Quest To Reduce Single Exit Noise Levels
 

So as many of you already know, having a single exit exhaust is freaking LOUD. Almost too loud depending on where you live/work and if your gf/wife has sensitive hearing lol.

Anyway, I have always liked the look of a single exit. It has a nice aggressive look to it when done right, and the weight savings are an added plus when you consider how heavy the OEM exhaust is.

After running a single exit exhaust paired with the BHR midpipe for a while, my love for the tone was soon suppressed with the random looks and the comments from friends about how loud it really got when I stomped on it. Driving through the parking garage at work was also funny depending on how sensitive people had their car alarms set. So I tried a few things out:

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CC Inserts
Source: Exhaust - CC Inserts - Car Chemistry, Inc.

These things are nifty, and their price was really nice. I went ahead and ordered one of the 3" ones, and was actually caught a bit off guard when i felt it in my hand. The darn thing is pretty heavy for its size. I will weigh it when i get home and will get some exact measurements. I tried installing this two places. First, I installed it in the front section of the intermediate pipe (basically right after the midpipe). Didn't really do a darn thing for noise, but totally snuffed engine output a bit. Wasn't noticable at all during normal driving, but once you hit an on-ramp and really got on the throttle, you felt something "holding you back".

The next thing I did was move it further back to the axle back portion of the single exit. No dice. Although it didn't really kill off the performance like the former test did, it also didn't really do anything for sound. There was a slight muffle, but nothing that really warrented the need to have something extra in my exhaust.

This was ultimately removed.

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https://lh5.googleusercontent.com/-2...004_230648.jpg

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Dynomax Race Bullet
Source: Dynomax® Performance Exhaust | Mufflers | Race Bullet Mufflers

Man these things are popular and it is thanks to its design. Essentially a straight through design, where the inside of the canister matches the size of your inlet and outlet diameter. The perforated interior with fiberglass packing is what aids in noise suppression.

The design of the intermediate pipe of the single exit exhaust allowed me to mock up something which allowed me to place this muffler in my flow path. This will come as a shock to some, but probably not to those who have done exhaust design on these cars, but the bullet actually made the exhaust louder lol. What it did do, is remove the lows from the exhaust, but left the highs. This gave the impression of a louder exhaust. This was pretty much counterintuative to what I was looking for. Not to mention that you can expect the packing to become obliterated after some miles.

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Auger Style Inserts
Source: Dynatech Auger Style Muffler, 11 x 3 Inch - Speedway Motors, America's Oldest Speed Shop

At first glance some of you will be able to recognize these inserts. They are very similar conceptally to some popular resonators. Now let me preface this review by saying this: This really isn't an alternative to a Moroso (and others) style muffler. The reason being because inserts like this lack the one characteristic of the resonators that prevent it from harming performance, and that is the enlargement of the chamber. For example, a moroso style muffler spans out about an extra inch over the inlet/outlet diameter.

Now with that out of the way, I was tempted to give this a shot. At the price, I figure 'why not'. Better than listening to speculation from those who haven't tried, and if anything, I would try/fail/educate.

Once i recieved this thing, wow ... super light. Not going to lie, in my hand it felt similar in weight to the insert that was a quarter of its size lol.

It isn't perfect though, and you NEED to have some time, a grinder, or some vice grips. The reason being that when it says it is 3" ... it is seriously 3". It just wont slide in without some finesse, or, if you want to drop it in to weld it, you surely need to grind down the edges a bit to allow for a smooth fit.

I installed this at the axleback of the exhaust, right before the muffler. The reason being that A. Folks like BHR have gone to great lengths to strengthen their resonators against the heat of a rotary, you can tell by looking at the welds. Knowing that, I wanted this as far back as possible. Also, being far back, conceptualy, would present the least restrictions as the exhaust velocity would have tapered off a bit after going through my midpipe and right before hitting the muffler. I wouldn't recommend placing this insert any further upstream.

Now, all that aside, first fire up, DAMN, a hell of a lot quieter. Now in my head I had the "been here before" feeling. So I took her for a drive. No more cabin drone, and no more super loudness under normal driving. Not done yet though as the true test is really throwing it on the highway and hammering it.

