3.6L exhausts

[JK_Dave]

I appreciate your first hand experience here sir. Can you help me understand something you said though? How would additional back pressure (caused by the loop) aid in assisting the exhaust valves staying closed? Perhaps I just can't conceptualize it, but I would think additional back pressure would push against the valves trying to keep them open.

Increased exhaust pressure can have a number of effects on an engine, such as increased pumping work, reduced intake manifold pressure, cylinder scavenging and combustion effects.

At increased back pressure levels, the engine has to compress the exhaust gases to a higher pressure which involves additional mechanical work and/or less energy extracted by the exhaust turbine which can affect intake manifold boost pressure. This can lead to an increase in fuel consumption, PM and CO emissions and exhaust temperature. The increased exhaust temperature can result in overheating of exhaust valves and the turbine. An increase in NOx emissions is also possible due to the increase of engine load.

I know you need some back pressure, otherwise during your valve overlap where oxygen is filling the combustion chamber and fuel is being injected, and your exhaust valve hasn't completely closed, you would lose some of the O2/fuel mixture out of your exhaust stream. But for the purposes here, I can't imagine you're losing enough pressure from that bank of cylinders the loop is on to say that it could disturb the engine too much.

I'm not an engineer, but I like to think I'm making a somewhat reasonable argument here. I'm not saying "I'm right, you're wrong" so please don't take it that way. I love constructive arguments.

 

[NFRs2000NYC]

I appreciate your first hand experience here sir. Can you help me understand something you said though? How would additional back pressure (caused by the loop) aid in assisting the exhaust valves staying closed? Perhaps I just can't conceptualize it, but I would think additional back pressure would push against the valves trying to keep them open.

Increased exhaust pressure can have a number of effects on an engine, such as increased pumping work, reduced intake manifold pressure, cylinder scavenging and combustion effects.

At increased back pressure levels, the engine has to compress the exhaust gases to a higher pressure which involves additional mechanical work and/or less energy extracted by the exhaust turbine which can affect intake manifold boost pressure. This can lead to an increase in fuel consumption, PM and CO emissions and exhaust temperature. The increased exhaust temperature can result in overheating of exhaust valves and the turbine. An increase in NOx emissions is also possible due to the increase of engine load.

I know you need some back pressure, otherwise during your valve overlap where oxygen is filling the combustion chamber and fuel is being injected, and your exhaust valve hasn't completely closed, you would lose some of the O2/fuel mixture out of your exhaust stream. But for the purposes here, I can't imagine you're losing enough pressure from that bank of cylinders the loop is on to say that it could disturb the engine too much.

I'm not an engineer, but I like to think I'm making a somewhat reasonable argument here. I'm not saying "I'm right, you're wrong" so please don't take it that way. I love constructive arguments.

I am not an engineer either, but I do know that the pentastar needs those exhaust loops and a fair amount of backpressure to run properly. It is not like an LS motor where the straighter the better. I have read people's accounts (not on a jeep forum) that the pentastar runs horribly when backpressure is removed. As for the valves, backpressure would aid in their timing and control of opening/closing.

 

[JK_Dave]

I am not an engineer either, but I do know that the pentastar needs those exhaust loops and a fair amount of backpressure to run properly. It is not like an LS motor where the straighter the better. I have read people's accounts (not on a jeep forum) that the pentastar runs horribly when backpressure is removed.

My engine runs just fine without it. What do you mean "horribly"?

As for the valves, backpressure would aid in their timing and control of opening/closing.

That's what your timing belt is for.

 

[NFRs2000NYC]

My engine runs just fine without it. What do you mean "horribly"?



That's what your timing belt is for.

They claimed it was running rougher, etc. I have no experience in this regard so I definitely won't argue. Supposedly those loops are there for equal exhaust flow but who knows. If you are running without the loops and all is well, then, I stand corrected. I just hope that if you get a ticking head chrysler won't give you sh!t for the missing loops.

 

[jnabird333]

That's what your timing belt is for.

I am not an expert at engine management/performance, but what I can tell you is Chrysler spent a MAJOR amount of time money developing the exhaust on the 3.6L JKs. The loop is a complicated bend and was tricky to squeeze into the real estate they had to work with. It also makes line installation more difficult. If it wasn't needed (or even if it had little benefit) it wouldn't be there.

To your belt comment... Valves are no longer controlled solely mechanically. Also it is possible to float a valve open regardless of belt and/or chain position. This is more prevalent on hydraulic lifters, but even the valve lash of a solid can cause leaking. These differences are tough to tell by a butt dyno.

For the holding close question, too low of back pressure can allow the exhaust valve to open ever so slightly on the compression stroke. Again, I'm not an expert ant this... This is what I have learned from dealing with the experts. In order for me to properly control a machine I have to intimately understand the process. (Plus, machine run-offs often offer BS time )

 

[cozdude]

so i have been doing a little trolling on other forums to see if i can contribute to this thread at all. i have found that on many other forums people have also talked about a loss in torque (something crazy like 30-40 ft/lbs) when removing the loop but as mentioned on 5 hp or so was lost. also the pipes were made equal length due to them meeting at the Y pipe. something about the fumes and the pressures flowing evenly is extreamly important as well. last but not least one exhaust manufacture chimed in and said that the designed there exhaust to be after the loop because thru testing the found that the loop is that important.

im just relaying a little more info i saw on it.

