New exhaust?

stoutdog · **Posted:** Wed Jul 01, 2009 1:16 pm

(Edited)

One of my first mods on my new (used) Jeep will be to replace the junky exhaust system. I'd like to get y'alls opinions on a couple of things... Keep in mind, I'm looking to stay as close as possible to the stock sound and improve mpg (i.e. remove the stock exhaust brake).

1) Magnaflow or Aero Turbine? I'm torn. Any user input would really be welcome. Neither, hack the old one off and straight pipe her! Or straight Magnaflow, if you must have a muffler.

2) I've heard a lot of talk about messing with the CAT. Is it worth it and legal? Not legal, no improvement mpg wise.

3) 2.5 in or 3 in? A while back I was told it wouldn't make much difference, if any, but I'd like more opinions. 2.5 in, no advantage to a 3 in other than a little more noise

Thanks!

linewarbr · **Posted:** Wed Jul 01, 2009 2:14 pm

I'm thinking about straight-piping, myself. Here are a couple of links, one is a discussion of exhaust smell and the catalytic converter, and one is an install with some sound recordings.

http://www.lostjeeps.com/forum/phpBB3/vie ... sc&start=0

http://liberty.eurekaboy.com/magnaflow.htm

CRD Joe · **Posted:** Wed Jul 01, 2009 3:48 pm

Im doing a cat back 3" no muffler. None of my four diesel vehicles have mufflers. They arent necessary with a turbo charged engine.

DGM635csi · **Posted:** Wed Jul 01, 2009 6:16 pm

2.5" is more than enough volume for even a modded CRD IMO. I went 2.5", straight piped the cat, junked the OEM muffler and replaced with a 24" magnaflow stainless muffler, and installed a 3" Gibson turn down tip to finish it off. The sound it audible, but not intrusive. You can definitely hear the turbo more, expecially at full throttle, and its got a little bit of a low pitched resonance at slow speeds at light throttle. Most likely, cruising at low rpm at those speeds (<35mph) combined with light throttle application is not creating enough exhaust gas to form laminar flow throught the pipes since there is now no restriction post turbo. As soon as you apply a little throttle, the resonance goes away. I would like to reiterate that this is not an annoying resonance. I personally love the way it sounds now, and I stand outside everytime my wife borrows the jeep just to hear it drive off, and also to pray that it returns in the same condition in which it left. Oh, and mileage seems slighlty improved along with slightly decreased spool up time. I think 3" on a <200hp diesel would resonate like crazy, and the added weight would probably far outweigh any extra perforance gains over the 2.5" system.

stoutdog · **Posted:** Wed Jul 01, 2009 6:45 pm

DGM635csi wrote:

2.5" is more than enough volume for even a modded CRD IMO. I went 2.5", straight piped the cat, junked the OEM muffler and replaced with a 24" magnaflow stainless muffler, and installed a 3" Gibson turn down tip to finish it off. The sound it audible, but not intrusive. You can definitely hear the turbo more, expecially at full throttle, and its got a little bit of a low pitched resonance at slow speeds at light throttle. Most likely, cruising at low rpm at those speeds (<35mph) combined with light throttle application is not creating enough exhaust gas to form laminar flow throught the pipes since there is now no restriction post turbo. As soon as you apply a little throttle, the resonance goes away. I would like to reiterate that this is not an annoying resonance. I personally love the way it sounds now, and I stand outside everytime my wife borrows the jeep just to hear it drive off, and also to pray that it returns in the same condition in which it left. Oh, and mileage seems slighlty improved along with slightly decreased spool up time. I think 3" on a <200hp diesel would resonate like crazy, and the added weight would probably far outweigh any extra perforance gains over the 2.5" system.

Great, thanks. Eurekaboy recommended I go with the 2.5", and that was after he used a 3" straight pipe. He said the difference was negligible if anything.

Forgive my ignorance, but what is involved in straight piping a cat? I understand replacing the muffler with a straight pipe, but what does the cat even do?

