Real talk about saw porting theory (no arguments)

[drf256]

Can someone clear my head? I've been staring at my 365xt with a degree wheel. I've heard raising exhaust and transfers is what they need, increasing strato duration, leave strato, gut strato. Intake, barely gets mentioned other than DO NOT go wider (no skirt).
In fully stock form, I'm at: Ex-99, Tr-116, In-74 and .030" squish.
I see I have 17* blowdown. If I raise exhaust I lose compression time on the upstroke right?

Where I get lost is if the strato ports are left operational, how can you increase duration on them? Seems to me that you could not exceed the intake duration, or better yet, they need to be the same.

I'm trying to wrap my head around stratos. Just another part of the cycle to ponder and confuse me.

One bullder here, well known to build some serious saws, says to "equal out the stratos"-make them open and close at the same times as the intake port(s). Until I have a strato jug in my hand, I won't understand this.

It does seem like the factory is giving you more tools to work with. More oil/fuel rich charge in the crankcase where the lubrication is needed and more transfer area.

My little brain tells me that strato saws should like less blowdown than a similarly designed non-strato dual/quad. They should have more transfer pressure with the first part of the charge being fresh air only. This would only be true if the stratos weren't "gutted". I assume that this means they are connected to the regular intake tract after the carb throttle plate and are filled with charge instead of just fresh air.

I've got a lot to learn here.

 

[paragonbuilder]

Your far from wrong and trapped charge is very good point. It is wasted space and fuel. I beg to differ on the surface area. A lil bit is gained but not much as you stated. More area = a bit more push.

I never did buy into the stock piston argument. Once we tinker with them nothing is stock so why worry about the piston being an OE drop in?

In fact I hope to try out a popup in my next ms361 build.

You beat me to it!
By the way, what is your name? I'm Dan


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[drf256]

You beat me to it!
By the way, what is your name? I'm Dan


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His name is Lightning Dan. Can't you read?

 

[Lightning Performance]

Hey Doc when you get your head wrapped around those strato feeds be sure and fill me in PLEASE! I get the concept but not all of the working theory.

Let's just go with "Vern" from the sticks ;-)

 

[Lightning Performance]

I could be wrong Doc but, I think the modern strato ports are staggered in their opening points to induce swirl like the offset on transfer openings. Just measure a piston in the side pockets heights.

 

[paragonbuilder]

His name is Lightning Dan. Can't you read?

No. I have a hard enough time with pictures...


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[Al Smith]

It's been said you get max pressure after about 20-25 degrees after top dead center .How in the world you would measure that is anybodies guess .

Then some prefer to keep the ex at around 100 after ,keep the power stroke long and some that like to raise it up,more RPMs .I've measured some stock like a 700 McCulloch which was 96 after and if I'm not mistaken so is a Stihl 200T and both of them have plenty of grunt .What the answer is must depend on other factors .
I don't think there are any one size fits all situations .more so personal preferences .I do know on every Stihl I've modified I've raised the ex some what and they have plenty of grunt .Of course on a Mac there isn't much you can do and I don't think it would help being at 96 already .
I know one gent who would raise them up to 92-93 after ,long blow down, under 20 thou deck clearance for cookie cutters .Now we're talking a 17,000 RPM engine .With a thinned race chain and 20 thou rakers they would fly .----but it was a cookie cutter not suitable for a work saw and likely not to last real long .

 

[Lightning Performance]

I made it to page two of the "Year book". What a hoot!
Time for me to catch twenty winks or so. Same bat time same bat channel.
Carry on

 

[wcorey]

Since the stratos intended purpose is to purge the cylinder with fresh air so less of the fuel/air charge from side transfers can get pushed out the exhaust, you'd think then that for the strato charge to accomplish this it would need to happen somewhat ahead of the fuel/air mix.
So I can see where the blowdown would need to be staggered in the stratos favor.

Edit: Now that I'm looking at it with a cylinder in hand, I need to revise this substantially.
No time at present, will fix it latter. Sorry Al...

 

[wcorey]

... I beg to differ on the surface area. A lil bit is gained but not much as you stated. More area = a bit more push.

I have to also disagree on the 'more push'.
More surface area yes, but it's still pushing on the same cross sectional area of the cylinder/column regardless.

 

[penzone]

I have to also disagree on the 'more push'.
More surface area yes, but it's still pushing on the same cross sectional area of the cylinder/column regardless.

To say it another way, the force normal to the dome still sums up as the same resultant force pushing down the axis of the cylinder.

As for more pressure at the rings than at the dome, it really depends on ignition timing, flame generation and speed. I think it could be higher, lower or equal depending on the final system.

 

[Dub11]

Not sire if I missed this or not and I know its going to come from experience but what is the sign telling you to raise the transfer ports? Or what tells you to add bridge or finger ports? I have a head probably not lonng for this world and something inside me is saying just do it.

 

[drf256]

@wcorey

How are ya Bill. See you soon bud. Found this interesting pic on EBay. I'm still trying to understand these stratos. I guess the piston acts as the chamber and the port?

MS261

 

[Lightning Performance]

I may be wrong. Will be wrong again I'm sure.

Know this I have 40+ years as a wrench and 35+ years doing port work and such. The comment "his name is lighting" I will leave alone because I dought it was a compliment. Most of what I have learned was not from a book. It is first hand from others.

 

[drf256]

I may be wrong. Will be wrong again I'm sure.

Know this I have 40+ years as a wrench and 35+ years doing port work and such. The comment "his name is lighting" I will leave alone because I dought it was a compliment. Most of what I have learned was not from a book. It is first hand from others.

Was a joke towards Dan. I was simply jesting that Lightning was the first name in your user profile. It was neither meant as an insult nor compliment towards you.

 

[penzone]

It's been said you get max pressure after about 20-25 degrees after top dead center .How in the world you would measure that is anybodies guess .

With a pressure transducer in the head and a Bentley probe or encoder on the crank. I'm actually working on this sort of thing at work right now (not on chainsaws though). I've done it a few times over the years. The data is very interesting and really helps me get my mind wrapped around what's going on.

 

[Adirondackstihl]

You beat me to it!
By the way, what is your name? I'm Dan


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[paragonbuilder]

View attachment 63536

Who dat?


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[jake wells]

he looks to be 36 or 37 yrs old

 

[jake wells]

i don't know how to port but i know my saw that scott ported has pissed off some people locally in my area.
its a spunky little thing