Ms461 saw design

[Chris-PA]

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Thanks for posting that - do you have a link to the original document? They appear to be using two terms - one is "Delayed Scavenging Technology", and the other is "Delayed Stratified Scavenging Technology". The MS461 is the first one.

The document you showed says they are indeed using cylinder pressure to blow exhaust down the transfers to delay the arrival of fuel to the cylinder, thus reducing the opportunity for fresh charge to be lost out the exhaust port.

Contrast this approach to a piston ported strato, which uses the fresh air of the new charge to delay the arrival of a (much richer) fuel mixture. The piston ported strato only delays a small amount of the fresh charge volume, which contains a very rich mixture, but the majority of the air for the fresh charge is not delayed, and in fact can be advanced. Using exhaust gases means the entire fresh charge, fuel and air, is delayed.

Also, about that ramp under the piston, it says: "Intake side ramp in crankcase designed to optimize direction and velocity of fuel charge for maximum cooling and lubrication"

 

[windthrown]

The 461 is not stratified.

The 461 is not a stratified engine.

Well, call it what you want: delayed scavenging, or I what call exhaust scavenging. The 461 design stuffs a buffer of exhaust gas into the transfers and that becomes a layer between the fuel charges to keep raw fuel from spilling out the muffler, which in my book is what defines a stratified layer, as I described earlier. So I refute your claims and contend that the 461 is a stratified saw. And I do not care if your name is Brad, Randy, or God.

 

[KG441c]

Ch

Thanks for posting that - do you have a link to the original document? They appear to be using two terms - one is "Delayed Scavenging Technology", and the other is "Delayed Stratified Scavenging Technlogy". The MS461 is the first one.

The document you showed says they are indeed using cylinder pressure to blow exhaust down the transfers to delay the arrival of fuel to the cylinder, thus reducing the opportunity for fresh charge to be lost out the exhaust port.

Contrast this approach to a piston ported strato, which uses the fresh air of the new charge to delay the arrival of a (much richer) fuel mixture. The piston ported strato only delays a small amount of the fresh charge volume, which contains a very rich mixture, but the majority of the air for the fresh charge is not delayed, and in fact can be advanced. Using exhaust gases means the entire fresh charge, fuel and air, is delayed.

Also, about that ramp under the piston, it says: "Intake side ramp in crankcase designed to optimize direction and velocity of fuel charge for maximum cooling and lubrication"

Chris im on.a d9 dozer on a mobile phone trying to upload the url but had no luck. May have to wait until I get to computer tonight

 

[Mastermind]

I get what you are saying......but the port timing numbers tell a different story.

 

[KG441c]

Well, call it what you want: delayed scavenging, or I what call exhaust scavenging. The 461 design stuffs a buffer of exhaust gas into the transfers and that becomes a layer between the fuel charges to keep raw fuel from spilling out the muffler, which in my book is what defines a stratified layer, as I described earlier. So I refute your claims and contend that the 461 is a stratified saw. And I do not care if your name is Brad, Randy, or God.

I Think we r confusing intake stratification with what Stihl is calling stratified delayed scavenging? When it boils down to it though Ill choose what Brad and Randy says as they have done their homework and Id trust their advice anyday

 

[Chris-PA]

Well, call it what you want: delayed scavenging, or I what call exhaust scavenging. The 461 design stuffs a buffer of exhaust gas into the transfers and that becomes a layer between the fuel charges to keep raw fuel from spilling out the muffler, which in my book is what defines a stratified layer, as I described earlier. So I refute your claims and contend that the 461 is a stratified saw. And I do not care if your name is Brad, Randy, or God.

It is stratified in a sense. Stratified was a lousy name choice, as it sounds like the old stratified charge systems they played with in cars back in the day. It's nothing like that. Those attempted to have stratification, or separation of layers in the combustion chamber at ignition, where a rich mixture would burn out through a lean region.

