ok i have a set of hardin marine water jacket type headers. the heades are a casted water jacket type. i know i got from my pump to the water jacket to fill them with water so that it can be preheated  before entering the block. the water then extis the water jacket and enters the engine. Should it enter at the top of the motor at the thermostat or enter in the water pump ports on the front of the motor.

after the water leaves the engine it is routed to the exhaust to exit the boat. Now on the stock hardin marine exhaust there is an intermediate pipe that connects the header to the transom. This pipe also has a water jacket on it. My question is can i just replace that with regular stanless tubing? if the water is just getting dumped out the back of the boat anyway why would i need a water jacket back there.

I was just going to create new intermediate pipes and weld a bung in there for the exit water. but was not sure if this was ok or not. i cant imagine what it could hurt by doing it this way. i just wanted to see what you guys thought.

Here's a diagram I found.

thanks guys.

ok here is where i am a little confused. if you follow the red line back to where it dumps at the snails. On my new exhaust set up i am going to run 4 inch stainless and i was going to weld a bung in there for the water to enter the exhaust pipes and leave the boat. is this going to work just fine?

4 inch?   Why the heck so big?