Has anyone with a 2019 or newer 6.2L Sierra/Silverado successfully built a 1/4 Wave Resonator/J-Pipe to eliminate drone after a muffler delete? I am in the process of planning and trying to see which length will work best. My drone is the heaviest around 1500 RPM which is high 70's on the highway. It's not bad now but I know if I ever tow, it will be annoying.

Also, if anyone knows a good welder that would be willing to build one and ship it to me, I'd love their contact. I'm in a small area in Oklahoma and when I say "1/4 wave resonator or helmholtz resonator", I get some pretty odd looks. I'm looking to get a 3.5in "T" so I can install the resonator at home.

I have attached a rough drawing of what I'm looking for.

 

Theres a formula on here some where that will give you the length you need for that, I've used it several times on my truck, G8 and friends vehicles that drone like crazy...... My local muffler shop here in texas did a set for my G8 for 100 bucks. Its also known as a tuning tube to some people.

 

I've done the calculation but I'm not 100% confident that is my true trouble zone or that my math is 100%. What shop in Texas?

 

Arkansas Performance Exhaust in Sherwood, AR. A friend of mine owns the place, I have no idea if they'd be interested in building and shipping but doesn't hurt to ask.

 

I'm in weatherford texas, its Chris' Muffler shop but really any muffler shop should know what they are doing when you tell them what you want. You could go so far as to make it adjustable but thats up to you.

 

Thanks. I travel to the DFW metroplex area a few times a year.... especially around the holidays so, I may be able to get something done there. My local muffler shop looked at me stupid when I asked about a resonator pipe to eliminate drone and automatically pointed toward some Magnaflow passthrough resonators he had hanging on the wall. He can weld but he's no engineer.

Thanks for the input.

 

Wow. I need a fifth gear.

 

Sorry to resurrect an old post but did you ever find a solution for your drone at 1500rpm? I have awful cabin drone with the cruise set on the freeway in my 6.2L Silverado. I had a muffler delete and now a flowmaster that's quieter everywhere but freeway drone. I'm looking at this system from Magnaflow part #19534 it has "no drone technology" or a J-pipe type helmholtz resonator in front of the muffler. Thanks!

 

A "formula" for that is pretty simple, really. Unfortunately the application can be GREATLY oversimplified and render the end product highly variable in its effectiveness.

The principle behind this is that the sound in the exh pipe is a wave, consisting of pulses at a frequency of RPM ÷ 60 × 4 (convert minutes to seconds, then since there are 4 cyls per revolution). Each pulse in this train consists of a peak of positive pressure followed by a peak of negative pressure. Some part of each pulse (ideally, exactly half, but in the RW, usually somewhat less) will then be diverted down the resonator pipe, reflect off the far end, return to the junction, and combine with the pressure that exists there when it arrives. If the total time it takes the pulse to travel down the pipe and back is exactly ½ of the time between pulses, then the positive pulse will re-arrive exactly at the time that the negative part of the next pulse also arrives, cancelling it out; and likewise for a negative pulse which will return to the junction and coincide with the next positive pulse. Obviously for the total round trip to take ½ of a cycle, the pipe must be ¼ of a wavelength.

The calculation then is, to figure out what frequency (RPM) you want to cancel, find the speed of sound in the exhaust, calculate the wavelength of a sound of that frequency, and choose the length accordingly. Speed = frequency × wavelength, or with a tiny dollop of elementary-school algebra, wavelength = speed ÷ frequency. The speed of sound in free air at standard temp & pressure (1 bar, 0°C) is about 1100 ft/sec. For example, if you want to cancel an 1800 RPM drone, then the frequency of the sound will be 1800 ÷ 60 × 4, or about 120 Hz. So, the wavelength of the 120 Hz sound wave in free air is about 1100 ÷ 120, or, just a shade under 10'. Your quarter-wave pipe would then want to be about 2.5', or, 30". Substitute the RPM you want to cancel out into that pair of equations to get your length.

But that's a bit of an oversimplification. The speed of sound in air increases with temperature, by roughly 1 ft/sec per °F; so your pipe probably wants to be a bit longer than that. The question then is, by how much. You could maybe measure your exhaust's temp after it's been running at that RPM for awhile and get a rough idea although not totally accurate. My guess is that the exh gases are probably 150 - 200° hotter than the pipe, but that's just strictly a guess. Ideally you could probe the gases, or in the absence of that you could use an infrared gun on the pipe and make an educated guess. However all that may be, it's probably getting close to "measure with micrometer, mark with chalk, cut with axe". In any case, if it turns out that the exh gases are close to, say, 400°F, and approximate that the speed of sound in there is therefore nearer 1500 ft/sec, in which case your pipe would want to be somewhere more in the range of 3 to 3½'.

Yet another oversimplification is pretending that the sound in the exh system is a pure travelling wave, as if the exh stream is uniformly travelling down the pipe and doesn't interact with the pipe at all, like the output of a radio transmitter in a transmission line. (yes I have spent many years of my "career" as a radio and sound engineer) In reality it's not: there are all sorts of reflections in there, giving rise to standing waves. These are patterns of pressure along the pipe that just "stand" there, in the same place all the time, instead of travelling down the pipe. If you could look at the pressure along the pipe, there would be places at any given speed that would always have high sound intensity (large variations between the positive- and negative-going peaks of the sound wave), and others that would have lower intensity. That means it will probably make a YYYYUUUUUUUUUUJJJJJJJJJJJE difference where along the exhaust you put your resonator pipe. There could easily be certain places that are 2 or even 3 times as effective as certain others.

That part then, is the same as finding the ideal location for a X- or H-pipe: you always try to put those where they connect the peaks of the pressure in the 2 sides. You'd want to do something similar with your resonator. Since the temp of the gases in the exh vary according to the pressure, you can paint your exhaust with a stripe of temp paint, run the motor for awhile at the RPM of concern, and see where the temp is highest. That's the ideal place to put your resonator, if you could. Subject of course to the limitations of your space.

Keep in mind that all of this is tuning for one specific frequency, like making an organ pipe. It will only be effective over a range of RPMs around that frequency, maybe ±20% at best, and probably less. So, for a couple hundred RPM on either side of the peak.