Hi Barry, The problem with a non-damped gauge is that the gauge's own inertia will cause it to over swing, and amplify the pressure changes beyond their true extent. I wouldn't pay too much heed to it - all it is telling you is that there are dynamic pressure changes, you cannot use such a gauge to infer anything about their magnitude. As far as I can tell, we have good reason to think that if the IP relief valve is removed, and the system works at no pressure, then the engine will run poorly. However, I havent seen anything that suggests any measurable difference in operation between running at, say, 15psi and running at 20psi.