Discussion Starter

[pbillyi69]

what does the other half lool like? does it mirror that side? are the ports in the same place?

 

[huskihl]

what does the other half lool like? does it mirror that side? are the ports in the same place?

Identical…nearly

 

[pbillyi69]

so then the upper opens on the intake side at the same time on both sides does it create a specific flow pattern like a whirlpool or like a mushroom cloud effect up the side and towards the chamber?

 

[pbillyi69]

i have many more questions. how far down does the top of the piston go? what angle is on the inside top edge of the upper port does the bottom inside angle match the top? it looks to me like the exhaust port is way too small and just an oval

 

[drf256]

Like Shawn said above about the uppers, I think the opposite works betterer, and that’s why Stihl changed it over the years.

That’s a small upper for an MS660, or maybe what I see when I look down the jug is just an illusion. They are tremendous and unlike the nice tight square 064 uppers.

I believe the exhaust side should open first to start a bigger loop. That way the exhaust side flows away from the exhaust port while the transfer pressure is the highest. Less short circuiting. I try to imitate the new quad design, enter at 90* roof on the exhaust side and 30/45 on the intake side of the upper. If you look at where Stihl opens them now on quads, both uppers generally open on the exhaust side.

The lowers make sense too. Look at where Stihl takes its transfer path on its newer saws. The crank lobes should push charge forward in the case (but by the same premise they can pull it away also).

The exhaust funnel makes me wonder is the cooling of the exhaust in the muffler can creates a lower pressure area from the contraction of the gasses and aids in scavenging. Never really thought about it much, but regardless of exhaust back pressure, cooling it should lower the absolute pressure in the can. The opening in the plating is limited by the area the rings can safely ride over as well.

The bell shaped combustion chamber has pretty much gone away also over the years. The newer bands (261/462) look much more like the flat bands that are typical in port jobs.

Every tunnel in that jug is shaped like a funnel. Has to be a reason.

Interesting stuff. Thank you Moobs.

 

[Ketchup]

I feel like there are some other models out there that open on the intake side first. Can anyone think of any?

Also, I think the intake looks like a funnel because it’s wider and shorter at the plating and circular where the boot meets. The area is probably about the same both places. @Mastermind, can you confirm that? Hard to tell in 2D.

 

[Mastermind]

I feel like there are some other models out there that open on the intake side first. Can anyone think of any?

Also, I think the intake looks like a funnel because it’s wider and shorter at the plating and circular where the boot meets. The area is probably about the same both places. @Mastermind, can you confirm that? Hard to tell in 2D.

More area at the plating I believe...but not a lot.

 

[Outback]

Or Stihl and husqvarna love beta testing in the real world. There could be a good reason, or maybe the stihl engineers are just effin with ya. 2 stroke bikes make ton of power per cc, yes they move and have pipes, but... Chainsaws are all about improving as slow as possible. The oems want decades of incremental improvement, not giant leaps they may not be technologically capable of trumping again easily.

 

[Mastermind]

Or Stihl and husqvarna love beta testing in the real world. There could be a good reason, or maybe the stihl engineers are just effin with ya. 2 stroke bikes make ton of power per cc, yes they move and have pipes, but... Chainsaws are all about improving as slow as possible. The oems want decades of incremental improvement, not giant leaps they may not be technologically capable of trumping again easily.

Over the years that I've been doing this, I've watched the oems change to become ever closer to what one of us guys that mods saws would have done.

 

[farminkarman]

Over the years that I've been doing this, I've watched the oems change to become ever closer to what one of us guys that mods saws would have done.

I would be curious to see what the OEMs would do if they didn’t have to satisfy the epa.

 

[Powerstroke Cowboy]

Obviously I am a noob to all this. But, that does bring me to a question. I like the angled uppers. But what about a twist? As in, what would happen if instead of the angled uppers being the same, what of they where the opposite of each other. One open towards the exhaust and one towards the intake. Then, along with that have the lowers designed to deliver the air to the uppers on a twist/angle so the air enter the cylinder swirling around the outside of the cylinder.

Swirling air is very good for combustion efficiency.

