Rearwheel dyno numbers

Here is how Richard from Kimble Motorsports build a combined X-pipe and high flow CATs system for Bob R's C5

Next step in our designing a custom exhaust system is to baseline what the sound level (DB) our existing system outputs so that as we design after the X-pipe that we have a good flowing 3 inch system but is below a -94 DB sound level.

Here we capture engine RPM and speed in MPH at the same time recording cabin level sounds ( with windows open) as to exhaust sound in frequency and DB level.
Average exhaust sound was around 3300-4000 Hz at around -60 DB

Click below and download 2 exhaust sound recordings.

As we design from the X-pipe to muffler tips we then can compare before and after sound end results and assure we are not above the maximum DB levels tracks limit too.

More images of X-pipe testing

First design has the exhaust from the long tube header collectors 46 total inches to the muffler tips.
As image shows the mufflers take up 24 inches of that length.
Weight of stock exhaust with no cats was 65 pounds, total designed system is only 23 pounds.

In testing the sound as to DbC level is too high,
average inside of car with windows up is about 110 DB and as much as 128 DbC near the rear wheels.
Measuring as to ear quality levels as DbA inside measured 92 and outside 102 DbA.
We want final design under 95 DbA and less then 85 DbA inside.

Important to keep in mind is what levels of sound human ears can take

Types of Hearing Loss

There are many different causes of hearing loss. The following are the general categories into which hearing loss falls:

Otosclerosis - is a disease that causes bony growth on the ossicles and causes the stapes to become immobile, thus not allowing sound to be transferred into the cochlea. This is the result of a disease that affects the movement of the stapes, located in the middle ear.

Meniere's disease - is a problem involving fluid pressure within the cochlea. It causes the sufferer to experience intermittent episodes of hearing loss, dizziness, and tinnitus. These episodes can occur anytime and for varying amounts of time.

They are often associated with stress.
Drug induced - some medications can result in damage to the auditory system with prolonged use.
They are called ototoxic. Here are a few drugs that are known to cause hearing loss: aminoglycoside antibiotics (such as streptomycin, neomycin, kanamycin); salicylates in large quantities (aspirin), loop diuretics (lasix, ethacrynic acid); and drugs used in chemotherapy regimens (cisplatin, carboplatin, nitrogen mustard).

Tumors - one of the common tumors in the ear is called a vestibular schwannoma. These tumors develop around the 8th cranial nerve, which is also known as the auditory nerve.
Trauma - trauma to the ear can include fractures of the temporal bone, puncture of the eardrum by foreign objects, sudden changes in air pressure, and very loud noises.

Presbycusis - this hearing loss is caused by natural aging of the human body and begins after age 20, but often it is not noticed until the ages of 55 to 65. Presbycusis affects the high frequencies in the speech range, making understanding and hearing speech difficult.

Noise-induced hearing loss (NIHL) - this is hearing loss due to exposure to either a sudden, loud noise or exposure to loud noises for a period of time. A dangerous sound is anything that is 85 dB (sound pressure level - SPL) or higher.
Dangerous Decibels focuses on noise-induced hearing loss.

Noise-Induced Hearing Loss (NIHL)

Of the roughly 40 million Americans suffering from hearing loss, 10 million can be attributed to noise-induced hearing loss (NIHL). NIHL can be caused by a one-time exposure to loud sound as well as by repeated exposure to sounds at various loudness levels over an extended period of time.

Damage happens to the microscopic hair cells found inside the cochlea. These cells respond to mechanical sound vibrations by sending an electrical signal to the auditory nerve.
Different groups of hair cells are responsible for different frequencies (rate of vibrations). The healthy human ear can hear frequencies ranging from 20Hz to 20,000 Hz. Over time, the hair cell's hair-like stereocilia may get damaged or broken. If enough of them are damaged, hearing loss results. The high frequency area of the cochlea is often damaged by loud sound.

Sound pressure is measured in decibels (dB). Like a temperature scale, the decibel scale goes below zero. The average person can hear sounds down to about 0 dB, the level of rustling leaves. Some people with very good hearing can hear sounds down to -15 dB.
If a sound reaches 85 dB or stronger, it can cause permanent damage to your hearing. The amount of time you listen to a sound affects how much damage it will cause. The quieter the sound, the longer you can listen to it safely.
If the sound is very quiet, it will not cause damage even if you listen to it for a very long time; however, exposure to some common sounds can cause permanent damage.
With extended exposure, noises that reach a decibel level of 85 can cause permanent damage to the hair cells in the inner ear, leading to hearing loss. Many common sounds may be louder than you think…

A typical conversation occurs at 60 dB - not loud enough to cause damage.
A bulldozer that is idling (note that this is idling, not actively bulldozing) is loud enough at 85 dB that it can cause permanent damage after only 1 work day (8 hours).

When listening to music on earphones at a standard volume level 5, the sound generated reaches a level of 100 dB, loud enough to cause permanent damage after just 15 minutes per day!
A clap of thunder from a nearby storm (120 dB) or a gunshot (140-190 dB, depending on weapon), can both cause immediate damage.

In fact, noise is probably the most common occupational hazard facing people today. It is estimated that as many as 30 million Americans are exposed to potentially harmful sounds at work.

Even outside of work, many people participate in recreational activities that can produce harmful noise (musical concerts, use of power tools, etc.). Sixty million Americans own firearms, and many people do not use appropriate hearing protection devices.


