Resonator vs. muffler question...

[KILLSHOTS]

Hey guys,

My understanding is that our stock exhaust systems were Helmholtz-tuned to banish inherent resonance in 2 general ranges: 1800ish RPM and 3400ish RPM. In addition to deadening engine volume, of course, the resonator was tuned to handle one of these resonance tasks and the mufflers were tuned to handle the other...again, just my understanding so far.

So, if my understanding is correct, my question is: which is which? Do the mufflers quell the drone at 1800ish and the resonator at 3400ish, or vice versa? Or am I way off about the whole thing?

This kind of info might be really helpful, I think, for anyone considering any sort of modified exhaust system, as opposed to an off-the-shelf Corsa, B&B, etc.

Thanks!
Chris

[mike100]

I was kind of eluding to this comment in my earlier discussion on the other thread, but putting different mufflers and keeping the resonator and pipes other wise unaltered is a good bit louder than keeping the stock muffs and putting something else in place of the resonator. Loud muffler with the stock resonator drones loudly at 1800 rpm. I forget what the resonator is tuned for specifically.

I had a 95 vette LT1 coupe all stock except it had twin outlet borlas from an L98 car. It was so loud. I ended up putting single outlet dynomax turbo mufflers which helped a lot, but even that was somewhat loud.

[XfireZ51]

Part of the issue is defining what is BOOM and what is DRONE. Now that I have removed the spare tire and carrier, I get more boom from the rear compartment.
I'm wondering if putting the spare tire carrier back on w some sound deadening will help muffle that.
Playing w my NPP switch, the difference between one exhaust outlet v two is so obvious. :)

[WARP TEN]

.... Loud muffler with the stock resonator drones loudly at 1800 rpm. I forget what the resonator is tuned for specifically......


Mike is correct--the Helmholtz resonators in the stock mufflers are tuned to quiet the 120 Hz resonance at about 1,800 rpm and the stock resonator handles the 230 Hz resonance at about 3,400 rpm. Our engines are notorious for those resonance peaks.

I wrote an article many years ago for the then-equivalent of the HOB after I had an acoustics engineer wire the car and write a report for me. Here is the section on resonance. Remember it was written quite a few years ago so technology has improved in many systems--Bob

Controlling Resonance. If resonance is a concern to you, the only way to really tame it is to utilize a devices called Helmholtz resonators (or quarter wave tuners). To my knowledge, only the stock system and the Corsa use such devices; Corsa’s trade name for its patented approach is Reflective Sound Cancellation (RSC).
What is it a Helmholtz resonator? Imagine a closed coffee can with an opening into it. Exhaust doesn’t pass through, but sound waves can enter and, depending on the size and shape for a specific frequency, cancel each other out. If you cut open a stock muffler, you will discover that the rear half of the muffler is in fact a closed chamber with a pipe opening into it for sound waves. While you can notice the resonance points on both the stock and Corsa systems when you go through them under load, they are muted and much less objectionable than others. While Flowmaster doesn’t turn to the Helmholtz principle for resonance control, it does use a patented sound canceling design that utilizes V-shaped deflectors to lessen unwanted sounds.

[FU]

We are dealing with this now on the blue car.
Trouble using the C6 ZO6 tip's is the size of the muffler's are very limited. Currently I'm looking for quieter set of muffler's that will fit in the limited space with the ZO6 tips.I currently have a full 3" system with and X pipe. The mufflers are Dynomax 17228's. This combination it still too loud for me just tooling around.

Anyone have a beter solution ?

I'm just thinking of bolting on a stock muffler.

[WARP TEN]

We are dealing with this now on the blue car.
Trouble using the C6 ZO6 tip's is the size of the muffler's are very limited. Currently I'm looking for quieter set of muffler's that will fit in the limited space with the ZO6 tips.I currently have a full 3" system with and X pipe. The mufflers are Dynomax 17228's. This combination it still too loud for me just tooling around.

