I've had two 4.0 and one 5.4 all with the flooding hull left open.
Unless you need INSTANT acceleration onto the plane I feel that it is best left open.
Once you close the hole it's always somewhere for water to get into and cause problems.
I found that it was possible to come up to a speed where the bow was high enough that the forward vents were clear of the water and the bow up trim would empty the hull in a few seconds. You could then nail it!
(All three of mine had 2 strokes though)
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