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The accompanying table of sound readings was taken at Thunderhill Park
on October 26th, 2002 and is ABSOLUTELY MEANINGLESS.
There are several reasons for saying that the readings are meaningless.
Unfortunately, we placed the meter where people were lifting for Turn 1,
so we didn't get a reading at an appropriate power level. The meter
was a hand held unit so readings taken can not be referenced precisely
to location used by height, set back from the track, any tilt and position
on the track for repeatibility. Each track is a very unique situation
in terms of sound. Laguna Seca, for instance, is very difficult because
sound is measured in a canyon with reflections coming back at the meter
from the banks on driver's left. Any given car will read quite different
at each track.
So far, Thunderhill Park is only using the handheld meter to verify
very loud cars and the lack of any muffling device at all (they define
over 103 dBA on their meter as very loud). They understand that this
measurement is neither precise nor repeatable, but quite subjective.
They have been asked by the county to institute a noise
control program with no further guidance or requirements. They
are attempting to comply. Infineon Raceway (Sears Point) is getting
the same program. SCCA has been setting up a sound meter at Sears
as part of their program for a while now. Sears is installing a fixed
sound meter, similiar to Laguna's program, inside Turn 1at the far North
end of the grandstand. We expect that Sonoma will insist that they
start a program next year that is 103 dBA for us.
The useful message and information here is that we will have to use mufflers at ALL TRACKS next year. The readings from Thunderhill show that 103dBA is pretty straightforward to meet. If we are held to other levels or other scales than the "A" weighting, this may change. Many of us were startled that the number 99 white Neon with a really nasty rasp, read only 99dBA. Our suspicion is that while the car sounded painfully loud to us, the weighted reading ignored a bunch of the sound energy in the higher frequencies because these don't carry over distances as the lower pitches do.
Mufflers are needed, now. Mufflers are also becoming standard
in most race venues which has prompted the development of many new low
restriction mufflers capable of handling high horsepower race engines found
in Sprint Cars, for instance. It doesn't take much to get below 103dBA
and if done correctly, you may even gain power. Circle Track magazine is
a great reference for this kind of issue. See their April 2002 issue,
for instance.
| ThunderHill Sound Readings 10/27/2002 | ||||||||||||||
| Car Type | Purpose | Motor | Fuel | Comp | Cam | Induction | HP | Headers | Pipe | X-Pipe | Exit | Muffler #1 | Muffler #2 | Reading |
| Merc Cyclone | Track | 347.00 | 110 | 12.5 | Crane | Carb | 3" | 3" | Dr. Gas | Dump | 6" Dyno Max | 99 dBA | ||
| Mustang | Combo | 302.00 | 92 | 10 | Injected | 2" | 2.5" | Dr. Gas | Side | 12 x 2.5 | 12 x 2.5 | 90dBA | ||
| Mustang | Track | 351C | 110 | 12.5 | Crane mech | Carb | 2.5" | 2.5" | H-Pipe | dump | Flow 2 ch | 85 dBA | ||
| Cobra | Combo | 351.00 | 110 | 9.25 | small roller | 1 plane carb | 530 CHP | 2" | 3" | Side | 10d Super trap | 85 dBA | ||
| Mustang | street | 4.60 | 92 | 9.75 | Injected | 2" | 2.5" | H-Pipe | rear | stock | Stock | 84 dBA | ||
| Neon | Track | 2.00 | 97 | 9.5 | stock | Inj Blk Dog | 2.5" | N/A | rear | 30" Bullet | 99 dBA | |||
| Mustang | Track | 5.00 | 110 | 11 | Vic Jr | 320 | 2" | 3" | Griggs | R-side | Griggs | 96 dBA | ||
| 68 Mustang | Street | 289.00 | 92 | stock | Carb | 2" stock | 2" | none | rear | 27" glass pack | 82 dBA | |||
| Cobra | Track | 427.00 | 110 | Carb | 500CHP | Side | 94 dBA | |||||||
| NASCAR | Track | 351.00 | 110 | 99 dBA | ||||||||||