Would there also be a chance you would loose less out the exhaust?

Or am I trying to bring to much diesel engine action to a 2-stroke motor?

Don't pound on me to hard!! LOL.

 

[farminkarman]

Obviously I am a noob to all this. But, that does bring me to a question. I like the angled uppers. But what about a twist? As in, what would happen if instead of the angled uppers being the same, what of they where the opposite of each other. One open towards the exhaust and one towards the intake. Then, along with that have the lowers designed to deliver the air to the uppers on a twist/angle so the air enter the cylinder swirling around the outside of the cylinder.

Swirling air is very good for combustion efficiency.

Would there also be a chance you would loose less out the exhaust?

Or am I trying to bring to much diesel engine action to a 2-stroke motor?

Don't pound on me to hard!! LOL.

Too much diesel tech, lol. For proper scavenging in a two-stroke, you don't want mixing of the spent gases and the fresh charge. You want the fresh charge to blow in under the escaping exhaust and loop up & around toward the combustion chamber. The swirl you are talking about can be helpful up near the combustion chamber after the ports are closed. This is why it is important to have a tight squish band clearance to push the charge into the chamber closer to the spark plug.

 

[Mastermind]

Obviously I am a noob to all this. But, that does bring me to a question. I like the angled uppers. But what about a twist? As in, what would happen if instead of the angled uppers being the same, what of they where the opposite of each other. One open towards the exhaust and one towards the intake. Then, along with that have the lowers designed to deliver the air to the uppers on a twist/angle so the air enter the cylinder swirling around the outside of the cylinder.

Swirling air is very good for combustion efficiency.

Would there also be a chance you would loose less out the exhaust?

Or am I trying to bring to much diesel engine action to a 2-stroke motor?

Don't pound on me to hard!! LOL.

Just have to give it whirl (pun intended)

 

[Woodwater]

Let say me one thing. The Cylinder doesn't work as a half.

 

[TreeLife]

My thinks...is by angling the transfer in that way, the tiny point of exit when the port first opens would have excellent pressure/velocity, and aiming it towards the intake would cause better cylinder filling creating a swirl effect.

I dont know, I'm just a dumb guy.

 

[Woodwater]

would be good to sit in there and have a look.

an transparent 2 stroke engine, and let smoked air through.

 

[Ketchup]

So why has everything gone to the exhaust side of the upper opening first? It seems like scavenging would work best if the intake side filled first and then pushed the exhaust from the intake side of the piston crown up towards the chamber and then down to the exhaust. I guess the exhaust side opening first has enough force to shoot all the way across the crown and hit the cylinder wall, then the intake side assists travel up the cylinder wall towards the chamber? Seems like opening intake side first would work just as well. Maybe it’s about putting more momentum in the exhaust side to create a stronger boundary between exhaust and fresh charge. If the exhaust side opens with less “pressure” (or momentum?) it may short circuit out the exhaust more easily.

 

[qurotro]

I would be curious to see what the OEMs would do if they didn’t have to satisfy the epa.

Heat is another issue. Lots of those high output 2 stroke are water cooled with a strong crank.

 

[Powerstroke Cowboy]

Just have to give it whirl (pun intended)

Good one. Hahaha!

Too much diesel tech, lol. For proper scavenging in a two-stroke, you don't want mixing of the spent gases and the fresh charge. You want the fresh charge to blow in under the escaping exhaust and loop up & around toward the combustion chamber. The swirl you are talking about can be helpful up near the combustion chamber after the ports are closed. This is why it is important to have a tight squish band clearance to push the charge into the chamber closer to the spark plug.

Gotcha, I had a feeling it wasn't that simple. Thank for the explanation.

Is there any why to get the air swirling when the ports are closed?

 

[farminkarman]

Heat is another issue. Lots of those high output 2 stroke are water cooled with a strong crank.

Heat certainly can be a limiting factor, but for a lightweight package, you aren’t going to see tuned pipes and case reed induction. I would just be curious how much closer the OEM would get to selling a saw that would compare to a ported saw. Even without the EPA side, there is still the noise issue they would have to work around.