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cmbernal86

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The location is 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.

Thanks @brian42. Location does matter though, right? I was under the impression that the 90 degree angle needed to start as far back into the exhaust as possible. I could very well be wrong.

Either way, the drone is 50%+ gone. I'm so happy to be able to hear the exhaust rumble!
 

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brian42

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I was operating under Pascal's Law where the pressure in a system is felt equally throughout the system. I figured that would translate to frequency/wavelength transmission within a given system. :unsure:
 

Bt10

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I was operating under Pascal's Law where the pressure in a system is felt equally throughout the system. I figured that would translate to frequency/wavelength transmission within a given system. :unsure:
One end of the system may generate 5 psi, while there is no pressure at the other end, hence, flow. Temp drop across the system also plays a part in the fluid density and pressure.
 

TDP154

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@cmbernal86 Awesome man! Glad it worked out for you. Don’t worry about the placement.
I don’t doubt that there is a -most efficient- spot to put a j-pipe due to temperature fluctuations throughout the system, as your frequency is directly related to temperature, but in the practical world from research and experience it is a virtually unnoticeable difference. The temp just needs to be ball-parked, which means the placement can be pretty much anywhere. So I would say everyone here speculating is correct one way or another
 

HEMIJAKE

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Cool thread. When I had my mustang, there was a manufacturer (can't remember which) that was making catbacks with j pipes. People swore by them. They were pricey, but good pieces.
 

cmbernal86

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So i'm in a bit of a pickle here, drone at 1500 is gone and great for city driving, however, drone is now kicking in on highway driving at exactly 64-66 mph at 1900 RPM. The drone is not nearly as bad as before and tolerable for a while but i can't imagine cruising at this speed/ rpm on a 3+ hours road trip.

I just got back from calculating my drone frequency at 99Hz and 125Hz, more-so at 99Hz.

Based on the drone formula, my J-pipe should be 34.1 inches (99Hz) or 27 inches (125Hz) respectively. My J-pipe currently is at 37 inches. Do i need to shorten the pipe and if i do, will drone disappear at 1900rpm and reappear at 1500rpm? OR, should I increase the size of the j-pipe but that would go against the formula, right?
 

TDP154

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So i'm in a bit of a pickle here, drone at 1500 is gone and great for city driving, however, drone is now kicking in on highway driving at exactly 64-66 mph at 1900 RPM. The drone is not nearly as bad as before and tolerable for a while but i can't imagine cruising at this speed/ rpm on a 3+ hours road trip.

I just got back from calculating my drone frequency at 99Hz and 125Hz, more-so at 99Hz.

Based on the drone formula, my J-pipe should be 34.1 inches (99Hz) or 27 inches (125Hz) respectively. My J-pipe currently is at 37 inches. Do i need to shorten the pipe and if i do, will drone disappear at 1900rpm and reappear at 1500rpm? OR, should I increase the size of the j-pipe but that would go against the formula, right?
I have no drone at cruising speeds, what gears do you have? What temperature are you getting out of each tailpipe after a long drive? Are your j-pipes the same exact specs as the exhaust system? If the gauge, diameter or type of steel are not the same, the wavelengths will not resonate the same as they do in your exhaust. This could make them less effective.
 

cmbernal86

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@TDP154 Ah, the temp of tailpipes i didn't bother measuring! Getting that done tomorrow and heading back to the muffler shop.

I have 8 gears and i'm almost certain the j-pipes are the same specs as exhaust but i'll double check with muffler shop. Thanks for the heads up!
 

Moparluver

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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.


Did you use a hole saw to tap into your main pipe? Was it just a simple bimetal hole saw? or did you get carbide tipped? What kind of pipe did you use? I'm guessing 16 GA 304 stainless? In my research, many examples I see of j-pipes people end up using pipe the next size smaller (so like 2.5" in this case) what made you land on going with the same size? I had a theory that smaller pipe *might* change how much attenuation you get at the target frequency?
 

