After years of racing everything from 1920's Bentleys to late 90's F1 cars meeting sound limits is a tricky problem.
The biggest thing is to know WHERE they are measuring the sound? Which side of the track are they on? You can lower your "measured dB" by making sure the microphone can't SEE the end of the exhaust pipe. If the Mic is on the right side of the track run the pipe out the left side etc. Side exit exhausts are the hardest to get within limits. If you run it out the back you can put a tip on it that you can aim to the left or right depending on the track and where the sound control station is located. This alone can cut 2-4db off the top. There are a lot of good mufflers out there now that do a good job of sound control without making a big dent in your HP. There is also the change in sound pressure levels depending on weather so the fact you were at 102 dB one day does not mean you won't be over the 103 dB limit the next day.
Also know that it isn't just EXHAUST noise you need to pay attention to. If you are running an air box on the intake and have it ducted to the front of the car the intake noise can sometimes be 98+ dB the sound control people don't care where the sound is coming from just that you are too loud. A few years ago, at Laguna Seca the B Sedan group was running and there were a number of Alfas that were getting busted for noise (I think they needed to be under 100db that day) and they kept working on the exhaust systems and could not get under the limit. One of them finally took the hose off the airbox that was running to the headlight bucket and suddenly they were legal.
Sometimes you just need to DRIVE the car differently as well. Once you know where sound control is located you may just have to "pedal it" as you go by. I raced a big block Corvette with side pipes at Laguna Seca once when there was a 103db limit. The 427 Cobra that I was racing was also running side pipes. We both had as much muffler on the cars as we could fit, with shields, tips turned down etc. The sound control shed is on the hill between Turns 5 and 6 before the bridge. It is on the Right side of the track about 70' feet from the edge of the track. Mac and I would come out of turn 5, short shift to 3rd gear, dive to the left side of the track and go to 1/2 throttle until we went under the bridge and out of range. They kept telling us we were "getting close" at 101.5-102 db all weekend. On the last lap of the last race of the weekend we both lit up the tires coming out of 5 and laid 4 black tire marks all the way up the right side of the track to the bridge. If we had not gotten the checkered flag that lap we would have been BLACK FLAGGED for noise!
My recommendation is run the exhaust all the way to the back of the car, Fit in as much muffler as you can fit. Design it with an adjustable tip that you can AIM away from the Sound Nazi. Be prepared to modify your cold air box if needed. Also be prepared to "pedal it" if you have to.