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I was looking into the magnaflow or another brand name exhaust with hopes of adding a little more HP and more importantly increase the gas mileage. I know this topic has been beat to death with return on mileage for money spent lol but I was curious as to just replacing the muffler not whole exhaust system. I looked under XK and most exhaust looks great the muffler has a few spots that are pitted bad and I am sure in time will rust further. I see that most sellers only list the 4.7 and hemi 5.7 as models so was curious if those fit for the 3.7 I do like the sound ive heard on youtube lol but for me its more of performance. I plan on the K&N air filter also as well as replacing spark plugs too. Id rather do other mods to start (lift kit, mud flaps, bull guard and off road lights) but figure some basic stuff cant hurt. Also the whole exhaust systems are expensive....so looking for recommendations or ideas.....or if anyone even just replaced the muffler itself? Had a friend with grand cherokee and he said he put oringal mopar muffler on was 512$ just for the muffler he didnt want cheap one lol.
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I would not go into this expecting a mileage improvement OR a performance improvement; especially just replacing the muffler. If you want it for the sound, then by all means, do it for that reason. But anything else is going to be negligible or all in your head. What minimal gain you could see in performance would come from a more complete exhaust replacement/upgrade.
 

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If Hp and mileage are a concern then I would look into a custom tune or a Hypertech Max Energy tuner. You can find them on ebay occasionally for cheap. model number 52001 (older and updatable to work with 3.7L, I have this one) or 52501 will work
 

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I read in owners manual that the XK was set up for 85 ethanol and not the 87 but you can use either gas? So that would affect gas mileage. So yeah might be worth investing in programmer to adjust the fuel burn for 87? Also I do like the sound of those mufflers but as long as it doens't make gas mileage worse then I am ok with them :).
I figure if I do need to replace the muffler I might as well get something that will add little more to XK without to much more cost. ALso why are so many people having the exhaust welded? Is that only for off roading reasons? I dont plan to do that much trail riding but would that be the reason?
 

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I read in owners manual that the XK was set up for 85 ethanol and not the 87 but you can use either gas? So that would affect gas mileage. So yeah might be worth investing in programmer to adjust the fuel burn for 87? Also I do like the sound of those mufflers but as long as it doens't make gas mileage worse then I am ok with them :).
I figure if I do need to replace the muffler I might as well get something that will add little more to XK without to much more cost. ALso why are so many people having the exhaust welded? Is that only for off roading reasons? I dont plan to do that much trail riding but would that be the reason?
I dont even have 85 available here in CA. 87/89/91 only. The tuner allows for 87 or 91 octane tunes.
 

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I read in owners manual that the XK was set up for 85 ethanol and not the 87 but you can use either gas? So that would affect gas mileage. So yeah might be worth investing in programmer to adjust the fuel burn for 87? Also I do like the sound of those mufflers but as long as it doens't make gas mileage worse then I am ok with them :).
I figure if I do need to replace the muffler I might as well get something that will add little more to XK without to much more cost. ALso why are so many people having the exhaust welded? Is that only for off roading reasons? I dont plan to do that much trail riding but would that be the reason?
Welded is better primarily because of the possibility of exhaust leaks when using clamps. It's just a more permanent and fool proof solution. That said, I cut my muffler off my WJ and clamped in two different ones over the years and had no issues.
 

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Before I traded in the XK, I had a Thrush Welded Muffler on my 3.7L. From the videos, it sounds exacltly like the flowmaster 44, at less than half the price, $35 on Amazon w/ free shipping. I LOVED the sound results, but it probably decreased my mpg since I was so prone to make it roar after that lol. I even was asked by a local mechanic what engine mods I had done since he last saw it, since the sound was so much beefier. Lo and behold, it was just a simple muffler swap that cost me just $40 for a muffler shop to weld in. Another advantage to swapping the muffler is aftermarket sets are around half the size of the huge stock muffler.
 

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I dont even have 85 available here in CA. 87/89/91 only. The tuner allows for 87 or 91 octane tunes.
That's normal octanes for regular (87), plus (89) & super unleaded gas is normally (92/93) octane on the east coast, maybe 91 octane super-unleaded is a California emissions thing.

Flex fuel is E-85 Ethanol.

I don't know about California, but, plenty of Gas stations here on the east coast have it available.


I am getting ready to modify my exhaust in the next few months.


I'm not going to mess with any headers or the Catalytic Coverter, but, I did find a nice Cat-Back system I am going to try;


http://www.carid.com/2008-jeep-commander-exhaust-systems/afe-mach-force-xp-exhaust-systems-45737490.html
 

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The more air you can flow through the motor, the more power it will make. Note that is increased air flow through the motor, NOT pump more gas into it, NOT just make air flow into easier, NOR just make air flow out of it easier, etc, etc.....

You can't flow out more air than you flow into the motor, you can't flow more into or out of the engine ports than the engine ports themselves can flow, etc, etc. You can't flow more air out of the muffler than the pipes, Catalytic Converters and Exhaust Manifolds themselves can flow into the muffler.