In these 2-strokes the strato idea is to delay the arrival of the fuel into the chamber, so that less is lost out the open port. The Zenoah/husky system does that by delaying just the fuel part and letting the transfers flow the air for the fresh charge through a separate intake path, while this attempts to delay all of it by filling the transfers with exhaust gas.

 

[KG441c]

It is stratified in a sense. Stratified was a lousy name choice, as it sounds like the old stratified charge systems they played with in cars back in the day. It's nothing like that. Those attempted to hae stratification, or separation of layers in the combustion chamber at ignition, where a richmixture would burn out through a lean region.

In these 2-strokes the strato idea is to delay the arrival of the fuel into the chamber, so that less is lost out the open port. The Zenoah/husky system does that by delaying just the fuel part and letting the transfers flow the air for the fresh charge through a separate intake path, while this attempts to delay all of it by filling the transfers with exhaust gas.

I still say its Stihl fancy name for plugged up like all get out muffler!! lol! I say open her up and pollute!!! lol

 

[Mastermind]

Hear me when I say that by no means am I some expert on this stuff. I'm just a hack with a Foredom.....but I've seen a lot of saw guts.

I'm open minded, and willing to learn. When I'm wrong I'm cool with it....I see that as an opportunity to learn. Everything I have learned about two stroke theory tells me that what Stihl is saying here is impossible though.

What I see is this at any rate......the same muffler that the 460 uses. Exactly. No more back pressure is found here.

The port timing numbers do not suggest that the exhaust could possibly flow down into the transfers. The transfers open too late in the down stroke for the compression pressures to allow it. The 460 opens sooner.....and would be more likely to back flow.

The carb does have a much smaller jet, and the coil is different.

 

[blsnelling]

Sounds like marketing gimmick to me. The cylinder works no differently than a 460, other than where the transfers are fed from.

 

[Chris-PA]

Hear me when I say that by no means am I some expert on this stuff. I'm just a hack with a Foredom.....but I've seen a lot of saw guts.

I'm open minded, and willing to learn. When I'm wrong I'm cool with it....I see that as an opportunity to learn. Everything I have learned about two stroke theory tells me that what Stihl is saying here is impossible though.

What I see is this at any rate......the same muffler that the 460 uses. Exactly. No more back pressure is found here.

The port timing numbers do not suggest that the exhaust could possibly flow down into the transfers. The transfers open too late in the down stroke for the compression pressures to allow it. The 460 opens sooner.....and would be more likely to back flow.

The carb does have a much smaller jet, and the coil is different.

I don't doubt it. Doing google searches on "delayed scavenging technology" yields almost nothing. It's kind of hard to imagine a saw with timing that would do what they claim would run worth a darn. And they continue to introduce saws with piston ported strato.

 

[Mastermind]

I have no idea how it could work........but the 661 is built on the same ideas.

They are getting them past EPA somehow.....

 

[KG441c]

Are the quad port cylinders any more efficient than a dual?

 

[Mastermind]

I think they are, because of higher velocities.

 

[KG441c]

So with all this in the open and u gut the muffler and relieve that back pressure then u have a basic
old school saw with a quad transfer cylinder with a fancy do hicky in crankcase to cool piston!! lol

 

[KG441c]

I think they are, because of higher velocities.

Randy with the higher velocities would it impede heat transfer from cylinder or accelerate heat transfer?

 

[Mastermind]

I'm not sure it would make much difference. That sort of stuff is over my head though.

 

[splitpost]

Crankcase pressure ,positive and negative are the keys here

 

[KG441c]

Crankcase pressure ,positive and negative are the keys here

please explain

 

[Ron660]

please explain

Get it ported!!

 

[blsnelling]

If the 461 has "Delayed Stratified Scavenging Technlogy", then so does the MS260, MS361, MS440, MS460, MS660, and MS880. You can throw a bunch more Stihl, Husky, Dolmar, and many other saws in there as well. Like we're trying to tell you, the port timing and flow of fuel charge and exhaust are no different in the 461 than any other typical 2-stroke saw. Stihl is #1 in OPE for a reason. One of the biggest reasons if marketing, and you guys are buying it without logic to back it up.