I once had a GP SlowPoke with a K&B .28 (with muffler) on it. I knew it was quiet but didn't really appreciate how quiet until one day at the field when several guys were out with their large gassies and the noise level was fairly high. My habit on days like that was to take off and climb to get above them then throttle back and orbit at about half throttle until they either ran out of gas or landed from fatigue in looking up. Once they were all down it suddenly got very quiet. With almost a full tank I would then enjoy a clear sky and do my thing. One day while I was the last plane up a guy walked over and asked me if my plane was an electric. I answered him by bringing it down and into a low fly by so he could hear that .28 at full bore...still quiet. Often to see if it was still running I would put it into a climb. If it went up it was still running. Those mufflers were very effective. I hope the new K&Bs are as quiet.