MCarp22 HalfDork
May 6, 2012 12:32 a.m.

So I had a new exhaust made up for my SE-R with what I hoped would be a decently quiet muffler and resonator:

It looks great and sounds awesome at full throttle, but WOW is the part throttle cruising drone brutal to the point where I don't want to drive the car! I guess this is one of the drawbacks to a DIY exhaust, and i'm kinda stuck with it. At first I had looked into ways to insulate the cabin, but it seems it is really hard to cut out the low frequency stuff with insulation. So I was on the internet and found this:

branch resonator discussion

And it seems like that would work pretty well to fix my problem. Anyone out there ever try making one before?

Toyman01 UberDork
May 6, 2012 7:19 a.m.

Nice looking exhaust.

I've never messed with a branch resonator, but when I did the exhaust on the RX-7 it would drone pretty bad. I ended up cutting in a second resonator made out of a glass pack that solved a lot of the problem.

I do like the idea of the branch resonator. In theory, it should work very well by changing the resonance frequency of the exhaust system. Even if you could only move the drone to a different RPM it would help. Might be tough to package under some cars. I'll have to keep this in mind when I do the exhaust on the Roadmaster.

Go ahead, be the guinea pig and then let us know if it works.

MG Bryan SuperDork
May 6, 2012 7:25 a.m.

Assuming it's sized properly, it should work well.

Anecdotal evidence from S2000 owners is positive. The factory exhaust has a small branch resonator and duplicating it on aftermarket pieces supposedly eliminated most, if not all, of the droning.

May 6, 2012 8:29 a.m.

Try a google search. this seems interesting: http://www.planet-9.com/cayman-boxster-modifications/50861-exhaust-drone-resonator-fix-design-construction.html

To tell the truth, I've neve heard of a drone problem on a single exhaust - only dual exhaust systems. Everything from different sized mufflers on each side to adding a resonator on one side to wrapping the exhaust or using thicker pipe.

Please let us know if you learn anything!

carguy123 PowerDork
May 6, 2012 9:19 a.m.

They come standard on S2000s and work well. Everyone who removes them gets drone. Put a pipe in a pipe that lets you slide the outer pipe in and out until you find a length that gets rid of the drone then weld it at that spot.

kevlarcorolla Reader
May 6, 2012 9:43 a.m.

Carguy has the right idea,I've read on a bmw forum about a guy that played around with this using an app on his phone to find the frequency and then came up with a spread sheet to plug the required info into(engine size,# of cyl,rpm,gearing etc etc)which then spit out the lenght of tube required to cancel that frequency. Short of messing with all that math a sliding piece of pipe to experiment with should work just fine,based on what he was doing the pipe will need to be maybe 18" to 30" long.

carguy123 PowerDork
May 6, 2012 10:09 a.m.

I'll measure it later, but I'd almost bet the S2000 pipe is only about 6" long.

I'll post length and diameter this afternoon and that should be a good starting place.

BTW I love the 2 90 degree bends in your exhaust flow. I'm sure those help a lot.

MCarp22 HalfDork
May 6, 2012 12:12 p.m.
carguy123 wrote: I'll measure it later, but I'd almost bet the S2000 pipe is only about 6" long.

What RPM does the S2000 cruise at 60-70?

carguy123 wrote: BTW I love the 2 90 degree bends in your exhaust flow. I'm sure those help a lot.

Hey! I like having a gas tank!

Moving_Target New Reader
May 6, 2012 12:31 p.m.

http://forums.corral.net/forums/general-mustang-tech/496793-exhaust-drone-completely-gone-12.html#post10903602

I've got a nasty drone on my Mustang since installing the Magnadrone catback so I've kept this corral link around for when I decide "enough is enough".

carguy123 PowerDork
May 6, 2012 5:15 p.m.

My dongle is 6" long by 1.75" OD.

I'd post pics, but this site won't let me. I have to first post them elsewhere and then link which causes all kinds of useless threads when the pics disappear.

I can't remember what the car cruises at, but I'm thinking at about 3,500 prm

EvanB UltraDork
May 6, 2012 5:41 p.m.
carguy123 wrote: I'd post pics, but this site won't let me. I have to first post them elsewhere and then link which causes all kinds of useless threads when the pics disappear.

Slightly less useless than when you don't post them at all.

MG Bryan SuperDork
May 6, 2012 6:38 p.m.

This isn't a factory exhaust, but it is for an S2k.

MCarp22 HalfDork
Aug. 5, 2012 2:16 p.m.

