ranjr

Sorry but just because you say it's so doesn't mean there doesn't need to be proof. I'm not asking anyone to disclose top secret information here, just what the facts are using this crossover pipe on the 3.6 in the JK.

I understand that exhaust pipe size can directly affect flow but to what degree are we talking about? 5HP at 6000+ RPM or 10trq across the board. Many don't rev theses bricks over 4000 so the loss would not be a concern if it only drops up top.

Again a dyno graph comparing before and after is the only true method to measure this.

Imposter_LRF

I'm not saying that there doesn't need to be proof. I am not an AFe employee and therefore I cannot speak to their intentions, however I can speak to the intentions of Chrysler as I have been working on one of their programs that utilizes this exact engine and a very similar Y-Pipe in order to get as much power out of the vehicle as possible from the factory (while still keeping safety factors and reliability in mind).

If you don't believe what I have to say below, that is fine because I have accepted that you may be a born skeptic, and I am okay with that. But, for those of you who want to be "in the know" about the design and trust my 8 years of being engulfed in exhaust system engineering at Dynomax's parent company who strictly work on a day to day basis with OEM's, as well as the last year+ that I have dedicated to this particular style of exhaust system, please read the information below. I will answer any and all questions that pertain to the Jeep exhaust if you have them after this:

The Y-Pipe has the "goofy" turn around loop in it in order to make the exhaust system equal length on both sides of the Y-Pipe. The reason the OEM chooses to do this, and any other person that is attempting to increase horsepower/torque without going to a true dual system with equalizer pipe, is to take advantage of the exhaust pulses.

When the engine fires it sends an exhaust pulse down the exhaust. Now because the engine does not fire cylinders directly opposite of one another at the same time, each exhaust pulse has a different length of pipe to travel down. When individual pulses hit the Y-Pipe area, the velocity (caused by the diameter of the pipe...this diameter is critical here in order to keep up flow velocity) causes the open passage down the other side of the Y-Pipe to go into a vacuum. This vacuum "sucks" the next exhaust pulse down the tube with greater velocity (high pressure wants to go to where low pressure is, simple fluid dynamics here and remember that one side is lagging behind the other because we dont fire the opposing cylinders at the same time). This in turn reduces the backpressure on the engine and will actually allow the engine to put out more power because it doesn't have to work as hard on the exhaust stroke to "push" the exhaust gases through the system because they are already being pulled out! This is called scavenging.

Now, bear in mind we are not talking about HUNDREDS of horsepower here. We are talking anywhere from 6-8% or slightly more (depends on application). Torque is also changed by a very similar percentage. Therefore, if we were to use a non-equal length Y-Pipe, we would not get this scavenging effect and the engine would, in fact, have to "push" the exhaust flow down the pipes.

I apologize, I do not have dyno graphs to share with the class because the information I have is currently "intellectual property" so I can't give it out. But basic design and function, because it is already in production, can be shared

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Newish topic...

And finally to the point of the power being at mid to high RPM (4000+) where hardly anyone will use it...why did you buy the pentastar? I mean, there are numerous reviews that say that low speed operation is nearly the exact same as the 3.8L and offroad crawling you would not notice a difference. Furthermore they state that the place where the pentastar shines is in passing power, acceleration onto the highway, etc. which would be...tada!...the higher RPM range. If you were only using low speed, then you should've saved some cash on got an outgoing 2011. Just my on that topic...

captkrunch

The loop in the exhaust is before the y pipe . The stock y pipe is not equal length but I'm guessing the loop plus the short side of the y pipe is supposed to be equal to the longer pass. side. The afe y pipe moves the crossover back further but still connects at the same collector point , probably very close to stock length just a different bend on the passenger side.

Imposter_LRF

After looking at the EVO Pro-Tek pics, I would like to apologize for the misunderstanding.

I know understand why the AFe pipe exists! In seeing the pictures I instantly thought that the pipe was there in order to replace the "goofy" pipe in the hot end of the exhaust. Now that I see there pics, shown below here, I realize that they are moving the crossover pipe aft of the transmission crossmember.

Therefore, all the theory of exhaust system acoustics still applies, HOWEVER, you will still have equal length Y-pipes (or damn near equal), which will result in no power loss!

GO AFE!

Once again I apologize for the misunderstanding and now that I see these pics...their design intent is clear to me. They wanted to keep all the power and have the ability to run a long or short arm suspension system and not hit the driveshaft on the exhaust .

ranjr

I personally bought one for the 5 speed auto, the Pentastar was a bonus that is rarely used to its potential. I have no issue running the motor to redline but it only makes more horsepower than the 3.8 in the extreme upper end of the rpm band and it's near impossible to spend much time there on the street.

Imposter_LRF

Makes sense

offcamber

You must have seen a different graph than I? The one I saw had the pentastar outperforming the 3.8 pretty much everywhere. Having driven both, it's obvious there is nothing similar between the two.

ranjr

Maybe, but I'm pretty sure it was the same as there's not many to be found. I think it comes down to your opinion of "outperforming". I think that's a little too generous and should be more like "edge out" because the only real noticeable difference is when the 3.8 has quit and the 3.6 continues for another 1000 rpm.

It's been said many times that the true performance improvement for the 2012s is the 5 speed automatic not the Pentastar.

bbolander

That makes a lot more sense and makes the mod more interesting. Still would like to see one installed on a 2012 and hear how the install went If it moves the crossover behind the crossmember it looks like a pretty tight fit there, I imagine they've worked that out. Doesn't look easy to get the old one out and the new one in though. I was thinking the catalytic converter would be downstream, but it looks like there are two of them right after the engine upstream. Does that make it a legal mod in California when smog check time comes?

Imposter_LRF

Since you are not changing the actual emissions system, it would be legal there