Part 8: The Stratified Chainsaw

[Ketchup]

On my 362 I noticed the strato butterfly doesn't open till like half throttle, while most others seem combined and open at the same time? Could that be used as variable port timing? If the thought has any merit I can try it this spring, while I wait for the woods to dry up.

( I'm thinking that the closed butterfly will negate the lost vacum from an aggressive port timing)

I was just messing with my Strato Wild Thing. It’s just like the 362: cold air butterfly doesn’t open until mid throttle. I think it has to do with how hard the venturi pulls fuel at lower rpm. It must pull a lot more at WOT or the saw would just lean out and die.

Or it may indicate the cold air mixes more at lower RPM. If the air is just shooting through and out the exhaust as a block it wouldn’t lean out the saw as much.

 

[Ketchup]

I thought this was relevant to this thread because I have noticed some strato intake setups on some saws allow spitback to get in the strato intake. Like the ms441 for example. Some have baffles purposely to keep spitback out of the strato. Makes me wonder why...

I think some stratos have a mix side and a lean mix side (instead of straight air). The piston windows in a 201t have arms that reach into the mix intake port and open first.





I’m not totally sure why. It must lower fuel efficiency and make emissions worse. It may just help with lubricating long pistons or it may be another part of the mixing game.

 

[timberjack90]

I've thought about my previous post a above some more and I'm pretty sure it wouldn't work. when I turn the saw over and watch it high duration is high duration regardless of the closed butterfly. It wouldn't get spit back, but idle and case compression would certainly suffer even with the butterfly closed. I would only make strato equal duration or less than intake, based on my limited knowledge.

 

[kneedeepinsaws]

What a great thread!!! Truly some awesome posts here in which I’m trying to wrap my head around. Time to get the ol 372xt cylinder and piston and start examining and understanding.

 

[kneedeepinsaws]

Ok me thinks I got this.
The strato ports assist more fuel into the combustion chamber which in turn promotes better scavenging.
this explains why there are only two ports for the transfers instead of four on the non strato engines.
Piston goes up the fuel port and strato ports suck into the crankcase helping mix the fuel air charge. Piston goes down and then the transfers start pushing mix into the cylinder, at the same time this positive pressure is pushing air back up through the intake through the strato ports, pulling the fuel charge behind it into the combustion chamber more efficiently than without the strato ports.
So in turn you are getting more fuel air charge into the combustion chamber with this design.
I played around with my 372xt piston and cylinder last night seeing what happens here.

 

[Mastermind]

Piston goes up the fuel port and strato ports suck into the crankcase helping mix the fuel air charge.

Ah.....nope.

 

[kneedeepinsaws]

Ah.....nope.

Damn, more research I guess...

I did mean to say piston goes up, fuel air goes through the intake tunnel to the case and strato air helps mix it.
I’ll study it further when I get home

 

[Mastermind]

strato air helps mix it.

Wrong.

 

[huskihl]

Wrong.

It’s like a @tree monkey breadcrumb trail lol. Lett’em figure it out on their own

 

[Mastermind]

It’s like a @tree monkey breadcrumb trail lol. Lett’em figure it out on their own

I spent years sharing what I was learning.....and a lot of it was probably wrong. The more I learned, the less sure I was of it being correct. These days I'd rather just stand back and watch.

 

[Bjorn]

https://opeforum.com/threads/transfer-port-back-flow.18941/ More to think about.

 

[farminkarman]

For those of you not familiar with the concept of stratified charged two-strokes, the main idea behind them is to reduce the amount of unburned fuel being lost out the exhaust port during scavenging. The idea is to use air only to push the exhaust gases out of the cylinder first, and then follow that up with air/fuel. I am oversimplifying the process, but in a nutshell, that was and is the goal. As some of you know there are other designs that provide similar results without the use of strato ports.

 

[Stump Shot]

It’s like a @tree monkey breadcrumb trail lol. Lett’em figure it out on their own

Well... at least the @tree monkey bread crumb trails did always lead you to the place you ought to be, might be three years later, but you were in the right spot. Lol

 

[Lightning Performance]

I spent years sharing what I was learning.....and a lot of it was probably wrong. The more I learned, the less sure I was of it being correct. These days I'd rather just stand back and watch.

So... he just said idgaf... rolling with what works!

 

[Lightning Performance]

1. People start passing out and hit the floor.
2.The light at the end of the tunnel is probably an oncoming train.
3. While you are reading this, something is going wrong but you don’t know it yet.

This^

 

[Ketchup]

For those of you not familiar with the concept of stratified charged two-strokes, the main idea behind them is to reduce the amount of unburned fuel being lost out the exhaust port during scavenging. The idea is to use air only to push the exhaust gases out of the cylinder first, and then follow that up with air/fuel. I am oversimplifying the process, but in a nutshell, that was and is the goal. As some of you know there are other designs that provide similar results without the use of strato ports.

What other designs are you referring to?

 

[kneedeepinsaws]

Well looking at it again one thing is certain, on the downward stroke of the piston the transfers are open for a brief time to the strato ports on the piston and air/fuel does move back briefly up the stratos.

 

[Mastermind]

Well looking at it again one thing is certain, on the downward stroke of the piston the transfers are open for a brief time to the strato ports on the piston and air/fuel does move back briefly up the stratos.

Check this out.

 

[kneedeepinsaws]

Check this out.

View attachment 293593

Yes I see the definition there, so what layers are we referring to here?

 

[kneedeepinsaws]

A layer of fuel/air and a layer of air?