Too Loud

[dsmith]

Stu

I am in Newtown and am in the process of getting my Cobra registered. Was the car titled in another state or is it a new build?
If you care to call me, I can tell you what I am doing 426-3141 days
648-0548 eves.

david smith

[Don]

Stu, I do not know Mike personally, but only from his posting, might want to send him an e-mail or PM using the info in his Profile.

I did check CT DMV Section 14-80a-4a , Allowable Noise Levels since Jan 1, 1979. The maximum dB for a stationary test is 72 dB for soft site( grass ) and 74 dB for hard site ( pavement ). Section 14-80a-9a mentions the distance for measuring the dB. The baseline is 48 feet or more but less than 58ft. An adjustment to the dB reading is made up or down for readings either closer or farther away than the baseline range. The max reading is 81 dB for a hard site, highway operation above 35MPH, using the 48 to 58 ft baseline for measuring.

[stush]

I have my own dB meter and I know at idle from my measurements I am fine. They then have you rev it in neutral and do another measurement, presumably what they are equating to 35 mph. I will have to PM Mike cuz I heard from someone that they may not accept Supertrapps.

Stu

[Don]

Stu, curious on the procedure the DMV is using for the 35 MPH test. Did they have you hold the RPM at no higher than the equivalent of 35 MPH in the highest gear ( 4th, 5th, ) or just rev the engine w/o any regard to the peak RPM.

Not knowing what type of dB meter the DMV is using, some models can be set to hold the peak dB recorded as the high which might be above the equivalent of 35 MPH @ 50 ft. in high gear.

Might want to check with Jay @ Vintage- Motorsports in Middletown., 860-790-0987. I think he indicated in another Thread that the Backdraft Cobra passed the dB test w/o the use of trapps.

With the CT emissions standards for Composite/ Kit Cars being tightened as of January 1, 2007 for new registrations and now the use of the dB meter, additional challenges to register in CT.



Don

[Hans-Olof Blom]

In Sweden the measurements are done during full acceleration. The person doing the test will drive about 30mph in second gear and approx. 30ft before the measuring point he floors it. The allowed level is 85dBA.

I stuffed my side pipes with 6 steel wool balls in each pipe and added a plug made from expanded metal to keep everything in place. See pictures!

I adjusted the carb linkage so pedal to metal was only about 70% of full throttle.

My Cobra was really quiet and when I heard it during the test I was sure it would pass.

BUT, I was told to come back and WITH mufflers. The measured sound level was 90dBA so it was not even close.

After my first attempt last fall the weather was too bad for another try. But within a qouple of weeks I will try again. I have now added a construction made of Al-discs on a wire with tubes as spacers. It is now very very quiet but a bit hard to start.

[stush]

the test was done stationary with revving the engine in neutral...not what I feel is truly accurate if that is there equivalent for 35 mph. At idle I know from my own meter I am around 67dB. On my own testing I was around 81-82 or so in my driveway at 50 ft.

Stu

[stush]

excellent pictures. How do you keep the plug in place? is everything threaded over the long wire/cable?

Stu

[Cobranut]

I don't think I'd let some government employee try that in my car.
I doubt his skills are up to controlling a big smokey burnout past the guy holding the meter.
Not to mention that the exhaust combined with the screaming tires would probably blow the sound meter.

David

[quote=Hans-Olof Blom]In Sweden the measurements are done during full acceleration. The person doing the test will drive about 30mph in second gear and approx. 30ft before the measuring point he floors it. The allowed level is 85dBA.

[Hans-Olof Blom]

I tried to keep the plug in place with the 2 piano wires that can be seen in the picture. That was not enough so I added a threaded rod with 2 long nuts. I just expand it inside the pipe so it can't move. So far it seems to stay in place.

It is also important to decrease the sound from the inlet which can be substantial.

The person doing the test is not a government employee. He is a member of a non profit organization of inspectors for this kind of vehicles. The inspectors are usually experienced builders of cars.

For the next try I have the Al discs on the wire, 6 steel wool balls, and the plug made from expanded metal in each pipe. I have also disconnected the second stage on my carburetor. I really hope this will be enough!

[Ant]

We are about to get a decibel test here in NZ probably about 90DB measured 0.5 M away from tailpipe, this is going to be a problem for my engine, so heres what I intend on doing,

Fit an auger/three disc chambered baffle into the tail pipe, they are easy to fit into 3" or 3.5" curved tailpipes, but the insert baffle can only be probably max of 8" long total, and can be made to fit around the curve pending shape - anything is possible, even if you use three big washers and have the gas into the center of the first one out a cut out in the through pipe then through a series of holes in the next washer, and then back through a cutout in pipe and through center of the exit washer. This works motorcyle guys have them and I used it in my first Cobra, and for obvious reasons it doesnt help performance!