On the drive to work today, completely different sounding exhaust, in a good way! Still had that nice deep roar of the single exit, without the booming loudness in the cabin. At WOT, no measurable drop in performance from the butt dyno (nothing like what i felt with the CC insert), while still maintaining that awesome rotary whine.

Of course, time will tell, but hopefully this thing lasts. At the price it can't be beat.

When I get home today, I will measure the dB level as I am sure that many people would benefit from the noise suppression depending on the tracks that they race at.

https://i86.photobucket.com/albums/k...s/100_0295.jpg
(not my pic, but exactly what mine looks like when viewed from the axleback inlet)

Here is where the auger style insert was installed

https://lh4.googleusercontent.com/-W...004_230741.jpg

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Auger Style Video Clips





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Auger DB Readings

App Used: https://play.google.com/store/apps/d....decibel&hl=en

Test 1: 11ft from muffler exit, phone along exit axis

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Test 2: 1ft from muffler exit, phone along exit axis

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Test 3: In cabin, windows open, phone close to ear

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Test 4: In cabin, windows closed, phone close to ear

https://lh5.googleusercontent.com/-z...4-17-18-29.png

*All photos taken during engine idle after 30 mins of driving.

Good write up with some useful information .

But ...................... where's da pics ?

I'm at work so once I get home I will get some pics and data out there :).

Nice work, this is some helpful info!

I have the rr single exit as well and one of my issues with it was that it was way too loud. Originally I had my OEM exhaust paired with a obx non resonated midpipe and wasn't much louder than stock. Until I got the rr exhaust... That sound could make your ears bleed lol, it was extremely loud... It sounded like it had no muffler pretty much.

So I decided the midpipe had to go, I had a gutted cat lying around and put it on the car. It made a huge difference and the car is sooo much more bearable. I don't know how quiet the bhr midpipe is, I know it's perhaps the most quiet midpipe available. Not sure how it does compared to a gutted cat, but the gutted cat is working great for me. It is another option for those who have a too loud exhaust.

Posted From RX8Club.com Android App

Turbos make great resonators :)

At a great expense.

Nah, my entire engine build and turbo build cost less than your average Audi transmission. And in the muscle car world spending $10,000.00 on an engine alone is par for the course.

I have heard that the BHR takes a lot of the edge off of the highs on the exhaust note compared to other pipes, but the deep roar was still there. Man oh man the worst part was driving to work on I291 in CT. Its 2 lanes on each side, with jersey barriers on the sides and separating the median. Holy crap the exhaust would echo off of that and back into the cabin lololol.

Didn't have that issue today :)

I'll see if I can get some DB readings. Unfortunately I don't have any 'before' readings. Would any of you that have single exits and a midpipe grab some readings for me at idle, mentioning how far away from the tip you are getting the readings? I was just gonig to do with with a phone app, granted not super accurate, but will maybe give us an idea.

I can get some db readings as well just so you can get some data of different setups. How far away from the exhaust do you want the readings from?

That would be great! Honestly I am not too familiar with acoustics to know what the best distance would be without contributing too much noise. I am sure it differs with each phone. How about 1' away?

edit: Anyone know the measured distance is at level-restricted tracks?

Use the rule from Formula SAE so it is easily comparable.

http://students.sae.org/cds/formulas...3fsaerules.pdf

ARTICLE 3: EXHAUST SYSTEM AND NOISE CONTROL

IC3.2 Noise Measuring Procedure

IC3.2.1 The sound level will be measured during a static test. Measurements will be made with a free-field microphone placed free from obstructions at the exhaust outlet level, 0.5 m (19.68 inches) from the end of the exhaust outlet, at an angle of forty-five degrees (45°) with the outlet in the horizontal plane. The test will be run with the gearbox in neutral at the engine speed defined below. Where more than one exhaust outlet is present, the test will be repeated for each exhaust and the highest reading will be used.

IC3.2.2 The car must be compliant at all engine speeds up to the test speed defined below.

