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It's important to compare dBs in a consistent manner. Things like distance, frequency Scale (A, C...), and meter response, proximity to buildings and so forth can make huge differences.
Went through a bunch of dB stuff on my E30 M3 recently. Got black flagged a few times for excessive loudness although no meter was in use. Usually the SCCA uses a 95 dB at 50 feet, A scale, slow response approach but they have no final consistent spec at this time, and local concerns trump this anyway. Site owners respond to letters and angry calls from locals and neighbors who don't use meters.
Some anecdotal information:
E30 M3 has an 8000 RPM 2.3 liter lump with high flow cat leading to Borla muffler. At one meter, revving in neutral peaks at 117dB (A scale: mostly measures sound over 1000 Hz, slow response). Since sound drops 6 dB every time you double distance, the reading would be in the low 90s at 50 feet, borderline.
I added a magnaflow resonator after the cats and before the Borla and the readings changed downward by 8-9 dB. No more black flags. Same basic sound but louder. Most of the removed sound was in the range the meter measures, leaving a good portion of the mean sounding lower frequencies intact The resonators are straight through and don't harm output.
I tried a few "at-the-track" mods such as fiberglass stuffing one tip, hose clamping perforated metal soda can in place, etc. Those cut sound but noticeably hurt output too. To get a large sound reduction from restriction as in the soda can approach requires something like an extra 8-9 PSI of backpressure - not good.
Changing the final muffler amongst aftermarket options changes the SPL by maybe 1-5 db: not that much in many cases. Adding another stage as in what I noted above seems to be more effective but is pricey and can't be done at an event.
Is the Elise a cat-muffler approach or is it cat-resonator-muffler?
It would be interesting to see the meter tests on the various Elise options.
Stan
Went through a bunch of dB stuff on my E30 M3 recently. Got black flagged a few times for excessive loudness although no meter was in use. Usually the SCCA uses a 95 dB at 50 feet, A scale, slow response approach but they have no final consistent spec at this time, and local concerns trump this anyway. Site owners respond to letters and angry calls from locals and neighbors who don't use meters.
Some anecdotal information:
E30 M3 has an 8000 RPM 2.3 liter lump with high flow cat leading to Borla muffler. At one meter, revving in neutral peaks at 117dB (A scale: mostly measures sound over 1000 Hz, slow response). Since sound drops 6 dB every time you double distance, the reading would be in the low 90s at 50 feet, borderline.
I added a magnaflow resonator after the cats and before the Borla and the readings changed downward by 8-9 dB. No more black flags. Same basic sound but louder. Most of the removed sound was in the range the meter measures, leaving a good portion of the mean sounding lower frequencies intact The resonators are straight through and don't harm output.
I tried a few "at-the-track" mods such as fiberglass stuffing one tip, hose clamping perforated metal soda can in place, etc. Those cut sound but noticeably hurt output too. To get a large sound reduction from restriction as in the soda can approach requires something like an extra 8-9 PSI of backpressure - not good.
Changing the final muffler amongst aftermarket options changes the SPL by maybe 1-5 db: not that much in many cases. Adding another stage as in what I noted above seems to be more effective but is pricey and can't be done at an event.
Is the Elise a cat-muffler approach or is it cat-resonator-muffler?
It would be interesting to see the meter tests on the various Elise options.
Stan
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3,523 Posts
Stan, a few details about the exhaust systems can be found here. mikester dug up a spec that I haven't looked into that stated "...The legislation require the use of Society of Automotive Engineers test procedure J1169, which employs the A-weighted dB scale to measure exhaust sound--based on 95 decibels at 20 inches. ... "
>>>The legislation require the use of Society of Automotive Engineers test procedure J1169, which employs the A-weighted dB scale to measure exhaust sound--based on 95 decibels at 20 inches. ...<<<
95 dBA at 20 inches? Man that's a lot different than tracks calling out 95 dBA at 50 feet!
My M3 is now pretty tame yet still sporty. I don't think it can do 95 dBA at 20 inches though. I'll have to try that out.
