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TDP154

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After much research and being bombarded with “You’re crazy. That’s not gonna do anything. That’s a waste of time” when telling older gear heads about j pipes, I got a j pipe made and installed. And......... it freaking works. Math doesn’t lie.

For those who don’t know what a j pipe is, also called a quarter wavelength pipe, (a helmholtz resonator is a bit different, but from what I see it is used synonymously with j pipe, which imo it shouldn’t) a j pipe is a closed off exhaust pipe with a 90 degree bend at one end which is welded to your truck’s exhaust pipe. The idea is that different RPMs have different frequencies, and with a correct length j pipe the sound waves will bounce off the closed end, travel back down the pipe and cancel out the frequency, eliminating the drone.

But you may ask, if the drone is so bad why don’t you change the muffler? Why don’t you just put the stock exhaust back on? Why don’t you just suck it up and deal with the drone? Because you can keep the exhaust note you love and cut out the headache inducing drone at the cost of a new muffler (that may or may not even be better!)

Your j pipe needs to be the same material, gauge, and size as your exhaust system. I bought a 90 and a 48” straight tube from Summit Racing. The 90 cost $35 and the straight tube cost $60.

I opted to make it a DIY project rather than take it to a muffler shop. If you want to pay someone to do it you may have to shop around because not everyone really grasps this concept, despite its simplicity.

To calculate what length your j pipe needs to be, you have to decide what RPM the drone is the worst. For me, my 2020 Ram 1500 (with a 5.7 hemi) droned the most at 1500 rpm. Next would be 500-700 rpm (idle.) The drone will occur at double the revs both ways, so this is true for 3000 rpm and 750 rpm as well. How noticeable it is will depend on your setup. (i.e. muffler(s) and pipes).

I have a Rough Country catback exhaust kit. It’s 3 inch, 16 gauge 409 stainless steel. The muffler is two-chambered. Some gears were worse than others, but if you were trying to maintain speed on the interstate at 65+ mph, go up hill, or otherwise drive under load then the drone was horrible.

Here is the calculation excel sheet I used:

To pick your frequency, you can measure with an app or use the basic chart provided on a different page in the excel sheet. I felt the app didn’t work well for me, (I probably just didn’t know how to use it) so I just went with the basic universal chart. 1500 RPM for an 8 cylinder is 100 hz.

Next you will need to measure your exhaust’s operating temperature. After driving around for awhile, I used an infrared digital thermometer aimed inside the tailpipe. Your results may vary widely, as mine would be anywhere from 130 F to 170 F. The muffler would be a consistent 200 F. I guestimated 170 would be the operating temp while driving.

Then you just match up your temperature on the left hand column with the frequency (in Hz) on the top row and you will have the number of inches your j pipe needs to be. My result was 37.15. The total length includes the bend. I made it an even 37 inches.

I saw a youtube video of excellent results from a guy with a 5thgen whose j pipe was 36 inches, and he only changed his muffler. He had stock exhaust pipes and resonators. It is possible this drone is universal at this RPM for our trucks regardless of the aftermarket exhaust system, but let me know if that is not true.

Fabricating the pipe you will need to weld obviously, and a metal-cutting hole saw in the diameter of your pipe. I got a Milwaukee 3” hole saw from Home Depot for $23. The hole saw was to cut (using a drill press) a circle off each side of one end of the 90 bend so it would fit more flush on the perpendicular exhaust pipe on the truck. You can use one of the circles you cut out as the end cap for your j pipe after some flattening and trimming.

The pipe can really fit on either side of your exhaust, whether on the driveshaft side or frame side. Sure, it would be “safer” to have it frame side but there’s lots more room to work with on the driveshaft side so that’s what I went with. Use a sharpie to trace exactly where you want your pipe to be so you don’t have to try welding under the truck. In my situation I don’t have a lift. Use your hole saw to cut out a hole where your traced for your j pipe to go. Tac weld first, then test fit again.
Also, make sure your flange bracket is on the front of the pipe where it should be BEFORE you weld your j pipe on. Don’t ask how I know this to be pertinent information. Also, I angled my j pipe upwards slightly so water won’t pool in there.