As I am going to probably use more than one exhaust pipe per side underneath the car it will be harder to fit a baffle but I guess its all relative.

Under floor systems, face the exit downwards and slightly inwards to center of car.

Have a 3000 chip in your MSD so they cant rev your engine to the required 4000rpm when you get pulled over, I have an adjustable dial type MSD which will be in easy access while driving.

Drive really quietly around town and let them get used to you, as I only live in a small town that may work.

[Don]

AJ, are you referring to an approach similar to the Car Chemistry disc system ?

http://www.carchemistry.com/techinfo...n.php?qstId=10

Car Chemistry also sells " Stainless Steel Muffler Packing Material " . The Packing is intended to be installed between each chamber of the Car Chemistry Insert. CC states " Reduces sound additional 2-4 decibels " Seems to be a substantial reduction for a small amount of material, could not find any tests to verify the dB reduction claim.

Part Number: SSIK-12

[Don]

Vance & Hines makes an after muffler baffle for Harleys: Pro Pipe Lowend Power Baffle. Part number V21299 and is available at Harley dealers.

There are two models, the above having a solid end cap in the center tube and the other model having a 1/2", + or -, hole in the endcap for less restriction.

The baffle will not fit inside the 3" exhaust pipe as is since the mounting rings are 4", but can be machined to fit in the exhaust pipe just before the turn out. The turn out would need to be cut out ,baffle fitted, and then rewelded.

Appears the baffle uses the same approach as Car Chemistry discs

[Don]

Stu, dB readings with a 351W, using an auger style muffler, Car Chemistry 3 discs w/o the steel wool packing, no plug in the CC center pipe before the muffler , and a Vortex cone after the muffler. dB Readings are at 50 ft, on hardtop from the side:

Idle: 70
RPM range:
2000: 80
2500: 82
3000: 85
Quick full throttle and immediate release: 89

Used the MAX HOLD setting to retain on the meter the max dB

[stush]

Don,

Thanks for your measurements. Going back tomorrow to Weatherfield. Have a CC 3 disc insert with packing. No center restrictor. Sounds more muffled but my home measurements were still a little high I think...very windy day throws it off. They measured behind the car though I think the state statue is supposed to be perpendicular but not less than 70 degrees. Is that right? Since they measured from 50 ft behind the car were they in the wrong? I made a restrictor like the fellow showed in the picture but used perforated Al and expanded metal. Seems to have lowered it further. Will be testing again later if the wind dies down. Check with your knowledge about how the test should be done with regards to angle of measure and let me know.

Stu

[Don]

Stu:

Go to:

http://www.ct.gov/dmv/cwp/view.asp?A=801&Q=252796

Scroll Down to " Are Glass Packs Legal " and click on
Sec 14-80a-1 through 14-80a10a

Should get the PDF file,"Maximum Permissible Noise Standards", on pages 164 to 166 is Section 14-80a-7a Measurements of Noise Emissions, which is the standard the DMV Inspectors should be using for testing , the test site diagram is on page 166. May or may not be a good idea, but depending how the inspection is going, ask the Inspector if they are follwing the standard mentioned above which is Sec 14-80a-1a to 14-80a-10a

The test site diagram, for the 35 mph test, must, I think but not sure, be a side reading as the test should be conducted as the vehicle approaches and drives by. Otherwise, from the rear or front the vehicle would be accelerating, not a constant 35 MPH

For the 35 MPH simulated test where they ask to accelerate the motor, might want to consider not exceeeding a RPM than the equivalent of 35 MPH in high gear. When I was racing the motor to a quick full throttle, really got some extrteme high readings as the RPM far exceeded the equivalent of 35 MPH.

Note: I have had problems copying the DMV link above, might not work. I do not have the software to copy the PDF file.

Car Chemistry and Vortex Cone both mentioned their hardware is most effective as close as possible to the primaries.

GOOD LUCK !!!!!!!

[stush]

Passed inspection this time. The sound was so muffled they didn't even bring out the dB meter. Thanks everyone for all your help. This website is worth its weight in gold.

Stu

[Don]

Stu

CONGRATULATIONS

Way to go, the best way for a natural high when the DMV Inspector stamps the forms " Passed "

Any other words of wisdom for those that will have their Composite/Kit inspected, and specifically the CT inspection on noise, etc., etc.,

Regards

Don