shiners780

I did a search, but couldn't find data on exhaust decibel levels. I just installed a LR 3" straight through exhaust (no cat and no muffler) on my 1988 944 Turbo. This is a track-only car. My concern is if I will be exceeding the acceptable decibel levels at certain tracks, usually stated as being 86-94 db maximum. My questions are:
1. Has anyone used a sound meter to determine db levels on a comparable car with a LR straight through?
2. Where would I find a sound meter to measure my specific cars' sound level?
3. How far away do the tracks measure the sound from? I would assume at the side of the track, maybe 40-50 feet away?
4. Assuming I'm too loud, what would be the best way to "muffle" the sound to bring it down to an acceptable level without creating too much restriction?
Thanks!!! I'm hitting a track next week with a 94 db level restriction and I'm concerned.

jerome951

Each track has different methods when measuring sound (i.e. which portion of the track and how far back from the track surface). This is typically determined when the track is being built and through negotiations with neighboring communities. Typically they will measure sound either just inside the track wall or at the edge of the track's property (so wind direction can play a role).

My guess is you will have little trouble passing the sound check. The turbo really quites the sound.

You can do a couple of simple things.

If they test you and you are over the limit, don't go WOT at that point of the track (may be frustrating).

Also, you can buy a piece of bent exhaust pipe (e.g. 70-90 degrees) to put over the end of the exhaust outlet and turn it away from where they are measuring.

I know one guy w/ a (loud) 911 who had to go out and buy sink drain strainers and attached them to his exhaust outlets. Looked funny but it was just enough to pass.

Let me know how it turns out as I'm planning to install the same exhaust system over the winter.

shiners780

Jerome951:
Someone else told me also that the turbo tones down the sound enought that I won't have problems, however I would still appreciate to know if anyone has definitive db levels.
As far as not going WOT at the check point, wouldn't they move the check point knowing (and they will be able to hear) that you're lifting in front of them? I guess I'm paranoid that way.
The bent piece of pipe is a good idea, maybe I'll take one just in case so as to be prepared.
I'll post after the event whether or not I got busted.
Anyone else with db numbers???

MPD47

Hey another Rochester member! I've got the LR 3 inch with a Vitesse Stage III setup, and it's LOUD. I'm pretty sure it's over 94db though I couldnt tell you exactly how much. We're going to measure it sometime this month before I put the muffler on. I'd recommened the Borla XR-1 it's straight through, so it shouldnt restrict much, but helps muffle the sound a small amount.

RKD in OKC

The LR 3 inch exhaust with the Magnaflow muffler measures 93 db from 10 ft directly behind the car at 4000 rpm WOT.

RKD in OKC

Oh yeah,

My car with the 4 inch LR exhaust measures only 94 db with the 4 inch version of the Magnaflow muffler. The Magnaflow muffler is the round straight through type with the holes around the inside with sound deadening filler. I can't imagine it costs very much HP. My 928 GT only lost 3 hp wide open, no cats, and factory straight thru muffler vs the same setup with no muffler.

shiners780

Thanks guys! I would like to NOT install a muffler of any kind if I can avoid it. Truth be told, I like the noise! While on the track with the stock exhaust, the wind was loud enough that I couldn't hear the exhaust/engine at all. I like to be able to hear the exhaust so I know what the engine is doing, rather than relying only on the dash gauges. You can tell a lot from the exhaust sound, and the LR 3" straight through definitely puts out sound.

MPD47: Where are you getting your exhaust sound test done at? I was thinking maybe a car audio shop might have a db meter? They have "sound off" contests with the ricer crowd and must have some way to measure the volume.

RKD: That's good news...93 db from 10 feet behind the car probably equates to less than 85 db from track side.

Anyone else with measured db results from track side?

MPD47

Shiner, I *think* Stereo Shop in Henrietta has one, but I'm not sure. I know a friend of mine has one, so we're just gonna use that, as we know it's accurate to about 115db.

eastendr

We have noise restrictions at UK circuits too !

If you look at the results table on my website HERE you will see a load of typical 944 exhaust noise figures taken at a recent shoot out dyno day.

Both idle and 2/3 red line rpm (4,000 RPM) are taken with my noise meter placed 1 metre away from the exhaust tip at an angle of 45 degrees horizontal. We use Din 'A' weighting to the figures.

HTH

Rick.

shiners780

Well this was much worry about nothing. I never did get a db reading on my exhaust, however I had no problems at Tremblant due to excessive noise. In fact, once you get your car out on the track, it's amazing how much more quiet it seems than it does in the garage! Many louder cars there, all with no black flags. Thanks to everyone who replied.

Mike Buck

Yes, that 355 Challenge car at Tremblant was very very loud. No way was he even close to 94dB.

I didn't even risk it myself. Had my straightpipe with me, but left the muffler bolted up instead.

Which turbo was yours?

Jake951

You can buy a relatively inexpensive sound level meter from Radio Shack. Here's the link . It's not exactly a laboratory-grade instrument, but it isn't bad either. A lot of audiophiles (including me) use them.

Mike K.

Don't get all excited because you didn't get black flagged. Vince ( track manager) never showed up once with his meter. Alex in the 355 knows the rules and is well prepared to fix his exhaust should he get warned.
Vince will usually stand in the tower and check the noisier cars and warn the organizers who the problem cases are. They are given a second chance but, should they fail again they are told not to run anymore.
I believe he is a lot more tolerant during the week but, that is just my opinion.
Were we running in the same group? I was in the blacks, yellow gt3.

shiners780

I was in the dark blue 951 with the yellow splitter #392, I ran in the blue run group (first time at MT). Had the most incredible time on that road trip!!! Definitely signing up again next year!