Hey Guys, I need to pick some brains. I have a 2000 Donzi 33 ZX.

I am currently in the process of refreshing my 540BBC Engines. The boat has manifolds that go through the hull with no captins call/silent choice. I would like to add a Captins Call/silent choice for Idling around in small congested areas. My worry is the CAM that is currently in theses engines. I would like a second opinion if it was cause water reversion with the manifolds going through the prop. It doesnt sound too choppy IMO. the RPM seems pretty stable at idle on the TACH.

These engines have 54875LUN Cams. Both engines made Peak Tq at 4500RPM on the dyno @ 683 Lbs-FT, and Max HP was at 5800RPM @ 692HP.

Cam specs are:
Advertised Duration IN/EX : 299/304
Duration @ .050" IN/EX: 240/245
GROSS Valve Lift IN/EX: .612"/.612"
Lobe Sep Angle/Intake Center Line: 112/110 Deg

Its running Stainless Marine Manifolds.

Boat ran 84-85MPH on GPS with 30P Bravo props. Pretty fast for its size and weight.

If you have any recommendations it would be great!. These motors were built by someone else, We are just refreshing them since they had a little bit of blow by. If we add Captins call and there is Reversion what would happen? Honest question. Will it hydro lock or is it just extra humidity on the valves?

how high does the tail pipes go when they start to turn down?

I have had it at least twice where the manifold to riser gasket was leaking water back into the engine and it turned the oil milky but never hydrolocked. Have also ran engines with cracked manifolds and same story, milky oil but never hydrolocked.

this isnt related, but i once ran a big block with a chunk cracked out of lifter galley and I ran it long enough that water forced the dip stick out and I had a steady stream of water coming out the dip stick tube

This is what it looks like. Maybe a 8-10" rise. Also the water exits the side of the boat through the black/blue hose. I would need to change this setup for silent choice though. thoughts?

So, your current exhaust is dry ? Ie: no water comes out the tailpipes ?

thats what it looks like. Im not very familar with these tails. ive always has the wet ones. i just got the boat last fall and only drove it twice before having to pull the engines from excessive blow by. i have very little seat time in it. i didnt like how loud it was without captins call as an option. Theres a time and place for it. maybe im just getting old LOL

I personally think you WILL have reversion with that cam and water backing up from captains call going thru the prop. What about just adding mufflers? I had 5" tails on my Baja with water added at tips, hearing damage loud. I ran ggb mufflers then lost ine and put cheap Gibsons on. They looked extremely restrictive but boat really didnt loose any speed. Ran 99.5 with smallest pulley with them off and maybeb98.2 w then on fwiw

Thats definatly a thought. Is it the duration or the LSA that makes you think my cam will have some reversion?

yes

It's a factor of overlap. Duration and LSA. Also a factor of exhaust tubing dia...as well as intake port velocity.

Arcticfriends has the answer...mufflers.

Just a factor here, generally, you need 2.2cfm of exhaust airflow per 1 HP, IOT have unrestricted exhaust flow. If you have less...it just restricts it a bit until you develop sufficient backpressure to generate pumping losses that can't be ignored.

Mufflers would be a cleaner solution. Some can bolt on outside, under a swim grid...that is not really seen anyway.