3.6L exhausts

J

just-lift-it

LOSER
SO was reading through another forum and a guy wanted to put exhasut on his 2013 rubi, and people were telling him NOT to do this because of the back pressure and what not designed into the pentastar that he will achieve horrible milleage after swapping out exhasut?

Anyone on this forum heard about this as well? seeing as there are way more JK on here then the other forum not sure if they know what they were saying or not!

any real world experiances over just theory in general??
 
noroad

noroad

New member
I took the loop out and stright piped it due to it hitting my long arm, and also took the ugly part off under the taile gate that rusts (sounds pretty good for free mod, little noise) leaving the normal exhaust to dump out under the driver seat. I am on 37s and was on it before, i can tell i lost a little hp but not enough to bother me, also lost about .5 to 1 mile after the cutting. hope that helps.
 
cozdude

cozdude

Guy with a Red 2-Door
i think Eddie has said before to leave the loop in. it does have something to do with backpressure and that chrysler made it that way for a reason. you can move it but try to keep it in. im sure he will chime in with the full reason why later when he wakes up
 
Linebacker

Linebacker

Caught the Bug
cozdude said:
i think Eddie has said before to leave the loop in. it does have something to do with backpressure and that chrysler made it that way for a reason. you can move it but try to keep it in. im sure he will chime in with the full reason why later when he wakes up
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I think this is good advice. Aftermarket manufacturers often make big claims re: HP & MPG. I'd be skeptical. Jeep spent lots of dyno time getting this stock system to perform with an eye on noise, HP and MPG. You can spend major bucks and get everything from going backwards to slight gains. I know on some of my past projects I earned the award for most money spent with the least return. I'm gonna do the air filter first and then install a smaller axle back muffler for clearance and keep the resonator for a little quiet and hopefully not upset the factory balance. That's the goal anyway.:twocents:
 
J

just-lift-it

LOSER
yeah well most guys on this forum run what like Dyno max or something? but its mainly the 3.8L so thats a different story thats why i wonder whats the trueth and whats myths people have made up haha

thanks
 
cozdude

cozdude

Guy with a Red 2-Door
just-lift-it said:
yeah well most guys on this forum run what like Dyno max or something? but its mainly the 3.8L so thats a different story thats why i wonder whats the trueth and whats myths people have made up haha

thanks
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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 .
 
OverlanderJK

OverlanderJK

Resident Smartass
I run the dynomax evolution comp on my '12. It's designed for a 07-11 but I put it on anyway. Yes I get worse MPG's but not by much, maybe .5-.75, mainly because I like the sound.
 
JKFlyer

JKFlyer

New member
so i have a 10 so not pentastar, but i did a catback with 3" pipe and i definitely lost backflow pressure and "umph" in general. It was an AFE power and was just too loud. So i went to the Quadratex Exclusive 2.5" magnaflow.....much better. got soem power back due to 2.5" pipe and sound much mellower, which is my personal preference. hope thsi helps
 
J

just-lift-it

LOSER
Well I actually run the MBRP cat back full system for 12-14 jku and i notice worse milleage but i can no idea it if from the skinny pedal or not haha but i love it is nice and loud when i get on it climbing hills and stuff with a nice bark to it ;) but when i purchased it i had never seen a thread talking about such a thing so i never thought twice not that i even give a shit its a jeep there no such thing as milleage haha its just inetersting to know!
 
NFRs2000NYC

NFRs2000NYC

Caught the Bug
I ran a dynomax VT on my last rig, and while it sounded ok, I definitely noticed a loss of power. When I went back to stock, I definitely felt an increase in low end torque. On my 14, I left the OEM exhaust in. Its also nice having a Jeep thats whisper quiet...god Im getting old. :D
 
Sithwindu

Sithwindu

Member
I have the dynonax comp for my 2013, kit install is after the y pipe so no worries on the loop( yes it's for back pressure reasons)

Most people might experience less gas mileage for one main reason, more skinny pedal to hear that awesome sound!! Seriously lol. I didn't notcr any chance cause I put my exhaust on same time I did lift as 35's so kinda hard to tell heh
 
J

just-lift-it

LOSER
so the concessus is the "loop" is the pressure point anything from the crossmember back like replacing resi and muffler doesnt affect it? which is most bolt on systems so thats good!

I didnt like listening to my sewing machine 3.6 so the exhasut drowns it out now :p
 
JK_Dave

JK_Dave

Caught the Bug
Until someone can post up before and after dyno graphs of a stock system vs. aftermarket, be wary of any claims one way or the other in regards to hp. Gas mileage is affected by so many variables (temp, gas quality, environment, driver, etc) that unless you did a test in a controlled lab, there's no way to prove an aftermarket exhaust loses gas mileage in and of itself.

My :twocents:

My disclaimer: I have the aFe 2.5" cat back with Y-pipe and I cut out the factory exhaust loop, which I thought was stupid. Adding restriction to an exhaust just to make it equal length makes no sense to me.
 
