Closed or open port

[urbandekay]

Hi,

Could someone explain to me what is meant by a closed and an open port, I understand a closed port to produce more power but what are the other advantages or disadvantages. Thanks

[wyk]

I'll show images of both then go on with some explaining afterwards:

 

Open port on the left, closed on the right:

 

 

"Closed port"

 

 

That is an Echo 500ES AKA Shindaiwa 502s punched out to 51cc. VS 45cc by the factory. The transfer covers have been removed from the outside of the cylinder to give you a clean look at the inside workings.

 

Here are a pair of 375xpw closed port cylinders:

 

 

As you can see, closed port allows you not only to keep the incoming charge away from the heat and turbulence of the piston, but also allows the engineers more room to design the route in which that charge takes before entering the combustion chamber.

Edited January 17, 2014 by wyk
Put wrong photo up at first...oops

[wyk]

Hrm, the cylinder on the left in that 375xpw pic looks more like a HyWay BB top.

[spudulike]

And don't get hung up on that cylinder base on the first pic left hand side, it is a clam style engine where the base of the cylinder forms the upper part of the crankcase.

 

Closed transfers are generally found on more expensive Pro saws and open on semi pro/homeowner saws, there are many exceptions to this, the MS200 being one of them.

 

As Wes says, closed ports generally have better flow and velocity plus a rounder top to the transfer is far better than the angular affairs usually found.

[urbandekay]

So, if I understand correctly the difference is that an open port the transfer part is open to the bore and in a closed port the transfer is buried within the head

[spudulike]

So, if I understand correctly the difference is that an open port the transfer part is open to the bore and in a closed port the transfer is buried within the head

 

Yes:thumbup:

[mikerecike]

And there are basically 3 types of port? Transfer ports (moving the fuel mix up and down?) and the intake and exhaust ports?

[wyk]

And there are basically 3 types of port? Transfer ports (moving the fuel mix up and down?) and the intake and exhaust ports?

 

Basically, yes. On some older saws, there are boost ports. You could also add fingers ports that act as both transfers and boost ports. Some of the strongest ported saws I have ever seen had open transfers with finger ports. Here's one done by Mastermind Work Saws.

[urbandekay]

Thanks for all the explanations given. Is anyone able to say what difference in power could be expected where the only difference between two engines is one is closed and one is open ported. I know this is an impossible question but someone might be able to give a rough idea

[urbandekay]

Basically, yes. On some older saws, there are boost ports. You could also add fingers ports that act as both transfers and boost ports. Some of the strongest ported saws I have ever seen had open transfers with finger ports. Here's one done by Mastermind Work Saws.

 

How do such additional ports work?