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Discussion Starter · #1 ·
Hello. I picked up a new-to-me old school jet boat and just have a couple questions so I dont screw anything up. Its got a 455 Olds with over the transom Bassett headers and Hardin 4-port thermostat kit.

The plumbing is laid out closely to this diagram. From the pump, there are 2 separate gate valves. One line is for water going into the engine, and the other for water going directly to the headers. Previous owner was running the headers dry due to some leaks at the fittings beyond the gate valve. I'll sort that out later I guess.

From the engine gate valve, water goes to a tee and into the front of the motor, but when its cold the thermostat doesnt allow water to flow through the engine. Instead, there are 2 dump lines from the thermostat housing that go overboard. When thermostat opens, water flows through engine and then directly out the 2 dump lines overboard.

Because of the system having 2 dump lines constantly going directly overboard, think it's best/OK to run with gate valve wide open or is there still a chance of too much water pressure?
 

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You are in the same boat as me except the thermo housing. Just bought my first jet boat also. 455 olds. What I've been reading is the most important part is to control the pressure in the motor 5 to 7 psi is all you need to keep from blowing head gaskets and water in the oil. When I bought mine the owner said he had talked to people and they set him up. Only took the boat out once and was scared to really get on it because I wasn't sure. I'm totally not sure if it's right, so I'm going to park it for the winter and do alot of research for next year. Seems that there is not alot of support in 2022 for the old school jet boats. When I do research it's always from a few years ago. Maybe we can help each other out. I'll keep in touch. Mike
 

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I don't have a Jet Boat, but I installed a pressure gauge for water on my Boat. I did it after seeing a few Jet Boat guys do it. My Boat has a thermostat in it, and I was curious about the water pressure it carried. It also has a ball valve on the engine water exit line and I wanted to see how regulating it affected the pressure.

Motor vehicle Automotive design Automotive exterior Rim Auto part


Automotive tire Hood Motor vehicle Automotive design Rim


Bottom of this picture, you can see the ball valve on the water exit side.
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This may or may not help, but it might give you an idea or two.

Mod
 

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Discussion Starter · #4 ·
Previous owner ran gate valve fully open, said the guy who built the setup told him to do it that way. My guess is because maybe the lines are large enough and it has 2 dedicated dumps that are always open and unrestricted. Thanks for the advice guys. A pressure gauges seems like a great idea.

Where are you located, 1974 Hondo? Im in Norcal and boat on The Delta.
 

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Thanks Mod for the explanation and the video. Also lov the quote- vote with your wallet. Matty I'm in Southern Ohio, Cincinnati. Local lakes and sometimes the Ohio River. I have the same setup as you I think. 455 with Bassett headers. Previous owner put a ball valve on the line feeding the headers to regulate the pressure. Not sure what it is set at either. This stuff is all new to me. Come to find out, you have to do all your testing and tuning while it's in the water. Can't run the jet pump on dry land. That makes it hard to do anything in the driveway. I'm going to do the same thing add a gauge to the manifold to see what is going on. If you don't mind keep me updated on your progress. Mike
 

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Discussion Starter · #7 ·
Does the water pressure gauge need to be on the top of the intake manifold or can it be inline between the jet pump and motor? Was thinking I can tap into the plumbing right after the gate valve off the pump and run a hose from there up to the driver's seat where the gauge would be, so I can see it while under throttle.

If I put it on the intake manifold, I cant see it while driving, unless I run a line from there to a gauge where I can see, but that would be more of an eyesore there than if it was back down right after the gate valve.
 

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My thinking is - once you set the water pressure to your desired pressure with the gate valve. the pressure is now set and should never change regardless of motor RPM. So you wouldn't need to monitor the gauge while driving. The part I would be watching would be the engine temp at different speeds. May need to add a pound or 2 of pressure to control motor temp? Like I said before this is all new to me also but, in my mind this seems like it would work.
I did talk to one fella and he said he put 1/4" valve by his seat to control water pressure to his headers. It was hard to understand but, I think he was adding slight pressure to cool the headers at idle/no wake and when beaching his boat?
Not sure about that one - I would think by adding 2 much water it would suck water into the pistons on the cam overlap.

Keep me posted Matty
 

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Discussion Starter · #9 ·
I agree, once water pressure is set, should not really need to mess with it any further. But, in this case, I would still need a gauge initially, even if just temporary, in order to find that sweet spot for the gate valve.

