When I talked to someone at DA they said that JTEC did their own testing and Slimline was the muffler tested by DA. I was also told that the Slimline gives slightly better RPM. Whose info is correct? I don't know...;. I am using the Slimline and getting 6750 RPM on a PT 26x10 prop. My impression is that there is still quite a bit more vibration as compared to my 3W-106 twin on another airplane. Seems about similar to the DA-50 vibration on a smaller airplane.