TDP154

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Did you use a hole saw to tap into your main pipe? Was it just a simple bimetal hole saw? or did you get carbide tipped? What kind of pipe did you use? I'm guessing 16 GA 304 stainless? In my research, many examples I see of j-pipes people end up using pipe the next size smaller (so like 2.5" in this case) what made you land on going with the same size? I had a theory that smaller pipe *might* change how much attenuation you get at the target frequency?
Yes I used a Milwaukee bimetal hole saw. Used a drill press to cut out a hole in the main pipe and used the cut circle to weld on the end of the j-pipe after some flattening and trimming. I used 16GA 409 stainless to match my exhaust system. Because I'm targeting a specific RPM drone to cancel out, I want the wavelengths to respond exactly as they do throughout my exhaust system. You are relying on those drone wavelengths to return back the other way, unchanged, after bouncing off the end of the j-pipe in order to cancel out. I have no doubt that j-pipes of different sizes work, but for the purpose of targeting what you perceive to be the worst RPM you need to keep as few variables as possible.
 

Natro33

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This is a great write up. I have a 19 ram 5.7. I spend a lot of time around 77-80 mph for travel. I notice a booming drone around this speed as my RPM's are between 1800-1950 RPM. I've turned off active noise cancellation and this did improve things quite a bit but I'd like to get all drone out of the cabin. My math tells me I need a 28" j-pipe. I haven't had time to check the exhaust temps and I'm not sure i'm technical enough to get the correct measurement.

@cmbernal86 suggest 36" but i think this would target the 1400-1600 RPM range. What are everyones thoughts on what length I should try.

Thanks for the help
 

TDP154

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This is a great write up. I have a 19 ram 5.7. I spend a lot of time around 77-80 mph for travel. I notice a booming drone around this speed as my RPM's are between 1800-1950 RPM. I've turned off active noise cancellation and this did improve things quite a bit but I'd like to get all drone out of the cabin. My math tells me I need a 28" j-pipe. I haven't had time to check the exhaust temps and I'm not sure i'm technical enough to get the correct measurement.

@cmbernal86 suggest 36" but i think this would target the 1400-1600 RPM range. What are everyones thoughts on what length I should try.

Thanks for the help
Hi Natro,

To get the bad news out of the way first, it will be virtually impossible to get rid of 100% of the drone in the cab with a j-pipe alone. Because a j-pipe is tailored to a specific frequency, it will quiet that RPM range down completely but you will then notice a little bit as you approach your targeted RPM and drive beyond it. The only way to get rid of the drone 100% is with the right muffler, resonators and potentially multiple different-length j-pipes if your setup is especially bad for drone. By no means am I trying to discourage you, as the point of the j-pipe is to get rid of the headache-inducing frequencies which it does very well.

As far as measuring your exhaust’s temperature, get a digital laser gun thermometer and aim it inside the tailpipes after a long drive. Here is an example:


With the temperature you will be able to find out how long the j-pipe needs to be. Do some more test driving—for the spreadsheet, commit to an RPM number (don’t base off of a range) that you consider to be the worst and use that in your calculation.
 

Natro33

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Hi Natro,

To get the bad news out of the way first, it will be virtually impossible to get rid of 100% of the drone in the cab with a j-pipe alone. Because a j-pipe is tailored to a specific frequency, it will quiet that RPM range down completely but you will then notice a little bit as you approach your targeted RPM and drive beyond it. The only way to get rid of the drone 100% is with the right muffler, resonators and potentially multiple different-length j-pipes if your setup is especially bad for drone. By no means am I trying to discourage you, as the point of the j-pipe is to get rid of the headache-inducing frequencies which it does very well.

As far as measuring your exhaust’s temperature, get a digital laser gun thermometer and aim it inside the tailpipes after a long drive. Here is an example:


With the temperature you will be able to find out how long the j-pipe needs to be. Do some more test driving—for the spreadsheet, commit to an RPM number (don’t base off of a range) that you consider to be the worst and use that in your calculation.
Thanks a lot. I do have a digital thermometer so I’ll capture the temp tomorrow. I reviewed the spreadsheet you have and I do understand it better than I did before. I have an appointment Monday for the j pipe. The exhaust shop I’m taking it to said they’ve done a number of these, so, that made me feel better.
 

TDP154

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General update to the thread: I disabled ANC with Crutchfield part number 794ANCCH3 and it improved the drone further. As stated before I still have some drone around 3000 rpm, but disabling ANC definitely took the bite out of it. Highly recommend—also for if you upgrade your speakers.
 

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