failure that seems to be more common these days and a 2nd full rebuild. I'm currently on the 3rd OPDG.

For what you're trying to do, I'd recommend a good high-flow muffler at first, keeping the 3rd in place for sound reasons. If you are willing to do some testing of your own, check on your laws and if OK or you feel comfortable with it, remove the third and install either a second high-flow setup or other "sound chamber" of sorts to help dial out the sound. The factory cat is compossed of a steel corrugated cardboard type setup that will be very difficult to remove or "gut out" if you wanted so I wouldn't waste the time with that. I mentioned the ceramic stuff in the one I have now-it will come out easy enough and I might try it on mine as I will be either eliminating it and going back to strait pipe or trying another sound chamber in front to quiet it down a bit. I'm afraid the strait pipe to high flow muffler will be too loud for your liking. Also, with regards to having a "shop" do it, if you did request a removal, I highly doubt most "big" shops would be willing to do that due to regulations. You might try and find a smaller owner-operated shop you can negotiate things with a little easier. Even without, I do prefer the smaller owner/operator shops as opposed to the bigger chain outlets but that's just me.

Hope that helps.

Best of Luck,

Mike

bob1340 said:

If you are concerned about noise/drone on the road I suggest running the pipe out straight at the rear instead of down. ... I cut the curve off and ran it straight back and could tell the difference in sound in the cab.

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Bob, that really drives home to me just how subjective this topic can be. Back when I installed my Rokmen tank skid, I cut the turn down off my of factory tailpipe so that it was flush with the angle on the rear of the skid. To me, I was really surprised that the exhaust seemed louder while driving, just from cutting the turn down off. Exact opposite of your percpetion. For that matter, I've ridden in a Jeep with the 40 series and thought it was way too loud, myself. Not even implying I'm right and you're wrong, just pointing out how much this topic really comes down to individual perceptions and preferences.

And now that I think about it, my ears and my hearing are probably part of it too. I have a lot of permanent noise induced hearing loss and moderately severe tinnitus that rages 24/7. I'm completely deaf to many high pitched sounds (I can't hear most electronic "beeps" for instance), can't hear them at all. But then there are certain loud noises at certain frequencies that cause me sharp pain. When I talked about exhaust drone becoming physically painful after awhile, I meant that literally - it's one of those types of sounds I can not only hear, but that it hurts me to hear. Considering stuff like that, it's not surprising some of us have very different perceptions of something like the sound of an exhaust system.

bob1340 said:

Power gain? Mileage gain? If so not much.

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That's the gist of my uncertainty, right there. Mike got some good gains, but I'm thinking most of that was from losing the 3rd cat. Not sure how similar my experience would be, keeping the 3rd cat and just changing out the muffler. I can live with a little bit louder, as long as it's not "too loud" and not really noticeable on the interstate for long runs. Which, it sounds like I'd be fine with the Spintech, Borla, Dynomax or others. But, it would be foolish to make it any louder at all, if it's not going to improve MPG by at least a small but measurable amount.

Really undecided... I may just put this one on the shelf for now. Go ahead and just modify the tailpipe to clear the new gas tank and circle back and decide about a cat back or new muffler later.

Just don't know!

- DAA

rjh said:

[quote='05TJLWBRUBY]...I mentioned the ceramic stuff in the one I have now-it will come out easy enough and I might try it on mine as I will be either eliminating it and going back to strait pipe or trying another sound chamber in front to quiet it down a bit. I'm afraid the strait pipe to high flow muffler will be too loud for your liking. Also, with regards to having a "shop" do it, if you did request a removal, I highly doubt most "big" shops would be willing to do that due to regulations. You might try and find a smaller owner-operated shop you can negotiate things with a little easier. Even without, I do prefer the smaller owner/operator shops as opposed to the bigger chain outlets but that's just me.

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If you elliminate the material in the down-cats and/or go to a straight pipe, how do the O2 sensors come into play? Do you remove them entirely? Use some kind of electrical doo-dad to fake the signals back to the PCM?[/quote]

Sorry for the confusion-the two uppers I won't mess with. They are monitored and have the pre and post O2 sensors. I don't do anything with them, just leave them stock, as-is.