Issue in my scenario is how do I get it set initially. I would need a gauge that I can see while driving (under throttle), even if it's just a temporary setup, because I dont have anyone who can help by riding in the back of the boat to watch a gauge installed back there.

Once I have the gate valve set for correct water pressure, I probably wont need to monitor a water pressure gauge anymore, since I do have an engine temp gauge at the dash that would alert me to any possible water flow issues.


The purpose of that valve by his seat is so he can turn on water to the headers when above 1800-ish RPM, and shut off the water when at idle. Dont want water in the exhaust at low RPMs due to water reversion, like you mentioned.

Im having my exhaust Cerakoted because I plan to run them dry. Cerakote will help minimize the amount of heat they put off and wont be as ugly with all the discoloring of the chrome that has occurred in mine due to previous owner running them dry. This way, I also dont have to worry about water reversion.
 

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Great info on the water valve for the headers. I would think you could hook up a garden hose to the motor and set the pressure.- Motor running or not. I don't think the pressure would change from idle to whatever RPM.

Been thinking about doing the same thing to my headers. Post a picture when you get them done.
 

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Discussion Starter · #11 ·
Will do. Just dropped them off today. Should have them back in 2 weeks or so.

I've read not to run it on the hose with the engine off. Start engine first, then turn on water. Shut off water, then stop engine. Another thing to worry about when running on a hose on the trailer is the pump impeller and ring being dry. Some disconnect the pump shaft from the motor, while some run another hose up the back of the pump to try to flood it with water.

Typical house water pressure is probably in the 40-60 PSI range. When under full throttle, I've read the jet pump can be more like 100-300 PSI.

I think what I may do is attach a 15' hose to the 3/4" hose attachment fitting I have in front of the gate valve coming off the pump, and run that hose up near the driver's seat where I can see it, and stick a pressure gauge on the end of it. This way I can glance at the gauge while under throttle, then adjust the gate valve from there, all while watching the engine temp as well. Keep adjusting gate valve to find that sweet spot that keeps engine temp ideal with not too much water pressure. My only concern with this idea is if its OK to check water pressure at a spot between the gate valve and engin,e or if the gauge needs to be on the actual intake manifold itself.

After all this, I can then remove my temporary water pressure gauge set-up, or just leave it and tuck it between the seat and gunnel.
 

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Discussion Starter · #13 ·
Found a bit more info on where to check water pressure. I learned that pressure coming out of the jet pump into the boat is at its highest, then it slowly drops from there as it travels through the block and out the dumps overboard. Based on this, I think Im good/safe to temporarily monitor water pressure right after the gate valve, since pressure beyond that will be slightly lower anyway. This makes sense in my head because for those who run pressure relief valves, the valve is usually plumbed right after the gate valve, so essentially that relief valve is "monitoring" water pressure at that location and opening up at say 15psi, or whatever they set it for, to dump excess overboard.
 

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Hello. I picked up a new-to-me old school jet boat and just have a couple questions so I dont screw anything up. Its got a 455 Olds with over the transom Bassett headers and Hardin 4-port thermostat kit.

The plumbing is laid out closely to this diagram. From the pump, there are 2 separate gate valves. One line is for water going into the engine, and the other for water going directly to the headers. Previous owner was running the headers dry due to some leaks at the fittings beyond the gate valve. I'll sort that out later I guess.

From the engine gate valve, water goes to a tee and into the front of the motor, but when its cold the thermostat doesnt allow water to flow through the engine. Instead, there are 2 dump lines from the thermostat housing that go overboard. When thermostat opens, water flows through engine and then directly out the 2 dump lines overboard.

Because of the system having 2 dump lines constantly going directly overboard, think it's best/OK to run with gate valve wide open or is there still a chance of too much water pressure?
 

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I'd run the pressure gauge on the manifold to see what the head gaskets are seeing. In my set-up, I can reach/feel the thermostat housing adapter from the drivers seat. And making a pass and looking at a pressure gauge behind me is a quick head snap to see the pressure.

A note on the WJ pump-
These have a plastic wear ring, and heat, like running without water, like on the hose, will, I repeat, WILL KILL the wear ring. They're a self clearancing (sp?) piece.

The Berkeley style pumps don't like it either, and one piece of sand between the wear ring and impeller can destroy the pump too.

The sources I have, wear rings are no longer available.

Dan'l
 
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