Mounting height and water pressure issues

justinhip

Seaman
Joined
Jun 18, 2006
Messages
52
I have a 1992 250 v8 on a 23ft Robalo CC. The engine has decent water pressure, around 15lbs at cruising speeds. At the upper end of the throttle range the water pressuer starts to bounce. I am wondering if my engine is a bit too high? Also, on acceleration or cruising in choppy water, the engine performs best basically in the fully down position. I have the anti cavitation plate set so its just slightly below the keel, approx 1/4". I also noticed, this should be fun to describe, but when underway, at the transom the water does not look to be moving past the hull but seems to back up to the transom like a following sea. My other past boats seem to leave a depression in the water at the transom from the v of the hull basically so you can kinda see the top of the anti cav plate. Is this because of the hull or poor setup on my part. Not sure if this makes any sense? I kinda have assumed that this boat is kinda heavy to easily trim with a single OB and no trim tabs.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Mounting height and water pressure issues

Under no circumstances should the AV plate be below the bottom of the hull when the AV plate is parallel to the keel. The water running back up the transom is because the plate is too low. Depending on the technology level of your prop and your set up, the plate will probably be about an inch or more up.

Some V8 basics to keep in mind when setting up - a 20" or long model is actually 23". A 25" model or x-long is actually 28".

Very cool motor by the way.........
 

Dhadley

Supreme Mariner
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Feb 4, 2001
Messages
16,978
Re: Mounting height and water pressure issues

As for the water pressure, make sure there is nothing in front of the gearcase (transducers, speed-o pick up etc). That stuff needs to be 8-10" away from the gearcase. Make sure you use the 5001595 water pump kit, not the 5001594. Make sure the cooling system is working right, including the t-stats.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Mounting height and water pressure issues

Most outboards usually end up with the antivent (cavitation) plate about an inch above the bottom.It seems something about your boat or setup doesn't allow
that. Perhaps a dirty, fouled or distorted bottom or a poor prop.Only time I ever saw water moving toward the transom was on a boat loaded so much it couldn't plane but managed to start to clear the water away.
 

justinhip

Seaman
Joined
Jun 18, 2006
Messages
52
Re: Mounting height and water pressure issues

Well, thats some good info....I have the wrong water pump and engine is too low...There is nothing close to the engine. I have a transducer 18" from the centerline of the keel but thats it. The wash behind the hull does look like the boat is heavily loaded but it really honks. If I nail it from idle the prop cavitates a bit then gets going. If I get it to a light cruise and hammer it, it jumps out of the water and runs. The boat has been to 55 and accelerating but everytime I try running wide open, someones always in may way (the back bays up here are narrow). It seems like its got another 5mph or so before she maxes out
 

justinhip

Seaman
Joined
Jun 18, 2006
Messages
52
Re: Mounting height and water pressure issues

BTW, the wheel is stainless steel, 21 pitch I believe and assuming factory if ever existed. The thing was black when I got it so I had assumed it was aluminum. Did know it was ss intil it got a bit sandblasted.
 

justinhip

Seaman
Joined
Jun 18, 2006
Messages
52
Re: Mounting height and water pressure issues

oh, what is the difference between the 1594 and 1595 pump kits?
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Mounting height and water pressure issues

The 1595 pump is a high pressure pump.
 

Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Mounting height and water pressure issues

BTW - what's the top rpm & speed?
 

justinhip

Seaman
Joined
Jun 18, 2006
Messages
52
Re: Mounting height and water pressure issues

at WOT she runs at about 5500. I dont know what the top speed is cause since Ive had a GPS I havent had a good cler run to let her go. I guestimate somewhere between 55 and 60 which isnt bad for s 23 CC. But it is for fishing and family so speed doesnt really matter as much as making from point A and back to point A
 
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