Seems like welding a big arse fender washer on the bottom side of the lid, at the opening, and choking each stack by AT LEAST 50% would do the trick and still look cool. making your own butterfly-valve type dampeners would be cool too maybe do both. Id say if you can come close to the area of a weber exhaust, you'd be in the ball park. Anyway's that 's what worked for me
"Assumption is the Mother of all F___ups!"