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Part Three: The Transfer Ports

Mastermind

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OK.......so we've covered the exhaust port.

http://opeforum.com/threads/part-one-the-exhaust-port.7279/

And the intake port.

http://opeforum.com/threads/part-two-the-intake-port.7290/

Now let's talk about the transfer ports.

We have two port engines, four port engines, boost ports, finger ports, bridge ports....bottom fed transfers, bore fed transfers......and transfers fed from the bottom front of the jug. We can open things up......or we can close it down.

Crank stuffers should be talked about here.......as should case volumes.

Who wants to kick things off?
 

David Young

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I think we grind out a lot of engineered goodness the factory gave us in the name of flow. The first thing we all have done is open the hell out of the lowers. I think the best flow will be when the duct is even sized the whole way through.

I believe the transfer design in the 346/357/372 and stihl 361 and the new echos are just about optimized. then they come out with the stratos and change the whole game.
 

srcarr52

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I think we grind out a lot of engineered goodness the factory gave us in the name of flow. The first thing we all have done is open the hell out of the lowers. I think the best flow will be when the duct is even sized the whole way through.

I believe the transfer design in the 346/357/372 and stihl 361 and the new echos are just about optimized. then they come out with the stratos and change the whole game.

I think a lot of compromises are made on factory transfer ports for the ease of casting and being able to maintain manufacturing tolerances.
 

Stump Shot

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So is the timing number of the transfer opening critical to performance like I would think it is? Is the main thing to look for the difference between the transfers and the exhaust. Is there kind of a sweet spot to look for and try to achieve?
 

Mastermind

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So is the timing number of the transfer opening critical to performance like I would think it is? Is the main thing to look for the difference between the transfers and the exhaust. Is there kind of a sweet spot to look for and try to achieve?

In my humble opinion, there is nothing more important to performance than the relationship between the three ports that we are discussing.

That means blowdown, and case compression time.
 

David Young

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I think a lot of compromises are made on factory transfer ports for the ease of casting and being able to maintain manufacturing tolerances.
what is the manufacturing benefit of the lip on the bottom of the lowers of just about every 2 port jug?
 

Adirondackstihl

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Here's a transfer question that might get kicked around....

I'm currently rebuilding a 346 for a co-worker.
All OEM.
Question is, should I blend the lowers and cut the cylinder extensions to match the case or leave it alone? Why... Case volume?

I'd port the whole cylinder if I had the tooling and knowledge.
 

Moparmyway

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Here's a transfer question that might get kicked around....

I'm currently rebuilding a 346 for a co-worker.
All OEM.
Question is, should I blend the lowers and cut the cylinder extensions to match the case or leave it alone? Why... Case volume?

I'd port the whole cylinder if I had the tooling and knowledge.
If a picture is worth a thousand words.............................here are two pictures

Is case volume or flow more important ?
IMG_4131.JPG IMG_4130.JPG
 

srcarr52

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what is the manufacturing benefit of the lip on the bottom of the lowers of just about every 2 port jug?

It probably has to do with the interface between the core for the transfer tunnel with the core for the chamber and rough cylinder wall, to make the obtuse angle the core must get too thin.
 

Mastermind

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Moparmyway

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Considering that at BTC flow would be negligible, is that really helping anything?

Just asking for a counterpoint.
But that picture isnt just about flow now, is it ?
 
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Moparmyway

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I'm not picking up what your putting down.

Sadly I'm fairly thick and can't read between the lines. lol

To answer your question a little more directly (just a little) ......... is the benefit of trimming those sides more for dwell @ BDC, or for when the piston is approaching BDC ? ;)

Also, that is a 346 cylinder ............... notice how the lowers arent hogged out to match the gasket/case ?

So, I believe that they are both important in a work saw (flow and case volume) and should be considered together, depending on the intent. A race saw would benefit from opening up the lowers to match the gasket and the case, increasing case volume and decreasing velocity at the lowers
 
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