Sound DB levels (race track BAN)

[Stentor]

I believe that Tom from Tom's Motorsports in Las Vegas fabricates pipes for track use (not too restrictive, but keep the noise below required levels).

http://www.tomsmotorsportsinc.com/About%20Us.html

[bobcowan]

This is becoming more and more of an issue. The tracks I use are in the middle of nowhere, without a house to be seen for miles. So we don't really have sound limit here.

But other areas it's a real problem. 600hp running through a single side pipe can be darned noisy. dB radings taken in the cockpit are not that reliable, because it's influenced by noise from wind, tires, transmission, diff, etc. The sound reading need to be taken from the side of the road/track.

The spiral/auger core mufflers Wayne mentioned are from LoBack. They are custom made to whatever length you want. You can get 30" mufflers to fit. Uless you have a Classic Roadsters, then you could probably fit a 34-36" muffler.

The other company to look at is Classic Chambered Exhaust, built by Iron Man. It's essentially a glass pack. I recently installed his 28"x3" muffler. The mufflers I replaced were shorter smaller glass packs from FFR. I also angled the opening 45* towards the ground. I did a write up on the installation.

I'm quite pleased with the results. It is definatly quieter than it used to be. And the sound is softer, more mellow. I hear mechanical sounds now I didn't hear before. It doesn't assault the ears like it used to. I'm going to the track in a few weeks, and we'll see how they sound at speed.

That may help. I saw a picture of a simple exhaust mod that someone did to get them below spec. It was a simple alum sheet mounted about 6" in front of the opening. The exhaust soiund hit the sheet of alum, and broke up (I guess). Anyway, it worked for him. That would be easy to do, and easily removable.

[computerworks]

Originally Posted by badrich

I plan on running the autocross at Sears Point for SAAC 35, but will be real hurt if I get black flagged. I *might* consider the track, but am afraid my beast is faster than I am. We'll see. Rich

Rich...it looks like Autocross will not be on the SAAC-35 schedule, so start thinking about the Track.

The full schedule and agenda for SAAC-35 should be released by this weekend.

[computerworks]

Ernie..

Infineon (Sears Point) (SAAC-35) has a 103db limit on weekends, with special exceptions for certain big events.

It looks like SAAC is planning 3 open track days (Fr-Sa-Su)... Friday is NOT a weekend day, so you will be permitted to run unmuffled on that day.

There is a strong possibility that we will get a waiver for Saturday as well...so keep that in mind when it comes time to register for an OT slot.

[Excaliber]

With no sound limit, I'll uncork the headers and be a serious hooligan!! Ye Haw.

My game plan is to continue to pursue "legal" sidepipes, regardless of track specifications.

I just changed my reservation to arrive Thursday so I can play on Friday!

[Don]

I inquired with Lime Rock Park on their max db level, but do not know how or where within the Park the measurement is taken:

" The normal day to day db level is 83. However, we do have what we call "Test & Tune" days in which there is no db level restriction. Those days are: 4/13, 5/11, 6/15, and 9/28 "

Sounds louder when sitting in either the infield or outfield. For those that have not been to Lime Rock, it is in a very rural area, adjacent to small towns and in a valley, no grandstands, a large portion of the viewing on both the infield and outfield is on the sloping land looking down on the straight and the first 3 corners. Paul Newman drove the Datsun 280ZX & 300 ZX at this track for Bob Sharp, he lived in southwest CT.

This summer the NASCAR Modified race cars ( open wheel ) will have their first race at Lime Rock, running clockwise. The 5/11 " Test & Tune" day mentioned above will include the Modified cars for tire testing etc

http://www.limerock.com/

[badrich]

Regarding SAC-35, I'm all for track time for those who are interested, but am disappointed to hear of the lack of an autocross. Autocrossing is a great way for virtually *all* Cobra drivers to take their machines out and learn how to drive them spiritedly without the downside of losing it in a turn on the street or the track. And it can be *very* exciting and competitive. Please don't tell me they won't let us run the quarter mile either. Rich

[computerworks]

Originally Posted by badrich

Please don't tell me they won't let us run the quarter mile either. Rich

Drags are a big part of the event on Friday.