The 3rd cat, or lower is what I'm talking about here. With what I've found on my rig, I will either remove it again entirely for good this time, or I MIGHT clean it out. It's not monitored, the computer doesn't know it's there. Total removal does nothing to the computer as it's not monitored so it doesn't know it's there or not. My thinking is that from what my exhaust guy told me last time, I MIGHT try using it as a "chamber" rather than putting another muffler in. Not sure what it would do. It's easy enough to cut out and weld back in, just finding the time to do it. To date, I've only experimented with the total removal, nothing to do with cleaning it out yet or adding a second. I want a fairly "quiet" rig overall and would only do this to see if it would be more quiet than with the strait pipe. BTW-the strait pipe is nothing more than eliminating the 3rd, and running strait from the 90 at the engine skid, back to the muffler. Nothing messed with up above that as mentioned earlier. Sorry for the confusion.

Again, I'm not telling ANYONE to do this as it's a legal issue-this is just my experience from the testing I've done. I know where I had the best performance/mileage, so I'm going back to it.

Best of Luck,

Mike

still have not done any exhaust work on the rubi but I will. I plan on mimicking Mike's setup when I can afford it or whenever my stock stuff gets a hole in it/ripped off. whichever happens first LOL.
however, I had an XJ cherokee before the wrangler and its exhaust got ripped off while wheeling which led me to need to do something. the idea of replacing stock with stock is never an option with me, but having an SUV for the first time and also being a bit older changed my exhaust choices significantly.
years ago I had a flowmaster 40 series on my S10's as well as gutted cats. the drone on them was HORRENDOUS and that was with the muffler under the open truck bed. did not want that with the enclosed cabin of the XJ.
so after what must have been days or even weeks of online research, I decided the dynomax catback with their "turbo" muffler was the way for me to go. and for that vehicle it was perfect. except for a wrong style rear most mount, it fit like a glove, went together quickly & easily, and was fairly inexpensive. it was very sedated noise wise. just a touch more tone at idle and while cruising, not noise, but more tone if that makes sense. But when you laid into it, it had a deffinite throaty growl to it. still not much louder than stock but a better sound. I didnt feel much difference in power, nor see any gain in mpg but I have seen DYNO tests on same year as mine XJ's with the dynomax mod ONLY and it added 5hp with no loss of torque. no surprise I didnt feel anything with only 5hp gain but in my mind knowing there were proven results I was happy.

I have always heard GOOD things about spintech mufflers and have always wantted to try one, just never quite got around to it on any of my vehicles. I also heard they are very DEEP sounding which is one reaosn I never tried it on the XJ. however I have pretty much made up my mind (with a lot of my decision being based on Mike's testimony) that when I do get the exhaust done on the wrangler, it will be a spintech muffler.

I was doing the same search. Went to put on a high clearance skid and I need a shorter muffler and a longer intermediate pipe to push it out from skid area towards the rear to make things easier.

Intermediate pipe is easy- get one from an unlimited...add shorter muffler

I spent a ton of time on you tube trying to listen to various setups with the 4.0- took some patience. Searches for opinions here and other boards helped also.

I have different conditions to fulfill- a teenaged boy who wants it a little louder, and a middle aged father that wont mind some loudness since he drives something else most of the time.

What I've found is that there are tons of mufflers with sounds from quiet to obnoxious, but fewer short mufflers than I thought. Sound wise after listening to u-tube and taking in other opinion I think we are going to try the flowmaster delta 40. It didn't sound bad to me on the clips.
Flowmaster recommended a 60 series which is tuned for 4s and 6s, for what its worth, but I think the case is too log for what I have in mind.

On the cat I believe its illegal to remove federal emissions equipment.
Second I believe that the headaches involved with bypassing the cat and keeping the ecm happy with respect to drivability aren't worth the trouble. I thought there was a after cat o2 on the later models. maybe not a big deal if not. I would also think about where you get the vehicle serviced and will they have any liability working on it. Will they work on it. Will they even know?