The cherry-on-top aspect about a j pipe is that, in actuality a perfectly straight and perpendicular pipe is most effective for targeting a specific RPM drone. Obviously that is not feasible on a vehicle. But the bend in the pipe actually helps with dampening drone at a wider range. About 250 RPM +/- will also go away. So for me, my 1500 RPM and 750 RPM drone is gone, and with the +/- 250 rpm my 500 rpm idle drone is gone too.

It is so much quieter in the cab yet you still retain the sound of your exhaust. Cannot recommend enough. More people need to know about this!

UPDATE: After a week and a half, everything is going great. I noticed I still have some drone at 2800ish RPM. Not bad because it’s only when I want the exhaust to be loud and it only drones for a second. Overall worth every penny. I am going to add some sort of bracket to my exhaust pipe for the end of the j pipe to rest on so the welds don’t crack later on.
 

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Moparluver

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This is awesome! Thanks for taking the time to write this up! Maybe I missed it.. did you take your pipe off to cut the hole in the side? Or did you leave it in the truck? I would assume you are right, that it doesn't matter much what muffler you run, it's the total length of the exhaust that creates the drone at that rpm. That said, is yours the short box crew cab?
 

TDP154

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This is awesome! Thanks for taking the time to write this up! Maybe I missed it.. did you take your pipe off to cut the hole in the side? Or did you leave it in the truck? I would assume you are right, that it doesn't matter much what muffler you run, it's the total length of the exhaust that creates the drone at that rpm. That said, is yours the short box crew cab?
Yes I removed the piece of pipe that connects the header Y-pipe to the muffler, where a stock resonator would be. Just to make it easier cutting and welding. I measured, test fit, and marked with it on the truck though. And yes, a quad cab but I guess that is a short crew cab.
 

Mclovinnnnn

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After much research and being bombarded with “You’re crazy. That’s not gonna do anything. That’s a waste of time” when telling older gear heads about j pipes, I got a j pipe made and installed. And......... it freaking works. Math doesn’t lie.

For those who don’t know what a j pipe is, also called a quarter wavelength pipe, (a helmholtz resonator is a bit different, but from what I see it is used synonymously with j pipe, which imo it shouldn’t) a j pipe is a closed off exhaust pipe with a 90 degree bend at one end which is welded to your truck’s exhaust pipe. The idea is that different RPMs have different frequencies, and with a correct length j pipe the sound waves will bounce off the closed end, travel back down the pipe and cancel out the frequency, eliminating the drone.

But you may ask, if the drone is so bad why don’t you change the muffler? Why don’t you just put the stock exhaust back on? Why don’t you just suck it up and deal with the drone? Because you can keep the exhaust note you love and cut out the headache inducing drone at the cost of a new muffler (that may or may not even be better!)

Your j pipe needs to be the same material, gauge, and size as your exhaust system. I bought a 90 and a 48” straight tube from Summit Racing. The 90 cost $35 and the straight tube cost $60.

I opted to make it a DIY project rather than take it to a muffler shop. If you want to pay someone to do it you may have to shop around because not everyone really grasps this concept, despite its simplicity.

To calculate what length your j pipe needs to be, you have to decide what RPM the drone is the worst. For me, my 2020 Ram 1500 (with a 5.7 hemi) droned the most at 1500 rpm. Next would be 500 rpm (idle.) The drone will occur at double the revs both ways, so this is true for 3000 rpm and 750 rpm as well. How noticeable it is will depend on your setup. (i.e. muffler(s) and pipes).

I have a Rough Country catback exhaust kit. It’s 3 inch, 16 gauge 409 stainless steel. The muffler is two-chambered. Some gears were worse than others, but if you were trying to maintain speed on the interstate at 65+ mph, go up hill, or otherwise drive under load then the drone was horrible.

Here is the calculation excel sheet I used:

To pick your frequency, you can measure with an app or use the basic chart provided on a different page in the excel sheet. I felt the app didn’t work well for me, (I probably just didn’t know how to use it) so I just went with the basic universal chart. 1500 RPM for an 8 cylinder is 100 hz.

Next you will need to measure your exhaust’s operating temperature. After driving around for awhile, I used an infrared digital thermometer aimed inside the tailpipe. Your results may vary widely, as mine would be anywhere from 130 F to 170 F. The muffler would be a consistent 200 F. I guestimated 170 would be the operating temp while driving.