[Cobra #3170]

Ron,

Thanks for the tip on exhaust, I'll just leave my stainless specialties mufflers on and run as is on Friday. I also agree with badrich, an Autox is a good way to get the cobwebs out without hurting the car. It would undoubtedly improve on track safety for those who participate in both.

Originally Posted by computerworks

Ernie..

Infineon (Sears Point) (SAAC-35) has a 103db limit on weekends, with special exceptions for certain big events.

It looks like SAAC is planning 3 open track days (Fr-Sa-Su)... Friday is NOT a weekend day, so you will be permitted to run unmuffled on that day.

There is a strong possibility that we will get a waiver for Saturday as well...so keep that in mind when it comes time to register for an OT slot.

[RodKnock]

Gosh, I hope they don't have any sound limits as I roll into my parking spot.

[Rare Iron]

Actually, LOTS of race tracks all over (including drag strips) now have sound restrictions. Personally, I think this is 100% ridiculous since almost all of these tracks were there before any residential building began around them, so I agree with the "airport" scenario completely. Don't like the noise? Don't buy a home there!

Making something really quiet means killing the exhaust flow. You can take a nice chunk of dBA's off without losing HP by using a muffler that absorbs the sound. If you stick something in the flowpath of a Cobra sidepipe exhaust, you are really going to lose a lot of flow. Making a 600 HP motor lose 15 dBA is no easy trick. If you do it, you'll lose a LOT of HP.

[Excaliber]

My original motor showed a loss of 96 horse power with the side pipes installed.

That was a 7,000 rpm engine with high riser heads and a solid roller cam. I would guess the loss is considerably less with lower rpm and a milder cam, but still, it's a bunch to be sure!

Kind of makes me wonder about these BIG horse power dyno numbers. Flywheel horse? With or without side pipes? At what DB are these side pipes? And what good is the h.p. if you can't get on a race track????

[twin turbo]

With turbos and loback mufflers I was warned I was too loud at 92 decibels for late night drag racing. The limit was 90 decibels. My car is pretty darn quiet http://www.youtube.com/watch?v=VjhVbsb_f-U. Cheers.

[badrich]

This weekend I'll be getting three pulls on a chassis dyno, along with a bunch of Corvettes and one other Cobra. When my engine was first built at Shelby, it registered 558 HP at the flywheel. When it was rebuilt, a few trick things were done, including replacing a conventional juice lifter cam with a hydraulic roller model with more modern top end components. It runs smoother and pulls better all the way to beyond 6000 RPM. No need to go over that for street/autocross use. I'll be curious what the chassis dyno says on Saturday. I hope no Chebbies get *much* more than me. Rich

[jmortensen]

Bumping this thread to prove that I searched...

I have a carbed LS 5.3 with side pipes. Headers into merge collector into my own muffler. I tried to ape the Burns Stainless racing muffler with the two pieces of angle iron in the flow path. welded two piece of stainless angle at 90 degrees to each other at 1/3 and 2/3 of the length of my 18 inch muffler. Went past the SCCA sound meter at 102 dB.

Looking to do something that will get me under the 96 dB limit the first time. I was smart enough to put V-band clamps on each end of the muffler when I put them together, so I can add another muffler (spiral tech? supertrapp tip?) or I can just take these off and put different mufflers on and see where that gets me (classic chambered?, spiral tech, arizona exhaust?).

Just looking for people experienced with side pipes. FWIW, the car is not a Cobra, but I think the same sort of thinking applies; small, lightweight car with a lot of hp.

Any help appreciated.

[Tommy]

This may not be the best suggestion you get, but here goes. If you know which side of the track the microphone is on, direct both exhausts out the other side. That means a rework of the exhaust system, possibly more weight, and maybe changing it from track to track. I don't know of another solution to reduce sound levels without inhibiting engine performance. .... Maybe you could rotate the end piece on the sidepipe nearest the microphone to direct the exhaust more under the car than outward. But keep the gases out of the cockpit.

[Don]

An alternative, not knowing whether the dB reduction will be achieved. Harley Davidson has baffles for their exhaust systems which can be modified and installed after the muffler, into the exhaust extension/turn out.

[xlr8tr]

wonder if you had an exhaust cutout in the tailpipe turnout section that re-directed the exhaust exit UNDER the car. Just a shorty that points under the car. Maybe with a diffuser to spread the noise more under the car.