Echo Cs 730 hybrid build.

[Red97]

Wondering if I shouldn't age/ heat treat this jug before prepping for the sleeve?

Guess I probably ought to double check the material I have used...

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[chipper1]

Indeed. Very easy to come up with/start projects...

It's a curse.

Only be broken by finishing said pro


Ahhh shiny!!!





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Let me know next time you guys are gonna be running these, I'll swing by or meet you up this way.
Oh in regards to the projects curse lol.

 

[Red97]

Any thoughts on combustion chamber shape?

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[tree monkey]

hemi

 

[Red97]

hemi

Kind of what I was thinking.

Squishband wide or narrow... 50%?

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[tree monkey]

50% of area

 

[EvilRoySlade]

50% of area

Really? I’m genuinely asking why. I’ve often wondered how much area squish can be tolerated. And do you want it all parallel to piston surface.

 

[tree monkey]

that's about what a stock saw is, 50% is deceiving to the eye

 

[EvilRoySlade]

Yes it is. I just did some quick math on a 50mm cylinder, it’s a band 15mm wide.

 

[EvilRoySlade]

Yes it is. I just did some quick math on a 50mm cylinder, it’s a band 15mm wide.

Nope 7.5mm
I’m a *pretty boy. Ha dumbas s

 

[Red97]

Really? I’m genuinely asking why. I’ve often wondered how much area squish can be tolerated. And do you want it all parallel to piston surface.

Smaller band leaves more volume for combustible mix, but less of a buffer from detonation.

Larger the band the opposite is true.

Yes should be parallel or you lose squish velocity.

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[EvilRoySlade]

Smaller band leaves more volume for combustible mix, but less of a buffer from detonation.

Larger the band the opposite is true.

Yes should be parallel or you lose squish velocity.

I was thinking more blank slate like you have. What is the best design option, cut 50% area then make the dome to your desired combustion chamber volume.

 

[Red97]

I was thinking more blank slate like you have. What is the best design option, cut 50% area then make the dome to your desired combustion chamber volume.

That brings up a good point about volume.

Say the band is fixed at 50% would more volume/less comp offer better performance? Vs more comp less volume.

Like you said these variables aren't practical to modify in a factory jug.

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[Lightning Performance]

Will it get a pop up?

Volume vs compression...
I find when your close to optimum it becomes a toss up. More of one or the other yielded no different overall time in quarter mile runs. It did make a difference in where the power was delivered. More bang area made more grunt. Wider band and lowered compression made more horses up top. That won't change with a port vs valve motor ask me how I know, not!

Edit: All testing was done below 10,000 rpm, most times lol.
Have not tried it with chainsaws, yet. Done it on bikes and such. Many two and four stroke. Street and off road.

 

[Red97]

Will it get a pop up?

Volume vs compression...
I find when your close to optimum it becomes a toss up. More of one or the other yielded no different overall time in quarter mile runs. It did make a difference in where the power was delivered. More bang area made more grunt. Wider band and lowered compression made more horses up top. That won't change with a port vs valve motor ask me how I know, not!

Edit: All testing was done below 10,000 rpm, most times lol.
Have not tried it with chainsaws, yet. Done it on bikes and such. Many two and four stroke. Street and off road.

Don't think I'll do a pop up.

Front runners are big bore 372 piston.

Or a wiseco 52mm full circle piston I have heard about.

Transfers are just going to be straight ports and bottom fed. Not ideal, but can be made to run pretty good.

Thinking maybe just 1 large transfer tunnel with no divider and 2 ports in the sleeve?

Here is a pic of the stock tunnels, don't think I will need to cut out that much. Seems they wanted a ton of case volume on these saws?

Long stroke, small bore.

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[Lightning Performance]

The long stroke is all volume. You'll need some velocity now.

1 How will you size the tunnels?
2 You should end up with a perfectly sized transfer opening. Oh btw, what is that?...
3 Quad port ?

 

[Red97]

The long stroke is all volume. You'll need some velocity now.

1 How will you size the tunnels?
2 You should end up with a perfectly sized transfer opening. Oh btw, what is that?...
3 Quad port ?

That is the stock 590 cylinder.

Quad port, with the large lower cutouts. Used a full circle piston. 45mm

Thinking the velocity is going to come natural, +7mm piston forcing charge through roughly the same size tunnels. I can get a bit more volume out of em, but not a ton, as the jug still needs to fit the case.

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[Sty57]

if you need a place to store a mill I have room for it

Just sold this one at work ......

 

[Red97]

Well I ran 3 tanks through back to back this morning. 24" light feels really good.

Most was large cherry, bar buried and quartered. Saw feels like it is finally settling in.

I'm pretty happy with it. Did about 1/2 a tank of piled limb wood. That is were the weight/balance really shined

I haven't cut that much in close to 3 years lol.



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[Red97]

Looking at some surface area fin calcs...


Ain't no way I'm out smarting them on this subject.


Gonna try my best just to copy the stock fin arrangement.

Obviously the iron sleeve will have some effect. But hopefully I'll be in the ball park when it come to jug cooling.

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