Then you just match up your temperature on the left hand column with the frequency (in Hz) on the top row and you will have the number of inches your j pipe needs to be. My result was 37.15. The total length includes the bend. I made it an even 37 inches.

I saw a youtube video of excellent results from a guy with a 5thgen whose j pipe was 36 inches, and he only changed his muffler. He had stock exhaust pipes and resonators. It is possible this drone is universal at this RPM for our trucks regardless of the aftermarket exhaust system, but let me know if that is not true.

Fabricating the pipe you will need to weld obviously, and a metal-cutting hole saw in the diameter of your pipe. I got a Milwaukee 3” hole saw from Home Depot for $23. The hole saw was to cut (using a drill press) a circle off each side of one end of the 90 bend so it would fit more flush on the perpendicular exhaust pipe on the truck. You can use one of the circles you cut out as the end cap for your j pipe after some flattening and trimming.

The pipe can really fit on either side of your exhaust, whether on the driveshaft side or frame side. Sure, it would be “safer” to have it frame side but there’s lots more room to work with on the driveshaft side so that’s what I went with. Use a sharpie to trace exactly where you want your pipe to be so you don’t have to try welding under the truck. In my situation I don’t have a lift. Use your hole saw to cut out a hole where your traced for your j pipe to go. Tac weld first, then test fit again.
Also, make sure your flange bracket is on the front of the pipe where it should be BEFORE you weld your j pipe on. Don’t ask how I know this to be pertinent information. Also, I angled my j pipe upwards slightly so water won’t pool in there.

The cherry-on-top aspect about a j pipe is that, in actuality a perfectly straight and perpendicular pipe is most effective for targeting a specific RPM drone. Obviously that is not feasible on a vehicle. But the bend in the pipe actually helps with dampening drone at a wider range. About 250 RPM +/- will also go away. So for me, my 1500 RPM and 750 RPM drone is gone, and with the +/- 250 rpm my 500 rpm idle drone is gone too.

It is so much quieter in the cab yet you still retain the sound of your exhaust. Cannot recommend enough. More people need to know about this!

UPDATE: After a week and a half, everything is going great. I noticed I still have some drone at 3000 RPM. Not bad because it’s only when I want the exhaust to be loud and it only drones for a second. Overall worth every penny. I am going to add some sort of bracket to my exhaust pipe for the end of the j pipe to rest on so the welds don’t crack later on.
Super cool! I feel like I don’t have much drone in the truck but man I wish I knew about this when I had my straight piped challenger! Lol. Thanks for the detailed write up!
 

Moparluver

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Yes I removed the piece of pipe that connects the header Y-pipe to the muffler, where a stock resonator would be. Just to make it easier cutting and welding. I measured, test fit, and marked with it on the truck though. And yes, a quad cab but I guess that is a short crew cab.
That makes sense.. I still have that resonator in place.. I wonder if there's still enough room for the Jpipe with that still there? I have a simple welded in magnaflow, so I'd have to make a cut to get that section of pipe out. I know you said that you based your speed of sound on 170 degrees by measuring the exhaust temp... but the air inside is likely hotter than the pipe itself.. from what i've read ~ 400 degrees? although I'm sure it cools along the way.. from what the calculations say, it looks like the same length pipe will change your center frequency ~ 200 RPM with a ~200 degree gas temp difference. Alternatively, depending on that temp and it's impact on resonance to achieve the same center frequency, the difference could be as much as 7" in length. I can't seem to find anything that tells me definitively what to base that temp off of.. Were you able to?

I suppose the alternative is to make it adjustable (clamped pipe over the open end of the resonator) so that you could accommodate the min/max length with your target center frequency. Once you find center, you could simply weld the pipe in place.

The other interesting thing about that theory is that if the pipe temp is the paramount metric, you'd think that the resonance would change with temp! I've never noticed my drone changing RPM's though..

Lastly, I wonder how much attenuation the jpipe gives? does it actually get quieter at your center frequency then the rest of the range? And what controls the level of attenuation? The diameter of the jpipe? I don't expect you to know the answers to this, just interesting musings..
 

