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Open Port VS. Closed Port

TK

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Alright. I've got three different cylinders that I'd like identified - but I'll have to post the pics of them tomorrow. I honestly don't know exactly what I'm looking at, thought I did but I'm confused.

Anyway, what benefit is there to a closed port, and what benefit is there to an open port? When would one want one over the other? If anyone has a pic to post please do.
 

StumpysCustoms

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This is an open transfer

this is a closed transfer


The closed tranfer design is more desirable because it has better flow & more volume.
 

TK

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Awesome, exactly what I needed. I had an idea of something else before, then I see a different cylinder completely and was kinda set back thinking there were three different types??? Poor confused boy :lol:

I'll still post pics tomorrow of the 3 different ones I've seen so you can see what my feeble mind was thinking.
 

Spike60

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There are 3 different types, (at least), as there are 2 styles of closed ports. The first is the standard closed port as shown in the pic. This style was used in saws like the 288 and Jonny 670. All fuel/air mix flows through the windows in the piston.

Then there is the modified closed port as used on the 346, 372, and 390 with the transfers open at the bottom to matching cutouts in the crankcase. A little more effecient path for the fuel air mix to travel. Plus it allows for more tuning of the saws performance characteristics. 1 or 2 transfers per side, how big, how much contour or "hook" they have. Most saws like this don't use a windowed piston, but some do, like the Jonsered 930 Super. This syle is more of a Jonsered thing anyway, as most of the old metal Jonnys like the 70E, 52E and 910 had cylinders like this, and they used non-windowed pistons.

Then you have stuff like the 353 and 359 with the removable side plates. Technically, you could call them modified closed port cylnders, but they are pretty crude and unimaginative behind the plates. But then that's why they respond so well when you open them up a bit. Really, this is the same idea with the 372XT, but they've obviously given more thought to the contour and flow on the 372.
 

StumpysCustoms

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Here's the other closed port design that Spike is talking about.

Husky 372


Stihl MS361
 

TK

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Ok awesome, I'm not going crazy lol, that's perfect information right there. Here are the pics I mentioned I would post.


Husky 51, looks open to me


Husky 262, looks closed to me


Husky 365, this is what confused me. It looked open I thought because of how it mated to the crankcase, but then closed because of the port.... But I guess according to you guys' descriptions I can now see that this is a closed port cylinder :thumbsup:
 

TK

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I guess I can't like a post AND rep it. Sorry guys, only one rep for you says the rep nazi :pirate:
 

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