Part 8: The Stratified Chainsaw

[huskihl]

Delayed Scavenging: Why?

I think delayed scavenging means that the transfers intentionally open early and some exhaust gets pushed into them. And then when the residual exhaust pressure becomes less than the case pressure, the layer of exhaust in the transfers purges out the remaining exhaust.

 

[Mastermind]

I think delayed scavenging means that the transfers intentionally open early and some exhaust gets pushed into them. And then when the residual exhaust pressure becomes less than the case pressure, the layer of exhaust in the transfers purges out the remaining exhaust.

Yep. And I think.....just think, that the opening point being higher on the opposite side of where we were used to seeing it plays a role in the back feeding of the transfers.

 

[huskihl]

Yep. And I think.....just think, that the opening point being higher on the opposite side of where we were used to seeing it plays a role in the back feeding of the transfers.

The “V”

 

[Mastermind]

The “V”

Si.

 

[Ketchup]

So I’m confused. Some saws seem to be using a Delayed Scavenge strategy exclusively, others in combination with stratified intake. Am I wrong on that second bit? Using them together seems overly complicated.

 

[huskihl]

So I’m confused. Some saws seem to be using a Delayed Scavenge strategy exclusively, others in combination with stratified intake. Am I wrong on that second bit? Using them together seems overly complicated.

461, 661 are delayed scavenging. There’s more I’m sure

 

[P.M.P.]

Strato saws are GHAY

 

[Mastermind]

Strato saws are GHAY

Chainsaws are GHAY.

Fixt

 

[Stump Shot]

I think delayed scavenging means that the transfers intentionally open early and some exhaust gets pushed into them. And then when the residual exhaust pressure becomes less than the case pressure, the layer of exhaust in the transfers purges out the remaining exhaust.

I think there's a brief moment in time when the fresh air comes in it's stagnant, until like you say the case pressure builds up and gives it a push. This brief moment is when the mixing occurs... I think.
I've also been inclined to say it's not worth thinking too much about in the overall scheme of things making power. Not that something couldn't be chased down here, I just don't feel it's very big to go into that kind of detail. Just changing the exhaust to intake ratio should help alleviate much of this. Or... I could also be wrong though too and the next great thing for chainsaws comes from this very spot, to align the variables like ducks in a row.

 

[huskihl]

I think there's a brief moment in time when the fresh air comes in it's stagnant, until like you say the case pressure builds up and gives it a push. This brief moment is when the mixing occurs... I think.
I've also been inclined to say it's not worth thinking too much about in the overall scheme of things making power. Not that something couldn't be chased down here, I just don't feel it's very big to go into that kind of detail. Just changing the exhaust to intake ratio should help alleviate much of this. Or... I could also be wrong though too and the next great thing for chainsaws comes from this very spot, to align the variables like ducks in a row.

I was thinking 461 and 661 types. Non stratos.

 

[Mastermind]

I was thinking 461 and 661 types. Non stratos.

And 500s

 

[Ketchup]

Alright, I think I’m on board now. Delayed Scavenge isn’t a strato technology at all. It’s a combination of long transfer tunnels, upper port shape, blowdown timing and exhaust width. Case pressure is probably also very important.

I think delayed scavenging means that the transfers intentionally open early and some exhaust gets pushed into them. And then when the residual exhaust pressure becomes less than the case pressure, the layer of exhaust in the transfers purges out the remaining exhaust.

All that must happen pretty fast. The tunnels are building pressure and the chamber is losing pressure when the exhaust gets pushed in. Also if the exhaust took too long to push back out it would shorten transfer duration undesirably. IE, if the transfers crack at 116, they better be filling the chamber by 126. I’m sure transfer volume plays a role, but I can’t see that whole exhaust backflow phase taking more than 10-12 degrees. Probably more like 8 degrees. Does that seem reasonable?

I think there's a brief moment in time when the fresh air comes in it's stagnant, until like you say the case pressure builds up and gives it a push. This brief moment is when the mixing occurs... I think.
I've also been inclined to say it's not worth thinking too much about in the overall scheme of things making power. Not that something couldn't be chased down here, I just don't feel it's very big to go into that kind of detail. Just changing the exhaust to intake ratio should help alleviate much of this. Or... I could also be wrong though too and the next great thing for chainsaws comes from this very spot, to align the variables like ducks in a row.

I agree. But until I understand it I don’t know what I’m working with. I’d rather spend time on OPE than spend money replacing 661 jugs I screwed up. So far I don’t see a road to significant gains here but who knows? It seems possible certain models could be ported to create delayed scavenging. It might make them more fuel efficient if not more powerful.

 

[Mastermind]

I’d rather spend time on OPE than spend money replacing 661 jugs I screwed up. So far I don’t see a road to significant gains here but who knows?

I think I get a bigger gain percentage out of the 661 than any other saw I do.

 

[huskihl]

Alright, I think I’m on board now. Delayed Scavenge isn’t a strato technology at all. It’s a combination of long transfer tunnels, upper port shape, blowdown timing and exhaust width. Case pressure is probably also very important.




All that must happen pretty fast. The tunnels are building pressure and the chamber is losing pressure when the exhaust gets pushed in. Also if the exhaust took too long to push back out it would shorten transfer duration undesirably. IE, if the transfers crack at 116, they better be filling the chamber by 126. I’m sure transfer volume plays a role, but I can’t see that whole exhaust backflow phase taking more than 10-12 degrees. Probably more like 8 degrees. Does that seem reasonable?



I agree. But until I understand it I don’t know what I’m working with. I’d rather spend time on OPE than spend money replacing 661 jugs I screwed up. So far I don’t see a road to significant gains here but who knows? It seems possible certain models could be ported to create delayed scavenging. It might make them more fuel efficient if not more powerful.

Yep

 

[Stump Shot]

I was thinking 461 and 661 types. Non stratos.

...and just like that, all my ciphering right out the old window.