Great ideaI know Its not Laguna Seca but we have a 90 db limit down here and it is possible!! Have a 3" custom exhaust with a pair of dynaflow glass packs right after the headers, then another longer set after the Xpipe. flowed that up with a H pipe just to make sure, and At the end, there is a Dynomax Ultraflow muffler... We ended up a fraction over 90DB (90.4). Adding some turn downs to kill the 0.4 Db. Or might just wrap the muffler.
Its a ported and modified Gen1 with 468rwhp so its a noisy beast. On a gen3 with out headers and a big exhaust, should be much easier.
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When I ran my SCCA Corvette at Laguna Seca making 90 db was very difficult because the often low cloud cover amplified the sound and turn 5 is where you get back into power to get up the hill. . I ran Flow Master mufflers to which I added Supertrap mufflers. I also added plate on the passenger side of each exhaust to aim sound away from booth turn 5. Even with this set up there were time I could not make 90 db.Is 90 db even possible with a gen 3 stock motor at Laguna Seca.