Real talk about saw porting theory (no arguments)

[MattG]

I believe you mean dropping the jug so far it's free porting at TDC?

Sorry, I'm a bit late on this thread - only joined a few weeks back.

But can you explain what you mean by "free porting" ?

(FWIW, my only experience of this whole area, is of deleting base on my current 200T play toy, then emery-on-piston hand machining away the casting imperfections on the top of the jug, to give me about 0.020" squish. Since the base gasket was 0.5mm thick, I removed this same amount from the roof of the exh port. I've not started it yet.....still playing with the muffler....but on the rope with a brand new p+rings....it feels like plenty high on the CR).

 

[Dub11]

Sorry, I'm a bit late on this thread - only joined a few weeks back.

But can you explain what you mean by "free porting" ?

(FWIW, my only experience of this whole area, is of deleting base on my current 200T play toy, then emery-on-piston hand machining away the casting imperfections on the top of the jug, to give me about 0.020" squish. Since the base gasket was 0.5mm thick, I removed this same amount from the roof of the exh port. I've not started it yet.....still playing with the muffler....but on the rope with a brand new p+rings....it feels like plenty high on the CR).

If you watch you piston move through the exhaust or in take port windows free porting in this case would be aopen gap between the bottom of the piston skirt and the bottom of the port window.

Hope this helps if Iam wrong some one please correct me.

 

[drf256]

If you watch you piston move through the exhaust or in take port windows free porting in this case would be aopen gap between the bottom of the piston skirt and the bottom of the port window.

Hope this helps if Iam wrong some one please correct me.

Yup

It's anywhere there is space between the intending valve-acting portion of the piston and the port/case.

Most commonly seen at the bottom of the piston skirt at the exhaust floor when at TDC.

You can Freeport around the side of a skirt as well if the port is ground too wide.

 

[MattG]

Cheers dudes! I get it now

 

[MattG]

If you watch you piston move through the exhaust or in take port windows free porting in this case would be aopen gap between the bottom of the piston skirt and the bottom of the port window.

Hope this helps if Iam wrong some one please correct me.

Yup

It's anywhere there is space between the intending valve-acting portion of the piston and the port/case.

Most commonly seen at the bottom of the piston skirt at the exhaust floor when at TDC.

You can Freeport around the side of a skirt as well if the port is ground too wide.

So this sounds pretty bad to my naive ears. Since in the case of the Exh port at TDC, if sufficient back pressure exists, the exh gases will contaminate (and heat) the new charge.

I guess this kinda of thing is something to be aware of when reducing piston skirt dimension. So when peeps cut away the skirt on the intake side ( i.e. for more duration) do they deliberately only make the reduction on that side, i.e. not a matching one on the ex side? Does that not upset the weight balance of the piston?

(sorry if this has already been addressed earlier in the thread - i've not read all of it yet)

 

[mdavlee]

Tiny bit of free port doesn't seem to hurt. A lot of free port could be detrimental.

 

[EvilRoySlade]

I know there is lots of info about the 200 around here, it's not a saw I have ever played with though.
Freeport is when the bottom of the piston is above the floor of the exhaust port at TDC. Exhaust port is open to the crankcase at that point.

 

[MattG]

I know there is lots of info about the 200 around here, it's not a saw I have ever played with though.
Freeport is when the bottom of the piston is above the floor of the exhaust port at TDC. Exhaust port is open to the crankcase at that point.

Well when I get my 200 finished I'll try to upload a youtube clip on OPE for peeps to see

 

[Al Smith]

Everybody has thoughts on things and how things work .Regarding lowering the intake port I never found a need to do by cutting the port or piston skirt .Some do though .
I've widened a few in very conservative manner and it's worked for me .

In regards to a Stihl 020 or 200T they respond to modifications very well .However they are a dynamite little saw without doing a thing to them .A little remove the baffle plate from the muffler will work wonders .You might decide you don't need any more enhancement .

 

[MattG]

Everybody has thoughts on things and how things work .Regarding lowering the intake port I never found a need to do by cutting the port or piston skirt .Some do though .
I've widened a few in very conservative manner and it's worked for me .

In regards to a Stihl 020 or 200T they respond to modifications very well .However they are a dynamite little saw without doing a thing to them .A little remove the baffle plate from the muffler will work wonders .You might decide you don't need any more enhancement .

Yes, the Ts are fantastic saws even stock. In England, as we don't have EPA, they didn't come with a spark arrestor from new. My first one is stock except for me just opening the muffler outlet a tad. That one goes like a rocket!