TDP154

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That makes sense.. I still have that resonator in place.. I wonder if there's still enough room for the Jpipe with that still there? I have a simple welded in magnaflow, so I'd have to make a cut to get that section of pipe out. I know you said that you based your speed of sound on 170 degrees by measuring the exhaust temp... but the air inside is likely hotter than the pipe itself.. from what i've read ~ 400 degrees? although I'm sure it cools along the way.. from what the calculations say, it looks like the same length pipe will change your center frequency ~ 200 RPM with a ~200 degree gas temp difference. Alternatively, depending on that temp and it's impact on resonance to achieve the same center frequency, the difference could be as much as 7" in length. I can't seem to find anything that tells me definitively what to base that temp off of.. Were you able to?

I suppose the alternative is to make it adjustable (clamped pipe over the open end of the resonator) so that you could accommodate the min/max length with your target center frequency. Once you find center, you could simply weld the pipe in place.

The other interesting thing about that theory is that if the pipe temp is the paramount metric, you'd think that the resonance would change with temp! I've never noticed my drone changing RPM's though..

Lastly, I wonder how much attenuation the jpipe gives? does it actually get quieter at your center frequency then the rest of the range? And what controls the level of attenuation? The diameter of the jpipe? I don't expect you to know the answers to this, just interesting musings..
Your questions are very valid. The reading I did never had a definitive answer on what is the most accurate way to measure your exhaust temperature, but it seemed the ol' thermometer in the tailpipe was good enough for everyone who did it to their cars. I had that feeling as well, that surely the exhaust is cooling down tremendously by the time it reaches the tailpipe. That's why I went with the highest number I got.

Your alternative to have an adjustable pipe is also one that I pondered. My first few tries of calculating my j-pipe length was either 37 inches or 47 inches. I can't remember the overall length of room I measured under the truck, but I think I remember 47 inches would have been running into the muffler and I only had room for 45 inches. I had the discrepancy in length from indecisiveness on what RPM I wanted to target. I knew 1500 was the worst, but keeping the +/- 250 RPM wiggle room in mind I considered setting it up to target 1250 RPM to, in theory, cancel a wider range of drone for daily driving, while hitting my 1500 problem. I ultimately chose not to get greedy and go with hitting the worst RPM the hardest, and my judgement thankfully pulled through. Because I became dead-set on 1500 RPM I opted not to make it adjustable.

As far as exhaust note changing with temp, I agree with you. Everywhere I've read states temperature is one of the most important factors for calculating the length on a j-pipe, as it is 50% of the calculation, yet at the same time you just need a ballpark figure. I cannot tell a difference in sound from driving while the exhaust is hot or "cold".

And yes, going through the revs your drone will quiet down as you approach your targeted RPM, be mathematically non-existent at the chosen RPM, and then start to come back as you depart from it. Why that is has to do with the change in frequency of the sound waves being created based on the RPM. Once your j-pipe quarter wavelengths aren't crossing paths with your targeted RPM exhaust sound waves, they don't cancel anything out anymore since your quarter wave lengths are tailored to that RPM. But thankfully the 90 degree bend gives it extra range so for everyday driving, all of the drone is essentially gone. Put your foot down and it'll be back.

I should've added this when I originally created this thread. Here is a Youtube video of a guy explaining the science behind the j-pipe, whose method I ended up using. He also created the spreadsheet.

 
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cmbernal86

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Your questions are very valid. The reading I did never had a definitive answer on what is the most accurate way to measure your exhaust temperature, but it seemed the ol' thermometer in the tailpipe was good enough for everyone who did it to their cars. I had that feeling as well, that surely the exhaust is cooling down tremendously by the time it reaches the tailpipe. That's why I went with the highest number I got.

Your alternative to have an adjustable pipe is also one that I pondered. My first few tries of calculating my j-pipe length was either 37 inches or 47 inches. I can't remember the overall length of room I measured under the truck, but I think I remember 47 inches would have been running into the muffler and I only had room for 45 inches. I had the discrepancy in length from indecisiveness on what RPM I wanted to target. I knew 1500 was the worst, but keeping the +/- 250 RPM wiggle room in mind I considered setting it up to target 1250 RPM to, in theory, cancel a wider range of drone for daily driving, while hitting my 1500 problem. I ultimately chose not to get greedy and go with hitting the worst RPM the hardest, and my judgement thankfully pulled through. Because I became dead-set on 1500 RPM I opted not to make it adjustable.