Ok, here we are a couple months later, and I've been pretty successful. I calculated the resonator to need to be ~37" for 3000rpm, and had one made up:

Uploaded from the Photobucket Android App

It did a pretty good job of lowering the tone at the calculated rpm, and the exhaust was a good bit quieter overall for daily driving, but it was ineffective with the throttle open more than about 25%.

From there I did some reading, and it seems like the C4 corvette guys have issues with drone when using a dual-outlet muffler. Some experimenting with a wad of aluminum foil found that the exhaust got a whole lot quieter with a tip blocked off. So it was back to the welder for one last go, and the finished product is great. My android phone's dB meter shows about 69-71db while cruising at 70, which is just about where it was with the stock muffler. I decided to give it a coat of bbq paint:

Photobucket

Aug. 5, 2012 3:52 p.m.

When the muffler on my now-ex wife's Talon rusted through, I went with a stock replacement Walker Quiet Flow muffler over some cheap Ebay ricer piece... It had one tip open and one almost closed off. It worked great... The pic is of a Walker Quiet Flow for a C4 vette but you get the idea...

stan_d Dork
Aug. 5, 2012 5:25 p.m.

To reduce drone on my v8 240sx I put extended tips on it about 4" past rear bumper. It helped a lot at cursing speed.

cghstang HalfDork
Aug. 5, 2012 5:49 p.m.
stan_d wrote: It helped a lot at cursing speed.

I guess cursing speed can vary quite a bit from vehicle to vehicle .

I had the Megan Racing cat-back on my '91 SE-R and it was LOUD. I added a generic ebay "silencer" that fit inside the 4" tip and reduced it to 2" or so and essentially baffled the straight through muffler. It was completely liveable after that.

MichaelYount New Reader
Aug. 5, 2012 7:30 p.m.

There's some decent tech in this (long) thread about 1/4 wave tubes to balance out the harsh resonances. http://forums.corral.net/forums/general-mustang-tech/496793-exhaust-drone-completely-gone.html

novaderrik SuperDork
Aug. 6, 2012 1:01 a.m.
cghstang wrote:
stan_d wrote: It helped a lot at cursing speed.

I guess cursing speed can vary quite a bit from vehicle to vehicle .

I had the Megan Racing cat-back on my '91 SE-R and it was LOUD. I added a generic ebay "silencer" that fit inside the 4" tip and reduced it to 2" or so and essentially baffled the straight through muffler. It was completely liveable after that.

so you made your high flow muffler into a not-so-high-flow muffler and it made it quieter.. interesting.. is this why all the Hondas with the big exhaust tips only have a 1.5" opening in the middle of it?

44Dwarf SuperDork
Aug. 6, 2012 6:41 a.m.

Nice work on the exhuast. Moving the resonator farther away from the cat might have lessend the beat freq. That branch res work looks good too. Bet someone will think it was a dual exhaust set up that when unfinished..

You'll need to log in to post.

Also on Grassroots Motorsports

SPECtacular

1 hour ago in Articles

Which of BMW’s beloved 3 Series makes the best racing companion?

Reader's Ride of the Week: Rally Pumpkin

2 hours ago in News

Meet a really orange Honda Civic prepared for rally racing.

2016 Ram 1500 Rebel

3 days ago in New Car Reviews

After moving itself from a truck model to a make, Ram has begun to come into their own. The brand ...

Mazda Sells 100th Global MX-5 Cup Car

4 days ago in News

That's a whole lot of buzzing roadsters.

The Fuel Truth

4 days ago in Articles

Our team of mythbusters finds out which fuels are worth the money.

Your Cars: Legendary Eight-Six

5 days ago in Articles

A Scion Spin on the Car Star of "Initial D."

Reader's Ride of the Week: First Track Toy

6 days ago in News

A third generation Civic serves as a great first step into motorsports.

Grassroots Motorsports Experience Tickets Sold Out

1 week ago in News

But you can still come to our big tent and hang out with us at the Rolex 24.

Grassroots Motorsports Experience Tickets Available Now

1 week ago in News

There are only a few left after renewals from last year, so act fast.

Give Dad the Gift That Lasts All Year: Grassroots Motorsports Magazine

1 week ago in News

Consider your shopping for Father's Day complete.

NSX-ceptional: An In-Depth Look at Acura's New NSX

1 week ago in Articles

Acura regains relevance with its revolutionary new NSX.

Join Us for Red Bull Global Rallycross at Daytona This Weekend

1 week ago in News

Join us for some jumping, dusty fun.

OUR SPONSORS

Grassroots Motorsports Magazine

Subscribe Today

Also get your instant access to the digital edition of Grassroots Motorsports Magazine!

Learn More
XlCc4M0nJkThAL2RizCJSE0e62ttn4GA