C_Spray

Bob: I'm fine. This is a theoretical discussion for a friend. We're still at Tomes.

Flow readings would be from the dyno, indicating that the boat's not the issue. Strainers would be Gils.

mcollinstn

Flow numbers aside, my gut reaction is that:

* if the block temps (at the thermostat, assuming that water flow is in the normal "in at the circ pump and out at the stat housing" direction) are within spec (less than 190)...

* and you are introducing exit water from the H/E to the BOTTOM of the manifolds...

then you should not be damaging manifolds unless one side is getting all the flow, leaving the other side dry.

I'm all into specs and math, but you are telling us that the setup (both setups actually) is containing block temps well and is not showing heat saturation. The exit water from the H/E is not going to be any warmer than the exit coolant from the block. Can't be. Defies physical laws.

If you're feeding manifolds with 190 degree water at half of 30gpm (which it won't be that hot cause it cannot exceed or even match the block coolant temp) then even if it boils in the exhaust mans, the heat energy required to trigger the phase change will be removed from the manifold and should keep it "safe". Where there is a problem, though, is that I don't honestly think you CAN flow 15 GPM from the bottom of most manifolds. I don't think it will flow that much volume. You can dump a pretty healthy chunk into the tailpipes, but I don't think you can get that much thru the bottom of a manifold. Enough pressure, though, and you can do about anything. 30psi is a pretty good amount of pressure.

NOW, I've seen applications that integrate the bottom half of the manifolds into the closed (antifreeze) loop which dumps the heat back into the H/E. This requires more of the H/E, but ensures that you CAN't have a heat failure of the manifold without seeing it coming from a long way out via the temp gauge.

Keep us posted. This is interesting.

C_Spray

That's one part of the equation that makes a whole lot of sense. Say the right side has a sharp (forged) 1" hose barb x 3/4"NPT 90 degree fitting leading into it while the left manifold has a straight fitting (same sizes). As the water flow rate goes up, the effective restriction of the 90 degree fitting would just get worse and worse, wouldn't it? In other words, at idle (say 15 gallons/minute), the flow rate out of the two tailpipes might not be much different, but at higher rpm, the right manifold might not see nearly as much water flow, would it?

rmbuilder

Chuck,
The resistance @ the 90* would increase as both flow and pressure increased not to mention the interference due to the return pressure pulse of the coolant striking the outside radius at that angle.
The pressure/velocity differences in the inner/outer radii could aerate the coolant thereby reducing its thermal conductivity from that point.
Bob

C_Spray

Ok - That pretty much explains my theoretical issues. RMBuilder - What was your source for the quotes in post #8.

Thanks!