jet boat

Me and my dad, just bought, a 75 omega jetboat with a 455 olds, its has a jacuzzi jet on it. Ok my question is that people that we keep talking to says that if we get the jet out of the water for any amount of time that we are going to burn up the motor from running to many rpm while jet is out of the water. Now we are just boat at our local river which has about 20 some boats and watercrafts out at one time. Now what would be some advice on the subject could anyone shed some light on this and maybe any tips on this inboard jetboat we have?

 

It's pretty hard to go airborn, (It's not a jet ski) and not too good for the hull integrity. That is one big heavy engine all the way in the back of the boat and designed to stay IN the water. If you loose suction when WOT, there's a bigger chance of engine damage due to over reving. I have had two jets in the past, one with a 455 Olds and the other with a 460 Ford. Both had Berkely pumps. There's a lot of things to know if you've never had a big jet.
I wouldn't know where to start. I would be happy to answer any questions you might have and use that as a place to start.

 

well i think my biggest question was the pump, engine thing. O i do have one more. Someone was telling us about a valve that alowed a certin amount of water to the engine so that you can fine tune the valve so that your motor could warm up but not get to warm and so that you could turn it down if there was too much water and the motor never warmed up? Wasn't sure what kinda valve he was talking about kinda sounded like a valve that was on one of the water hoses or something. But yea we are very new to these kinda boats so anything, big, that you think we should know would be great.

Thanks

 

The engine is most likely cooled by water from the main pump through a small hose. It is not a good idea to impair this water flow. If you decrease the water flow to the engine, it will also decrease flow thru the exhaust. Doing so could damage the rubber exhaust hoses and possibly start a fire.
There's so much to say. I'll have to work out something for you. Meanwhile, posting any pics of the power plant would be helpful to see exactly what type of set up you have.

 

Check this out:
http://en.wikipedia.org/wiki/Jetboat

 

Try joining this Forum, if you haven't already:
http://www.justjetboats.com/

 

Jetboat cooling 101

As for jumping the boat, Don't worry about it! If your -really- want to nip-it-in-the-bud, install a MSD ignition system with a rev limiter. That's the typical fox for this.

For setting your cooling water in the jetboat..

Jetboat cooling 101

For Standard cast water cooled ehaust.

A) Water comes from your jetpump through a gate valve for adjustment.

NOTE : Why a gatevalve and not one of these cool ball valves? Because a ball valve is too easy to bump and then its out of adjustment. You want to adjust this once and forget it.

B) From the gatevalve the water "T"s off to the exhaust manifolds for preheating.

C) From the manifolds the water enters the front of your engine at the waterpump blockoff plate. (Its and Olds, I've done a few of these.)

D) The water exits your engine where the thermostat USED to be

NOTE : Do NOT let anyone talk you into installing a themostat or themostat kit on your jetboat engine. Installing a themostat will instanly blow the seals 'cause it closes and the jetpump instantly overpressures the block.

The themostat kits with a bypass solve this and give you a "feel good" with a temp guage that stays rock solid.. But they cause the engine to crack its heads as freezing water is switched off and on to the hot block to keep your guage steady. The simple valve system is -the- ticket on these machines. Your temp guage will swing all over the map, but your engine will last for many more years this way.

E) From the thermostat housing the water exits the craft at the "Snails". Jetboat guys call them snails, the real term is exhaust risers.

NOTE : Do NOT let anyone tell you that you need to restrict the outlet of your cooling water. Especially running and OLDS! Olds motors are notorious for popping the seal between the water jackets and oil pans. Typcially they blow where the intake manifold bolts to the cylinder heads.

NOW Setting your temp:
Because jetboat's tap cooling water from the drive pump, your engine will actually run its -hottest- at idle. So, knowing this, set the gatevalve (Remeber, not ballvalve) so the engine is running as hot as your are comfortable with. Say, 250 deg. AT IDLE.

You're done.

Once you hit the gas, your engine temp will lower as the amount of cooling water increases. This is normal and the engine will be fine with it.

NOW, if you are running water injected tublear headers, everything is different. In that case go to the Banderlog forums and ask how to set it up.

http://www.banderlog.com they have some local Washington members. A real great group.

Hope this helps!

-jim lee

 

Wow, that's a complicated setup if you run injected headers, why not just run a priority cooler with a built in mixer, that way you get a bypass for rock steady idle and wot temps with no increased block pressure, but the mixer 'mixes' the hot water comming out of the thermostat with the cold water from the jet unit before sending it through the block.

Also, if you are really worried about cold water going in, pre-heat it through the exhaust manifolds and oil cooler.

If you are making big power, or concerned about water pressure from the pump, install a pressure regulator at the water off-take from the pump.

As to jumping, simply install a rev limiter. Normally the damage doesn't occur from the over-rev, but more due to the shock loading as the jet goes from un-loaded to instantly primed and loaded, sorta like sitting in your car with your foot hard on the gas in 5th gear, towing up a hill, pulling 4000rpm, then dumping on and off the clutch. If the gearbox can handle it the engine won't be liking it!!