Inside the MS362

[breymeyerfam]

Thats easy... A 361

but with but better filtration!

 

[bitzer]

I think the easy way would be to draw fuel into the strato ports. How to do this I'm not sure.:dunno:

BTW this is a really good thread for the most part.

Yeah man, fuel thru the strato ports! Thats the ticket!

We're on the cusp of the future of chainsaw modding!

Thanks again Brad for opening the door!

 

[Wild Knight]

What is the optimal fuel to air ratio???

So then why is the mixture right when the strato ports are working?

Where does the extra air come from to lean out the mixture to the optimal level???

Lemme see if I am thinking of this correctly...

The intake is small b/c the total volume of air being pumped is a product of both the strato and the intake charges. The front of the strato scavenging charge pushes out the exhaust charge (and possibly aids combustion of residual hydrocarbons as they go out the exhaust port). The tail end of the strato charge combines with the intake charge, thereby leaning the rich charge coming in from the intake. Since the flows are combined, the intake doesn't need to flow as much as a non-strato cylinder and the intake charge can be a little richer. If this is correct, then it would stand to reason that the strato port needs to be enlarged proportional to the intake port. Also, the exhaust port would need to be enlarged proportional to the combined increase of the strato and intake ports to accommodate the combined charge. Transfers would also have to be matched to the new flow capacity.

I am curious is the strato is actually the bottleneck. If the strato were conservative, then the mixture would error on the side of rich, whereas if it had too much flow the saw would error on the lean side. Maybe that is why Blood's saw looked like it had been run too rich.

 

[Erick]

I think what you're saying is...go ahead and let those strato ports flow. Open then up and let the extra fresh air mix with the overly rich fuel charge. Ehhh? So what do you want? 25%-30% gains?

I think I should clarify my thoughts a little, there is only so much air that is needed to scavenge a cylinder ahead of the incoming charge.

When a standard two stroke scavenges the cylinder the incoming charge is mixing with burnt (spent) gasses therefore it must carry with it all of the air (oxygen) it will need for combustion. When the fuel charge enters a strato charged cylinder it is mixing with "open air" which contains it's own oxygen and therefore the incoming charge must be richer than the usual "standard" mixture.

Like I said there is only so much charge that is necessary to effectively scavenge the cylinder.

However if you can get more air into the incoming charge you can add more fuel. You would need to be very careful though to not short-circuit the incoming charge with to much of a "buffer"... fine line to walk there and disaster lurks around every corner.

 

[Erick]

Lemme see if I am thinking of this correctly...

The intake is small b/c the total volume of air being pumped is a product of both the strato and the intake charges. The front of the strato scavenging charge pushes out the exhaust charge (and possibly aids combustion of residual hydrocarbons as they go out the exhaust port). The tail end of the strato charge combines with the intake charge, thereby leaning the rich charge coming in from the intake. Since the flows are combined, the intake doesn't need to flow as much as a non-strato cylinder and the intake charge can be a little richer. If this is correct, then it would stand to reason that the strato port needs to be enlarged proportional to the intake port. Also, the exhaust port would need to be enlarged proportional to the combined increase of the strato and intake ports to accommodate the combined charge. Transfers would also have to be matched to the new flow capacity.

I am curious is the strato is actually the bottleneck. If the strato were conservative, then the mixture would error on the side of rich, whereas if it had too much flow the saw would error on the lean side. Maybe that is why Blood's saw looked like it had been run too rich.

Sounds like you've got a pretty good handle on it.

 

[gonecountry]

Yeah man, fuel thru the strato ports! Thats the ticket!

We're on the cusp of the future of chainsaw modding!

Thanks again Brad for opening the door!

Wouldn't opening the intake so that fuel gets into the strato cavities get more fuel where it should be?

 

[Taxmantoo]

Wouldn't opening the intake so that fuel gets into the strato cavities get more fuel where it should be?

Depends on whether it should be in the muffler.

Our two primary goals are to get all the exhaust out of the cylinder and replace it with air/fuel mixed at the proper ratio.
Once that's achieved, we can think about trying to get more than a full charge in the cylinder, which is hard to do without a big tuned pipe to stuff it back through the exhaust.

 

[bitzer]

Lemme see if I am thinking of this correctly...

The intake is small b/c the total volume of air being pumped is a product of both the strato and the intake charges. The front of the strato scavenging charge pushes out the exhaust charge (and possibly aids combustion of residual hydrocarbons as they go out the exhaust port). The tail end of the strato charge combines with the intake charge, thereby leaning the rich charge coming in from the intake. Since the flows are combined, the intake doesn't need to flow as much as a non-strato cylinder and the intake charge can be a little richer. If this is correct, then it would stand to reason that the strato port needs to be enlarged proportional to the intake port. Also, the exhaust port would need to be enlarged proportional to the combined increase of the strato and intake ports to accommodate the combined charge. Transfers would also have to be matched to the new flow capacity.

I am curious is the strato is actually the bottleneck. If the strato were conservative, then the mixture would error on the side of rich, whereas if it had too much flow the saw would error on the lean side. Maybe that is why Blood's saw looked like it had been run too rich.

