Re: Chris Craft log style wet exhaust conversion to center riser wet exhaust.
I will take a stab at this. I have a 307 225HP OMC Stringer in a 1972 Slickcraft SS215. I have the OMC manual for that year. It may be a bit different but has the log style exhaust so I assume the workings are similar even if the parts are in a different spot.
I don't believe I have a valve like doodad behind the distributor.
I have something that must be similar on top of the thermostat housing.
The manual describes the theory of operation and says: ( I will summarize rather than quote exactly to shorten this description.)
Water is picked up through the lower unit and carried from the impeller housing through passages in the vertical drive and through both end caps to the intermediate housing.
From the intermediate housing water is carried through two hoses on each side of the engine directly to the uppermost nipples of the upper thermostat housing and then carried downward through the lower thermostat housing where it enteres the flexible hose which attaches to the inlet pipe of the water pump on the engine. The water pump causes the water to be pushed into the cylinder block.
Water goes through the cylinder blcok rearward and then forced upward into the head. It then flows forward through the head. At the forward end of the head, the water flows into the lower thermostat housing. If it is sufficiently warmed up, the thermostat will be open and some of the water will be pumped upward past the thermostat into the upper thermostat housing and the rest will be returned to the water pump. The water that was pumped upward past the thermostat will enter the hoses connected to the lower nipples of the upper thermostat housing. The starboard hose runs directly to the manifold high rise elbow in order to cool the upper portion of the casting. The port hose connects to the manifold end cap nipple. Water flows rearward through the manifold into the high rise elbow and is mixed with exhaust gases prior to entering the exhaust hose. Then it goes through the adapter housing, the intermediate housing and vertical drive and out under water.
If the engine has not warmed up sufficiently, then the thermostat will be closed and the water will be diverted back to the water pump for recirculation through the block. The impeller continues to pump water but the water does not go through the block. It is necessary to provide a method of discharge and it is provided by a metered orifice. If the orifice were not present, the pressure would overcome the thermostat and it would take much longer to warm up the engine.
Now that description appears to be in regard to the inline engines.
The manual also has a flow diagram for the 225HP V8 engine and it is shows flow as follows:
Water is pulled in by the pump in the lower unit and pushed up through the vertical unit and through into the intermediate housing in a similar manner.
Then, it appears that water if fed into the rear of the log manifold and flows forward and into the upper thermostat housing. It then goes to the engine pump and through the block and the heads as noted before. Water then comes back up through the thermostat if it is warmed up enough to open the thermostat, and then flows from the upper thermostat housing back to the front of the log style exhaust manifold and through it the rear where it then mixes with the exhaust and continues on out.
If the water is not warm enough to cause the thermostat to open, then the new incoming water bypasses the engine and continues out through the exhaust as it would if it had first been through the engine.
The metered orifice referred to earlier is in the upper thermostat housing.
Don't know if that helps. Hope so.
Randy
