Resonator Location

[Mr Nick]

My Cutlass has a hint of rasp at a certain RPM I'd like to get rid of, and also reduce overall volume just a bit. I have room to install some 9" body Vibrant resonators either between the headers and H-pipe, or in the tailpipes just in front of the exhaust tips.

Curious is there is a difference in resonator effectiveness based on location?

[CamaroAJ]

Either or is fine. For example Cadillac puts the resonator under the car where the X-pipe would be. The Trailblazer SS had it at the very back by the bumper. I plan on putting mine after the X-pipe under the car because thats where I have room. Ideally if you could put them in with clamps and try both locations to see what works best that would be the ticket although more work.

[Mr Nick]

I emailed Vibrant my question and while it's a copy n paste reply, it does contain some good info:


There are 3 key points to keep in mind when choosing and installing a resonator and/or muffler.

1. Size. The general rule of thumb with Vibrant resonators/mufflers is that the larger the body of the device, the more effective it will be at reducing decibel levels, drone, rasp, etc. Larger volume of packing = more harmonic wave absorption. Alongside the volume of packing material making it more effective, is the shape. This is also part of the reason that the Ultra Quiet is a popular choice over bottle style resonators or round body mufflers. Each time your exhaust valve opens, an exhaust pulse wave travels down your exhaust stream. It bounces in all directions as it moves through the exhaust system. The frequency can be affected by the shape, size and length of chambers, tubing, etc. When the pulse wave gets to a suppressive device with packing material, it goes through the perforated core, into the packing material, gets dampened, hits the outside wall of the suppressive device and travels back to the center to rejoin the exhaust stream. In a round suppressive device, the limitation is to one distance for the pulse wave to travel from core to outer body compared to the Ultra Quiet resonator which has a shape with more variable and longer distances for the pulse wave to travel through. This makes it more effective at attacking a larger spectrum of wave frequency of the exhaust note. The same principle applies to a chambered suppressive device but placement becomes very important because the lack of packing material removes the ability to dampen vibration as the pulse wave travels through the chambers. They rely only on pulse wave reflection to cancel out frequencies. Also, keep in mind, larger diameter tubing exhaust systems can be more prone to increased drone or resonance as there is a larger internal surface area that is undampened for the vibration to be amplified or resonate from.

2. Placement. This also plays a key role in regards to reducing exhaust drone. For most applications we recommend placement of a resonator in the area under the front seats of the vehicle. Targeting this placement will be effective for drone frequencies that are exhibited at low to mid-range steady state throttle/engine load conditions (ie: highway driving). In many applications the room available for a resonator in this area is limited, so smaller body “bottle style” resonators are often employed. Installing a resonator in this area will help prevent that drone frequency from reverberating through the floor and into the passenger cabin. Keeping the resonator further upstream also benefits in cancelling out that drone frequency earlier in the system, preventing it from travelling the full length of your exhaust. Placement will be dependent upon available space as well and is often the most limiting factor for installation. Placement further downstream in the exhaust path will target higher RPM frequencies and overall decibel reduction. This is typical placement for most larger body mufflers. Use your best judgement in identifying where any drone is occurring, in some cases, resonance frequencies can be at their peak further downstream just ahead of the rear axle of the vehicle, this will be a drone emitting from the rear seat area. Target placement in the area where you identify any unwanted frequency is occurring.

3. Spacing. When you have a long length of exhaust tubing (more than 5’) without a suppression device, there is an opportunity for exhaust valve pulse wave resonance frequencies to be amplified- much the same way if you were to strike 2 tuning forks that are different lengths- the longer fork will have a higher amplitude of wave pitch along the length for vibration to grow. Your exhaust tubing behaves the same way with the pulse wave sent down from the exhaust valve smashing open and closed at incredible speeds- the longer the length without a suppressive device, the more opportunity for a drone frequency to be amplified. For this reason, it is also ideal to try to prevent placement of resonators and or mufflers too close together so they remain most effective across the length of the system.

All Vibrant resonators and mufflers feature a straight through perforated stainless core design to minimize flow disruption of the exhaust. They are not flow directional.

Inlet/outlets are sized by the inside diameter. This means the exhaust tubing will slip inside the resonator/muffler neck and a lap joint weld will be made on each end to install it.

[GoodysGotaCuda]

172861


I went with a helmholtz style and it's been great.