I think the only problem with that is that the intake can only be widened so much because of the limits of the skirt. It would have to be lowered more to increase mix volume, but by then you could lose velocity.

 

[ShoerFast]

Could also be setting up one h311 of a situation to start back-firing and popping if you add fuel to the Strato chamber? From the ground up, it is doing what it is designed to do, low emission power.

As mentioned, it's cool that the 362 is a clean running saw, sounds like it was well engineered, sips fuel, but might need a lot of extra work to match what a 361 as it was designed from the ground up to just make power?

The race would be against a 361, for me, I like the idea that there are fewer things that can go wrong with the 361 .

Look at what could happen down the road with the 362, destructive lean issues are now complicated. Even a slightly lean mixture now might take out the jug on a 362 where the 361 would just not run as well.

Running in extreme cold or heat and altitude changes might be a slightly harder tune in the 362 compared to the 361 ? Will the 362 be more fuel specific, and do poorly on older mix?

I'm old school, and never would have thought i would say that the 361 was old school, but it suits my needs better for now!

It will be interesting what Brad can get out of the 362, and there might be a day that we will really be looking at how much power we can get from a sip of fuel?

 

[bitzer]

Wouldn't opening the intake so that fuel gets into the strato cavities get more fuel where it should be?

I was just kiddin man! I don't think flowing mix thru the strato ports would work, because it wouldn't flow fast enough or get to were its supposed to go. The charges would be fighting each other I think if they did get there.

 

[Andyshine77]

Wouldn't opening the intake so that fuel gets into the strato cavities get more fuel where it should be?

If you could get the air fuel mixture correct, yes.

 

[gonecountry]

Depends on whether it should be in the muffler.

Some goes in there in the conventional 2 stroke would it be that much more with this design Im sure some will be traped and burn in the cyl.

Please dont mind my questions I still dont fully understand the strato design yet all I know is from pictures, drawings and animations. If I could actually see one in person I could proably answer a few of my own questions.

 

[Andyshine77]

I was just kiddin man! I don't think flowing mix thru the strato ports would work, because it wouldn't flow fast enough or get to were its supposed to go. The charges would be fighting each other I think if they did get there.

That's a very good point, especially considering the location of the transfers, it probably wouldn't work very well at all.

 

[volks-man]

I sat and stared at this P&C for a good long while trying to decide what I wanted to do with it. In the end, I basically treated it like any other saw. The only thing the strato really does is add that extra puff of fresh air to help push out the exhaust. I also believe I can explain why WOT tuning RPMs are not that high, and why it can't be pushed as far/hard as a 361.

Look at the intake port. It's only about half the width of a normal intake. It's limited by the pockets in the piston that carry the strato charge. All fuel comes through that one small intake port. So it only stands to reason that it can't flow what a traditionally ported engine can. I was able to widen it a little, but not much. I did lower it 4°, but it would need a lot more width to do more. The intake and carb are matched accordingly. So those are bottle necks as well.

sorry for jumping in late again. this is a great thread that is apparently on the cutting edge of modding these new-fangled strato saws. and i appreciate all of your open contributions to AS on modding!
i can't help wondering.
why wouldn't a hard core saw builder use the strato port for more intake charge? fit an adapter and a conventional carb to feed both the intake and the strato-intake fuel mix.
i have a hard time wrapping my head around this not being the way to go.
what is the downside?

 

[Andyshine77]

Most of the fresh air charge gets pushed out of the cylinder anyway, you would simply be wasting fuel. I was just thinking out loud before.lol

 

[fredmc]

All the "strato" does is scavenge exhaust. Why use fresh charge to do this?

 

[fredmc]

ah nevermind...

 

[woodgrenade]

So what would explain the overly rich conditions observed in the top of the cylinder? I don't think it is as simple as "Dirty Orange Bottle Stihl Oil". It was either a tuning mistake, or the saw wasn't being run allowing enough of the secondary (strato) air charge into the engine. Too much fuel, not enough oxygen and you have rich conditions. Does the strato intake only open at certain rpm's or engine temps? Or is it directly connected to the primary intake? I'm just thinking that the saw may have only been run a few times to "test cut" and not in any real world conditions like limbing, felling or cutting firewood with prolonged periods of idling. Just trying to put the strato puzzle pieces together!

 

[volks-man]

Most of the fresh air charge gets pushed out of the cylinder anyway, you would simply be wasting fuel. I was just thinking out loud before.lol

All the "strato" does is scavenge exhaust. Why use fresh charge to do this?

ah nevermind...

so which is it?
does strato scavenge, pull exhaust out, of the cylinder....
or
does it produce a wall of fresh air to stop the intake charge being scavenged?

1: you have a tiny intake.
2: you have to tune rich to compensate for fresh air in the strato.
aside from flow considerations... having everything that is introduced to the combustion chamber be at the proper air/fuel ratio cannot be a bad thing.

not being argumentative, just trying to understand and evolve.

 

[rms61moparman]

Most of the fresh air charge gets pushed out of the cylinder anyway, you would simply be wasting fuel. I was just thinking out loud before.lol

Maybe not if you have a resonator pipe pushing it back in there!!!