 

[MattG]

I'm posting this clip, which a member called @West Hill Saw House (I think) uploaded. I'm mentioning him to ensure that he's getting the credit. In the description of the clip this is said:

Hey Chainsaw fans, here is a tastly little bit-O chainsaw fun. 61cc is saw porting magic done by your host at West Hill Saw House/Dominant Saw in Central Vermont. This has a cut piston crown and base for the 35psi compression increase. The exhaust port timing was changed to 97 deg ATDC and Blow down of 22 deg. The original measured exhaust was 103 deg atdc with a blow down of 26. It now spins 14500 rpm free rev

Firstly I think the cuts and the saw are really impressive, secondly how is all this achieved? What actually is going on? The description quotes that he has reduced the exhaust duration and blowdown (but with a big CR bump), however this saw sounds like it is running very well at high revs. The description of work made me think of a torque port, but watching/listening and it's sounds like it's powering through like a revs port.

Thoughts?

 

[paragonbuilder]

Hi Matt,
97 exhaust is 12 degrees more duration than 103. He is using timing from atdc for his numbers.
So you are correct, it is ported for rpm.


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[MattG]

Hi Matt,
97 exhaust is 12 degrees more duration than 103. He is using timing from atdc for his numbers.
So you are correct, it is ported for rpm.


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Thanks Pal,

It sounded that way....and regards the numbers I guess I need to read my book again!

 

[MattG]

Hi Matt,
97 exhaust is 12 degrees more duration than 103. He is using timing from atdc for his numbers.
So you are correct, it is ported for rpm.


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Hello again

He also says the blow down has decreased 26 -> 22. That's the duration that the exh is open prior to the transfer opening, right? So I guess he must have seriously raised them (i.e. transfers), and obviously must know his sh!t pretty good, i.e. that a longer transfer duration trumps less blow down - if you catch my drift...

this is certainly sounding pretty scientific!

 

[mdavlee]

Hello again

He also says the blow down has decreased 26 -> 22. That's the duration that the exh is open prior to the transfer opening, right? So I guess he must have seriously raised them (i.e. transfers), and obviously must know his sh!t pretty good, i.e. that a longer transfer duration trumps less blow down - if you catch my drift...

this is certainly sounding pretty scientific!

Longer transfer duration is usually less blowdown.

 

[MattG]

Longer transfer duration is usually less blowdown.

Well yeah of course I guess that given he raised the exhaust which would increase blowdown if done alone, then he must've increased the trans by quite a lot to get an overall blowdown decrease. Correct?

I'm just really curious about, using that saw as an example, of how the performance was actually achieved.

In other words, it seems that trading down blow down for a lot more transfer gives this saw the edge at high revs. Maybe the increased volume blown in ensures more residual burn gets pushed out?

 

[mdavlee]

It all depends on the saw and case capacity plus where you want the power band.

 

[paragonbuilder]

Well yeah of course I guess that given he raised the exhaust which would increase blowdown if done alone, then he must've increased the trans by quite a lot to get an overall blowdown decrease. Correct?

I'm just really curious about, using that saw as an example, of how the performance was actually achieved.

In other words, it seems that trading down blow down for a lot more transfer gives this saw the edge at high revs. Maybe the increased volume blown in ensures more residual burn gets pushed out?

2 strokes are weird, one guy will get huge gains with short blowdown, and another will get them with long blowdown. Everything works in concert on these. One change precipitates another. There are some threads on the different aspects of porting here. Type in "part one" in the search bar to get started.


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[Al Smith]

Yes, the Ts are fantastic saws even stock. In England, as we don't have EPA, they didn't come with a spark arrestor from new. My first one is stock except for me just opening the muffler outlet a tad. That one goes like a rocket!

I don't know about the UK but according to the IPL those sold in USA,Canada and OZ had 6 screen holes while the standard,which I assumed to be Europe had 5 .If you pull the screen plate it gives you another hole which is what most people do .Even that is a slight improvement .

 

[Love it Stihl]

Hi I don’t do forums often but I find the best info in them so tell me if I’m highjacking.
I have a Stihl 032 that I’ve done some work to like dual port muffler widening and flattened exhaust port and removed a massive amount of intake port material and no head gasket. Runs great but I’d like a little bit more power cuz it seems to bog easy. Does someone have port timing numbers for me? I need to check them currently and I didn’t get the stock numbers cuz I wasn’t that knowledgeable back then. Or did I do something stupid???