h4nsm0l3m4n Posted August 24, 2009 Share Posted August 24, 2009 The next autocross event has me worried. Apparently noise is going to be an issue, some people with really loud cars are choosing not to go due to this fact. The limit is 92 db at 50 ft. My car has an MSA 6:1 header, 2.25 exhaust with a turbo muffler. Its pretty loud inside but I have no reference of how loud is too loud (92 db). Also, anything I can do real quick to muffle it in the even it ends up being too loud? I've seen the exhaust silencers but dont know how/if those will work out with the muffler/exhaust tip. Can anyone help me out here? This is supposed to be a really good event, I dont want to miss it! Quote Link to comment Share on other sites More sharing options...
Six_Shooter Posted August 24, 2009 Share Posted August 24, 2009 Wow, only 92db? Not very loud, IIRC that quiter than an average vacuum cleaner at about 10 feet. If you do an internet search you can find charts that show relative sounds to decibel readings. You can also test how loud your car is with a hand held decibel meter, Radio Shack used to sell these, not extremly accurate, but close enough to let you know. Have someone stand at the side of the road, or in a parking lot, and drive past them about 50 feet away and see what the reading is. Obviously obey all safety and traffic laws when doing this. You could also call good local independant car audio shops, that should have an RTA/SPL meter and ask them to test your car, explain what you're doing and what you need, and they should be able to help you out, there will usually be a small charge for this as well. Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted August 24, 2009 Author Share Posted August 24, 2009 Well the wierd part is that the limit is always set at 92 db and everyone has been racing all summer with no troubles. I guess its this particular event location that causes problems for them. The extent they will actually enforce the 92 db is questionable at best. Just the fact that the really loud cars (formula Vee, race prepped mazda rotary, some other race prepped straight piped cars) are worried that makes me question myself. I did do some searching and found this table: http://www.gcaudio.com/resources/howtos/loudness.html I dont think my car is louder than a truck... and definitely quiter than a subway or power mower... but then again I dont really rev it up unless I'm autocrossing and my helmet kind of muffles the sounds. I know it will be close to the limit, I would like to find some way of quieting my exhaust down real quick in case someone starts complaining. Either way, I wish I found this out before this weekend. I work out of town all week so I dont have any opportunity to do any testing basically until race day next weekend. Quote Link to comment Share on other sites More sharing options...
Guest Rolling Parts Posted August 24, 2009 Share Posted August 24, 2009 That is odd. Will it be driving through city streets? Most auto-x I see are so far away from complainers(with cell phones) that it's never been an issue. Heck, noise at airports is a lot more than 92dB! Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted August 24, 2009 Author Share Posted August 24, 2009 It will be in a fairgrounds parking lot. I guess theres houses across the street or so which have complained in the past. As I mentioned I dont know to what extent they will actually enforce the 92 db since they've never enforced it at any previous locations. However, I would like to know for myself as well in case it ever becomes an issue for me. I might just buy one of the radio shack units, do the test a few times and then return it for a refund... Quote Link to comment Share on other sites More sharing options...
johnc Posted August 24, 2009 Share Posted August 24, 2009 You should be OK with a 2.25" exhaust and a turbo muffler. But just in case, buy a 90 degree 2.25" bend, flare one end to fit over your tailpipe, and clamp it in place with the open end pointing away from the sound meter and angled towards the ground. It will look like crap but will knock at least 2db off your reading. Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted August 25, 2009 Author Share Posted August 25, 2009 Thanks John. I will try to rig up something, if anything it will be useful for driving down my street at 6 am for the race and not piss off all my neighbors. The 12a rotary swapped datsun 1200 that runs here uses what looks like a cover over its exhaust with six small holes along the perimeter... This may be a fairly dumb question but would something like that work even better? Quote Link to comment Share on other sites More sharing options...
Six_Shooter Posted August 25, 2009 Share Posted August 25, 2009 Thanks John. I will try to rig up something, if anything it will be useful for driving down my street at 6 am for the race and not piss off all my neighbors. The 12a rotary swapped datsun 1200 that runs here uses what looks like a cover over its exhaust with six small holes along the perimeter... This may be a fairly dumb question but would something like that work even better? That sounds like a Supertrapp muffler. Looks like this: Quote Link to comment Share on other sites More sharing options...
