[blazerman]

Does anybody know the correct way to check sound desibles? I have acsses to a desible meter at work and I would like to check all of our machines before we go to the local race next week.

 

[Bronson90]

Society of Automotive Engineers J-1287 test standard. The test is performed with a sound meter on the "A" scale measured 20 inches from the exhaust, with the engine running at a designated rpm. For example, a 450cc quad tested at 3,750 rpm.

1.7 Sound Requirements

a. Motocross ATVs must meet sound limits of 99 dB/a measured on the
"A" scale at 20 inches (500mm). Test procedure prescribed by the
AMA, is in accordance with SAEJ1287, with the following clarifications:
1. Test RPM will be determined by 306,000 divided by the stroke.
2. For enforcement the dB/a limits are absolute. Variations due to
changes in test conditions and instruments have been considered.
b. Post race testing can be done at the request of the Race Manager,
with the AMA Technical Inspector carrying out the test. The motorcycle
must meet sound limits of 101 dB/a measured on the "A" scale at 20
inches (500mm).

1.8 Sound Test Procedures

D3 Measuring the Sound

D3.1 Make sure the engine is warmed up and the transmission is in
neutral.

D3.2 Have the rider sit on the ATV with both feet on the ground, so that
the vehicle is vertical and stationary.

D3.3 Hold the sound meter:
a. At a 45-degree angle to the exhaust centerline (the normal
line of travel)
b. Parallel to the ground, at the same height as the exhaust outlet
c. 20 inches (0.5 meter) to the rear of the exhaust outlet
0.5m
0.5m
Determine the test RPM for the make, model and year of the
ATV about to be tested. The appropriate test speed for both
four-stroke and two-stroke high-performance competition
ATVs is determined from the Equation below.
Test Speed measured in RPM = 306,000 divided by the stroke
in millimeters

D3.4 Attach an electric tachometer or set the vibrating reed tachometer
to the test RPM
a. Have the rider or assistant read the meter of the electric
tachometer, or have the rider or assistant hold the vibrating reed
tachometer against any solid part of the vehicle
b. Have the vehicle operator slowly increase the engine speed to the
test RPM.
c. Have the vehicle operator or assistant signal when the correct
RPM is held (e.g., by tapping his foot).
d. Read the sound level meter when the correct RPM is held.

 

[blazerman]

Thanks for the info.
A couple of us are going to run the beginner class of the WORCS race when it comes to town next weekend, just want to make sure we can all pass tec inspection before we get there.