RTStabler51 · **Posted:** Wed Jul 01, 2009 7:54 pm

IIRC the turbo outlet is 2.5" and so is the exhaust until the muffler. IMO, replace that back. I have a MBRP catback on the way and will report back

AZ CRD · **Posted:** Wed Jul 01, 2009 9:38 pm

RTStabler51 wrote:

IIRC the turbo outlet is 2.5" and so is the exhaust until the muffler. IMO, replace that back. I have a MBRP catback on the way and will report back

Please do report back, but what about the catalytic converter? I'm with stoutdog ('sup fellow desert dweller?). What is it intended to do other than collect soot deposits? Is it restrictive? I'm thinking I should clean it out with a 3/4" pipe when I order my cat back.

I like the look of the black MBRP. What's it made of? Would it last as long as stainless?

stoutdog · **Posted:** Wed Jul 01, 2009 9:54 pm

AZ CRD wrote:

RTStabler51 wrote:

IIRC the turbo outlet is 2.5" and so is the exhaust until the muffler. IMO, replace that back. I have a MBRP catback on the way and will report back

Please do report back, but what about the catalytic converter? I'm with stoutdog ('sup fellow desert dweller?). What is it intended to do other than collect soot deposits? Is it restrictive? I'm thinking I should clean it out with a 3/4" pipe when I order my cat back.

I like the look of the black MBRP. What's it made of? Would it last as long as stainless?

AZ CRD, hey man. I'm hoping to join up with y'all for some trips after I get back to AZ in August... I'm a desert dweller for at least a few more years, finishing up grad school at ASU.

I'm interested to know if the cat is restrictive or not. Would gutting/removing it improve my mpg, anyone?

stoutdog · **Posted:** Sun Jul 05, 2009 12:54 pm

I know there are more people who can voice in on the necessity of the cat and whether or not removing/gutting it will improve mpg....

Or on any of my other questions...

Bueller?

DarbyWalters · **Posted:** Sun Jul 05, 2009 1:51 pm

I did a 3" straight pipe from the cat back. Does sound deeper and that is OK for me. Gutting the CAT is not really needed IMO...just like 3" was not needed (just my preference). The CAT on these is not much of a restriction (if any at all) and keeps you legal.

It saved me a bit of $$$ not putting on a muffler I didn't think I needed anyway...It also looks pretty nice with the 3" exiting tip...I extended it an inch or so to keep any soot off the rear bumper facia.

Joe Romas · **Posted:** Sun Jul 05, 2009 4:33 pm

If I were going to modify my exhaust I would first start by replacing that large restrictive drum of a muffler we have with a stright pipe and leave the cat and other pipes at the 2.5 they are :lol:

The problem is the muffler has a large restriction inside. As Darby said his is not loud without a muffler. So with just a stright pipe replacing the muffler you would have little cash outlay and then would know if the $$$ for a 3" would be worth it or just a good 2.5 muffler of your choice. On the cat, as I understand it it traps soot and then when the engine is hot the soot burns off. If you were ever to need one it would be expensive. Many feel that 3" is overkill for the size of our engines

Pablo · **Joined:** Thu Feb 02, 2006 10:06 pm **Posts:** 1201

I have the Aero. My honest opinion after 40,000+ plus miles with it is that I would not spend more money for it than any other free flowing muffler. .It is just a muffler. Much better than stock, but it is too expensive to justify the cash outlay versus the performance increase. If I had it to do over, it would be a straight pipe and I would take the money I saved and spend on something else: like a GDE tune, or a Provent.

kdlewis1975 · **Posted:** Sun Jul 05, 2009 10:34 pm

AZ CRD wrote:

RTStabler51 wrote:

IIRC the turbo outlet is 2.5" and so is the exhaust until the muffler. IMO, replace that back. I have a MBRP catback on the way and will report back

Please do report back, but what about the catalytic converter? I'm with stoutdog ('sup fellow desert dweller?). What is it intended to do other than collect soot deposits? Is it restrictive? I'm thinking I should clean it out with a 3/4" pipe when I order my cat back.

