GPRXP Open Loop Cooling

[Hydrotoys]

This has been posted in a few places, but I thought since it's paramount to putting the rxp engine in the gpr, this would be a good place as any.

This should be a good starting place using the rapid acceleration block off plate. It also uses reverse cooling, getting water to the head first. Testing has been done with this, with quite a few boats now.

We kep the engine pressure down around 15psi-20psi using an automotive oil pressure gauge duct taped to the dash. I've since installed a small water pressure gauge right on top of the adaptor, just for a quick reference. We are using a 1/4-turn SST valve on the incoming water to the engine. We are using a 3/8" hose as a restrictor to the intercooler/exhaust side.

Goal for temp is 150-160F to the engine.

SandiegoJoe also has dedicated a seperate line to his intercooler and his exhaust.

[Hydrotoys]

Transom plate modification. On the above diagram it talks about opening it up to match the 5/8" water line.

Since I was doing a new plate, I snapped a few pics, along with some sizes.

You can also increase your water supply by using an external 2nd cooling line, and feed the intercooler directly.

This mod is most useful for an intercooler such as the XSCOOLER that can utilize the high water flow. About all this would do for the Riva is blow the tanks off the p.o.s. so you really don't need it if using that style.

3/8"NPT Tap.
37/64 drill bit.
teflon tape
5/8"barb x 3/8"npt brass fitting.
1/2" drill bit.

-Remove the transom plate from the hull.
-Remove the external press-in fitting. Best way is to tap it out by putting something in the other side.
-Drill out the hole completely with the 1/2" drill bit all the way thru.
-Drill out the hole, except for the last 1/8" with the 37/64" drill bit from the engine side of the plate...leave the extra material on the pump side.
-Tap out the hole on the engine side.
-clean with soapy water.
-teflon tape your brass fitting and install.
-You may have to hog out the transom hole to allow the brass fitting to fit thru.

[boostaholic]

Forgive my stupidity but I'm new to PWC's in general, so the water we use for colling the engine, is pulled from outlets in the transom plate? That I assume just pull pressurized water out of the pump tunnel, pre-impeller??? OR After the impeller, and route it back to the transom plate? Does anyone by chance have a diagram of how/where the transom plate gets its water feed? Thanks.

[seadoo951]

The water gets pulled from the pump after the impeller and goes back to the transom plate and to the motor. This is done inside the pump and is not seen from outside the pump itself. When you remove your pump, and look inside with the impeller removed, you will be able to see how the water is routed.

Forgive my stupidity but I'm new to PWC's in general, so the water we use for colling the engine, is pulled from outlets in the transom plate? That I assume just pull pressurized water out of the pump tunnel, pre-impeller??? OR After the impeller, and route it back to the transom plate? Does anyone by chance have a diagram of how/where the transom plate gets its water feed? Thanks.

[addicted]

Mark,

I saw in Joe's build that after opening up this line, the ball valves that you guys use are almost closed. He proposed not drilling out the fitting, but there was never a conclusion. Not sure if I read it here or on your site. For a STOCK motor, do you think this is still necessary?

[Insanediego Joe]

Mike, I have no data to back that up. The system as described here works and works flawless...

[Hydrotoys]

Path of least resistance....

I say it depends on what your hardware configuration is. If you are using a Riva style IC or some other highly restrictive IC, your water needs are much, much lower, than those of us using XSCOOLER style IC's. You probably don't need to drill out anything in this case, and will need the quarter turn valve just to keep the engine temps above 160deg.

The reason being is that the XS core flow a ton more, and will reduce flow to the engine substantially if you seperate the manifold path from the IC path. In this case, I highly recommend opening up the path, so that you can get full pressure to the XSCooler, and in turn a much more effective intercooler temp.

[jeffsntx]

Mark, the diagram is showing an aftermarket I/C. Is 3/8 also a good starting point for the OEM intercooler as well? I was going to run a dedicated line for the intercooler where the Jetworks was plumbed on my 2 stroke set up.

[Hydrotoys]

If you are running the stock IC then use a small amount of 3/8" line (to duplicate the SD yellow restrictor) then step up the rest of the way with the large 3/4" line, and you should be okay. If it STARTS as a 3/8" supply, that might be perfect. Just hook in your large line to the IC, then manifold, then your standard 1/2 and 3/8" pissers.

To check it on the water, put a oil pressure gauge temporary on your dash, and tee it at the inlet water on the IC. You want around 35psi on that opening at WOT.

You DON'T want over 15psi on the engine open loop, if you are following the stock SD setup.

[JFizzleJR]

After finally experiencing my conversion ski run right I have a few questions regarding the open loop temp control.

Would having more than 15 psi to the engine cause the temp to fluctuate 40??+ with the smallest adjustment on the ball valve? Is there any mod that can be done to better help control the fluctuation before the engine has been running for a while? Any mastermind have input on how to implement a thermostat in the open loop system instead? What exactly are the advantages of the ball valve?

[addicted]

How can the engine run at 15 psi if the oem radiator cap is at 13psi?

Fizz,

read this. http://www.greenhulk.net/showthread.php?t=46509

I am in the middle of plumbing mine right now. please anyone tell me what i may be missing. I really want to keep the thermostat.

[Hydrotoys]

After finally experiencing my conversion ski run right I have a few questions regarding the open loop temp control.

Would having more than 15 psi to the engine cause the temp to fluctuate 40??+ with the smallest adjustment on the ball valve?
YES. The engine shouldn't see more than 20psi if you want to control the temp. Did you hook it up like the diagram or listen to 4 different folks and try and make the best of it? Something isn't right, if the simple ball valve doesn't work.

Is there any mod that can be done to better help control the fluctuation before the engine has been running for a while?
Yes, keep your pressure down below 20psi. At the same time, you should have no problems keeping the IC at 35psi which will keep it loaded with water properly and keep your exhaust cooled correctly.

Any mastermind have input on how to implement a thermostat in the open loop system instead? Find a SST/Brass thermostat, and find a way to put it in the stock system...but if you don't lower the incoming pressure to below 20psi, expect to see further issues.


What exactly are the advantages of the ball valve?
To maintain your pressure below 20psi in your engine. Without it you will see pressure fluctuations up over 50psi...or higher. The engine was NOT designed to deal with these pressure spikes. Lord only knows what kind of other damage you will cause by doing this...like forcing water into cylinders.

It's not that hard. Don't make it complicated.

[JFizzleJR]

Ok. The ball valve works. It's just touchy at times. I need to check the water pressure for sure. The routing I have is working fine. Thanks for the answers.

[Hydrotoys]

Guys,
Dan "Rapid Acceleration" designed a fool-proof system. IT WORKS. It works four different ways to Sunday. You can damn near plumb this puppy backwards forwards, upside down... as long as you maintain a pressure near what SD designed it for.

Feel free to find a better way, and please share it. But don't make this way seem so damn hard. It's mind-rottingly simple, and has worked in many situations. Dan did the very easiest path to this, and it's been made simple with diagrams and explanations.

[Hydrotoys]

Ok. The ball valve works. It's just touchy at times. I need to check the water pressure for sure. The routing I have is working fine. Thanks for the answers.

If your temps are fluctuating, it ain't working.