water pressure draw off location
 

I have two -4an lines off the back of my intake T'd into one -4an line to bleed out any air pockets. I would like to lower my water pressure a little more. Considering putting a -8an line off the front bung of my intake to a threw hull fitting with a ball valve to adjust pressure as needed. I have crossover with bypass and 5/8 restrictor in thermostat housing to build temperature. Is this a good location to bleed off water pressure? my concern is whether or not it would starve my exhaust of water being drawn from the front of the intake near the thermostat housing?? any input would be appreciated.. thanks

curious if this is a common setup??

What kinda pressures are you seeing at cruise and WOT? You using drive to pull water, or external pick up? Bravo or imco? If bravo is it a low water, side, or dual water pickup?

I have a transom mounted pick ups and they are adjusted as high as I can before introducing aerated water. At cruise my pressures are around 20 pounds. Have not opened up knowing pressure will just climb. I would like to knock it down to 10 pounds around cruise and 20 at wot. Would it be a good idea to pull water from the front of intake to a threw hull fitting. I have a ball valve there where I can adjust flow to get the pressure I want. Does it matter where you bleed water from on the intake? Is it possible that dumping water from the front would rob more water for the headers vs dumping water from the rear of the intake? Again I have bypass hose with crossover and 5/8 restrictor in thermostats housing to build temp.

You should get a WOT pressure, it may not climb that much. On mine with an imco lower I see 18lbs at cruise and 22ish wot. That's with a crossover no bypass, no restrictor, just an open flow system. I don't think you need to run a pressure relief until you know what the wot pressure is, at wot 20-25lbs is what most shoot for with an absolute minimum of 15lbs. I'm not a fan of the crossovers with bypass, in your case pressure isn't an issue, but often times pressure and block water flow is cause the bypass is so large. What does your oil temp run at cruise and wot? What's the reason for external pick ups vs using the drives?

I run oil thermostats so my oil temp is good I run 120 water temp. I'm just curious as to weather it matters to dump water pressure from the front vs the rear of the intake? I like the idea, of relieving pressure from the front with an 8an line to a ball valve at threw hull fitting to get the correct flow to get my pressure where I want it. I would like to leave my 4an line in the rear to relieve air pockets. Is it possible water would flow straight to my 8an dump and pass right by my 5/8 restrictor in the thermostats housing? Or would it flow out of the restrictor as it would my 8an dump ?

Water is going to take the path of least resistance, hard to say what path the water will take once it's getting pressure from the block. You have an oil thermostat so oil temp isn't a big concern here. The -4 crossover lines in the back of the intake dumping off is a good thing. If it was me I would first get a wot water pressure reading. If it was too high, then I would block off the bypass and remove the restrictor. That way all water goes through the motor, water in water out and has 1 path. I get what your asking, but no way I would want to add more rigging to the boat, more things to fail, and drill extra thru hulls when it doesn't have to be that way, that's why I'm asking the questions I am. Simple is better. JMO

I would not bleed off the front with crossovers. The idea behind the rear lines with a crossover is to bleed air and insure flow thru the engine not just the front of it.
I know you don't want input other than what I stated above but who is to say that at wot/top speed you won't pickup air at the pickups? The pressure could drop. Had that same issue with a friends 35.

I would like to keep my restrictor in place to build water temp. Without it temperature won't move. Does using the front bung on the intake to dump water pose a problem? Does the by pass hose supply enough water to cool the headers if flow is decreased threw the restrictor plate? That is main concern.

The issue with the crossovers with bypass are they bypass too much water through the exhaust. I have personally seen a crossover with bypass drop block pressure to 0psi at wot even with a Tstat, so started restricting the bypass hose only and pressure started to increase. So for that reason I'll never run a crossover with bypass again, as there is no way to tell how much water is actually flowing through the block even with dumps from the back of the intake. This same thing happened on multiple boats, one had to have an external pick up installed to get pressure. So It's either a circ pump and Tstat set up or crossover no bypass or Tstat set up for me.

Ok I thought my headers were not going to get enough water to keep cool with my eddie marine cross over with 8an bypass if I install a water dump in front of the intake. It sounds like plenty of Water gets bypassed to the exhaust. That's my whole concern weather or not my dump in front of the intake would hinder adaquite water flow to my exhaust.