IC3.2.3 If the exhaust has any form of movable tuning or throttling device or system, it must be compliant with the device or system in all positions. The position of the device must be visible to the officials for the noise test and must be manually operable by the officials during the noise test.

IC3.2.4 Test Speeds
The test speed for a given engine will be the engine speed that corresponds to an average piston speed of 914.4 m/min (3,000 ft/min) for automotive or motorcycle engines, and 731.5 m/min (2,400 ft/min) for “industrial engines”. The calculated speed will be rounded to the nearest 500 rpm. The test speeds for typical engines will be published by the organizers.
An “industrial engine” is defined as an engine which, according to the manufacturers’ specifications and without the required restrictor, is not capable of producing more than 5 hp per 100cc. To have an engine classified as “an industrial engine”, approval must be obtained from organizers prior to the Competition.

I would say probably ~10ft from what I've seen
I don't know the exact distance though

edit: just checked NASA rules...says it varies by track
Road Atlanta gets 10ft directly behind the car...but my exhaust comes out of the side :evil_laug

Buy and angled tip and point it downside. That will reduce noise readings ;)

I may get a dumpy (tip angled down) set up made to test it

Well that is the reasoning behind the design of the RB Race exhaust system.

Alright, not super scientific, but I tried. Here we go:

..... moved to OP for easier finding ....

85db is quiet lol

im telling you, it does a fantastic job without any noticable performance loss. Tomorrow I will get a buddy to ride with me and get some sound clips and db numbers of drivebys and such

What app are you using?

You silly banana

Damn im a newb lol. Sorry bro

Interesting design! Get some revving videos too?

I'll get some for you tomorrow :)

Alright ... check out the OP for some video clips. Will get some exterior drive bys later today :)

nice updates paimon

FWIW, 2 weeks with this installed and so far so good. And I have been beating on it quite a bit to get tuned. No increase in noise, no rattling, etc. Will keep posted on significant milestones (1 month, 6 month, etc) just incase it entices anyone to consider it.

I just wonder what effect it has on performance (if any)

I hope the lighter single pipe offsets the drop in horsepower. Subscribed. Interested to hear the long term results. I want to make the jump to a single but the noise limits in my area are strictly enforced.

If there was a loss in power, it is minute enough for me not to feel it.

Update for those still interested:

Been about 2 months now since I installed the auger insert, and things are still looking good!

Mind you that I haven't been babying this car either as I have been doing some tuning so the car has had plenty of time of sustained RPM driving even at 8000rpm.

The car is still quiet, no strange things that have happened, no performance issues, no sluggish feel.

The only "issue" that I can mention is that now that it is really cold out (if the car sits outside at work when it is like 18F here) i can hear a tiny rattling. This is probably because one of the auger blades is rattling against he exhaust pipe on the inside. The noise goes away after a minute or so once the exhaust system starts heating up.

Yep, figured as much. Right now I dont mind the rattling against the inner wall of the exhaust pipe since it goes away relatively quickly (and really only happens on very cold mornings).

As long as I dont go and start shooting out auger blades out of my exhaust i'll be happy lol.

And just to reconfirm for those who are just reading about this for the first time... this isn't an alternative for a quality midpipe, but a low cost solution for those who are dealing with a loud cat-back and are considering welding in an additional resonator.

Paimon did you start out with the bhr midpipe or did you have another one before that? Did you get any buzzing or much louder exhaust noise around 3.5-4.5k rpm with the bhr pipe, prior to installing all the stuff here? Also you went with the race roots single right?

I really don't mind how loud my exhaust is except between 3.5-4.5k because I spend so much time there in city driving. As I said in the other thread I am thinking of replacing one of my AP resonators with a bhr one and your answers to the above questions should help me know if it is worth my time.

I went from OEM to BHR. The only buzzing I really got was when I first installed hte pipe and that is only because I didn't have my midpipe properly aligned which cauesd me to have a very slight gap at the forward flange. What i mean is that I found on the S2, because of the very slight differences in the path of the exhaust, it takes some extra care to tighten the bolts up evenly.

