I'll do the test. I've wrote to WB customer service and that's what I recived: "The way we found this exhaust works best on this bike is 11 discs and the spark arrestor installed on the bike. You can take some of the discs off to quiet it down I wouldn't suggest going below 7 but, make sure the spark arrestor is installed. If you don't run the S/A then the bike will perform more like a stock bike. If you decide not to run the S/A then don't run any of the discs they have not function with out the S/A" I've send question about washers now so I'm waiting for reply and then we will now everything.