Inside the MS362

[Andyshine77]

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.

It produces a wall of fresh air, so the waist is clean, aka the escaping air doesn't have any fuel in it. no scavenged involved with strato engines at all.

Like Mike said, you'd need a pipe for that.

 

[volks-man]

It produces a wall of fresh air, so the waist is clean, aka the escaping air doesn't have any fuel in it. no scavenged involved with strato engines at all.

Like Mike said, you'd need a pipe for that.

o.k.
so if that (strato) wall was proper mix laden intake charge and the regular intake pulls a proper intake charge, produced by fitting a conventional carb to feed them both, you would no longer need the over rich carb tuning.

so like i said, why not port the snot out of the exhaust and drop the squish
and fit a conventional carb and adapter to the strato as well as the intake?
what is the downside other than regular 2-stroke emmisions and fuel consumption?

idk. just a hard concept for me to avoid trying. after all, this is pretty much uncharted terittory, the sky is the limit!

 

[Terry Syd]

Husky 450 mods

Over on the 'Saw Building 101' forum, Rick started a thread on modding his Husky 445 strato. Since it is the little brother to my 450 I jumped in and we have been doing some mods to the 445/450s. Here's a link to the thread -

http://www.arboristsite.com/showthread.php?t=107976

You can follow the various twists and turns as I work through modding the 450. The exhaust has been opened up (including a neat trick with the piston) and I am running a larger carb. The stock carb on the 450 has a 11mm venturi, I am running a 13.5mm venturi carb off of a 570.

My latest torque testing showed up another issue, the strato duration is a bit long for my engine. The intake duration is 144 degrees and the strato duration is 154 degrees. I am now in the process of shortening up the duration of the strato port to try and get it closer to the intake duration of 144 degrees.

Although the exhaust duration is only 150 degrees and the blowdown is only 12 degrees - the saw really revs with the bigger carb and the additional 16 mm strato butterfly. In fact, the stock air filter is a bit restrictive.

I'm coming around to the view that with the bigger carb in conjunction with the extra strato function the stock intake duration is adequate for high revs as this engine can suck air big time through two large ports.

Although I have a bigger carb on the saw, the exhaust is running very clean. I thought that with the bigger carb there would be less depression in the crankcase for the strato function to operate. Not so, the strato function is still doing its job.

This is the early stage on modding stratos and as Brad has proven, the potential is there - we just have to keep tweaking them.

 

[blsnelling]

Not to put a damper on the conversation, but putting a carb on both intakes would be way beyond the scope of a woods port. It just doesn' sound practical to me at all.

If you look at my pics, I did widen the strato ports some already. Is it possible to flow too much though the strato ports and cause the engine to run too lean? I don't know. If I do another one, I'll probably widen them a little more, but I won't get carried away with it. You have to keep in mind that I can't risk trashing someones new $700 saw. I think Cale will be very please with his 18%-26% gains.

As far as it not turning as many RPMs at WOT, no load, that really doesn't concern me. It's holding the RPMs well in the wood, and that's all that really counts. It would be nice to know why it behaves that way though.

 

[blsnelling]

Although the exhaust duration is only 150 degrees and the blowdown is only 12 degrees - the saw really revs with the bigger carb and the additional 16 mm strato butterfly. In fact, the stock air filter is a bit restrictive.

12° blowdown? Wow! This 362 had more blowdown than most traditional saws at 31°. I ended up with 24°.

 

[Terry Syd]

Blowdown

Yeah, 12 degrees blew me away also. I can't remember working on a two-stroke with only 12 degrees of blowdown. The transfers are up a proud 126 degrees of duration. It's weird, almost as soon as you can see into the exhaust port, you can see the top of the transfers appearing.

My first thought was to lift the exhaust, but I figured I'd wait and see what happened with the exhaust the way I worked it. The piston mod with the extra port area apparently helped to give it sufficient blowdown for the revs I'm getting. I'm sure there is some blackflow of exhaust into the transfers, however the strato function on top of the transfer charge shouldn't be allowing any mixing of the mixture and exhaust.

The transfer ports on the Husky are long tunnels from the front of the engine. The long duration of the transfers coupled with the long narrow transfer tunnels on the Husky allows it all to purge out. It took a while for me to get my head around it. I've just never seen a two-stroke ported like this.

 

[SpaayDawg]

Supercharged?

Remember when cars and trucks started coming with fuel injection and everyone said that it was "stupid" and "never work" and now every vehicle is, and it's been proven to produce just as much power (and sometimes more) in racing applications and have fewer emissions? That being said, Strato: It's new, it's weird, but it's here to stay.

When I saw the animations the first thing that came to mind was a supercharger. The exhaust creates a scavenging vacuum in the sides of the piston and then that vacuum pulls fresh air into them when over the cylinder ports. The fact that the engine is getting more air into it than through just the carburetor is a great thing!! The more air that is in the cylinder the more fuel can be put in there as well. That being said because this is a 2-stroke engine and not a Variable Valve Timed 4-stroke with a variable fuel flow rate there is going to be a rich condition at idle, and the strato probably accounts for the lower than we're used to max RPM's. There is probably a "window" in which the strato performs best though.

Because the exhaust flow at idle has a lower velocity than let's say at 10,000 then the amount of air than can be pulled into the piston ports from the strato is going to be lower. By the same account, there must be some limit to the amount of "vacuum" that can be produced in the piston ports by the scavenging exhaust because they are the same size regardless of rpm. the higher the RPM the faster the piston is moving in the cylinder and therefore the strato ports are open for a shorter period of time limiting the amount of air that can be both put into them, and pulled out of them.

