Too Loud

[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

[elgecko]

I am going to try Car Chemistry. Has any one tried their Cobra side pipe setup.
http://www.carchemistry.com/shop/ind...1/prevstart/0/
I fired my Cobra FE powered up this weekend and the neighbors grabbed their daughters and ran to the house.
A little sound reduction may be necessary, but not too much
Dave

[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!

[Don]

Hans, regarding the inlet sound supression. The Car Chemistry discs and the Vortex cone are more effective just after the primaries and before the muffler. From the CC specs: " The further back the insert is installed, the less effective they are at reducing sound " " The insets work off of the strength of the exhaust pulse as well as the heat of the exhaust " " A rich fuel mix will create a much louder exhaust note "

There are also two models of the CC discs, one having additional sound control.

They also make a series of their discs, 7 in total, which will fit inside an exhaust pipe, i.e. make your own muffler, referred to as " Side Pipe Inserts ", 3", 3 1/2 " and 4". However, the length is 33".There is a " Side Pipe Silencer Kit " which has 4 discs. Intended to replace the existing turn down on the side pipe as a bolt on rather than welding. From the picture, does not have a support bracket.

A contact at CC is Ken Mullinex, 972-937-7735, or

Car Chemistry
PO Box 455
Waxahachie, TX 75168

[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

[Buzzmobile]

Now, Pull all that crap outta there and go have some fun!

[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

[stush]

Best words of wisdom is stay calm and friendly. Make sure all your paperwork is in order. The car was so quiet this time they didn't even pull out the dB meter. Used car chemistry 3 disc inserts at the collector end and made a restrictor for the turn out of alternating discs of perforated aluminum and expanded metal which I cut and bolted together. The only trick was keeping it in place but the pictures posted on this thread were a great help and basically duplicated that. Still not sure what standard they use but after reading the state guidelines it is probably considered a stationary test. Thanks everyone for all the help and advice...now it is time to enjoy the car.

Stu

[Don]

In Grassroots Motorsports there was an advertisement for Vibrant Performance. I contacted the company referencing the CT dB standards and asking about a muffler specifically intended for Cobras. Included was the following comment . First time that I had seen a reference to an SAE standard on dB for exhaust noise.


"So you know, the Connecticut sound test you have referenced has been largely discredited by SAE (Society of Automotive Engineers) as being ineffective. In 1998 they released a new standard (known as J1169-1998) for exhaust noise testing that is the standard used by California and some other states. The new standard allows for a stationary db level of 95, at a distance of 1.5 meters from the tailpipe. This standard has proven to be very fair to manufacturers and enthusiasts alike. "

Anyone from CA familiar with the standard mentioned above ?


http://www.vibrantperformance.com/vi...rformance.html

[cobracobra]

Sorry I havnt logged on in a while....I finally passed yesterday and going today for my plates....1st inspector failed me on, get this 12 items! Needless to say 10 were BS! I can say that the supervisor there is a great guy and understands these vehicles(no names being mentioned) MAKE SURE WHEN MESURING YOUR SOUND YOU HAVE IT IN THE RIGHT SCALE..DB-A not C! @ idle I was at 66DBA but 81 at C. @ 2000rpm im at about 70DBA. thats with the supertrapps on and measuring on the safe side of 40 ft behind the vehicle, im about 1 DBA less @ 50 ft.....

-Mike

[stush]

Although the SAE may have discredited the standard, in the Peoples Republic of CT it is what they go by.

So the first time they only had you go up to 2000rpm? If I had done that the first time I may have passed. I do not know who the supervisor was but the guy doing reinspection was kind of a tough nut, then we he decided I passed he was friendly. When I came back after having paid the $50 VIN assignment fee, he took great care in selecting a place to put the tag. Complemented the car, wished me luck in my enjoyment, wished for plenty of sunny days to drive, and even asked if there is a way to get a soft top.

Stu

[Hans-Olof Blom]

Today I passed the noise test. I had 78.4dBA and the limit is 85dBA.

Yesterday evening I tested the car and it was still quite quick from 50km/h in 2:nd gear when I stepped on it. So I adjusted the carb linkage a bit more. The result of a new rest drive was that my Cobra is now slower than my old Volvo.

[Don]

HOB

What muffler and/or baffles did you use ?

[stush]

With Car chemistry triple discs in the collector and inserts I mad to put at the turnouts, the car barely made a peep. A 50 ft in idle could not even hear the car. Couldn't wait to get that stuff off. Congrats on passing inspection.

[Hans-Olof Blom]

I used all the stuff shown in the pictures I posted earlier. Plus I adjusted the carb linkage as much as possible. The carb barely opened when I stepped on it. The 2:nd stage on the carb was disconnected.