But not all of the "fresh air" charge will go out of the exhaust. The air is only taking the place of the burnt gases, thus leaving some volume behind to be mixed with the fresh fuel charge. I would think.
opcorn:
opcorn:
Inside the MS362
- Thread starter blsnelling
- Start date
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The strato charge (of air) is almost moot to getting gains from the engine. All it does is fill the cylinder with clean air creating a fuel charge free buffer on each stroke. All things considered it should be left alone to give the little puff of air at the right time.
The gains will come from the standard intake and exhaust and transfer porting that is always done.
Now, that over-simplifies because there will be some interaction between the clean air charge and the fuel-air charge. Timing between those two will also start to factor in. But overall, you can start with mods as if it were a regular two-stroke.
Mr. HE
That's the approach I took to it. Next time I'll probably go on down to 80° on the intake. I stopped at 77° on this one.
Terry Syd
Addicted to ArboristSite
Clean burn
On my saw the combustion chamber, piston and exhaust is running very clean, so I think this 362 carbon deposits may be related to very rich running during the break-in.
I also tried disconnecting the strato linkage and found the engine running excessively rich. The strato function is taking a BIG gulp of air, it is not a little puff of air. Heck, my saw came with a 11mm venturi on the carb, but has a 16mm strato butterfly. Couple that with the longer duration of the strato function and it is likely that the strato function is moving more air than the carb.
The idea of running a second carb on the strato port would probably make a good race saw. The race saw would likely have a more radical exhaust timing and would loose a lot more mixture out the exhaust port. If the carb on the strato port was set for a very rich mixture it would be flushing the sides of the piston and the combustion chamber with an extra rich mixture and then that mixture would get blown out the higher exhaust port.
This would allow the saw to run much cooler and could allow some outrageous compression ratios. Essentially, the saw would be more 'liquid' cooled and could handle the higher compression.
I'm going to keep tinkering with my saw. My next mod is to shorten the strato timing and see if I can improve the torque. I'll post the results over in Ricks 445 thread.
On my saw the combustion chamber, piston and exhaust is running very clean, so I think this 362 carbon deposits may be related to very rich running during the break-in.
I also tried disconnecting the strato linkage and found the engine running excessively rich. The strato function is taking a BIG gulp of air, it is not a little puff of air. Heck, my saw came with a 11mm venturi on the carb, but has a 16mm strato butterfly. Couple that with the longer duration of the strato function and it is likely that the strato function is moving more air than the carb.
The idea of running a second carb on the strato port would probably make a good race saw. The race saw would likely have a more radical exhaust timing and would loose a lot more mixture out the exhaust port. If the carb on the strato port was set for a very rich mixture it would be flushing the sides of the piston and the combustion chamber with an extra rich mixture and then that mixture would get blown out the higher exhaust port.
This would allow the saw to run much cooler and could allow some outrageous compression ratios. Essentially, the saw would be more 'liquid' cooled and could handle the higher compression.
I'm going to keep tinkering with my saw. My next mod is to shorten the strato timing and see if I can improve the torque. I'll post the results over in Ricks 445 thread.
But not all of the "fresh air" charge will go out of the exhaust. The air is only taking the place of the burnt gases, thus leaving some volume behind to be mixed with the fresh fuel charge. I would think.
True, which is why I said it really isn't that simple, but is for purposes of porting.
Any clean air left can be compensated for through tuning for the most part.
Mr. HE
Yeah, reading through your posts I could see that you did. It might seem simple and I think that some have trouble because strato saws have been made out to be complicated. In some ways they are, but in other ways they are a regular engine with an add-on.
You did good work on this one and are breaking new ground in many ways. Sharing this info will help many of us jumpstart our own experiments with these new engines.
Mr. HE
Terry, a lot of what you said makes sense from a racing point of view. It makes no sense for a working saw.
By most calculations the strato port will be moving up to a third of the air that goes through the saw. If port timing is right that 'clean' air will not be a major part of the charge in the combustion chamber.
Mr. HE
By most calculations the strato port will be moving up to a third of the air that goes through the saw. If port timing is right that 'clean' air will not be a major part of the charge in the combustion chamber.
Mr. HE
tdi-rick
Addicted to ArboristSite
and a well designed pipe would shove that right back into the chamber.
It could very well work as a race setup.
Terry Syd
Addicted to ArboristSite
Tuning
Rick, yeah a pipe on a racer. Here's another one I referred to in the other thread that could be used on a work saw - put a resonator on the strato port.
If the strato port had longer duration than the intake (as mine presetly has), then the blowback into the 'intake' at lower revs would occur in the strato port. Put a tuned intake on the strato port to pack that blowback mixture back into the engine.
The saw would have a short duration intake for idle, a longer duration at WOT, and then when the revs drop in big wood the resonator would compensate for the longer duration and keep the mixture from blowing back.
I'd love to be able to do that, but at this point I'm just going to shorten up the strato timing a bit.
On a race saw it would make a great deal of sense. Run dual carbs and have the longer duration strato port tuned to provide a good boost at the desired RPM. A Helmholtz resonsator can provide something like a 2 psi boost to a two-stroke intake. Couple that with a expansion chamber and the cooler running piston that allows more compression and the stratos are the new trick saw to be running.
