Mastermind Revisits The MS261CM Type II

[MustangMike]

And Bridge ports (to direct the charge to clear the cylinder).

 

[Keith Gandy]

And Bridge ports (to direct the charge to clear the cylinder).

Just my opinion Mike but in my mind I see fingers as purge and clearing a path for a fresh charge coming in and bridge ports more for direction

 

[Mastermind]

So the stratos actually do what fingers try to accomplish opening a few degrees in advance?

And Bridge ports (to direct the charge to clear the cylinder).

This is an excellent discussion, and needs some time devoted to it.

The strato ports are lower than the transfer ports, and so they are never feeding the combustion chamber directly. Like Scott was saying, they open a path between the fresh air intake and the transfer ports. That allows air only to back flow down the transfers toward the case. Then, as the pressure changes, the direction reverses, and that same fresh air is pushed into the jug above the piston. This "pure air" charge is supposed to clear the combustion gasses out without allowing excessive hydrocarbons to escape into the muffler.

Again.......as Scott said, this layering mixes, and merely dilutes the exhaust gasses enough that the EPA is happier.......

I've gotten big gains in these saws by shortening blowdown so that the diluted part is pushed on ahead further.

 

[Adirondackstihl]

This is an excellent discussion, and needs some time devoted to it.

The strato ports are lower than the transfer ports, and so they are never feeding the combustion chamber directly. Like Scott was saying, they open a path between the fresh air intake and the transfer ports. That allows air only to back flow down the transfers toward the case. Then, as the pressure changes, the direction reverses, and that same fresh air is pushed into the jug above the piston. This "pure air" charge is supposed to clear the combustion gasses out without allowing excessive hydrocarbons to escape into the muffler.

Again.......as Scott said, this layering mixes, and merely dilutes the exhaust gasses enough that the EPA is happier.......

I've gotten big gains in these saws by shortening blowdown so that the diluted part is pushed on ahead further.

So basically purple cow is potato + squirrel & green toaster

 

[MustangMike]

Various methods that attempt to achieve the same goal.

I've gotten big gains in these saws by shortening blowdown so that the diluted part is pushed on ahead further.

So, since you lower the jug, I presume this means that you raise the upper transfers???

 

[Mastermind]

So, since you lower the jug, I presume this means that you raise the upper transfers???

I'd be raising them even if I didn't lower the jug.


MS261

Stock:

Compression: 150psi
Squish: .026
Ex: 105°
Tr: 121-135°
In: 74°

Ported:

Compression: 210psi
Squish: .025
Ex: 105°
Tr: 118-120°
In: 82°

Notes: Cut .030 from the squish.

 

[Mastermind]

The transfers in the 261 have a hell of a slope in them.........what I do is make em open all at once.

 

[Onan18]

Basically the fresh air is creating a "Dam" between the fuel charge and the exhaust gasses (pressure differential) and pushes the spent gasses out of the exhaust port so less of the fuel charge is lost out of the muffler before having a chance to ignite and do work.

 

[Mastermind]

Basically the fresh air is creating a "Dam" between the fuel charge and the exhaust gasses (pressure differential) and pushes the spent gasses out of the exhaust port do less of the fuel charge is lost out of the muffler before having a chance to ignite and do work.

Very good analogy brother Joe.

 

[Chainsaw Addict]

I'd be raising them even if I didn't lower the jug.


MS261

Stock:

Compression: 150psi
Squish: .026
Ex: 105°
Tr: 121-135°
In: 74°

Ported:

Compression: 210psi
Squish: .025
Ex: 105°
Tr: 118-120°
In: 82°

Notes: Cut .030 from the squish.

So about what saw would the bananaed we 261 compare with on stock saw with more cc?

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[RI Chevy]

Basically the fresh air is creating a "Dam" between the fuel charge and the exhaust gasses (pressure differential) and pushes the spent gasses out of the exhaust port do less of the fuel charge is lost out of the muffler before having a chance to ignite and do work.

So the saw is more efficient. Lol

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[Mastermind]

So about what saw would the bananaed we 261 compare with on stock saw with more cc?

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There is no replacement for displacement in my mind. But it will give a stock 60cc saw a hell of a go.

 

[tree monkey]

So the saw is more efficient. Lol

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so they claim.

 

[Mastermind]

I check squish using this stuff......

 

[Mastermind]

I can barely feel it when the piston touches it......

Squished.....

 

[Mastermind]

Ready to port these mfers.......

 

[RI Chevy]

so they claim.

What's your take on it Scott?

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[tree monkey]

Ready to port these mfers.......

View attachment 89792

so we gotta wait till the weekend?

 

[tree monkey]

What's your take on it Scott?

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takes fuel to make power

 

[RI Chevy]

True Dat!!!

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