StrizzyChris

StrizzyChris

New member
JK_Dave said:
Until someone can post up before and after dyno graphs of a stock system vs. aftermarket, be wary of any claims one way or the other in regards to hp. Gas mileage is affected by so many variables (temp, gas quality, environment, driver, etc) that unless you did a test in a controlled lab, there's no way to prove an aftermarket exhaust loses gas mileage in and of itself.

My :twocents:

My disclaimer: I have the aFe 2.5" cat back with Y-pipe and I cut out the factory exhaust loop, which I thought was stupid. Adding restriction to an exhaust just to make it equal length makes no sense to me.
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So no offense intended, but it doesn't need to make sense to you. It only matters to the engineers that tested and knew that air flow created by this design was needed to optimize mpg torque and HP output by the engine. Trust me, if it weren't beneficial, they would have eliminated that small section of pipe on millions of Jeeps = millions more in profits :twocents:

Will your Jeep fun just fine? Sure. Will it run optimally as designed? No. Long term effects on engine wear? I don't know but also don't want to find out on my injury prone delicate flower of a 3.6L
 
JK_Dave

JK_Dave

Caught the Bug
StrizzyChris said:
So no offense intended, but it doesn't need to make sense to you. It only matters to the engineers that tested and knew that air flow created by this design was needed to optimize mpg torque and HP output by the engine. Trust me, if it weren't beneficial, they would have eliminated that small section of pipe on millions of Jeeps = millions more in profits :twocents:

Will your Jeep fun just fine? Sure. Will it run optimally as designed? No. Long term effects on engine wear? I don't know but also don't want to find out on my injury prone delicate flower of a 3.6L
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No offense taken Chris. I will politely disagree though. When engineers are designing exhausts, their priority is sound over efficiency of design. Hence the dual mufflers in the exhaust flow. Most of the general public wouldn't like a louder exhaust so engineers tune it in such a way as to muffle much of the sound. Even taking the stance that the "loop" doesn't impede performance, I don't think removing it is harmful any more than removing one of the mufflers from the exhaust.

I'm curious why you mentioned wear and tear on the engine though. Anything down stream from the engine shouldn't have any effect on the engine itself. Upstream definitely could.
 
jnabird333

jnabird333

-
JK_Dave said:
No offense taken Chris. I will politely disagree though. When engineers are designing exhausts, their priority is sound over efficiency of design. Hence the dual mufflers in the exhaust flow. Most of the general public wouldn't like a louder exhaust so engineers tune it in such a way as to muffle much of the sound. Even taking the stance that the "loop" doesn't impede performance, I don't think removing it is harmful any more than removing one of the mufflers from the exhaust.

I'm curious why you mentioned wear and tear on the engine though. Anything down stream from the engine shouldn't have any effect on the engine itself. Upstream definitely could.
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I'm not trying to stir the pot here but you are wrong. I designed the controls for the machines that make the exhaust system and worked closely with the engineers that designed the exhaust. Their foremost concern is performance to the rear muffler. Te rear muffler is designed to reduce as much sound as possible while not reducing flow... Thus it's massive size. Back-pressure is extremely important in today's engines as it aids in the closing of the valves and helps hold them closed. If you alter the back-pressure too much you can disturb this. Since the 3.6L engines already have a history of head issues there is some risk here. The loop is done to keep the back-pressure the same on both sides of the engine. Since it is mandrel bent it has little effect on flow. Aftermarket exhaust manufacturers understand this and this is why they leave it in.
 
Linebacker

Linebacker

Caught the Bug
jnabird333 said:
I'm not trying to stir the pot here but you are wrong. I designed the controls for the machines that make the exhaust system and worked closely with the engineers that designed the exhaust. Their foremost concern is performance to the rear muffler. Te rear muffler is designed to reduce as much sound as possible while not reducing flow... Thus it's massive size. Back-pressure is extremely important in today's engines as it aids in the closing of the valves and helps hold them closed. If you alter the back-pressure too much you can disturb this. Since the 3.6L engines already have a history of head issues there is some risk here. The loop is done to keep the back-pressure the same on both sides of the engine. Since it is mandrel bent it has little effect on flow. Aftermarket exhaust manufacturers understand this and this is why they leave it in.
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X2. This comment strikes a cord of truth with me. I had a long conversation with an exhaust system designer for Harleys (I know totally different engines, but the general design principles hold) and he stated there is a major tradeoff between stylin' and performance. A reasonably quiet performance muffler for the Harley would have to be the size of a '57 Chevy, but no one would buy it. I think this is what Jeep did with the stock mufflers they run today.:twocents:
 
NFRs2000NYC

NFRs2000NYC

Caught the Bug
Don't want to start too much of an argument, but I have been building and tuning race/sports cars for over a decade, and have a highly calibrated butt dyno. I can bet my Jeep's title that I lost power with an aftermarket exhaust, at least down low. From a standstill, it was VERY noticeable. It might have made power up top, but that's worthless on a Jeep. Since aftermarket exhausts are designed to increase flow, there is no getting around the fact that you are losing backpressure, and backpressure aids in low end power. More flow=less backpressure. Intake/exhausts are one of the reasons the same motor in different vehicles produces different power. Running a different exhaust for clearance issues/crawling is one thing, but for power? Waste of money IMHO.
 
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