Rick, yeah a pipe on a racer. Here's another one I referred to in the other thread that could be used on a work saw - put a resonator on the strato port.
If the strato port had longer duration than the intake (as mine presetly has), then the blowback into the 'intake' at lower revs would occur in the strato port. Put a tuned intake on the strato port to pack that blowback mixture back into the engine.
The saw would have a short duration intake for idle, a longer duration at WOT, and then when the revs drop in big wood the resonator would compensate for the longer duration and keep the mixture from blowing back.
I'd love to be able to do that, but at this point I'm just going to shorten up the strato timing a bit.
On a race saw it would make a great deal of sense. Run dual carbs and have the longer duration strato port tuned to provide a good boost at the desired RPM. A Helmholtz resonsator can provide something like a 2 psi boost to a two-stroke intake. Couple that with a expansion chamber and the cooler running piston that allows more compression and the stratos are the new trick saw to be running.
tdi-rick
Addicted to ArboristSite
Geez, that'd be worthwhile with piston porting.
Most of the (little) experience I had was with Rotary and reed valves so no where near the spitback you get with longer intake duration of a piston port.
Terry Syd
Addicted to ArboristSite
Timing
Same here, most of my work on two-strokes is with reed and rotary systems. Heck, a 70 degree closing time on a rotary is fairly high, but for a piston port it is industrial timing.
Like I said above, I am coming around to the idea on my strato that the stock intake timing of 144 degrees (72 degrees ATDC) is going to be adequate. The bigger carb on the intake along with the strato butterfly allows the engine to take a big gulp when everything opens.
The blowback I got in the strato port when torque testing indicated that I might be able to improve the torque if I could move the strato timing of 154 degrees (77 degrees ATDC) back closer to the intake timing. In fact, from looking at the jug (see the 445 thread) it appears that the factory originally had less timing on the strato function.
Same here, most of my work on two-strokes is with reed and rotary systems. Heck, a 70 degree closing time on a rotary is fairly high, but for a piston port it is industrial timing.
Like I said above, I am coming around to the idea on my strato that the stock intake timing of 144 degrees (72 degrees ATDC) is going to be adequate. The bigger carb on the intake along with the strato butterfly allows the engine to take a big gulp when everything opens.
The blowback I got in the strato port when torque testing indicated that I might be able to improve the torque if I could move the strato timing of 154 degrees (77 degrees ATDC) back closer to the intake timing. In fact, from looking at the jug (see the 445 thread) it appears that the factory originally had less timing on the strato function.
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cpr
Addicted to ArboristSite
Finally go to the bottom of this one. Great thread and lots of information to boot! I'd rep ya' Brad, but I can't! Great job as per usual. I can't wait for someone to put a 576xpat in your lap! I'd do it if I could swing it right now.
ECRUPPRECHT
ArboristSite Operative
would it be possible to put a 361 top end intake boot carb etc. on the 362 cankcase i noticed a diffrence in the impulse setup as it does not run a line is it a possible swap if some one wanted a new 361 after they are gone??
The entire saw is completely different.
davec
ArboristSite Operative
Here's some more info on a stock 362, FYI. I've had this about a month now and probably have about 15 hrs of use time on it. "Normal" use as I would consider it, except for the cold weather (10's-20's F) - felling, bucking, limbing hardwoods in the 3-24" dbh range (mostly in the 3-12" range).
I was cleaning it up and sharpening the chain tonight and decided to pull the spark plug to take a peek inside to see if I saw the running rich issue Brad first posted at the start of the thread. The piston had a couple tiny spots of deposits on the crown - nothing notable. I used regular Stihl orange bottle oil in the first 2 gallons of gas I made (prob 1.5 gals went into this saw) as it was all I could get at first. I switched to the Stihl HP Ultra after that for the next 1+gal of fuel (and from now on). No pics of the piston as I can't get a camera in there close enough to see anything. Carb is set pretty much right at factory settings. Haven't needed to tweak it so far.
Here's what the spark plug looks like too:
Just a bit more info on the saw, FWIW.
-Dave
I was cleaning it up and sharpening the chain tonight and decided to pull the spark plug to take a peek inside to see if I saw the running rich issue Brad first posted at the start of the thread. The piston had a couple tiny spots of deposits on the crown - nothing notable. I used regular Stihl orange bottle oil in the first 2 gallons of gas I made (prob 1.5 gals went into this saw) as it was all I could get at first. I switched to the Stihl HP Ultra after that for the next 1+gal of fuel (and from now on). No pics of the piston as I can't get a camera in there close enough to see anything. Carb is set pretty much right at factory settings. Haven't needed to tweak it so far.
Here's what the spark plug looks like too:
Just a bit more info on the saw, FWIW.
-Dave
Net-Knight1
ArboristSite Operative
By the way...how much have you payed for your 362's?
The Saw is not available in Germany yet, could someone ship it overseas?
The Saw is not available in Germany yet, could someone ship it overseas?
Wild Knight
ArboristSite Guru
Nice animation of the strato poritng and air flows. May have been posted elsewhere, but worth reviewing:
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Wild Knight
ArboristSite Guru
Figures 
Oh well, I saw the video while in the hotsaws forum today, and it made me think of this thread.
Oh well, I saw the video while in the hotsaws forum today, and it made me think of this thread.
FATGUY
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awesome video, +1