MaTTSuN Posted August 25, 2009 Share Posted August 25, 2009 i just went throught the same thing with my autox last sunday, i cut a 3inch plate from sheet metal and drilled some holes in it i spot welded it inside the pipe there was allot less noise but i did loose some power when i got to the track there was some louder cars running with no prob so i drilled the welds out and ran my 3 inch setup Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted August 25, 2009 Author Share Posted August 25, 2009 That sounds like a Supertrapp muffler. Thats the exact one! I did not realize it was a whole muffler setup though... I think what I may do is buy some pipe that will fit over my exhaust tip and weld a sheet metal cover on the end with some holes drilled in it, flare the end and clamp it over my exhaust tip. Seems like that should do the trick and I ought to be able to get it finished in an hour or so.. plenty of time... Quote Link to comment Share on other sites More sharing options...
johnc Posted August 25, 2009 Share Posted August 25, 2009 You're putting way too much thought and effort into this. I've autocrossed many times in San Diego and they have a 91 db limit. The 90 degree bend pointed away from the sound meter should work fine for your setup. It worked for my 2.8L that had a 3" exhaust and a straight through Borla XR1 muffler. Took it from 94 db to 91 db. - that and a early upshift at the right time. Quote Link to comment Share on other sites More sharing options...
tube80z Posted August 25, 2009 Share Posted August 25, 2009 The only bit of caution I might add is that if you have tripples (or even SUs) sometimes the intake noise is greater than the exhaust. In that case an airbox will help. Cary Quote Link to comment Share on other sites More sharing options...
h4nsm0l3m4n Posted August 25, 2009 Author Share Posted August 25, 2009 You're putting way too much thought and effort into this. I've autocrossed many times in San Diego and they have a 91 db limit. The 90 degree bend pointed away from the sound meter should work fine for your setup. It worked for my 2.8L that had a 3" exhaust and a straight through Borla XR1 muffler. Took it from 94 db to 91 db. - that and a early upshift at the right time. Fair enough, I'll just try that Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted August 26, 2009 Share Posted August 26, 2009 Most cars would have a hard time being as obnoxious as a tracked out dorito. Quote Link to comment Share on other sites More sharing options...
74_5.0L_Z Posted August 29, 2009 Share Posted August 29, 2009 This is related I swear: I currently have dual flowmaster 2 chamber mufflers (2.5" in/out). I've been running them for about ten years. The car sounds good and is not overly loud, however with recent engine modifications I feel that the exhaust system is holding me back. The flowmasters are known to be restrictive and this pair was not very well installed. So, I am starting to upgrade the exhaust starting at the back. I am cutting the two crush bent 90 degree bends and the two Flowmaster mufflers off the car and replacing them with mandrel bent 90s and probably a pair of Borla XR-1 mufflers. The main use of this car is autocross, so I am concerned that the Borla XR-1 mufflers may be too loud. I know johnc has experience with these, so I am interested in his opinion. Here are the engine specs: 327 ford stroker 10.5:1 compression 348 rwhp (I expect more after the exhaust modification) I like the Borlas because they are light, compact, and free flowing, but will the Borlas be too loud? Quote Link to comment Share on other sites More sharing options...
johnc Posted August 29, 2009 Share Posted August 29, 2009 XR-1s can be loud and generally need something else to meet noise restrictions. Quote Link to comment Share on other sites More sharing options...
(goldfish) Posted August 29, 2009 Share Posted August 29, 2009 http://www.radioshack.com/product/index.jsp?productId=2103667 Quote Link to comment Share on other sites More sharing options...
74_5.0L_Z Posted August 29, 2009 Share Posted August 29, 2009 OK. So, if you were looking for the lightest, smallest, best flowing muffler that would satisfy scca noise restrictions, what would you use? Quote Link to comment Share on other sites More sharing options...
josh817 Posted September 14, 2009 Share Posted September 14, 2009 The only bit of caution I might add is that if you have tripples (or even SUs) sometimes the intake noise is greater than the exhaust. In that case an airbox will help. Cary This is true. When I drive without any filters, its deafening loud. Especially if you're poking around under the hood. The intake noise is ridiculous. I'm running a 3" pipe to a 1 chamber flow master 3" in/out and its fine when cruising below 3000RPM but once you get higher things get crazy. As with the induction noise, it goes as follows: -Over 3000RPM with anything other than full throttle is loud but not crazy -Over 3000RPM wide open throttle, stupid loud. Check out my videos to get a general idea. The camera tends to lower all of its settings when over run with noise. The only way to compare is if someone is talking or shouting, you only see their lips move : http://www.youtube.com/user/josh817 Quote Link to comment Share on other sites More sharing options...
majordanby Posted November 13, 2009 Share Posted November 13, 2009 I am researching a 2.5inch exhaust for my S130 and I found the BORLA 40348 ProXS Muffler 2.5". I want to try and use that because it has a single 2.5" into it and dual 2.5" out of it. My theory is that having dual outlets will allow the muffler to release exhaust gas at lower velocity than having single in/single out. I am hoping that lower velocity will be quieter with similar performance to the single in/single out. Quote Link to comment Share on other sites More sharing options...
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