I think that more gains are to be had manipulating the strato ports, possibly opening the side ports in the piston allowing for more volume to be moved by the piston? widening the cylinder ports in relation to the exhaust and intake?

Sorry if I got alittle long winded, I'm just an engineering student that knows enough to get myself into trouble.

On a side note, does anyone ever see a 3rd piston ring being placed below the strato ports on the piston as to "seal" the fresh air away from the air/fuel that's in the crank?

 

[Terry Syd]

Strato butterfly

On the Husky, and I'm sure on the Stihl, there is a throttle linkage to the strato butterfly. The strato port is not open at idle. As you open the throttle to about 1/3 the strato butterfly starts to open.

That's what is interesting about my saw. At idle the duration is a short 144 degrees with only the carburetor flowing. However, at full tilt the duration is opened up to 154 degrees and has more than double the venturi area.

 

[stihlboy]

You are correct. Fred had it backwards. It would appear to me that the strato design is not feeding as much fuel under max load. The 361 and 362 were neck and neck in the smaller wood. Once you bury the bars, you can lean on the 361 significantly harder. I'm still very pleased with an 18% gain with the bar buried. Remember, this the technology that everyone's been afraid of for the last how many years, saying that it wouldn't take to mods well. I say we've proven that wrong. Slingr did a 441 and got good gains as well. I did one of the little Ryobi 10532 (Redmax GZ400), which is a strato, and it flat hauls.

ok, here is an issue. you need to focus on the 362s' bottom to mid range powerband. it has alot more potential than 18% but this is the first 362 messed with. try to port the strato portion of the cyl and run it richer so it leans out.


hmm i bet that will change after experimentation


good luck my friend, you shall figure it out and get that mid range increase.

 

[stihlboy]

Back off Fred.

sorry it was a long day

 

[bitzer]

About the premature Carbon build up

I think the seemingly excessive carbon build up on stratos may be due to the blast of cool strato air to the exhaust gases when the piston sweep occurs. The unburnt hyrdrocarbons then solidify to the piston crown and cylinder head. The way I am thinking is this, when you burn wood in a wood stove or especially an outdoor wood boiler, the smoke contacts the cool outside metal surfaces carbon and other chemicals solidify and stick to the sides forming creosote. Could the shot of cool strato air into the combustion chamber that sweeps it out cool some of the chemicals and possibly the unburnt hydrocarbons enough to solidify and "carbon up" the engine faster?

Also trying to devise an apparatus to make a carb flow thru the strato ports as well would be very difficult when looking at the postioning of the ports. It would take an enitre re-arrangement of the system otherwise the carb would have to flow up hill to get anything into the strato ports as well. If anything two carbs would work better, but the modifications would be impractical to say the least. The channel that the strato air flows through is also not static like a regular transfer. The strato air uses the cut outs along side of the piston to flow and trying to flow a denser mix charge thru that same channel probably wouldn't work. The gains Brad has gotten already are pretty damn good. As this "science" moves along I am sure more secrets will be uncovered.

 

[blsnelling]

I'm not sure how much cooler it'd be than the fuel charge. Although it does go to the base first.

 

[BigJ]

You can see the widened intake here, as well as a little flow work I did in the strato port. Again, I did very little to the strato part of the cylinder.

Late to this one, but couldn't you have widened a bunch more at the bottom of the intake port? It seems like the strato ports only would interfere with the top 1/4 of the intake. Obviously, you'd end up with an atypical shaped port with radically sloping sides (sort of like a bell shape), but that wouldn't be the first thing thats different about this saw.

Bah...nevermind - I just remembered the piston skirt width was the limiting factor...

 

[blsnelling]

bah...nevermind - i just remembered the piston skirt width was the limiting factor...

+1

 

[bitzer]

I'm not sure how much cooler it'd be than the fuel charge. Although it does go to the base first.

I'm just trying to figure out where the unburnt hydrocarbons go. They claim none are being released. So is the burn more efficient or are the unburnt H-Carbons left in the engine, or both? I don't know. Just trying to uncover the events and the carbon deposits left over.

 

[blsnelling]

What they're saying is that the fresh fuel charge is not used to expel the exhaust.

 

[Maldeney]

What they're saying is that the fresh fuel charge is not used to expel the exhaust.

I agree .................................................................................................................................. but I still say it also has to help the burn as well. Like was mentioned by in another post when the strato butterfly was disconnected the saw ran way rich.

 

[bitzer]

What they're saying is that the fresh fuel charge is not used to expel the exhaust.

That makes sense to me. I know that not everything in a fresh charge is burned because no burn is 100% efficient so regardless if it is pushed out by air or a fresh mix charge chemicals are being released. Thats just the nature of combustion. I get what you are saying and what they are trying to do. I'm just trying to account for that advanced carbon build up. I've been plagued by the strato for months, ever since I first opened mine. I wish I could hold that 362 cylinder in my hands for a while.

Does it look like the strato charge could enter all of the transfers from how they are postioned? My cylinder only has two transfers so I know where the strat air is going.

 

[Hddnis]

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

 

[Hddnis]

The idea of adding fuel to the clean air charge is just going to waste fuel. That charge is blown out the muffler. It would literally be throwing fuel away. Power is how much fuel/air mix you have on the combustion stroke, not how much fuel/air you run through the engine. Like all things, it has to be in the right place at the right time.



Mr. HE