As far as exhaust note changing with temp, I agree with you. Everywhere I've read states temperature is one of the most important factors for calculating the length on a j-pipe, as it is 50% of the calculation, yet at the same time you just need a ballpark figure. I cannot tell a difference in sound from driving while the exhaust is hot or "cold".

And yes, going through the revs your drone will quiet down as you approach your targeted RPM, be mathematically non-existent at the chosen RPM, and then start to come back as you depart from it. Why that is has to do with the change in frequency of the sound waves being created based on the RPM. Once your j-pipe quarter wavelengths aren't crossing paths with your targeted RPM exhaust sound waves, they don't cancel anything out anymore since your quarter wave lengths are tailored to that RPM. But thankfully the 90 degree bend gives it extra range so for everyday driving, all of the drone is essentially gone. Put your foot down and it'll be back.

I should've added this when I originally created this thread. Here is a Youtube video of a guy explaining the science behind the j-pipe, whose method I ended up using. He also created the spreadsheet.



Thanks for sharing @TDP154. I'm having a similar drone issue with my 2021 Laramie 5.7 HEMI e-torque between 1500 and 2000 (i'm rounding up).

I went with true duals with H pipe and the result was an awful drone. in a span of two weeks I installed a Flowmaster 50 HD. Swapped that out for a Magnaflow glasspack ( i forget the part #) and although the drone is less, it's still present at 3rd gear and around that 1500k'ish - 2000k band. I really do believe that drone is very common for our trucks around the 1500 RMP band.

I'll be installing a few Vibrant Ultra Quiet Resonators and giving the J-pipe a shot. Would you or anyone here recommend I install the longest possible j-pipe that i can fit?

Thanks,
Carlos
 

Bt10

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Thanks for sharing @TDP154. I'm having a similar drone issue with my 2021 Laramie 5.7 HEMI e-torque between 1500 and 2000 (i'm rounding up).

I went with true duals with H pipe and the result was an awful drone. in a span of two weeks I installed a Flowmaster 50 HD. Swapped that out for a Magnaflow glasspack ( i forget the part #) and although the drone is less, it's still present at 3rd gear and around that 1500k'ish - 2000k band. I really do believe that drone is very common for our trucks around the 1500 RMP band.

I'll be installing a few Vibrant Ultra Quiet Resonators and giving the J-pipe a shot. Would you or anyone here recommend I install the longest possible j-pipe that i can fit?

Thanks,
Carlos
With true duals, which side, or both? are you putting the j pipe on?
 

brian42

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For true duals you would have to put it on each side that has the drone since there's no crossover in the exhaust path from each side of the engine.

The J-pipe is a proven concept. Maybe not used as much in exhaust but you see it extensively with intakes. If you've ever looked at your intake tubing/piping and wondered "what is that extra piece attached to it that goes nowhere?"...it's a resonator to get rid of the unwanted noise for a comfortable, quiet driving experience just as TDP154 described above.

Thanks for posting your research and efforts. (y)
 
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ekaz

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Solo uses the same thing but they have an adjustable cap so you can tune it as needed.
 

cmbernal86

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Thanks guys! Going in this afternoon for my two resonator installs and two J-pipes. I'm thinking of keeping the J-pipe length at around 37 inches. I'll keep you posted!
 

TDP154

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Thanks guys! Going in this afternoon for my two resonator installs and two J-pipes. I'm thinking of keeping the J-pipe length at around 37 inches. I'll keep you posted!
Looking forward to the results! To emphasize brian42 true duals definitely need two J-pipes. I would imagine that would be a very tight squeeze to fit four parallel pipes all next to each other, but I'm sure something more creative is possible if it doesn't fit.

Also as a general update to this thread, for anyone who gets one I highly recommend having some sort of brace fabricated to support the end of the pipe for longevity's sake. Your welds later down the road will thank you for it. I used two exhaust clamps welded together.
 

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cmbernal86

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Looking forward to the results! To emphasize brian42 true duals definitely need two J-pipes. I would imagine that would be a very tight squeeze to fit four parallel pipes all next to each other, but I'm sure something more creative is possible if it doesn't fit.

Also as a general update to this thread, for anyone who gets one I highly recommend having some sort of brace fabricated to support the end of the pipe for longevity's sake. Your welds later down the road will thank you for it. I used two exhaust clamps welded together.

