SS Race dB Level?

[mfanatic325]

Does anyone happen to know the dB level of SS Race mufflers on Z4M? I have the mufflers only, and will be running Laguna Seca soon. As you know, Laguna has a strict 92dB sound level limit. And I'll be honest, I've grown quite accustomed to how the SS Race sounds, even as a daily driver. Perhaps it's due to the fact that I had been running muffler-less for about 3 weeks, waiting for the adapter piece (so that I could mate the SS cannisters to the OE x-pipe/section2 flanges) to come in
Anyhow, if I don't have to swap my OEM mufflers back on for track, that'd be best.
Any help would be much appreciated! TIA!

[mfanatic325]

Originally Posted by shift@red

With just mufflers I would imagine youll be ok.

haha yeah I think so too, but just want to be 100% sure before I go. It would really be a bummer if I were to get booted off track. I've seen an NSX get booted before

Anyhow, I'm thinking about just buying a relatively cheap Radioshack digital dB meter and trying it out. Will report with findings.

[mfanatic325]

Unfortunately neither of the two local RadioShacks nearby have a dB meter in stock, so I went ahead and ordered one off of Amazon (one that had decent reviews, for relatively cheap). Will report back with my findings in about a week or so when the dB meter comes in.

[mfanatic325]

Yay, my little digital dB meter came in the mail today. Seems to work okay. Just won't hold a steady dB level. On the back, it gives a breakdown of approximate levels:
30dB - library
60dB - normal speech
80dB - alarm clock
90dB - stock car stereo
110dB - loud thunder
120dB - rock concert
140dB - jet engine

Will try this out tomorrow morning with a cold start, and some in-cabin recordings as well. Will try to keep it a controlled environment for the most accurate results possible.

[dekaliber]

What is that 92dB measured at? Volume decreases quite dramatically with distance. A 92dB source at 1 meter becomes 72 dB at 10 meters, and 52dB at 100 meters.

[mfanatic325]

Originally Posted by dekaliber

What is that 92dB measured at? Volume decreases quite dramatically with distance. A 92dB source at 1 meter becomes 72 dB at 10 meters, and 52dB at 100 meters.

That is a really good question. After some further research, the sound check booth is located between the turn 5 and turn 6 straightaway (mid-track straight). And apparently, it is 60 feet away. I think I'll be fine, especially if I use one of those metal "macaroni's" attached to my exhaust tips lol.

[mfanatic325]

So for 92dB Laguna Seca limit purposes, I'll attempt to capture sound close to redline from 60 ft. away. Of course, this may take some time, as I'll have to find a otherwise unoccupied length of quiet road. Luckily I have just the one in mind, up in the nearby mountain, where I can do this safely and won't jeopardize anyone else besides myself and a friend that will be helping me record.

As for street purposes, California 95dB rules say that testing procedures involve putting a microphone no more than 20 inches away from a tailpipe, and to have the car rev to half of its total capable RPM. For this case, it'd be approximately 4k rpm. This will be easier to capture, as I can just do it in my driveway. Will post up recordings as soon as I can.

Per California code:
What is the exhaust noise test specified in 13 CCR? Can this be used for enforcement?

Section 1030-1036, 13 CCR, were intended to be used by Licensed Muffler Certification Stations as a means of detection if an exhaust system met the requirements of the Muffler Certification Program (When those programs were operational) They specify testing procedures for motor vehicle exhaust noise alone (as opposed to total vehicle noise). This procedure specifies a limit of 95 dB measured 20 inches from the exhaust pipe outlet with the engine operating in neutral, typically at speed of 3000-5000 rpm. It applies only to passenger vehicles. It does not apply to motorcycles or to vehicles over 6000 pounds gross weight.

Sorry for the delay!

[esqu1re]

Here's to you not surpassing the db. I doubt you will.

[mfanatic325]

haha yeah, luckily the distance between me and the sound check booth will probably help me pass
Perhaps I'll just stick to the left, as far away from it as possible
Or just let off a bit down that portion of straightaway.

[dekaliber]

Alternately, you could just test in your driveway from 6 ft away and make sure that the SPL doesn't exceed 112 dB. Seems very unlikely.

[mfanatic325]

Originally Posted by dekaliber

Alternately, you could just test in your driveway from 6 ft away and make sure that the SPL doesn't exceed 112 dB. Seems very unlikely.

6feet away and @ 112dB? Why? I thought I had gotten all the correct test scenario values already for controlled environment? Just curious where you got these criteria?

