Problem - Exhaust drone: Solution side branch, aka 1/4 wave resonator, or Helmholtz resonator

carguy123 wrote:

Driven5 wrote: In reply to MrJoshua: have me thinking that an easy and clean way to implement this may be to get a common aftermarket reversible 2:1 muffler. Rather than 1 in and 2 out, set it up with 2 in and 1 out. Run the exhaust in one of the inlets, and out the single outlet, and run a 1/4 wave pipe up off the second 'inlet'. With a clamped connection, it would be easy to test multiple pipe lengths to tune it 'just right'...Or even have an 'quiet around the neighborhood/town' pipe and a 'highway drone killer' pipe, depending on what you're doing that day.

I've not really looked at the inside of many mufflers, but the ones I have looked at wouldn't appear to like being run in reverse.

Maybe I should rephrase that...I don't know if it's common across brands, or which other brands it might be common to, but I do know that at least the Magnaflow 2:1 mufflers are designed to run either dual in/single out or single in/dual out. I believe there are others as well.

Anyone ever try the Car Chemistry exhaust baffle inserts?

http://www.carchemistry.com/3-disk-insert-2-1-2-diameter/

They get good reviews, and supposedly any drop in performance is minor.

The other possible best option I have found for drone reduction is adding a catalytic converter, if yours was removed or the car didn't come with one.

"Anyone ever try the Car Chemistry exhaust baffle inserts?"

We've stuffed lawnmower mufflers inside of the ends of the tail pipes in order to pass noise inspection, Made things much better with no adverse effects.

Three bucks each, Easy Peasy !

I wonder if a couple of throttle butterflies could be set in the pipe to adjust the effective length of the pipe as you drive. Set the first butterfly at one speed, them open it up for a slightly longer pipe tuned to another speed, and maybe another...

I'd have to have a switch or button to control the butterfly labeled "x-mph stealth mode" or something similar.

Benswen wrote: Anyone ever try the Car Chemistry exhaust baffle inserts? http://www.carchemistry.com/3-disk-insert-2-1-2-diameter/ They get good reviews, and supposedly any drop in performance is minor. The other possible best option I have found for drone reduction is adding a catalytic converter, if yours was removed or the car didn't come with one.

Those kinds of inserts are good in terms of noise reduction but can introduce a lot of backpressure into an otherwise open exhaust.

Which do you think would be less restrictive to exhaust flow - a catalytic converter, or one of those baffles?

I was thinking you could make one of those baffles into a mini baffled muffler - use 3" diameter 3-disk insert in a short length of 3" exhaust tube, with reducers on the ends to match the diameter of the rest of the exhaust. (It would look like a short 3" diameter glasspack/resonator.) Presumably a larger diameter baffle insert would be less restrictive than a smaller one.

The interior resonance in my SW20 is making me nuts, and I'm willing to sacrifice a couple horsepower to shut the thing up. It's quiet outside, (registered 72 decibels at the last autocross, in spots where "loud" cars were hitting 95-ish) but the low-pitched booming and droning inside is terrible. I'm using a 12 inch or so length resonator with a Dynomax Super Turbo, all with 2" OD tubing. I've tried a few different muffler/resonator configurations, and nothing has helped in terms of resonance/droning. A Heartthrob chambered muffler was probably best of the ones I tried, but still droned on the highway, and I noticed a butt-dyno gain with the Dynomax.

So, I'm to the point of trying one of those Car Chemistry baffles, or adding a second cat where the resonator is currently. (CA spec MR2's used a second cat in that spot.)

A cat would be less restrictive but will also reduce noise less...it's hard to have your cake and eat it too in noise vs. low restriction. A variable muffler lets you make the tradeoff any time with the flick of a switch, but they're expensive.

Since you're already running the chambered Super Turbo muffler I don't think the insert would add that much restriction. A side-branch resonator like we're discussing in this thread would make the most difference in reducing drone without increasing backpressure.

I like the side-branch, (and have investigated them at length) but they're really only effective over a small rpm range - my exhaust is loud inside the car at most rpms. Well, not loud in overall decibel level, but way too "boomy".

I guess I'll just have to keep experimenting.

Where does the exhaust tip sit relative to the rear bumper? Sometimes changing the position of that can affect the sound inside the car noticeably.

In reply to Benswen:

What rslifkin said, and also since it's an SW20 and the header is right behind you, do you have the firewall carpeting installed? It made a big difference on mine.

Yeah, it's still got all the shields and insulation. I replaced the exhaust manifold gasket (and studs, because of course they took the aluminum threads out with them, as Toyotas of this vintage are known to do) and the warped exhaust manifold and have determined that there are no leaks.

I built my exhaust rear section from scratch, and made sure that the tip extends well past the rear bumper.

This is a common complaint with this model, as far as I can tell.

I'm also considering adding a round single chamber muffler ahead of the Dynomax super turbo. I figure if the issue is the low-frequency noise, a chambered muffler further up the exhaust stream should break those low frequencies up a bit before getting to the bigger baffled muffler. Thoughts?

On a related note, if the stock muffler was quiet, I would gladly use it, but the stock muffler with the dual tips was just as bad if not worse than the super turbo.

This is relevant to my interests.

Add a vibrant ultra quiet resonator,case closed.

I have a 14" louvered resonator installed currently - I don't think a different resonator will help with my problem (tone, not volume). I ordered some piping from Summit to add a "branch" style resonator to kill the 3100-3600 rpm drone.

I think I'm going to use a chambered muffler followed by a long glasspack - the theory being that the chambered muffler will break the sound up, and the glasspack will bring the volume down.

Obviously a chambered muffler is less than ideal for performance, but we're talking about a Camry engine here. I prefer the sound of a chambered muffler over a turbo-style.

kevlarcorolla wrote: Add a vibrant ultra quiet resonator,case closed.

They do cut noise a good bit, but they won't fix a drone problem!

In reply to rslifkin :

Installed headers and full JBA exhaust on my 1st gen titan,sounded great for a couple weeks then nasty drone at 1700'ish rpm.(most common rpm for just driving)

 Decided to not spend the loot for an UQ resonator and built a 34" long tube installed after the muffler.

 Amazing,zero drone....I'm a believer now :)

Bit of a zombie thread revival- but one that I'm going to keep on hand down the line to use in trying to work out how to reduce exhaust drone in the DMC . (of course, if I put the Renesis in it, I may just have to wear earplugs while driving it...)

I have been looking at exhaust for the G35. I was surprised to see some of the cheap Chinese stuff has side resonators on them. 

Would it be possible to install multiple different helmholtz resonators to try to quiet different spots in the rpm range?