Anyone have a better solution ? I'm just thinking of bolting on a stock muffler.
Hi Frank--You know me--a stock system with cutouts. Had it out today with my architect son and showed him the hidden cutout switch. He loved it and said the car (with the 510 package) felt much faster than the '93. I still think there is a cutout solution that will preserve the spare tire carrier but I haven't yet figured it out. --Bob

[KILLSHOTS]

Hi Frank--You know me--a stock system with cutouts. Had it out today with my architect son and showed him the hidden cutout switch. He loved it and said the car (with the 510 package) felt much faster than the '93. I still think there is a cutout solution that will preserve the spare tire carrier but I haven't yet figured it out. --Bob
Hey Bob,

Check out Tony Davila's cutouts. His are just in front of the mufflers and pointed outboard, toward the wheels. His system retained the spare.

Chris

[WARP TEN]

Hey Bob,

Check out Tony Davila's cutouts. His are just in front of the mufflers and pointed outboard, toward the wheels. His system retained the spare. Chris
Hi Chris--Tony's definitely gave me inspiration. Mine have the electric motors so require a bit more space but in looking at his location I think there might be enough to clear the spring and other items. I will play with it when I get a chance. I also can see that they would work just ahead of the hangers where the pipes spread for the tire carrier. But I am not sure I want exhaust coming out under the middle of the car. If I change them I will publish the results. -- Bob

[msorenso]

We are dealing with this now on the blue car.
Trouble using the C6 ZO6 tip's is the size of the muffler's are very limited. Currently I'm looking for quieter set of muffler's that will fit in the limited space with the ZO6 tips.I currently have a full 3" system with and X pipe. The mufflers are Dynomax 17228's. This combination it still too loud for me just tooling around.

Anyone have a beter solution ?

I'm just thinking of bolting on a stock muffler.

I use to have 3 inch dual x pipe long tube headers magna flows when I purchased the car, I changed it to the SS ultra flows and bullet race mufflers up close to the headers with no luck, went to Corsa system

[Tony Davila]

Hey Bob,

Check out Tony Davila's cutouts. His are just in front of the mufflers and pointed outboard, toward the wheels. His system retained the spare.

Chris
Just in case you are looking for it.
http://www.zr1.net/forum/showthread.php?t=22689

[4-cam]

FU
Ive got 2- new Dynomax 17519 muffs that I would unload fairly cheap, say $125 for both, shipped. I went with the 17228 instead and just have these sitting around. The are not as loud as the 17228 I am told. I have not heard them on a ZR-1 but was told by Dynomax tech support that they do tone down the resonance more so than the 17228.
Where the 17228 spits in a Y configuration the 17519 splits in a T inside the muffler. This cancels the the resonance with the direction change but it is still considered full flow although i bet a bit less than the 17228. The external dimensions are the same size also. Pics below of the internals

[XfireZ51]

Just for clarification sake, anyone using cutouts. Would you ever drive around w them open or are they just for "performance outings"?
If you're looking for a quiet system, I would recommend the MagnaFlow cat back. Just don't expect it to flow enough for anything above 400rwhp.
I'll be glad to demo my Z06 system at BG for anyone interested. However, it is not "whisper quiet". You'll know you're not in a Cadillac.

[WARP TEN]

Just for clarification sake, anyone using cutouts. Would you ever drive around w them open or are they just for "performance outings"?
If you're looking for a quiet system, I would recommend the MagnaFlow cat back. Just don't expect it to flow enough for anything above 400rwhp.
I'll be glad to demo my Z06 system at BG for anyone interested. However, it is not "whisper quiet". You'll know you're not in a Cadillac.

I normally run my cutouts about 1/3 open for a little rumble. Fully open only for performance outings. When I approach my subdivision I close them to keep the neighbors happy because my wife used to complain she could hear me coming about three blocks away (when I had the Corsas). I also close them if I see a cop nearby who might hear me. --Bob

[XfireZ51]

Do the cutouts create an issue for the O2 sensor? Particularly on decel? Or do you run Open Loop?