You need to be under 92db from about 40 ft away at the exit of turn 5 just after getting back on the gas exiting the corner. The singles are making it with an airbox and the large Viper style silencer mounted across the back of the kart. According to Ian at Viper the bends are as critical as the silencer. My link pipe has a slight bend just inside the wing upright and then a 90 to go across the back of the kart.
I did some initial testing with the 100cc Yamaha stuff at a local sprint track. I used a Radio Shack db meter. I believe and can find out for sure but it was set to fast response “a” scale. NCK also did early track testing at Sonoma and Thunderhill. Those test results have been posted to our facebook page nckroadracing.
As we really have no twins on the west coast NCK is hoping some of the twin owners get together and do some testing in practice to see if 92db is possible. We believe that it is with the right equipment. CR125’s easily make it with a 14 to 17 inch silencer straight out the back and an airbox. With a little ingenuity a 250 twin should be able to comply. They run bike days there all the time at 90 to 92 db and the bikes find a way to make it. In our testing we shot for 90db to have a safety zone. First time we were there Laguna officials were extremely happy with our noise level. We only had one or 2 violations. One of which was a Yamaha guy who did absolutely nothing to try to quiet his kart.
The only things that really don’t have much chance of hitting the 92db are the aircooled 100cc reed motors like a reedjet.
We would love to see some of those blistering fast f125’s show up too.
If anyone needs additional info or wants to discuss it further send me a message and I will try to answer your questions or point you to someone who can.