What you are experiencing is probably the metal pinging that is characteristic of some straight through resonators (which i believe the AP has).

And yes, I have the RR single exit.

Lol very true ... hopefully no one is behind me though should it happen or they iwll be going home with a souvenir

Yeah it is a straight through resonator. I knew when I bought it that it was one of the cheaper options and it has sounded like that from day one. It might have gotten worse over time but I really couldn't tell. I had a hard time getting my midpipe to seal at the header>midpipe spot I had to go buy one of those carbon crush gaskets from race roots because nothing else would seal properly.

Update.

Decided to remove the rear portion of my exhaust to check on the auger insert. All looking fine so far! No rattle, no pinging, no tinning, nothing. From a naked eye I dont see any massive stress fractures in the welds.

nice

Just added an auger insert and 3" high flow cat to my agency power exhaust. I can now run with the 3" mid-pipe pleasantly. Before this I had to go to the stock midpipe because the drone at cruise was unbearable.
Thanks Paimon!

Glad others are benefitting from this. FWIW I still have no issue with mine and this after a ton of autocross sessions and a lot of sustained low to high rpms from tuning :)

Let the fear-mongers go pound dirt ....

It will be interesting to see a before and after dyno on this product. I looked into it a few years ago however I was not convinced at the time.

However, it sounds encouraging from what I am reading here.

I have heard of a really loud car dampened with J pipe/ side resonators. It uses the same principles as a resonance chamber installed in our intake system. This noise cancelling method has zero restrictions.

Yep, J pipe configurations are rather common for the 350/370 guys. Actually the Fujitsubo exhaust (or the obx knockoff version) uses a J pipe as well. Haven't heard a rotary up close with one.

As far as dyno goes, I would like to see the results too (unfortunately I just dont have the definitive need right now to dyno the car), but as far as 'seat of the pants' feel goes, i'd really have to say I 'feel' no loss. Harlan keep me honest here if you felt otherwise.

I didn't notice any change, but my teeth were rattling before when I opened up the throttle, so I wasn't keen on punching it.

I think the pipe is big enough that a little restriction doesn't matter.

How's this holding up? Are you still using this setup?

Totally missed this question. Still holding up, not a single problem after 2 seasons of autocross, and generally driving the car the way its meant to be driven.

The only "thing" i have noticed is some discoloration at the last bend of the exhaust, but that makes sense as the slight restriction along with the bend traps a bit more heat than normal. I'll have to take a picture to show so that we can compare to others who have a HKS/RR style single exit.

That's awesome to know. I previously had an RR exhaust a several years ago and got rid of it for several various reasons, but the time has come and I just ordered an HKS single exit again. If it ends up being up too much for my wife(or me even)then I will definitely be pursuing the auger silencer route.

Odd sounds quieter than my dual with a rev 2 mid pipe...BTW what kind of intake are you running ive got a weapon r one and I really wanna get that sound of the rotors winding back

AEM w/ the last bend chopped.

Thanks for this one. I ended up with a turbo XS. And, they no longer have silencers for it. I had an incredibly loud span from about 1,800 to 2,400 RPM. I do a lot of 40 mph cruising at this speed. It was really bad, like shake windows bad.


I bought one of the augers from summit, trimmed the pipe ends, and installed it. The bad range went away, most of the drone is gone, car runs find, did not seem to hurt performance. With eh XS over stock, I got a lot of low end power. Like drive around in 6th gear at 25 mph low end power. Installing this did not change that.


Install procedure:
In a straight piece of pipe, see if it fits. If it does, you win.

If not, look and see if there is an inside seam bead in the exhaust pipe. If there is, notch the spirals to allow for it. This will save in trimming. Does it fit now?


If not, a grinder is your friend. put first coil in pipe, see if you can straighten it to install the second spiral. If not, you need to grind some of the first spiral. Wiggle it. The pivot points that it wiggles around are the high points, grind them a bit and try again. Repeat.


Once I got the second one lined up, the rest of it went in easily. I tapped it in with a board.


again, highly recommended.

Glad you had similar results. Mine is still going strong !