This seems to be the meter position concept they are using for the SAE test:
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Someone posted that that would be something like 60 something dBs at 50 feet - which is quieter than a normal conversation, or watching TV news. Things like tire tread noise might start to be a factor for some cars. I know that the SCCA tries to avoid things like tire screech or a spoiler scraping briefly on the track during their noise tests. I'll read more about it, thanks for the link.
Stan
95 dBA at 20 inches? Man that's a lot different than tracks calling out 95 dBA at 50 feet!
My M3 is now pretty tame yet still sporty. I don't think it can do 95 dBA at 20 inches though. I'll have to try that out.
This seems to be the meter position concept they are using for the SAE test:
Someone posted that that would be something like 60 something dBs at 50 feet - which is quieter than a normal conversation, or watching TV news. Things like tire tread noise might start to be a factor for some cars. I know that the SCCA tries to avoid things like tire screech or a spoiler scraping briefly on the track during their noise tests. I'll read more about it, thanks for the link.
Stan
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25,241 Posts
that exhaust looks like the supposed new stage 2. Check out the similarity of the tips.
http://www.elisetalk.com/forums/showthread.php?s=&threadid=4147&highlight=stage
http://www.elisetalk.com/forums/showthread.php?s=&threadid=4147&highlight=stage
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Yeah, the tips are similar. From the side though, you can tell how they welded them on. On OEM units, that part is hidden by the diffuser. I prefer Lotus's design that tucks the tips in, so that they don't stick out from the diffuser too much. I wish Stage 1 and stock exhausts looked that way. Stage 2 may turn out to be too loud for the street (or even the track).
The reference is California Vehicle Code Section 27150.2(b).LarryB said:
If you want to see the entire vehicle code, it's here. There's some very interesting stuff in there (esp. the law specifically against exhaust whistles. Woo woo!) surrounded by a coma-inducing wasteland of legal-ese.
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Figured the comment about legislation was a state code. Still not sure if that's the method Lotus used to spec it. With the drop off over distance think we'll be OK for track, though officially not CA road legal with stage II or for that matter stage I?
I doubt it. When I got pulled over for a loud exhaust on my MR2, the officer got flustered when he found out I wasn't a high school student that he could intimidate after all and let me go so I will never know. My guess is it's more like a fix-it ticket, only more expensive.shay2nak said:
The wording in the CA Vehicle Code makes the driver suspected of a too-loud exhaust guilty until proven innocent, since it's the driver's responsibility to get it tested (and pay for the testing).
I am currently of the opinion that a non-stock exhaust just isn't worth the hassle, so I guess the law works (on me, anyway), just indirectly.
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Here in GA, I don't think you can get a ticket for having too loud of an exhaust note. There are trucks everywhere that are straight piped and raised about 4 feet. They are insanely loud and no one seems to get into any trouble.
For the record, I REALLY hope I don't get into an accident with one of those trucks while in an Elise.
-Whit
For the record, I REALLY hope I don't get into an accident with one of those trucks while in an Elise.
-Whit
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218 Posts
I agree, I live in WV.zcar222 said:
Actually, I turned off the ignition, but that's neither here nor there. The officer already made his decision when he turned on his blinky lights.shay2nak said:
The problem with the exhaust noise law is that you can be cited based on the perception of the officer. There is no objective measuring device with the officer so if your car is perceived to be loud, it is now your responsibility to prove otherwise.
An analogy would be getting a speeding ticket because a police officer watched you driving and said it looked like you were doing 45 mph in a 25 mph zone with no objective measuring device (radar gun).
The exhaust noise law in California used to be worse. It didn't reference a standards document (SAE J1169), so whether or not a car was too loud was completely subjective. So maybe we're halfway there.
Oh, and BTW, because of that incident, I now carry a copy of section 27150 in my MR2 glove box. Not that it matters. One of the mounting bolts for the exhaust pulled out of the sheet metal at an autox and the car is now effectively running a very short straight pipe. Too loud for the street, it's sitting in the garage.
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