Squish dilemma/Porting opinion

[merc_man]

What do you guys mean by freeport?

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[Deets066]

What do you guys mean by freeport?

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At TDC the bottom of piston skirt is above the bottom of exhaust floor. (Exhaust is open at TDC)

 

[merc_man]

At TDC the bottom of piston skirt is above the bottom of exhaust floor. (Exhaust is open at TDC)

Thanks. Been trying to learn a bit about porting.

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[stihlbro]

What do you guys mean by freeport?

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The piston opens the port when technically it shouldn't.

 

[merc_man]

The piston opens the port when technically it shouldn't.

Sounds like not much gains by doing this?

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[redfin]

I know your concerned with your base thickness, just for reference ive been running my 261 @ .015" squish at 205 psi with no issues.

 

[Paragon Builder]

.232

CAD at its best. Left the table to check.

Dan, the 026 I bought to the GTG didn't have bridges, but my 036 did.

Remember that saw? It's the one you used while you and I were cutting the pile apart.

That 036 was very strong! Put a smile on my face!


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[drf255]

Where is your intake and transfers as it sits now?

102.5/117.5/74

I disagree with that

I hope you are correct and I'll keep trying. I see a quad being a superior design. The OEM's have gone to it, even prior to strato. I doubt that's cause of an emissions thing.

Waving at muh friend and laughing because it don't seem like most are willing to do testing before and after. Good enough for you?

Still not getting your point. I plan on adding them to a perfectly fine running ported 10mm 044 I have. Will happen this spring. If we get our chainsaw Dyno off the ground, I'll check it before and after. if not, I'll do it with video in wood. Does that help you at all?

Different jugs may have different squish and different thickness on the base

100% true and tested by me over the last two 026 builds. The MS260 jug I'm using now had a .288 base thickness. I didn't measure the 026 jugs base that I used last time before the cut, but I took a less off the base than I did on this one. The 026 base after the cut was around 2.100, and that was with less taken off than the 260 which stands at .232. The 260 base is visually much thicker than a 026 base as well.

 

[drf255]

Square file, here's the jug they are going in.

I should get a big "You Suck" on this jug. It's a very early KS slant fin 10mm jug that had an unsquare and incorrectly done helicoil repair. I got it off eBay for $20 delivered. Pulled the helicoil and redid it square and correctly. So $30 all in.

Saw's got a loose .022 squish and is pulling 195psi after 2-3 tanks. Still climbing.




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[Paragon Builder]

Yup. You suck Al!


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[redfin]

102.5/117.5/74

Regardless what you do with ex you could stand to lower int a tad.

 

[drf255]

You really think?

I like crankcase compression. Wanted more to support the bridges and (physically) higher transfers, as well as the opened piston Windows.

I raised the roof a bit for more time/area.

The last one I did was at 78 and had a lot of spitback.

 

[KG441c]

You really think?

I like crankcase compression. Wanted more to support the bridges and (physically) higher transfers, as well as the opened piston Windows.

I raised the roof a bit for more time/area.

The last one I did was at 78 and had a lot of spitback.

Would freeport help the spitback? Same question in the other thread. Or we will say will she pass gas??? Lol??!! Will the freeport venting the system allow the full charge to get in with the long intake duration and get rid of the spitback? Just thinkin out loud

 

[stihlbro]

Good luck with your build. It should run well. There are several ways to achieve what you want, main thing is that you are happy with it when done.


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[drf255]

Would freeport help the spitback? Same question in the other thread. Or we will say will she pass gas??? Lol??!! Will the freeport venting the system allow the full charge to get in with the long intake duration and get rid of the spitback? Just thinkin out loud

Some pro here will come along soon and tell me all my theories are wrong, and then I will see it.

I think that spitback occurs as the intake charge begins to be compressed as the intake skirt descends past the intake roof. The freeporting will be closed before the intake skirts hits the roof, at least in this MS260 jug.

Good luck with your build. It should run well. There are several ways to achieve what you want, main thing is that you are happy with it when done.


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Thank you.

 

[KG441c]

Some pro here will come along soon and tell me all my theories are wrong, and then I will see it.

I think that spitback occurs as the intake charge begins to be compressed as the intake skirt descends past the intake roof. The freeporting will be closed before the intake skirts hits the roof, at least in this MS260 jug.


Thank you.

Im following u. If thats the case will the freeport neutralize or purge the crankcase at TDC ?

 

[redfin]

You really think?

I like crankcase compression. Wanted more to support the bridges and (physically) higher transfers, as well as the opened piston Windows.

I raised the roof a bit for more time/area.

The last one I did was at 78 and had a lot of spitback.

Your sitting at 43.5* of primary. I like your blowdown number where it is. You could run it as is and see if it needs more intake.

Edit: Talking with Randy, to much primary could potentially hold the saw back.

 

[drf255]

Your sitting at 43.5* of primary. I like your blowdown number where it is. You could run it as is and see if it needs more intake.

Edit: Talking with Randy, to much primary could potentially hold the saw back.

Plaese explain that figure, I dont understand.

 

[redfin]

Plaese explain that figure, I dont understand.

Primary is degrees measured from when intake closes until transfers open.

Good rule is 40* on most saws.

 

[Paragon Builder]

I say run it and see how it is! That way if you decide to change it and you liked this way better, I'll send you mine to do[emoji12].


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