Decibel Exposure Time Guidelines

Accepted standards for recommended permissible exposure time for continuous time weighted average noise, according to NIOSH and CDC, 2002. For every 3 dBs over 85dB, the permissible exposure time before possible damage can occur is cut in half.

Continuous dB Permissible Exposure Time

85 db 8 hours
88 dB 4 hours
91 db 2 hours
94 db 1 hour
97 db 30 minutes
100 db 15 minutes
103 db 7.5 minutes
106 dB 3.75 min (< 4min)
109 dB 1.875 min (< 2min)
112 dB .9375 min (~1 min)
115 dB .46875 min (~30 sec)

NIHL and Veterans

NIHL is of particular concern to veterans. Because NIHL is not immediately apparent (having a gradual onset), many veterans leaving the service are unaware of the full extent of hearing damage.
Although governments are now realizing the link between military service and NIHL, it took a long time and many lawsuits before any compensation was given to the affected veterans.
In 1999 the USA alone distributed $291.6 million in compensation for NIHL to some 56,792 veterans. The annual cost of compensation to veterans in France is estimated to be $60 million.
In Belgium two thirds of all payments made to veterans with disabilities correspond to NIHL. Many veterans damage their hearing during service.
They can, however, prevent more damage from occurring and they can save their remaining hearing after their military duties are completed.

Vehicle Exhaust Noise Level Certification

California law requires that all vehicles must be equipped with an adequate muffler to prevent excessive noise from the exhaust system.
It also prohibits the operation of a passenger vehicle (other than a motorcycle), or a truck with a Gross Vehicle Weight Rating (GVWR) of less than 6,000 pounds, that has an exhaust noise level greater than 95 (DbA) decibels, when tested under specified conditions.

If you have been issued a citation for operating a vehicle in violation of Vehicle Code Section 27150 or 27151, you must take your vehicle to a state Referee Center.

Note: The Referee is only authorized to inspect and certify passenger cars and trucks under 6,000 GVWR that have been cited for a violation of Section 27150 or 27151 of the Vehicle Code.
The maximum decibel level applies only to those vehicles. Citations issued to other vehicles (motorcycles, trucks exceeding 5999 pounds GVWR) are not part of this program. Check with the agency that issued the citation, and/or the court, to find out how to show proof of correction for these other vehicles.

The following steps outline the procedures you'll need to follow to get a certificate of compliance, which shows your vehicle's exhaust noise level is within the applicable standards.

STEP 1

If you feel your vehicle's exhaust system has been modified or has deteriorated so that the noise level exceeds current standards, you should have the exhaust system repaired before proceeding to step 2.

OR

If you have reason to believe that your vehicle's exhaust noise level meets the current standards, proceed directly to step 2.

Note that citations have a court appearance date.]
[Timely action can help you avoid additional fines and penalties.]

STEP 2

Have your vehicle tested at a state Referee Center. To make an appointment, call the Referee Scheduling Center at (800) 622-7733. Have the citation and vehicle registration with you when you call. The Center will tell you any fees that will need to be paid for the test.

STEP 3

The Referee will conduct an exhaust noise level test in accordance with the Society of Automotive Engineers (SAE) standard J1169, May 1998, to determine if your vehicle's exhaust noise level exceeds the noise standard (95db).

If your vehicle meets the standard, the Referee will give you a "Certificate of Compliance." Take the certificate to the court (See Step 5).

If your vehicle does not meet the standard, the Referee will give you a report that lists the recorded decibel readings. Your vehicle must be repaired to meet the standard of not more than 95 decibels (See Step 4).

STEP 4

If your vehicle does not meet the standard, additional repairs must be made before you can make a second appointment with the Referee Scheduling Center.

STEP 5

Once your vehicle receives a "Certificate of Compliance" from a Referee Center, present the certificate to the court as proof that your vehicle is in compliance with California law.

NOTE: Inspection fees and any necessary repairs are your responsibility. You may also be required to pay a fine and other legal costs when reporting to the court. Also, note that most citations have a deadline. Timely repairs can help you avoid additional fines and penalties.

If you have any questions, please contact the local law enforcement agency that issued the citation or the Bureau of Automotive Repair at (800) 952-5210

Second round of design and testing of the Team ZR-1 model NFW consists now of custom designed mufflers which reduced DBA at rear of car from 102 DBA to 94 and by driver area in a range of 82-90 DBA

We're in the process of doing testruns with OBD scanner to analyze the data as a compare to design 1 tests

Not a smart thing to do as this owner put in cutouts that is forcing all the time hot exhaust over time delaminates the fiberglass spring, causing failure of spring and also adds more heat to the transaxle that already gets too hot

Third round of NFW exhaust design has been completed.

We wanted a balance so that for those that wanted less DBA inside the car but not lose the sound or increase backpressure at the exhaust tips they could now choose to their liking by either using design stage two or :

We designed 3 inch tailpipes from our custom designed mufflers to ending out the back end.

Testing showed the DBA inside the car now running between 80 and 88 DBA with only a 2 DBA drop at the end of tailpipes.

There is a 2 DBA difference inside the car depending on if the windows are open or closed.

This allows those that buy our NFW system to choose the race ( higher DBA) and later could purchase our tailpipes of buy the total system and install or take off the tailpipes when need be

Attached is some audio recordings from part throttle to WOT, with recordings captured inside and with the mic mounted by license plates.

You will need to unzip the files to listen to the recordings.

Scope sound levels at part throttle