I had the opportunity to run my Renesis yesterday without any exhaust - It was loud but not nearly as loud as I had been expecting!  I ran it to 3200 rpm with my 88 inch pitch* 76 inch prop.   I will install the manifold and run it again.  Than I will add the muffler.  My wife commented that with the muffler it sounds like a regular car exhaust!   I do believe the side port exhaust is much quieter than the normal 13 B radial exhaust.

Dennis H.