Well the crossovers with bypass I have dealt with were 1" bypass's, yours being -8 is a 1/2" so talking 1/2 the size. If you are dead set on running the pressure relief, and don't want to use your -4 dumps from the back of the intake, why don't you move your water pressure line from the block to the front of the intake and use the port in the back of the block where the water pressure line was for the pressure relief.

My set up now consists of using my block drain for my dump which works great. water Pressure is where I want it to be. I was recently told it's not a good idea to bleed water pressure from the block drain. Was told it's better to bleed water pressure from the intake. Which is why I started this thread. Is the block drain just as good of a spot to bleed water pressure as the front of the intake? I just want to be sure before I go switching my line from the block drain up to the intake.

I'm confused, you are currently running a dump from your block drain?

Correct. just recently I was advised its best do dump water pressure from the intake. Thus my thought of dumping water from the front of the intake as a viable solution then my current set up using the block drain hooked up to a threw hull fitting.

I'd be careful here. Last thing you want to do is starve the headers for water. Headers do not like hot spots due to inadequate water flow. Most headers are designed to have at least a 1"OD line size feeding them.

I have ran my engines for almost 10 years now, without water thermostats, in cold 55-65 degree waters. Never had an issue from the water temps being cold. The gauge never moves.

I have been using the eddie marine cross over with -8an bypass for some time now with no problems with 5/8 restrictor in the thermostat housing. Is it best to bleed water pressure from the intake vs my current set up using the block drain? As far as cooling the headers go nothing should change correct? the amount of water taken from the exhaust shouldn't change vs my current set up using the block drain as a dump. Only change would be the location, now i'm dumping water from the intake.

Fwiw . I have supercharged 468s making 800hp. I have not been running dumps off the backs of my intakes for the past 4 years, and ive ran these engines very hard. I havent burned up valves, detonated , or anything of the sort.

Not saying i think the dumps off the rear of intake are a bad thing. But i believe its importance is overrrated. The water flows into the block , to the rear of the block, up to the rear of the head, and out the front of the intake.

I have had water temp sensors at the front of i take, as well as teed in at the rear water dumps on other engines, and never saw a difference in water temp at either location. The key i believe is to keep water moving in the block and heads. If running a water thermostat, without any holes in it, without a bypass hose like merc had between intake and circulating pump, sure you can form hot spots from air entrapment. The reason mercury didnt need rear water dumps, is because they always had circulation thru the block via the bypass hose.

Back to the OP's question. Blue, what size lines are from your thermostat housing to the headers ?

-8 an bypass hose on my crossover

the water flow to my exhaust shouldn't change from moving my current dump from the block drain up to the intake correct? the exhaust will obtain the same amount of water dumping from the intake as it would in the current location dumping at the block drain? is my thinking correct on this one?

I mean what size hose is actually connected to the water inlets of the headers ?

I agree with your thinking as far as the water flow to exhaust not changing.

What i am thinking, is if your actual line size feeding the headers is a restriction, say they are -10 or -12, by going to a larger diameter line, may reduce pressure to the point you dont even need the psi relief. You gain flow, and reduce psi at same time.

My buddy had high water psi. He had -12 lines feeding his exhaust. He switched over to -16, psi went down, exhaust ran cooler.

oh, i thought you were referring to my crossover bypass line that goes to the top of my thermostat housing. i have 1" hoses coming out of my housing that feed each header. my primary concern with switching my water dump from the block drain to the intake was the thought that some how the flow would be altered hindering my exhaust of the same amount of water as its current set up bleeding from the block drain. it seems that the flow of water to my exhaust would not be greater or less than its current set up bleeding from the block drain. Does that sound like a rational theory?? If so,, I think i will just put the dump at the intake and eliminate the dump at the block drain as its better to dump from the top than the bottom.

FWIW- I have -12 from my block adapter to the manifolds and the tails show no signs of overheating.

The flow is more critical with headers imo. I know my stellings can get pretty warm at idle speed. Wish they made different size sea pump pulleys. Im running an aftermarket 3v accessory pulley for the accessory belts. Its underdriving the sea pump. Might not sound like much but at 700rpm engine speed, the pump is only turning like 500rpm or something like that, where a stock setup might be turning twice that much at idle. Pump rpm is a big deal at idle, at 5000rpm not so much difference as the impeller isnt doing much there.

you are running a -12 off the left and right of your thermostat housing?

Yes. It's not yhe the factory housing but an aluminum piece.

I cleaned out my PM box, fyi