[mfanatic325]

So I did some idle recordings just now on the Z4M, all from less than 2 feet behind the muffler tips (per California recommended testing procedures of 20 inches away from muffler tips). Here are my findings:

upon cold cranking start (prior to idle drop) --> 100+ dB
cold idle (steady idle after rpm drop) --> 91-92dB

warm idle --> 91-92dB

So it looks like I'm already close to the CA street limit just by idling
Not...good...




Now I'm going to go try out my MR2, which has been unchanged since the last two times I've been @ Laguna (at least no changes to anything on the car that would contribute to engine/exhaust noises). Because I know my MR2 just barely passed (got black-flagged only once for sound). Will report back.

edit:
Just got back from MR2's recording. They go as follows:
cold crank (before idle) --> 96-97dB

warm idle --> 98-99dB

[mfanatic325]

Very interesting #'s so far, especially how the MR2 is actually louder when warm

But for California street legality purposes, these warm idle recordings won't suffice, as I'd have to be able to rev both cars to mid-RPM range (per car) and still be within 95dB.
And considering the MR2 is already @ 98-99dB when warm idling, it definitely won't pass CA law.

I think the Z4M might have a chance though

But as of right now, it is unsure of whether or not I will pass Laguna sound check, since sound isn't 1:1
Especially since both cars are different, and may very well sound different under load.

[dekaliber]

Originally Posted by mfanatic325

6feet away and @ 112dB? Why? I thought I had gotten all the correct test scenario values already for controlled environment? Just curious where you got these criteria?

It's just the amount that perceived loudness varies by distance. At 10 times the distance, the intensity of the sound drops by 20 dB. (92 dB @ 60 ft = 112 dB @ 6 ft.)

You'd have to get a reading of over 120 dB at 2 ft in order to surpass 92 dB @ 60 ft. That's pretty loud!

[mfanatic325]

Originally Posted by dekaliber

It's just the amount that perceived loudness varies by distance. At 10 times the distance, the intensity of the sound drops by 20 dB. (92 dB @ 60 ft = 112 dB @ 6 ft.)

You'd have to get a reading of over 120 dB at 2 ft in order to surpass 92 dB @ 60 ft. That's pretty loud!

ohhhh I see. Really? Is that consistent though? I mean, I study engineering, but I haven't gotten to nitty gritty fluid dynamics. But from what I do know so far, there may be other varying factors, no?
I just don't know if those proportions are exact.

Buuuut assuming you're right, then I'll try recording results throughout the rev range from 6 ft. away

[mfanatic325]

I did some revving today with a buddy about 6 ft. behind the car recording. The SS Race mufflers recorded just over 100 dB at that distance @ <6k rpm max when parked (ECU won't allow revving past this point, to protect the engine from any harm).

Then I did a 1st gear drive-by, trying to redline the car just as I passed the recording mic. Neither of the two tests reached 112dB @ a distance of 6 ft., which according to Dekaliber is the same thing as not reaching 92dB @ 60 ft. away.

All in all, I should pass Laguna Seca sound limit

If for whatever reason I'm kicked out this coming Monday for sound, I'll be sure to check in here

[mfanatic325]

Still thinking about it. I guess if a deal comes around I'll get one.

[mfanatic325]

Yay so I passed the 92dB (@ 60 ft. Distance) limit with flying colors. Didn't even get black-flagged once =]

[mfanatic325]

so after installing headers, my car registers on-track @ 96dB, so I had to be careful until the last session of the day today @ Laguna. With only a couple laps to go, I said to myself, "eff it..." and blew past the sound check hut. Shortly after, I received yet another meatball flag (3 strikes, I'm out)

Yet another wonderful track day. Can't hardly wait for the next

[Caddyshk]

Is Laguna Seca surrounded by tree hugging Pinkos or something? In addition; if you've had three strikes how are you going back?

[fatmatt0116]

how do you have headers in CA and still pass inspection?

[mfanatic325]

Originally Posted by Caddyshk

Is Laguna Seca surrounded by tree hugging Pinkos or something? In addition; if you've had three strikes how are you going back?

lolll yeah the surrounding neighborhood is one of wealth apparently. You know how rich snobby people are...they whine and bitch a lot. And since they contribute to the city of Monterey, their voices matter more over others. For whatever reason, the city thinks it best to cater to these rich folk and limit Laguna Seca's decibel limit; even though the racetrack has been around long before the wealthy neighborhood was even made
Btw, three-strikes rule is on a per-day basis lol, so I can go back no problem, just hafta lift off next to the sound hut.

Originally Posted by fatmatt0116

how do you have headers in CA and still pass inspection?

hah I'm going to have to get special smog