I have tried to read as many posts on the jet boat engine as I can...
There have been many people on here whom have started with the proverbial $500 hull and started from zero... This to me is Hot Boating at it's best. The core if you will.
The common denominator seems to be to ask a bazillion questions about the same thing, whether it be a 1970's LS6 or 460 Ford to a late model LS stroker...
The proven, get you in the water inexpensively and reliably recipe that I have used for over 20 years is this;
The list;
Cooling these beasts is easier than many think it is, oil temperature is actually more important. Too cold and the oil does not lubricate well, to hot and it turns into a frothy soup that can sustain pressure...
To get a reliable hold on the pressure and temperature, you first need to understand a few things.
These engines we use are automotive piles of wrecking yard gold... They were designed to run at 180*F at about 12 PSI for over 100,000+ miles at freeway speeds.
These engines really should not see more than about 15-20 PSI of water pressure. More pressure and gaskets will fail, freeze plugs will pop and money will be spent.
These engines DO NOT NEED to be temperature controlled for the most part. The temperature you will be reading on the gauge is for the most part irrelevant.
As long as you have sufficient water flow to keep the engine from developing steam and having a handle on the pressure, your good...
These systems need very few, extremely inexpensive parts.
I am not going to get into machining clearances at this point and time, I just can't sleep and figured this may help a noob...
Not going to get into the gate valve debate again, but...... from the jet pump, (speaking Berkeley but others definitely apply with a few differences) there is a 3/8" threaded hole on the left side of the suction piece.
For OT headers...
From that hole, install a 3/8MPT X 5/8" barb fitting, Push Loks works well here then go to high pressure hose (I use hydraulic hose, but you make the call). From the high pressure hose go directly to a 3/4" valve, the gate valve works just fine, is cheap, easy to find and infinitely adjustable, makes it a great choice.
Out of the __________ valve, install a male hose bib adapter for a male 3/4" garden hose fitting, brass only, plastic parts or for the whacker guys...
from there, go the female garden hose adapter to another length of 5/8" hose, this can be normal heater hose because your pressure drop will take place in the valve...
The 5/8 heater hose goes into a tee, this can be a special marine part, or a 1/2" brass tee with a few barb fittings installed, either way in my mind is totally acceptable.
The tee will be installed in the "Bullhead" configuration, this essentially means that you feed the "middle" fitting.
The outlets of the tee go into the front of the block where the original water pump was installed, this applies whether you have an Olds, an AMC, a Bowtie a Ford or MOPAR, they literally all work the same (essentially that is).
the water will exit the engine from two outlets in the thermostat cover, one outlet goes directly overboard through a 1/2 " or 5/8" hose to a through hull fitting, most moderate HP engines will need about a 3/8" hole size, the more HP developed, the larger the hole....
The other line will be your header water, this can be done any number of ways. The easiest is a header water control valve (the most common being the Bassett tee). I always recommend installing a secondary valve in line with this type of set up in case something keeps the valve from closing (these are prone to sticking in gnarly water with small sticks and debris).
This system is extremely easy to adjust.
With the boat in the water, open the gate valve (if so equipped) about three turns open and start the engine.
Water should leave the dump line immediately after the block fills up. there should be ZERO water at the headers at this point and time.
Rev the engine up a bit approaching 1800 RPM, the boat does not need to be moving to do this, the header water should just be starting to steam or mist at or very near this RPM, if not open the val a little until it does, if the water comes on early, pinch down on it a bit. Once dialed in, the engine temps should start to rise slightly at idle (may see 120* to 150*F) as soon as the engine speeds up, the temp will fall like a ganstas' pants...
Go boating, she should be stupid close and work properly for years...
You can get more elaborate if you want to, but this has been used tens of thousands of times and is proven to work great, once you start getting into the horsepower numbers in the high 700's, you may need an additional, yet smaller dump line for more cooling capacity.
I will come back to this thread and update it when time allows...
Hope this helps even just one person.
GT
