Car is 94 Z28 A4, CAI, 52mmTB, Shorty Headers, High Flow Cat, Flowmaster cat-back. I passed the sniffer np, but on the noise test I got 96db @2500rpm, the limit is 93. It's not that far from passing, any suggestions on how to quiet her down that 3db without doing anything major?

 

their are inserts you can get that are cone shape i believe-

think jegs or summit sells them-

** side note- i've hit 108 decibals cop warned me not to come back into his state with it still like that though

 

Things that make you go crazy..guess Harley's and UPS trucks are exempt?????

 

Where exactly do they place the microphone... ?? How far away and in what location with respect to your tailpipes?

 

Is that C weighting or A weighting?

 

I'm not sure exactly where the mic was, behind the car pretty close to the tailpipes, I was in the car reving to 2500 at the time. I have no idea what weighting they use, or even what that means, it's state of oregon.

I still have my stock TB and airbox, which seemed to make it a tad louder when I switched that stuff out. Do you think that will help any, or is it just one of those "percieved" differences?

This does seem kind of rediculas though, when I did all the mods I thought I was keeping it pretty mild for exactly this sort of thing. I used to live in denver and they did a dyno type run which more accurately measures the actual emissions of the engine. Here they just do a sniff at idle and 2500, and this damn noise thing. I know the car is loud compared to most, but very far from being the loudest thing on the road. Not to mention if you have OBD2 they don't even run your car, they just hook it up to a scantool and check for codes.

 

Not at all sure, but I think the high-flow cat makes the exhaust slightly louder than the standard (original) one. I would first check to see if you have any exhaust leaks. I agree that your set-up should be quieter than what a lot of people run.

The Weighting refers to how the different frequencies are emphasized by the noise measuring equipment. "C" weighting gives equal emphasis to all frequencies, including the low (bass) from an exhaust system. "A" weighting gives more emphasis to the upper frequencies like you might hear inside a commerical jet in flight. The ear is more sensitive to these upper frequencies.

I suspect they are using "A" weighting since they want to make sure the low sounds are fully taken into account. I know that the placement of the sound level meter can make a BIG difference with A-weighted noise levels. Moving the meter a foot can change the measurement by several dB. Also, if there's another car being tested nearby at the same time yours is, it could affect your reading.

First, I'd try going when the testing facility is pretty empty... not too many other cars there. If you fail, see if you can convince the technician to move the meter slightly to a different spot. If you still fail, I guess I'd put back the old air box, although I think the odds of it helping are pretty small. If none of that works, I'd look into those exhaust inserts that kingman109 mentioned. Hopefully they can be put in just for the test, and taken out after.

At 3dB, you're not off by much, maybe some of the ideas here will be enough to pass. If that all fails, try slipping the technician a $20 bill. Just kidding. (?) Some of these test centers have video cameras all over the place.

 

Car Chemistry makes disc type inserts, that slip into the pipe(s). They come in sizes from 2" to 4", and have 2-disc and 3-disc models. They claim the 2-disc units will reduce unmuffled systems to NHRA acceptable levels, and the 3-disc units are supposed to meet "street" limits with unmuffled systems. They are $46 each in 2.5" size.

There's also the Dynatech noise cones, slip-ins, but they only come in 3" to 4" sizes and cost $60 each. I bought a pair of 3" Dynatech turndowns with the noise cones inside them, with the intent of dyno testing them, along with measuring the noise reduction, but so far I haven't tested them. If you could figure a way they might work on your car, I'd be glad to loan them to you, if you pay the shipping.