Real talk about saw porting theory (no arguments)

[tree monkey]

@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

View attachment 63448

strato saws are complex, but the basic function is simple. fresh air comes in through the port on the lower right,(in the pic) through the channel in the piston and down the transfer ports to the crank case. the fuel charge enters through a conventional port to the crank case. on the down stroke, the fuel charge is pushed up the transfers, pushing the fresh air, trapped in the transfer tunnels, into the combustion chamber clearing the spent charge ahead of the fresh charge.

the transfers flow both ways.

 

[jake wells]

^^^ yeah what he said ^^^

 

[paragonbuilder]

strato saws are complex, but the basic function is simple. fresh air comes in through the port on the lower right,(in the pic) through the channel in the piston and down the transfer ports to the crank case. the fuel charge enters through a conventional port to the crank case. on the down stroke, the fuel charge is pushed up the transfers, pushing the fresh air, trapped in the transfer tunnels, into the combustion chamber clearing the spent charge ahead of the fresh charge.

the transfers flow both ways.

It's truly amazing that the flow can change direction well over 400 times per second, and still flow effectively. It's kind if brain numbing... but it works!


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[ELECT6845]

This could be the best porting thread on the internet EVER.

 

[Al Smith]

You'll find out most people don't get into too much specific methods because it's top secret .--well some think that.

 

[Adirondackstihl]

This could be the best porting thread on the internet EVER.

Hey Joe!!

 

[ELECT6845]

Hey Joe!!

Hello Hello

 

[jmssaws]

I ported the second best 066 cylinder I've seen today.
Stock with a oem gasket

 

[jmssaws]

I was able to get the exhaust down to 102 with less than 200lbs of compression.
Ain't gonna do that with very many 066 cylinders.

 

[drf256]

I was able to get the exhaust down to 102 with less than 200lbs of compression.
Ain't gonna do that with very many 066 cylinders.

Have you tried opening the chamber with the lathe yet J?

May be a way to make some horses into unicorns. Definitely would be more work. That's for sure.

 

[Dub11]

Have you tried opening the chamber with the lathe yet J?

May be a way to make some horses into unicorns. Definitely would be more work. That's for sure.

Unicorns are pretty fugging badazz

 

[jmssaws]

Have you tried opening the chamber with the lathe yet J?

May be a way to make some horses into unicorns. Definitely would be more work. That's for sure.

Intake duration becomes a problem.

 

[paragonbuilder]

Intake duration becomes a problem.

Epoxy?


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[EvilRoySlade]

Have you tried opening the chamber with the lathe yet J?

May be a way to make some horses into unicorns. Definitely would be more work. That's for sure.

In a way, this is why I started this discussion. Anything is possible but why do we travel that direction? On something like the 066 can transfers and exhaust not be adjusted enough without ending too high on compression? The whole idea is to have peak torque at optimal chain speed right?

With the big saws, can you target something like 9-9,500 peak power? A two-stroke that's not wound up to make power but one that pulls hard. I've seen it in the dirt bike world but they're using reeds, power valves and pipes to help. For you guys that have done this a lot, can you get there with timing alone?

 

[srcarr52]

In a way, this is why I started this discussion. Anything is possible but why do we travel that direction? On something like the 066 can transfers and exhaust not be adjusted enough without ending too high on compression? The whole idea is to have peak torque at optimal chain speed right?

With the big saws, can you target something like 9-9,500 peak power? A two-stroke that's not wound up to make power but one that pulls hard. I've seen it in the dirt bike world but they're using reeds, power valves and pipes to help. For you guys that have done this a lot, can you get there with timing alone?

Whats your definition of too high compression?

On 066's and especially 660's I am trying to get less than stock exhaust duration, which the only way to do that is to cut the squish band and drop the jug. This increases the corrected compression ratio which is beneficial up to some point, but you can always take material out of the combustion chamber to lower it if you want. This also increase intake duration which on these saws is bad news since they are already on the verge of being to long.

 

[jmssaws]

With 90% of 66 cylinders you will run out of piston before you get the exhaust down as far as one of the best cylinders.
You can open the chamber and loose compression but filling the intake doesn't work like the real thing and I don't like putting epoxy inside the cylinder,will it stay there forever? I don't know.

I've timed a bunch of 066/660 cylinders and can't recall seeing 2 alike,
If I take the average one with the exhaust at 96 and a good cylinder that's at 98 and port them to the same numbers the 98 cylinder will be the strongest for no other reason than it just is.
A lot of the 660 cylinder have really low transfers and intakes around 80 or 160 duration and once you cut 040 off to get the exhaust down your intake is out of control,the old cylinders have intakes from 76-78 and much higher transfers with shorter blow down and lower exhausts and will run better than the newer ones.

I've seen 93 117 84 on a stock ks red light cylinder and 100 122 78 on a mahle and everything in between.

That's kinda what got me interested in porting them because it's a crap shoot everytime.

 

[EvilRoySlade]

With 90% of 66 cylinders you will run out of piston before you get the exhaust down as far as one of the best cylinders.

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

 

[EvilRoySlade]

Whats your definition of too high compression?

On 066's and especially 660's I am trying to get less than stock exhaust duration, which the only way to do that is to cut the squish band and drop the jug. This increases the corrected compression ratio which is beneficial up to some point, but you can always take material out of the combustion chamber to lower it if you want. This also increase intake duration which on these saws is bad news since they are already on the verge of being to long.

In my inexperience I believe 200 is tolerable in ~48mm or less. Then 180 is safer 48mm on up. Just thinking its pressure area.

Do you ever convert degrees of rotation to linear movement? I know the numbers would be very tiny but a piston does travel less distance at the 90 and 270 mark it seems. I grabbed my physics books but it's been a few years, I'm a bit rusty. I think it's just stroke being diameter of crank circle, then circumference but conrod length has to be in there somewhere I'd think. I feel dumb it isn't coming to me.
It would help with the time/area goals I believe. But I have no idea.

 

[jmssaws]

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

Yes.
060 I believe is all you have and you have to have the right piston for that.
288 piston will buy more room but I don't like the pin bearing setup unless you build spacers and it's not worth it to me.

 

[srcarr52]

In my inexperience I believe 200 is tolerable in ~48mm or less. Then 180 is safer 48mm on up. Just thinking its pressure area.

Do you ever convert degrees of rotation to linear movement? I know the numbers would be very tiny but a piston does travel less distance at the 90 and 270 mark it seems. I grabbed my physics books but it's been a few years, I'm a bit rusty. I think it's just stroke being diameter of crank circle, then circumference but conrod length has to be in there somewhere I'd think. I feel dumb it isn't coming to me.
It would help with the time/area goals I believe. But I have no idea.

The equations you need are in Bell's book. You'll need the stroke and conrod length.