Holes open better holeshot and holes closed better top-end?

For thru hub exhaust systems.

Julie

Usually the vent holes are used for outboards. The vent holes don't usually have any effect on the top speed. As the boat picks up speed the hydrostatic pressure of the water going over the bullet and prop hub is greater than the exhaust pressure so the exhaust stops coming out of the vent holes. They are used to get the boat on plane.

Matt