What is an exhaust burp? are you talking about the "BUM-BUM-BUM",coming down a steep grade,in "granny"-gear?? My 261's done it since the day I first laid eyes on it ,25 years ago. Sounds even better with the headers and dual stacks. All of the old farm tractors that I've been around,have done the same thing,while in low-gear,decending a steep grade. Even more so,when loaded. All of the old busses had the same decelleration burps,as well. It doesn't matter what the make is,either. All gasoline engines do it,even the 2-lung "Johnny-Poppers". I always hear it coming from the tail-pipe(s),not from the manifold area.
