I bought a motor last winter that is a hp500 from the start with 525 intake, ignition and headers and is rebuild with new pistons etc..

Been running it slow for 10-15 houers then when i push it over 4000 rpm with my 28" bravo prop doing about 60 mph oil starts poring out of dipstick and small amount fram valve cover vent..

Boat is a 27" Fountain and Imco X drive, Oilpressure is 60 psi cold and about 40 worm going down to like 25 when it starts to leak.
Waterpresseur around 25-30

Same thing if a test a 24" prop but then at 5000 rpm same speed .

I have tried with less oil in the boat but still the same.

Strange thing is it only does 60 mph and should be doing at least 70-75 ? Feels like 150 hp is missing ? And piston rings are repleced ?

Some ideas please ?

Regards Carl

Sounds like someone forgot to put all the rings in it.

Sounds like to much crank case pressure, are there breathers in the valve covers ? have you checked the pcv valve in the lower half of the intake

do a leak down test,confirm the rings are shot and never buy another junk motor from kidapache again.

Thanks.

I have only checked the breather to the airfilter from the valvecover , seems ok, where is the pcv valve ? Yes almost sound like bad pistonrings to me aswell but the are new (or 15H ago).

Will check leakdown aswell and bite my nails =/

I don't see why you would waste your time doing a leakdown.

Probably a long shot, but I used some breather VC Grommets from Advance Auto that had "baffles" in them and was pushing some oil out of the crankcase. I started looking at the grommets real closely and the baffles were almost molded together and the entire "hole" for crankcase pressure to escape from was only about the size of a pencil lead. drilled out the grommets as a temporary fix and my problem completely went away.............

Just a far out thought.....

15 hours is plenty of time for a bad tuneup to damage ring lands , etc

Bad tuneup ? like wrong size on rings , pistons etc ?

make sure you have good/clear vent hoses from both valve covers, try to use 5/8 hoses, if the pressure builds up from lack of venting will push it right out of dipstick, as far as running, was it a HP500 EFI that they put a 525 intake on ? any tuning done ? the factory crap setup does not like changes and something mismatched will kill performance...