Made some wide open runs Saturday on my stock 1997 502 Mag MPI running 7 Lbs. boost pro charger. Brought motor back to idle and it sounded sick. Stalled and I restarted once. Then stalled again. I was in the middle of the shipping channel so I attempted to restart again and broke starter. I figured it blew the head gaskets and Hydro-locked.

Pulled her in the barn today and sure enough 3 cylinders were full of water and the spark plugs were wet on the other 5. Whats my diagnosis? full rebuild? Get lucky and replace head gaskets? I know there is a good chance I bent something in the motor.

At that point I'd prolly wanna do a full tear down and at least inspect everything.

Thanks, Looks like my season is over so I might as well pull the motor over the winter.

A slightly bent rod or hurt bearing. Any of that and your risking block problems. Even if everything else is good at least you know instead of being terrified every time you touch the throttle. Lol. Old saying better to be safe than sorry. Lol

I think the smartest approach is to put plugs in and start her up. Look at pressure and listen for noises/missing. Also, do it with the belt off the charger so you can hear better.
You can run it for a minute/minute and a half without concern of lack of water.
If it sounds ok....then buy a top end gasket set with arp's and swap out the head gaskets. After resurfacing the heads, buying the gaskets, and installing the arp's......you'll be in under a grand and potentially back on the water next weekend.

If anything is amiss.....blow by, rattling, missing....knocking.....time for a rebuild. Either way, use studs on the heads.....

Is this the one with the new Holley EFI system ? how long was the water sitting in the cylinders, is there any water in the pan ?

Pull it apart, unless you don't mind if it get's broken further.

I'm sure you'll find atleast a bent rod, or two, or three....and atleast one head not flat.

Yes it is the one with the Holley. I was doing some wide open runs to make sure the computer would learn the upper rpm ranges before I pulled my O2 sensor to run open loop. I haven't checked the data logs yet but believe this problem was caused by running 7 psi on stock motor. Water has been in cylinders for about 24 hours now. Starter is broken right now. I am purchasing a new starter tomorrow so I can turn the motor over and blow the water out of the cylinders.

Checked the intercooler and it was dry. I am surprised I have water in every cylinder. Boat does have flappers and the exhaust exits well above water line so I am sure it didn't come thru the tips.

Was running 86 mph trimmed out nicely before this happened. Didn't notice a problem till I slowly brought the motor down to idle after the run.

Judging by the dipstick there is no water in the pan.

Still debating my next move !

Headgasket blew (or cyl head lifted) and water went in those cylinders. It's a common plenum intake, therefore other good cylinders (if there are some) pulled water from there.

Same deal when a motor breaks a valve. Sometimes the valve head ends up in another cylinder in the other bank.

I am thinking I will rebuild over the winter. Upgrade motor to where it needs to be to stand up to the 7 lbs. of boost and possibly upgrade the cam. Any suggestions on builders.