Thanks for the heads up and photo @TDP154!

I installed my vibrant ultra quiet resonators yesterday. The sound decibels have gone down outside and inside the cabin. Nice rumble at idle and cruising speeds and even better at higher rpm's. Not the sound I was aiming for when i swapped my straight pipe to true duals but overall very happy with the sound. Perfect for the everyday driver. Although, not as bad drone is still present.
 
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cmbernal86

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Looking forward to the results! To emphasize brian42 true duals definitely need two J-pipes. I would imagine that would be a very tight squeeze to fit four parallel pipes all next to each other, but I'm sure something more creative is possible if it doesn't fit.

Also as a general update to this thread, for anyone who gets one I highly recommend having some sort of brace fabricated to support the end of the pipe for longevity's sake. Your welds later down the road will thank you for it. I used two exhaust clamps welded together.

On that note, here is a pic at my exhaust. not 100% sure but installing a j-pipe on the right exhaust might be a tighter squeeze than on the left. Do they each need to run on the side of the exhaust pipe or can they run slightly lower to the side of the pipe to allow it to fit? Does that make sense?
 

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TDP154

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On that note, here is a pic at my exhaust. not 100% sure but installing a j-pipe on the right exhaust might be a tighter squeeze than on the left. Do they each need to run on the side of the exhaust pipe or can they run slightly lower to the side of the pipe to allow it to fit? Does that make sense?
Nice setup. Strictly speaking, the pipe can be attached any way 360 degrees around your exhaust pipes. It could hang below your system because there's the most room, but I recommend against it so water doesn't get trapped in there and rust it out. Yes, water will sit in your muffler and resonators but when you start up the engine it gets blown out--I'm not confident in the water trapped in the j-pipe splashing backwards and exiting through your exhaust system.

They don't even need to be perfectly straight either, you could have a squiggly mess of exhaust tubing going any direction for the sake of fitment. If the j-pipe is the right length, diameter, steel, and gauge then it will work. If I had dual exhaust and there was no way to fit a j pipe on the outside of both pipes, (not sure if it would work with 3 inch pipe,) I would drop the middle of the exhaust system and weld the j pipes on the top. It would look clean and there (should) be nothing in their way.
 

cmbernal86

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Nice setup. Strictly speaking, the pipe can be attached any way 360 degrees around your exhaust pipes. It could hang below your system because there's the most room, but I recommend against it so water doesn't get trapped in there and rust it out. Yes, water will sit in your muffler and resonators but when you start up the engine it gets blown out--I'm not confident in the water trapped in the j-pipe splashing backwards and exiting through your exhaust system.

They don't even need to be perfectly straight either, you could have a squiggly mess of exhaust tubing going any direction for the sake of fitment. If the j-pipe is the right length, diameter, steel, and gauge then it will work. If I had dual exhaust and there was no way to fit a j pipe on the outside of both pipes, (not sure if it would work with 3 inch pipe,) I would drop the middle of the exhaust system and weld the j pipes on the top. It would look clean and there (should) be nothing in their way.

Thanks @TDP154!
 

brian42

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On that note, here is a pic at my exhaust. not 100% sure but installing a j-pipe on the right exhaust might be a tighter squeeze than on the left. Do they each need to run on the side of the exhaust pipe or can they run slightly lower to the side of the pipe to allow it to fit? Does that make sense?
As TDP154 mentioned you only have to install the j-pipe in the section you want to attentuate, it does not matter where.

I'm not sure if your muffler is chambered for each side (or if it's one big chamber) but, in your picture, you have a cross-connect between the two pipes between the cats and muffler (aka h-pipe) so, in theory, you only need 1 j-pipe to attenuate the drone.
 

cmbernal86

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Just got back from the Muffler Shop and WOW! What a difference. Drone zone (1400-1900 RPM) almost non existent. I can still hear it trying to drone once MDS is turned on at 3rd gear but nothing like before. The inside cabin almost sounds stock. I'm concerned that the J-Pipe isn't as close to the engine as i had hoped for. What do you guys think? Should i get it welded as far back as possible and make it an even 40 inches vs 37 inches?
 

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brian42

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The location would only be a personal preference based on clearance and appearance. The attenuation should be equally effective no matter where in the path it is located.
 
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