You have to figure out the choke point in the flow in/out of the engine, i.e. the most restrictive and replace or improve that portion to flow more and match the rest of the "System".

I don't know where the choke point is on the 3.7L in the Commander, but I doubt the Muffler is it.

If I'm correct, just changing out the Muffler with a freer flowing version is NOT going to do anything to increase the overall flow of air through the system, thus NOT going to increase the power. In the past, like 30 years ago or longer, vehicles were much poorer designed, and often the Muffler was always the choke point, today vehicles are much better designed and the intake/exhaust is much better balanced and thus there are really NOT many choke points at all. Often on todays vehicles, benefits are only realized after a huge effort to replace the entire intake and exhaust system with a specifically designed package for you vehicle.

Perhaps if you've installed a bunch of intake mods, exhaust mods, etc, maybe even changed the cam and ported and polished the head ports and intake manifold, the OEM Muffler might become the choke point and only then swapping out the Muffler with a freer flowing version might create a real benefit.

Keep in mind, the OEM exhaust is Stainless Steel (SS). SS does rust, just much, much slower than regular steel. The heat and moisture of the exhaust will rust the OEM SS exhaust system, but often it will still last a decade past when that rust first appears. Meanwhile, a cheap aftermarket muffler that is made out of "Aluminized Steel" will likely rust out 2-3 years after installation, leaving you wishing you still had the OEM muffler on the vehicle. That's NOT to say there aren't plenty of good quality aftermarket SS mufflers that will last as long as, or close, to the OEM Muffler. Personally I would NOT pick an "Aluminized Steel" muffler to replace the OEM Muffler, get a SS version at the very least.

If you just want a throatier sounding exhaust, that's fine, just don't expect a simple muffler swap is going to do anything but that for performance. Also, don't expect the exhaust of a 3.7L to sound the same as a 4.7L or Hemi with the same muffler.
 

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I read in owners manual that the XK was set up for 85 ethanol and not the 87 but you can use either gas? So that would affect gas mileage. So yeah might be worth investing in programmer to adjust the fuel burn for 87? Also I do like the sound of those mufflers but as long as it doens't make gas mileage worse then I am ok with them :).
I figure if I do need to replace the muffler I might as well get something that will add little more to XK without to much more cost. ALso why are so many people having the exhaust welded? Is that only for off roading reasons? I dont plan to do that much trail riding but would that be the reason?
Some Commanders came with Flex-Fuel equipped engines. It is usually well identified on the gas cap, dash and other places on the vehicle.

The engine and PCM have been equipped and is capable of recognizing if E85 fuel is being feed to the engine, and make the proper adjustments to run proper off of it.

I don't think the engine is optimized for one or the other, the way the Adaptive Speed Density Fuel Injection Management system works, it is going to optimize itself for what ever it is burning. Its just a matter if the "Chemistry" is compatible and if the parts of the engine and its supporting systems can survive the effects of alcohol as well as gasoline, and if the injectors have the MAX Capacity to inject the higher volume of alcohol that is needed compared to gasoline.

Regardless, the PCM and fuel injection system is going to hold the proper A/F ratios for all but warm-up and wide open throttle (WOT). The only thing a Hypercheck can change is, ignition timing (a huge effect) and A/F ratio during warm-up and WOT, plus a few other parameters that can effect the engine tune indirectly.

I'm NOT poo-pooing the Hypertech or devices like it. You just need to understand what it is doing to your vehicle. There are gains that can be made with some knowledgeable changes to the engine tune, if the owner "knows" what they are doing and acts accordingly.

Just keep in mind, the Manufacturer wants the engine to make as much power as possible, that helps him sells cars, but the Manufacturer also has to warranty the car, and wants the buyer to come back and buy another car from them in the future. So they have to balance that power with a safety margin for reliability and longevity.

And this is how the Hypertech and the like make their power, they cut into the Safety Margin the manufacturer builds into the motor tune.

Ford and some other Manufacturers have released specific guidance and clues to Dealership techs to help them identify if the engine damage being repaired under warranty was actually created by one of these tuner programmers. e.g. things like clues to exhaust temperature being exceeded damaging exhaust valves or other things, something the OEM Tune was designed to prevent, but a tuner program exceeded to get an extra 12HP.

Now, the manufacturer builds in that safety margin the assumption the buyer is the lowest common denominator idiot that has no idea how a car and its engine works, that just gas and goes and will continue to drive thousands of miles on a malfunctioning engine before fixing it. And Hypertech is assuming its customer is above the lowest common denominator idiot and does understand how a car and its engine works. Thus you can cut into that safety margin a bit, to gain a little more power, with the owner knowing when to intervene before there is any damage.

Honestly, I don't think you'd create that much of a problem for some minor changes with these things. Folks optimize the tune for mileage before a long hi-way trip, folks get a minor increase in power and throttle response with a little more aggressive ignition timing (they also know how to recognize detonation and back off when they encounter it), etc, etc......

BUT, if you think you can increase engine power by 33% by just plugging something into your OBDII port, and that engine will last just as long and trouble free as if it stayed in the OEM tune, you have another thing coming.
 
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