[Mr Nick]

I saw your thread about that, however I don't have any drone issues on the Cutlass. It's rasp while accelerating around the 3,000RPM range.

[65 drop top]

Just from a looks standpoint, I would not put them just in front of the exhaust tips. That’s just not the right look for a classic car. Have you considered a different style muffler instead of resonators?

[Mr Nick]

I took that into consideration. My tailpipes are tucked up totally out of view. I would mock them into place first, and if the body of the resonator is visible while standing back from the car a bit, I won't install them there.

I have thought about swapping the mufflers, but I'm a big fan of the Hooker AeroChambers overall so I'd like to keep them and just add small resonators. However, I just bought a little Eastwood welder and will be learning how to use it... I see many different exhaust combinations in my future!

[65 drop top]

Off topic, but you said you’re going to learn how to weld, there are some really good tutorials on youtube. Spend some time there and then get a TON of scrap metal to practice on. Good luck and have fun with it, it’s a handy skill to have.

[Mr Nick]

Thanks, I'm really looking forward to learning the skill. There is an Eastwood retail store near me which I purchased the welder from, they offer private and small classroom style lessons. I'm going to head there first, then practice at home, then watch the youtube videos. I haven't held a welder since high school over 20 years ago, so a real live person to answer questions will be nice.

[eville]

I’ve been contemplating taking a community college welding class.

[Bad Fishy]

Hi Goody, first off...nice ride! I’ve seen your car in several blog posts!

I just had a new exhaust installed, along with a significant top end motor upgrade, but my new system has some drone. I’m using Dynomax Ultra Flo’s, 2 1/2”. Previously I was using the same but 2 1/4”. Also added an X pipe. I’ve looked at the sound apps and calculations to determine the proper length of pipe.

I see you have J-pipes, but what are those attachments at the end? Exhaust cut outs? Would like to know more about that as I am also considering something similar - don’t have room for cut-outs AND J-pipes in separate locations. If they are cut-outs, they still seal tight enough to produce the resonance-killing backwave? if they are not cut-outs, what are they? I appreciate any help.

[67-LS1]

WOW!
I’m off to the wrecking yards to search for a Silverado with this new style resonator.

https://www.asme.org/topics-resources/content/shrinking-exhaust-resonator-new-automotive-design

[andrewb70]

WOW!
I’m off to the wrecking yards to search for a Silverado with this new style resonator.

https://www.asme.org/topics-resources/content/shrinking-exhaust-resonator-new-automotive-design

Please post pictures!

Andrew

[67-LS1]

From what I can tell you might get 1, 2 or 3 depending on the engine and they are in the rear.
Appear to be on 2018> Silverado/Denali

189580189579189578189577

[andrewb70]

This is very interesting. Might be time to take a trip to the JY with a sazall.

Andrew

[Lonnies Performance]

It is bad enough people are cutting the cats off of parked trucks, now another reason to park indoors.

I had to run out & look under my '17 to be sure I didn't have them.

[67-LS1]

This is very interesting. Might be time to take a trip to the JY with a sazall.

Andrew

There are some discussions about these on some truck forums. The obnoxiously loud crowd are yanking these when they do cat-backs. I’m going to call a couple of the truck customizers around here and see if they might have any in their scrap bins.
Not many 19’ trucks in the salvage yards around me.

[67-LS1]

Watch the guys hand on the pipe….

https://youtu.be/vQDmpXBd2ro

[68Formula]

It is bad enough people are cutting the cats off of parked trucks, now another reason to park indoors.

I had to run out & look under my '17 to be sure I didn't have them.

Actually you did have them... sorry about that :lmao:

[cwylie]

How did you calculate the length?

[ProTouring442]

How did you calculate the length?

https://play.google.com/store/apps/details?id=com.evg.evgeny.helmholtz2&hl=en_US&gl=US

[CarlC]

For those that like to deep-dive on the patch-type resonators, here you go (download needed): https://www.researchgate.net/figure/Sectioned-view-of-the-three-layered-RFP-stack-as-per-Abrams-patent-3_fig1_338429628

.

[67-LS1]

Yikes, over my head….

[BK2LIFE]

very intersting.

any find where they are sold yet?>

[67-LS1]

I actually got some of these awake back but haven’t gotten around to installing them. Plus the pipe is 2.75” and my system is 2.5”213063