So I've been thinking about the feedback I got from my earlier post about head gasket choice and unregulated water pressure in raw-water cooled jet boats. I teach high school engineering and immediately thought of Pascal's Principle, which states that the pressure in a fluid is the same throughout. So, a "gate" or "ball valve" would have no effect on regulating the pressure in a raw water cooled engine. These would affect the rate of flow (volume) but not the pressure. A water pressure regulator (like the one in your house) that typically has a spring in it is needed to affect pressure. It was pointed out that water pressure may exceed 100 psi. My boat engine's oil pressure is frequently between 60-80 PSI. I completed the head swap on my 350 Vortec and did a compression check. Cylinder pressures are 200-206 PSI for all. Out of curiosity I Googled maximum pressure in a combustion engine. It turns out that this is roughly 100 times the compression ratio or 4 times the compression test number. That puts my Vortec firing pressure at 800-900 PSI. Other engines running turbos or diesels may be approaching 1,500-2,500 PSI. With MLS gaskets all passageways have steel around them similar to the combustion chamber. The soft 5/8" rubber heater hoses handle the pressure of the raw water cooling without blowing off or bursting. All this has me thinking that the raw water pressure is not a big deal for an engine that among other things sees 800+ PSI pulsing thousands of times a minute. Opinions?