Mercury marine makes a valve that has a 1" bypass line that when pressure gets to 25psi it starts bypassing water to keep pressure from going higher. This goes before the water pump. The value is not cheap, looks cheap but is high dollar but worth it compared to the other options. If you do a search on here you will find the part number.

The reason for the bleed off the back of the intake is to keep from getting steam pockets.

The same smart gentleman that came up with the Drive Guardian ( My buddy Mike) recently received a Patent on another great idea. Self adjusting water pickup for perfect pressure. I`m exited about that one
Stay tuned
http://www.marinedesigncorp.com/water-pick-up.html

He`s also got some other cool stuff in the works like a add on to make a crash box shiftable..


I control my pressure before the motor with a blow off valve on my bellhousing cooler.

thank you for all the reponses, i have stellings big tube exhaust with brodix hvh intake. i have seen engines with the 4AN lines bleeding off the rear as i have and then an 8an line coming out one of the front bungs of the intake to a threw hull with a ball valve to control flow as well. is that a common system that wont starve exhaust of water. my cross over has the bypass while i run a 5/8 restrictor.

We want to keep our transom pickup in clean water so we r about as high as we can go. It definitely pulls in the water much more than bravo style pickups. Think we will plump an 8an line off the front of the intake and draw pressure from their .

Id like to find a way to slow the flow thru the motor to build some heat yet have full flow to the manifolds . Trying to figure that out with a no provisions in the intake for a stat and a cross over

Dan what intake do you run?

BDS .. I hear you have some experience in this area ...



From sea pump to cross over out the intake into headers



I switched out -16 line from intake to headers to -10 to see if I could slow it down a bit and restricted the rear intake drain to 1/8 .. helped a little but I dont want to restrict too much water to GEN 3 manifolds.


I thought about running a second line from top of bellhousing cooler (where the blow off is) to bottom of manifold (Gen 3 have 2 water inlets ) to keep the manifolds happy

Ya Dan thats a ruff one. I have never been a fan of those style intakes for pleasure boat applications. Restricting water coming out of the intake will have two bad effects, raising block pressure & restricting water to the exhaust manifolds. I really wish I could be of more help on this one.