Closed transfers vs open transfers

[Mitymouse]

I have been reading alot about saw mods and porting, getting ready to try it for myself, and I keep reading comments about open transfers and closed transfers. Could someone explain what is the difference.

Thanks

 

[klickitatsacket]

open transfers have straight line shot from top to bottem with the sides being angled to help direct flow in towards the intake wall.

Closed transfers are better refered to as looped transfers. They are built so that the charge is moved in such a way that the charge is moving in more of a horizontal plain then the open port.

When the transfers first open the high presure pushes all charges directly accross the top of the piston at a 90 degree angle from the wall. After pressure starts to drop the charge starts to be more influenced by the internal angles of the wall and the direction of the flow starts to move towards the back wall above the intake prt and moves up the wall.

The open port becasue of it's straight shot direction tends to push more of the charge up instead of back as the port opens more.

With the loop port the charge is directed out and then back into the cylinder so that charge comes in more at a horizontal direction helping to clean out the back corner better.

On smaller 2 stroke engines the amount that is trapped by the inefficient open ports is not as dramatic as it is in largers engines. I would assume that the cost of production out weighs the minute amount of HP lost.

 

[troutfisher]

Nice...opcorn: opcorn: opcorn:

 

[Mitymouse]

Thanks for the great explanation. I can see how the closed transfers would be better. I assume the open transfers are easier polish though.. Is there much benefit to be gained by polishing the transfers??