I like the look of the black MBRP. What's it made of? Would it last as long as stainless?

Stating the obvious, the catalytic converter cleans up the exhaust to some degree. There is a honeycomb, with as much surface area as possible, impregnated with a concoction of precious metals including the likes of platinum, palladium, and iridium. Probably the main thing it does it remove unburned hydrocarbons from the exhaust--there's always going to be a tiny amount--by converting them to CO2. It's apparently not as much problem for a diesel, but in gassers, the cat converts carbon monoxide to CO2. It might do a little conversion on the NOx compounds, but not enough to keep us from being cursed with EGR valves.

I'd suspect that it gathers a good amount of soot. Many will do hard runs to blow the soot out. Long highway runs could promote the burning off of some of it with nice steady warm exhaust temps assuming there is sufficient residual oxygen in the exhaust.

Cats are actually worth a fair amount when scrapped due the precious metals.

stoutdog · **Posted:** Sun Jul 05, 2009 11:19 pm

I've tried to summarize y'alls input, see my original post. Let me know if I got anything wrong or you have another opinion!

Looking at MBRP cat back systems, I just can't justify the expense of $400+ for little to no gain over a simple straight pipe or Magnaflow 2.5".

Unless I've misinterpreted what a number of you have said, the best and easiest thing to do is just cut out the old muffler and put a piece of 2.5" pipe in between. Nothing fancy. Right?

Thanks again for all your help, keep the input coming!

RTStabler51 · **Posted:** Mon Jul 06, 2009 12:04 am

stoutdog wrote:

Looking at MBRP cat back systems, I just can't justify the expense of $400+ for little to no gain over a simple straight pipe or Magnaflow 2.5".

You're looking at the wrong places. You can get the aluminzed one for 300, or SS for 341 with free shipping.

I looked at it from the 'ease' stand point, as I can install it in my drive way and don't need something that's going to look like crapped stuffed up under there.

chrispitude · **Posted:** Mon Jul 06, 2009 6:39 am

RTStabler51 wrote:

You're looking at the wrong places. You can get the aluminzed one for 300, or SS for 341 with free shipping.

I looked at it from the 'ease' stand point, as I can install it in my drive way and don't need something that's going to look like crapped stuffed up under there.

Agreed. I went with the stainless steel Magnaflow catback, and I'm glad I did. It was an easy driveway project, looks nice, sounds great, and will last. I didn't have to go to an exhaust shop and read five year old car magazines while I waited.

- Chris

stoutdog · **Posted:** Mon Jul 06, 2009 7:38 am

Unfortunately, I don't have the tools or space at my apt. to do this myself, so it's a shop job either way.

If I read this right, the catback replaces the piping from the cat to the muffler, the muffler, and the piping after the muffler. My question is, what is wrong with the original piping that it needs replacing or is this just a preference thing?

Also, could you link me to where you are finding them for the low $300s? I can find the aluminized, but would only consider the SS.

chrispitude · **Posted:** Mon Jul 06, 2009 8:12 am

stoutdog wrote:

Unfortunately, I don't have the tools or space at my apt. to do this myself, so it's a shop job either way.

Do you have a local buddy with a garage, perhaps? Although even if it's a shop job, I can't imagine they'd charge much to swap the new setup on for you. Just go some place which is only going to charge you for the 30 minutes it will take, rather than an hour just because they can. On a lift, it's probably a 20 minute job tops.

- Chris

linewarbr · **Posted:** Mon Jul 06, 2009 8:25 am

Went to the Magnaflow website, but I could only find a product listing for the 3.7 gasser Liberty?

Joe Romas · **Posted:** Mon Jul 06, 2009 8:33 am

linewarbr wrote:

Went to the Magnaflow website, but I could only find a product listing for the 3.7 gasser Liberty?

That's part of the problem. Chrysler used the same muffler for the 4 cylinder gasser, 3.7v6 gasser and our CRD's :shock:

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