Will this force enough air down and past the fins to cool properly?

Do I need the "tunnel" behind the cylinder fins to direct the air down and out of the cowl?

OR:

Can I cut the tunnel off right after it clears the back of the fins?


I might end up trying to bury a can muffler sideways under the motorbox. I'm running out of room and I don't want cut a huge hole in the side of the cowl for the muffler to hang out. If I cut the sides of the tunnel off right behind the cylinder that will at least keep the air around the fins for the full pass down the sides of the fins. But I would not have any way to forcefully direct that hot air out of the cowl. That would open the area behind the cylinder for a sideways cannister muffler.

Obviously, I still need to cut an exit hole on the bottom of the cowl. That exit hole will take up all the space behind the cylinder fins. It's about 2" x 3" square.