 

[JK_Dave]

I am not an expert at engine management/performance, but what I can tell you is Chrysler spent a MAJOR amount of time money developing the exhaust on the 3.6L JKs. The loop is a complicated bend and was tricky to squeeze into the real estate they had to work with. It also makes line installation more difficult. If it wasn't needed (or even if it had little benefit) it wouldn't be there.

To your belt comment... Valves are no longer controlled solely mechanically. Also it is possible to float a valve open regardless of belt and/or chain position. This is more prevalent on hydraulic lifters, but even the valve lash of a solid can cause leaking. These differences are tough to tell by a butt dyno.

For the holding close question, too low of back pressure can allow the exhaust valve to open ever so slightly on the compression stroke. Again, I'm not an expert ant this... This is what I have learned from dealing with the experts. In order for me to properly control a machine I have to intimately understand the process. (Plus, machine run-offs often offer BS time )

To be fair, I was assuming Chrysler's intent when designing this system and applying a generality to them that cost was their primary concern. You make a good point and I can't argue that it wouldn't be there if it didn't serve some purpose. The loop serves it's purpose to make the exhaust equal length for both cylinder banks. Could they have also designed a true dual exhaust to accomplish the same purpose? Sure, but there are compromises there with how the tubing would be run and not interfere with other components. Is it possible that it's removal causes any harm to the car? Sure, but I'm certainly hoping not. At least no harm that could make anyone say the words "warranty claim". I do promise to report any complications I encounter down the line by running without it though!

 

[jnabird333]

The company I worked for made the tube bending, notching, sizing, and trimming machines for several companies. I can't speak for all, but Gibson and Magnaflow do not do long term engine life tests with and without their product, (or at least they didn't on the products I was involved with.) They only do a before and after Dyno runs. Most of their gains are found in the higher RPM (More Flow). The bottom line is that they likely (I don't know about all) have give no consideration for long life issues where the Chrysler engineers have.

To your point though, It is far easier to make a system and simply leave the loop in. To my point, it has little effect on flow so why remove it.

Please don't get me wrong, If I was looking at a suspension system that involved a loop delete, I wouldn't let it sway me. However, If I could leave it in I would.

Additionally, I run rear muffler-less and have noticed no adverse effects. Beyond the sound when it is first started and running on open-loop control. Once warm the sound is okay. Although I plan to change to an Dynomax EVO system soon...

 

[JayKay]

My thoughts about it are if so many people are saying they saw a decrease in HP/TQ or no change at all after removing the loop, leave it there. I believe the only reason it would need to be removed is to clear a long-arm suspension lift, then remove it if that's the case.

 

[JayKay]

The company I worked for made the tube bending, notching, sizing, and trimming machines for several companies. I can't speak for all, but Gibson and Magnaflow do not do long term engine life tests with and without their product, (or at least they didn't on the products I was involved with.) They only do a before and after Dyno runs. Most of their gains are found in the higher RPM (More Flow). The bottom line is that they likely (I don't know about all) have give no consideration for long life issues where the Chrysler engineers have.

To your point though, It is far easier to make a system and simply leave the loop in. To my point, it has little effect on flow so why remove it.

Please don't get me wrong, If I was looking at a suspension system that involved a loop delete, I wouldn't let it sway me. However, If I could leave it in I would.

Additionally, I run rear muffler-less and have noticed no adverse effects. Beyond the sound when it is first started and running on open-loop control. Once warm the sound is okay. Although I plan to change to an Dynomax EVO system soon...

100% agreed

 

[Cajun JK]

So from what I am reading here, if I put the axel back dual Magnaflow black muffler on my 2012, it could cause issue with the motor?

 

[NFRs2000NYC]

So from what I am reading here, if I put the axel back dual Magnaflow black muffler on my 2012, it could cause issue with the motor?

No, definitely not. Axleback exhausts only replace the muffler sections. Cat backs replace everything AFTER the loops (eliminating the OEM resonator.)

 

[DynoMax Exhaust]

i think even with the dynomax Evolution it keeps the factory hoop. the new muffler goes on after it. eddie runs it on Rubicat. Even the Dynomax rock crawler keeps the loop .

Correct. Our guys talked with the Jeep engineers and they put the loop in there to intentionally to get all they could out of the 3.6. We still haven't dynoed a 3.6 with our system yet.... but on the 3.8 we saw nominal gains (high single digits). Best thing is getting rid of that bulky rear muffler. :beer:

Edit
Jnabird, great info!!!
NFRs, a lot of system lose low end TQ, but see gains throughout the power band. Your butt-dyno is pretty spot on.

 

[metaldemon]

Someone here mentioned Hardleys. This is a perfect example. They have been turning gasoline into noise since 1903, without the benefit of making any horsepower.
Just because it is loud or sounds good doesn't mean it is better. The only reason I would replace the rear muffler was because of its size.

 

[cozdude]

Correct. Our guys talked with the Jeep engineers and they put the loop in there to intentionally to get all they could out of the 3.6. We still haven't dynoed a 3.6 with our system yet.... but on the 3.8 we saw nominal gains (high single digits). Best thing is getting rid of that bulky rear muffler. :beer:

Edit
Jnabird, great info!!!
NFRs, a lot of system lose low end TQ, but see gains throughout the power band. Your butt-dyno is pretty spot on.

Thanks for the reply! I'm looking forward to eventually running your rock crawler exhaust on my '11 2 door for the small gain you notice but also because it sounds amazing!!


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