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:

=~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~
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.

https://lh5.googleusercontent.com/-w...004_230642.jpg

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

=~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~

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.

https://lh4.googleusercontent.com/-7...004_230609.jpg

https://lh6.googleusercontent.com/-i...004_230626.jpg

=~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~

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

=~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~
Auger Style Video Clips





=~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~ =~=~=~
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

https://lh6.googleusercontent.com/-9...4-17-18-39.png

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

https://lh6.googleusercontent.com/-T...4-17-18-03.png

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

https://lh5.googleusercontent.com/-I...4-17-18-15.png

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