How much air is needed on a 435hp 3208 or equivalent?

5akman

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40' Snowball gillnetter
Installing a dealer remain in my AK gillnetter which is currently powered with a 210NA. Engine is completely under floor with no additional air ducting. I can't believe the 435hp is going to run right in that closed environment. How much additional ducting (CFM or sq inches) of ducting do I need to add? The aft cabin bulkhead intersects right at the mating line between the engine/trans so it won't be hard to do, I just need to know how much area to allow.

Thanks

Lance
 

F/V First Team

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1/2" per hp is the common rule of thumb.

So 217.5 sq inches. If you put a positive pressure blower system in, you can make the opening smaller since the blowers will be forcing the air into the engine room.
 

CEShawn

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Do you guys ever up that size to compensate if you want to add additional diffuser or 90 degree's to cut down on the noise lets say if the vent is in the cockpit or for that fact even a cockpit vent?
 

captainlarry84

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KristenFormer Charter Captain
Air

Hard to say. Run the boat a WOT for starters then open up the engine hatch. See if you pick up any RPMs or if the exhaust changes. This little test will give you some idea of air flow to the motor.
 

Phoenix37

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where are the intake vents on most DEs? I dont recall seeing scoops or anything like that on them.
 

8943post

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I had to smile when I read this post, we had an early nineties 39 SeaRay with twin 3208TA's for power. My CAT guy came down to run the overhead and asked about air intakes for the engines...originally this boat was designed by SeaRay with twin 454's, they offered CATs later as an option.

We decided to take the boat out and do the "Hatch lift test"...at WOT there was no way to lift the engine hatches because of the suction! We ended up modifying the air intakes to feed those V8's, boat ran a lot better afterwards!

Air intake on our Duffy is midship under the wash rails both sides and also under the transom washboards both sides...lots of fresh air that flows under the deck to the engine.
 
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CEShawn

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I can tell you a lot of downeasts that I have been on have had air related issues. Its amazing after you dial that in, get the right sets of gaskets for hatches how quiet everything becomes.

I was on one that changed its intake from the cockpit to the outside of the hull with those nice Vetus intakes and was amazed.

I know I definitely have to vent my cockpit better, want to put something in back but worry about even some small noise coming back, hence the 90's in there.
 
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