Starboard front






On dyno

From your in boat photos...

Your risers don't have a lot of down angle. They're dumping raw water into the risers just before the rubber exh hose?

Mercruiser had a large issue with their cast risers when they removed the dam at the bottom of the riser exh port.

The exhaust pulses really turbulate and atomize the raw water at lower rpm. Even drawing it back. Some YT vids with acrylic clear tubes in place of the rubber hose, showing how violent they are. Your cam isn't small, and maybe paired up with shallow angle risers you're getting some water spray back and it falls into the exh manifold.

Also raw water cooled exh man condensation is a potential factor.

That is where I would start looking.

Your merc water pump in the lake has to be
pushing more water pressure than on the dyno with that electric pump. We're you able to figure out if your head bolts or intake manifolds required sealant when being installed?

Didn't the 525 EFI like to revert water? I think the smaller engine compared to the 525 might even make it more of an issue. Water pressure is a thing, too, though I think the 454 block is less likely to have issues. 502 blocks can actually weep out the sides at the head/block mating surface.

Sorry you have to be dealing with this.

To Tortilla's point, Alex shared with me that this was originally a TRS boat and when it was converted to a bravo the holes in the transom stayed where they were, then moving the engines back probably decreased the angle on the tails exiting the transom ? we talked about this the other night how flat the exit slope was....would also running flappers on the end of the pipes increase the exit flow of water

Are the water pickups the same as they were with the trs drives?

pick up through the drive and belt driven water pump / fuel pump on side of engine

Side note check your fuel pump often for gear lube... I'm not a fan of the water pump mounted fuel pumps.

But as far as water pickup, I would think the TRS was designed for more cooling capacity because it also has to cool a transmission, where the bravo drive does not. Not sure if that has anything to do with the pick up height, hose routing, etc just a thought based on a TRS drive has to cool and engine and transmission, where a bravo only has to cool the engine.

Edit: I worded the first part about the fuel pump a little funny, there won't actually be gear lube in your fuel pump, but there is a cam off the water pump that drives it and what seems like is only a tablespoon of gear lube to lube it, is around a 1/2 cup and is the same style plugs as an outdrive fill/drain

I disagree, Im running two stage pumps off of bravo style lower pickups cooling fuel, PS, engine and intercooler's ........... the trans cooler on a trs drive is no bigger than a PS cooler

Not that im disagreeing with you at all, and you are likely right, but what about water pickup height if the x dimension was not changed from trs to bravo? And also it's been a little while since I have seen a trs transmission, but they are not a separate cooler and the water lines go directly into the transmission?