Update: we ran a 10.01 Wednesday night 1.382 60 ft times with a full tank of gas and a significant head wind, through the mufflers. We were at 10.16 best the last couple trips to the track and I installed a 1 inch blend spacer.The spacer is the only thing I changed. On the first pass which is almost always the slowest it ran a 10.06. That is a tens better than is has ever run with no muffler on a Cool morning. It sure seems to like that spacer. I removed a 3/8 four hole, so maybe it didn’t like that one.